New trends in vinyl ester resins

Rev Chem Eng 2014; 30(6): 567–581

Shipra Jaswal and Bharti Gaur*

New trends in vinyl ester resins

Abstract: Vinyl ester resins (VERs) are high-performance unsaturated resins derived by the addition reaction of var-ious epoxide resins with α-β unsaturated carboxylic acids. These resins have always been classified under unsatu-rated polyester resins. However, VERs have remarkable corrosion resistance and superior physical properties as compared with these conventional polyester resins, which make VERs a class of their own and hallmark of today’s resin industries. Hence, there is a need to review the avail-able literature on this important class of thermosetting resins separately. In this article, an attempt is made to review the state of the art of VERs, including synthesis, characterization, curing, thermal, chemical, oxidative properties, and applications. The main focus is on the lat-est developments in this area.

Keywords: corrosion resistance; cross-linking reactions; mechanical properties; thermosetting resins; vinyl ester resins.

DOI 10.1515/revce-2014-0012Received February 20, 2014; accepted July 14, 2014; previously pub-lished online September 6, 2014

1 IntroductionVinyl ester resins (VERs) are widely used thermosetting resins in solvent storage tanks, sewer pipes, building and construction, coating, automobile structural parts, swim-ming pools, and marine composites (Brown and Mathys 1997, Mouritz and Mathys 1999, Varma and Gupta 2000, Zhang et al. 2000, Brody and Gillespie 2005) because of their low cost, excellent chemical and corrosion resist-ance, outstanding heat performance, favorable mechani-cal properties, and better processibility. These are the addition products of epoxy resins and α-β unsaturated carboxylic acids (Young 1976, Launikitis 1982) and are structurally similar to unsaturated polyester (UPE) resins

(Figure 1). Shell Chemical Co. first commercialized these resins in 1965 under the trade name Epocryl. Dow Chemi-cal Co. then introduced a similar series of resins under the name Derakane. VERs are used in place of UPE resins since the unreacted carbon-carbon double bonds and the ester group, present in the backbone of UPE resins after curing, provide sites for hydrolytic attack, oxidation, and halo-genation, which make the cured UPE resin unsuitable for aggressive environments (Mallision 1987, Cheremisinoff and Cheremisinoff 1995, Juska and Puckett 1997), whereas in VERs, the ester linkages are present only at the terminal ends of the chains. VERs incorporate the thermal stability and mechanical strength of the epoxy backbone, and the presence of double bonds at the chain ends provides it the ease of cure that is comparable with that in UPE resins. These resins are costlier than UPE resins but are still widely used since they have excellent chemical resistance, low water absorption, as well as low shrinkage during cure as compared with polyester resins. Moreover, unlike epoxy resins, vinyl esters (VEs) have controlled cure rate and do not need any curing agent to form a cured network. Neat VERs having high viscosity (105 cps) may vary from semi-solid to solid. Reactive or nonreactive diluents are used to provide workable viscosity levels and enhanced reactiv-ity (Varma et al. 1985, Bhatnagar and Varma 1989, Gaur and Rai 1992a,b, Choudhary and Varma 1993, Malik et al. 2001) to control the cross-link density and affect strength, percentage elongation, hardness, chemical resistance, scratch resistance, and surface finish. The physical and handling properties of VERs depend on the source of vinyl termination (methacrylate or acrylate), the amount and type of co-reactant, and the molecular weight of the resin backbone. Although acrylate VERs are more suscep-tible to hydrolysis than methacrylate VERs are, they are preferred in radiation cure inks and coatings because of better reactivity (Launikitis 1982). The use of other unsatu-rated acids such as crotonic and cinnamic acids has also been reported (Jackson 1980, Zaske 1998). Although con-siderable work has been done on VERs, a comprehensive review dealing with the state of the art of these resins has not been published. In this paper, an attempt was made to review the synthesis, characterization, and physicochemi-cal, thermal, and mechanical properties of VERs.

VERs with wide structural variation can be prepared by the reaction of different epoxide resins with various unsaturated acids (Figure 2).

*Corresponding author: Bharti Gaur, Department of Chemistry, National Institute of Technology, NIT Hamirpur (H.P.) 177005, India, e-mail: [email protected] Jaswal: Department of Chemistry, National Institute of Technology, NIT Hamirpur (H.P.) 177005, India

Brought to you by | University of UtahAuthenticated

Download Date | 11/27/14 1:30 PM

568 S. Jaswal and B. Gaur: Vinyl ester resins

Synthesis of VERs is usually catalyzed by tertiary amines, phosphines, and alkalies or -onium salts (Jackson 1980, Rao et al. 1986, Peter et al. 1991, Boutevin et al. 1993, Zaske 1998, Aggarwal et al. 1999, Gawdzik and Matynia 2001, Srivastava et al. 2002, Pal et al. 2003) in the temperature range of 80–110°C and taking reactants in stoichiometric ratio. Complete esterification of the epoxy resin in practice is difficult because of gelation of the product before an acid value below 10 is attained. Therefore, an excess of epoxide resin is always employed in the esterification reactions (Sandner and Schreiber 1992, Wheelar 1955). The reaction is monitored by determining the acid value and by Fourier transform infra red spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR), and Carbon-13 nuclear mag-netic resonance spectroscopy (13C NMR) performed on the samples withdrawn at regular intervals (Boutevin et al. 1993, Aggarwal et al. 1999, Gawdzik and Matynia 2001, Malik et al. 2001, Srivastava et al. 2002).

2 Next-generation VERsVERs in the neat form are highly viscous and, when used with reactive diluents, show low viscosity during curing, which leads to wastage of material and results into com-posite starving of matrix resin in certain applications such as sheet molding composites (SMCs). Structural modifica-tions of VERs can be done to get workable viscosity levels without using reactive diluents. It has been reported by Oprea et al. (2000) that the reaction of secondary hydroxyl group of VER with diisocyanate gives a resin with low vis-cosity. On the contrary, chemical modification of the side hydroxyl groups by dicarboxylic acid anhydrides produced half ester acids using pyridine as catalyst, which led to thickening of resin during cure, as reported by Rao et al. (1987) and Swisher and Grams (1971). In order to obtain a product that shows faster cross-linking ability in UV light, Wang (2003) synthesized siloxane-based epoxy acrylates.

3 Bio-based VERs

Ecofriendly VERs using renewable sources, e.g., cardanol from cashew nut, can be synthesized to reduce viscosity, curing time, and concentration of styrene (Sultania et al. 2010). VERs prepared from rosin-acid-based epoxy resin have been reported, with improved coating abilities of VERs due to faster drying and better chemical resistance (Atta et al. 2006). Carbohydrate-derived isosorbide can be used as core scaffold to synthesize novel and innovative VERs with extremely low viscosity. These can fulfill the requirement of high-performance composite resin since these have higher cross-link density and give a high Tg value of 245 ± 9°C compared with any other commercially available VERs. These have the potential to be used as viscosity modifiers without adversely affecting any other qualities of the matrix material for high-performance composite resin (Sadler et al. 2013). Aliphatic matrix resins derived from cycloaliphatic VER and glutaric acid showed reduced UV absorption. These can be used to obtain coatings and fiber-reinforced composites with extreme durability to sunlight (Starr et al. 2001). Photo-stabilization of VER was also reported by synthesized interpenetrating polymer network modified lignin (Rosu et al. 2009).

In order to obtain the starting material for the syn-thesis of VERs from a renewable source, use of mycrene, which is an oily liquid obtained by cracking on β-pinene of turpentine, has been reported by Yang et al. (2013). These mycrene-based VERs have rapid curing (∼50 s) in the pres-ence of UV light. These resins also show excellent thermal stability and good shore hardness. Attempts have also been made by Li et al. (2013) to obtain VE bio-copolymer derived from dimer fatty acid polymerized with glycidyl meth-acylate and maleic anhydride modified dimer fatty acid polymerized with glycidyl methacrylate resin. These were further copolymerized with styrene and have been shown to exhibit superior mechanical and thermal properties.

CC

O O

O O CH2 C

CH3

CH3

CH2 O C

O

CHCH C

O

CH

CH3

CH2

n

OHHO

Unsaturated polyester resin

CO CH2CHO

CH3

CH2

CH3

OHn

O

CH2OC CCH2CH

OH

OC

CH3

H2CO

C

CH3

CH2

Figure 1 VER based on BPA epoxy.



S. Jaswal and B. Gaur: Vinyl ester resins 569

C CH2CHO

CH3

CH2

CH3

OHn

OCH2CH2CH

O

CH CH2

O

C O

CH3

CH2

CH3

O

C O

O

CH2

O

O

Diepoxidized Hydrogenated Bisphenol A

Cycloaliphatic Epoxy

CH2

CH2

CH2

CH

O

O

NCH

CH2

CH2

CH2

CH2

CH

O

O

N

CH

CH2

CH2

CH2

CH2

CH

O

O

NCH

CH2

CH2

CH2

CH2

CH

O

O

N

CH

CH2

CH2

S

O

O

CH O CH2CH

O

CH2CH2 CH2CH

O

O

O CH2CH

O

CH2

O CH2CH

O

CH2

CH2CH2

O CH2CH

O

CH2 O CH2CH

O

CH2

n

Tetraglycidyl Methylene Dianiline

Tetra Glycidyl Sulphone Dianiline

Tri Glycidyl Triphenylmethane

Epoxy Novolac

C CH2CHO

CH3

CH2

CH3

OHn

OCH2CH2CH

O

CH CH2

O

C O

CH3

CH2

CH3

O

Diglycidyl Ether of Bisphenol A

CH2

CH2

CH3 CH

CH

CH

COOH

COOH

COOH

COOH

CH3

CH CH

CH

Unsaturated Acids

Acrylic acid:

Methacrylic acid:

Crotonic acid:

Cinnamic acid:

Figure 2 List of different epoxy resins and unsaturated acids used for VER synthesis.

4 Curing of VERsVER is dissolved in a reactive cross-linking monomer such as styrene, vinyl toluene, α-methyl styrene, p-tert-butyl

styrene, divinyl benzene, methyl methacrylate, etc., in order to reduce its viscosity. These react with the back-bone polymer in the presence of organic peroxides and hydroperoxides or azo and diazo compounds as free




radical initiators to form a three-dimensional cross-linked network. It has been reported that fatty acid monomers obtained from renewable resources (La Scala et al. 2004a) and bimodal blends of VE monomers (La Scala et al. 2004b, 2005) can replace styrene as reactive diluent to reduce emission up to 78% (La Scala et al. 2004c). At low temperature, promoters such as tertiary amines and salts of metals like cobalt octoate or naphthenate can be used to fasten the decomposition of initiators (Saunders 1973). A mixture of initiators is used when a large temperature increase is expected (Zaske 1998). Inhibitors like hydro-quinone, tertiary butyl catechol, and toluhydroquinone are added in very small amounts (in ppm) to the resin for-mulations to inhibit premature gelation by consuming free radicals that occur naturally in the resin. This improves the shelf life of the resins.

The curing of VER containing styrene as reactive monomer involves three possible reactive paths: styrene-VE copolymerization, styrene homopolymerization, and VE homopolymerization. During the curing process, the physical state of thermoset resins changes from liquid to gel and, ultimately, to a glassy solid. It is believed that the heterogeneity of free radical cross-linking systems during such reaction is an inherent result of the physi-cal aspects of the free radical reaction and is explained through widely accepted microgel theory (Saunders 1973, Yang and Suspense 1991, Hsu and Lee 1993a,b, Chiu and Lee 1995, Chen and Yu 1998). The curing of VE/styrene, like vinyl-divinyl system (Dusek and Spevacek 1980), shows an induction period due to the presence of inhibi-tors and cage effect (Ziaee and Palmese 1999), in which the inhibitor consumes the free radicals and very little polymerization takes place. In stage I, which is the period of accelerated propagation, the styrene monomer was found to react at a slower rate than the VE monomer. The kinetics of copolymerization is thought to be governed by the intrinsic reactivity of the styrene and VE double bonds and not by diffusion. In stage II, the polymerization rate is dominated by Trommsdorff effect (Dua et al. 1999). According to Ganem and Mortaigne (1993), the polymeri-zation of VE monomer decreases and polymerization of styrene increases throughout this stage. The reason for this is attributed to the higher mobility of the styrene mol-ecule in the entire network, owing to its smaller size. The VE double bond at the end of stage II becomes immobile in the network due to its larger size. Toward the end of the reaction, i.e., during stage III, the VE ceases to react while the rate of consumption of styrene continues to increase, which leads to the formation of polystyrene until vitrifi-cation takes place (Ganem and Mortaigne 1993, Dua et al. 1999). The polystyrene formed cannot be extracted from

the fully cured VE resin as polystyrene chains are either entangled within the matrix or that each chain is indepen-dently grafted to the matrix (Ganem et al. 1994).

The cessation of the consumption of the methacrylate double bond of VE led to the suggestion of biphasic struc-ture and, subsequently, to the belief in the formation of microgel with the occurrence of polymerization-induced phase separation in VE/styrene systems. Atomic force microscopy photographs of cured VE/styrene system also endorsed the theory of microgel formation by showing nodular morphology (Ziaee and Palmese 1999) or closely packed microgels around 100 nm in diameter (Brill and Palmese 2000) during the early stages of curing reaction. Clusters of coral-like microgels with a maximum size of 4 μm were also observed by Li et al. (2004) using scan-ning electron microscope on the fractured surface of a sample cured at 80°C. The density of clusters was found to decrease when the isothermal curing temperature was increased to 120°C. It was also observed that after curing, the biphasic structure disappeared (Li et al. 2004). Rey et al. (2000) investigated the morphological changes during the course of copolymerization reaction between tetraethoxylated bisphenol-A (BPA) dimethacrylate and styrene or divinyl benzene. They reported the formation of microgels using dynamic light scattering. Aggrega-tion of microgels of diameter between 19 and 40 nm into clusters was observed up to the gel point, after which the macroscopic network is developed. The size of the cluster was found to be greater for divinyl benzene due to the large number of pendant double bonds as compared with styrene. It was also observed that with increasing cure temperature, the size of the microgels and clusters became smaller. The two-phase structure of VE matri-ces, unlike that of UPE resins, was found to be organized rather than random structured, which gives excellent hydrolytic stability to VE resins (Mortaigne et al. 1997). Various methods employed to study the curing behavior of VERs are differential scanning calorimetry (DSC) (Chang 1992, Lee and Lee 1994, Cook et al. 1997), infrared (Ganem and Mortaigne 1993, Brill et al. 1996, Li et al. 1999, Brill and Palmese 2000), gel time studies (Abadie et al. 2002), dynamic mechanical thermal analysis (DMTA) (Scott et al. 2002a), torsional braid analysis (Stone et al. 2000), and thermal scanning rheometry (Martin et al. 2000).

A variety of kinetic models have been used to relate the rate of the cure reactions of the thermosetting resins to time, temperature, and the extent of cure. These kinetic models may be autocatalytic (Lee and Lee 1994, Auad et al. 1999) or mechanistic (Kamal and Sourour 1973, Rey et al. 2000). Of these two models, mechanistic models, despite giving better prediction and interpretation of the




curing reaction, are not easy to use in the process simu-lation (Yang and Lee 2001). Autocatalytic models are, however, generally preferred to mechanistic models since these are expressed by a relatively simple rate equation and are developed ignoring the details of how reactive species take part in the reaction. The autocatalytic model developed by Kamal and Sourour (1973) is being used by many workers.

VERs exhibit autoacceleration in the polymerization rate, which results into a single peak and cessation in polymerization before the full conversion; i.e., vitrifica-tion takes place (Mousa and Karger-Kocsis 2000). Many workers though have observed two overlapping peaks or a shoulder in isothermal DSC scans (Lem and Han 1984, Lee and Lee 1994, Cook et al. 1997, Mousa and Karger-Kocsis 2000). Li et al. (1999) and Yang and Lee (2001) suggested that the first peak was observed due to the copolymeriza-tion between styrene and VE double bonds, whereas the second peak was caused by the homopolymerization of styrene monomers. It has been reported that with increas-ing styrene content, the overall isothermal rate of curing of VERs decreased and the shape of DSC isotherm also changed from one peak to two. It has been reported by Li et al. (1999) that promoter concentrations and cure tem-peratures affected the reaction rates but did not change the copolymerization mechanism between styrene and VER and therefore did not influence the structure forma-tion of copolymer. On the contrary, according to Ziaee and Palmese (1999), the selection of cure temperature does affect the structure of the VER/styrene network. They compared the curing behavior of this system at 30°C and 90°C, respectively, by considering the reactivity ratios of VE and styrene at these two different temperatures. It has been reported that at 30°C, both active styrene and VE prefer to react with VE double rather than a styrene monomer. However at 90°C, an active VE prefers to react with styrene monomer while active styrene still prefers to react with VE double bond, thus yielding different struc-tures at two different cure temperatures.

According to Lem and Han (1984), the first exotherm peak arises from the cross-linking reaction that starts at lower temperatures with free radicals generated through a reversible complex formation between the initiator and the promoter. However, according to Cook et al. (1997), the shoulder or the first smaller peak may be due to short-term polymerization, attributed to H2O2 (present as impu-rity in methyl ethyl ketone peroxide) initiation followed by a broad maximum in the polymerization rate due to Trommsdorff effect.

An increase in isothermal cure temperature (Lem and Han 1984, Dhulipala et al. 1993) accelerated the rate of the

40

End

othe

rmic

Exo

ther

mic

Hea

t flo

w

60 80 100 120 140 160 180

2

1

3

Temperature (°C)

Figure 3 DSC scans for the curing reaction at 10°C min-1 of VERs containing 40 wt% of (1) methyl acrylate, (2) ethyl acrylate, and (3) butyl acrylate.

reaction. Due to vitrification at low temperature, it was observed that with an increase in isothermal cure tempera-ture, there was an increase in heat of cure and a decrease in residual heat during postcuring and net effect on the total heat of cure was minimal. As in the dynamic conditions, the resin cures thoroughly above the glass transition tem-perature (Tg) and vitrification does not take place; the heat of cure is found to be more than the total heat of cure under isothermal conditions. The effect of different reactive dilu-ents on the curing behavior of VERs has been studied by many researchers (Jackson 1980, Varma et al. 1985, Bhat-nagar and Varma 1989, Gaur and Rai 1992a, Choudhary and Varma 1993, Malik et al. 2001). The addition of α-methyl styrene in VER increased the gel time and suppressed the peak exotherm (Bhatnagar and Varma 1989). Typical DSC scans (Gaur and Rai 1992b) for the curing of VERs contain-ing methyl, ethyl, and butyl acrylates at a program rate of 10°C min-1 are given in Figure 3. Less polar ethyl acrylate was found to be more reactive to VER as compared with methyl and butyl acrylate due to large differences in the polarity of acrylates.

The effect of concentration of styrene on thermome-chanical properties has also been studied using the DMTA technique. Glass transition temperature, Tg, can be deter-mined with significant levels of sensitivity by monitoring the changes in the storage modulus, E′, loss modulus, E″,




or the loss tangent, tan δ, as a function of temperature. It has been reported that the Tg and the temperature of the tan δ maximum were not significantly affected by styrene content. The magnitude of the rubbery modulus was found to increase while the tan δ maximum decreased with the increased cross-link density (cross-linkable methacrylate group) (Scott et al. 2002a). The effect of cure temperature on dynamic mechanical properties has been investigated by Cook et al. (1997). They found that for the samples cured at room temperature, two apparent glass transition regions at approximately 65°C and 115°C were exhibited in the DMTA trace. In contrast, only one transition was observed for the “fully” cured sample. The reason for this anoma-lous behavior was attributed to the additional cure that occurred on further heating during the DMTA experiment, which provided sufficient molecular mobility to recom-mence the curing process, causing a shift in the transi-tion region and an increase in the modulus. Martin et al. (2000) determined gel time and vitrification time using the DMTA technique. According to them, gel time is the time at which the maximum in tan δ curve appears and corre-sponds to the difference between the storage and the loss modulus, i.e., the time at which the resin begins to cross-link, generating maximum difference between the elastic and the viscous behavior. The second maximum in tan δ curve gives the vitrification time (Figure 4). The viscoelas-tic behavior of the material in this time interval is due to the increase in either the storage or the loss modulus.

5 Photopolymerization of VERsVERs are the most common thermosetting resins used for the fiber-reinforced polymer (FRP) composites that can

0

0.0

0.2

0.4

0.6tan

δ

tan δ η′η′′

η′′ (

kPa-

s)

η′ (k

Pa-s

)

0.8

1.0

1.2

1.4

20 40 60 80 100 120 140

100

200

300

400

0 0

20

40

60

80

Time (min)

Figure 4 Storage modulus (G′), loss modulus (G″), and tan δ vs. time for the VER from DMTA.

be cured in light using various photoinitiators at room temperature. It has been reported that photoinitiators like bis-acylphosphine oxide, its blends with α-hydroxy ketones, and camphorquionone/amine in the VER/styrene system were found to provide the fastest curing, best through-cure of the composites and gel coatings, high styrene incorporation yields, and good mechanical properties (Cook 1992, Baikerikar and Scranton 2001, Sitz-mann et al. 2001, Scott et al. 2002b, 2003a,b), which lead to significant productivity enhancements. However, rate of photopolymerization varied with the type of monomer used as reactive diluents due to the different reactivity of these monomers.

6 Effect of low-profile additivesTo improve fracture resistance and to control volume shrinkage of VER, they are usually blended or reacted with different thermoplastics and nonreactive additives or modifiers such as PVAc, PMMA, and polyurethane-based low-profile additives (LPAs). The mechanism of shrinkage control has been studied extensively in the case of UPE resins. PVAc initially forms soluble or stable dispersion with UPE resin before cure. During curing at concentrations higher than the critical value at around 5 wt% PVAc levels, a co-continuous structure is obtained as PVAc is pushed to the surface of the growing microgel particle, which reduces the tendency of the resin particles to coalesce, which leads to the formation of continuous PVAc phase interpenetrating the cross-linked network phase (Han and Lem 1983, Bucknall et al. 1985, 1991a,b, Suspene et al. 1991, Lucas et al. 1993, Kinkelaar et al. 1994, Cook et al. 1998). Although LPAs do not show the same shrinkage control efficiency in VER as in UPE when cured at low temperatures, they are effective in reducing the surface defects and internal stresses (Cao and Lee 2003) due to shrinkage by thermal expansion of thermoplas-tic phase and development of void structure within this phase. Saturated polyester formed from block copolymer of dibasic acid and an ethylene oxide/propylene oxide can be used as LPA for the high-temperature SMCs using VER as polymer matrix. The addition of polyester showed good physical properties and zero shrinkage for these compos-ites (Cook et al. 1998). It is observed that increased LPA concentration, low initial heating rate, and high peak temperature were considered to be the most desirable conditions for shrinkage control. The curing behavior of VERs is not affected significantly by the presence of PVAc or its phase precipitation. Conversely, it has been reported




elsewhere that the addition of LPA decreased the rate of cure and also the final degree of cure of the resin (Han and Lem 1984).

7 Mechanical propertiesVERs are preferred materials for structural composites due to their excellent mechanical properties and tough-ness (Table 1) (Cassis and Talbot 1998). The rigidity of the prepolymer, the type and concentration of reactive dilu-ents, and the cross-link density are the major contributing factors to the mechanical strength of the cured VER. It has been observed that an increase in the cross-link density results in an increase in the glass transition temperature and modulus (Scott et al. 2002a) and a decrease in strain-to-break and impact energy (Cassis and Talbot 1998). The VERs produced by epoxy novolac with methacrylic acid provide more unsaturation sites than BPA-based VERs do and produce greater toughness, resiliency, solvent resist-ance, and heat resistance due to epoxy backbone of dif-ferent molecular weights. Dilution with styrene resulted in a decrease in glass transition temperature (Choudhary and Varma 1993) and tensile strength and an increase in the elongation of neat resin casting and glass-fiber-rein-forced laminates. Cure temperature, cure formulation, and curing method also affect the mechanical properties of VERs. Ziaee and Palmese (1999) found that the fracture toughness of BPA-based VER samples cured at 30°C using cumyl hydroperoxide as initiator and cobalt naphthen-ate as promoter and then post cured at 125°C was three times greater than for the samples cured using the same formulation at 90°C and post cured at 125°C. Ganglani et al. (2002) reported that using N,N-dimethyl aniline as an accelerator during cure lowers the tensile strength, fracture toughness, and strain-at-break and results in maximum methacrylate conversion. Benzoyl peroxide was debated to be a better initiator as compared with cumyl hydroperoxide. Microwave curing in a shorter time

results in an increase in strength and stiffness than curing in natural conditions.

8 Rubber toughening of VERsVERs are limited by their brittleness (Pantano et al. 2002), especially when good impact behavior is needed. One of the methods used to increase toughness is the modifica-tion of the resin with high-molecular-weight reactive liquid rubbers such as polybutadiene, butadiene acrylonitrile copolymer, polyepichlorohydrin, and polyacrylates, with molecular weights in the range of 2000–5000 gmol-1 (Ullett and Chartoff 1995, Auad et al. 2001, 2002, 2003). During cure, the discrete rubber-rich second phase formed in the matrix improves its fracture toughness provided that this second phase meets certain criteria relative to size, shape, volume fraction, dispersion, and adhesion. However, poor miscibility and poor reactivity of rubber with resin are sig-nificant problems in achieving a suitable morphology for toughening. A nonhomogeneous mass is formed that is undesirable for the composite processing and resin control during cure. Attempts were made to improve the compat-ibility of rubber with VER by increasing the temperature, ultrasonic treatment, and use of surfactants (Dreeman et al. 1999); however, they failed to improve compatibility. The use of butadiene-acrylonitrile (VTBN)/epoxy-terminated butadieneacrylonitrile-based rubber modifier without the use of compatibilizers has been reported. These modifi-ers, while limiting plasticization of the resin matrix, gave a system increased fracture toughness and stress intensity factor (Dreeman et al. 1999, Robinette et al. 2004).

Siebert et al. (1996) were able to obtain an approxi-mately 540% increase in stress intensity factor with high rubber levels, which also led to significant plasticization of the resin matrix. However, a limited amount of rubber should be added so that the modulus and the strength of base resin will not be affected (Achary et al. 1991, Ullett and Chartoff 1995, Auad et al. 2001). Modification

Table 1 Mechanical properties of cured UPE resins and VERs (Malik et al. 2000).

Property Ortho-resin

Iso-resin

BPA fumarate

Chlorendic BPA-based VE resin

40 wt% fiber-glass-reinforced BPA-based VE resin

Tensile strength (MPa) 55 75 40 20 80 160Tensile modulus (GPa) 3.45 3.38 2.83 3.38 3.5–3.9 11.0Elongation at break (%) 2.1 3.3 1.4 – 4.0 –Flexural strength (MPa) 80 130 110 120 140 220Flexural modulus (GPa) 3.45 3.59 3.38 3.93 3.7 9.0Heat distortion temperature (°C)

80 90 130 140 100 –




of low-molecular-weight hydroxy terminated polybuta-dienes (HTPB) through reaction with diisocyanate gave a more compatible resin system, which led to improvements in adhesion and mechanical strength (Achary et al. 1991, Pham and Burchill 1995). End capping of polybutadiene with various end groups and the mechanical test results for the VER toughened with modified polybutadiene are listed in Tables 2 and 3, respectively (Pham and Burch-ill 1995), which shows that with increasing length of the end groups, the ability to provide a tougher cured resin improves such that the energy to propagate a slow crack increases 10 times. Addition of only 5% modified rubber led to a 2- to 3-fold increase in stress intensity factor and 10-fold increase in energy required for fracture in VERs. Toughening of VER matrix is also reported to be carried out by blending the resin with core-shell polymer addi-tive with a polybutadiene core, which is useful for typical structural commercial materials, e.g., polymer concrete with increased flexural strength (Burchill et al. 2001). Sat-urated elastomeric comb copolymers prepared with the backbone of polyacrylate with a carboxyl group at each end and pendant chains derived from the macromer of polycaprolactone in a manner analogous to that of CTBN have also been reported as reactive modifiers to improve the toughness or flexibility of thermosetting resins, includ-ing epoxy resins and VERs (Yu 1996). Due to the absence of double bonds, these reactive modifiers are preferred to the conventional CTBN elastomers as these are more resistant to UV light and thermooxidative degradation and can be used at elevated temperatures.

9 Thermal, oxidative, and photostability

VERs containing fillers and reinforcements are com-monly used in elevated temperature applications,

especially in areas demanding electrical and corrosion resistance. Although fillers and reinforcements improve the stability of the composites at high temperatures, the resin, at some point, begins to dissociate chemically. The cross-linked resins, irrespective of the composition of VE or the vinyl monomer, undergo spontaneous decomposi-tion at temperatures of around 300°C, which is a char-acteristic of the vinyl polymers. Single-step degradation has been obtained using a thermogravimetric analyzer (TGA) for cured VER containing 40 wt% styrene as dilu-ents (Gaur and Rai 1992a, Agarwal et al. 2002). Two-step degradation thermogravimetry scan was reported when a mixture of styrene and methyl methacrylate was used (Agarwal et al. 2003). The decomposition behavior of epoxy novolac-based VER samples of varied acid values (11–48 mg KOH g-1 solid) containing 40 wt% of styrene as reactive diluent using TGA (Gaur and Rai 1992a) showed the cured product with the lowest acid value precur-sor to be the most thermally stable, with a lifetime of 16.58 years at 400°C. In VE, networks based on BPA cured in the presence of benzoyl peroxide and exposed to UV with λ ≥ 300 nm in the presence of oxygen formed unstable hydroperoxides, which led to the fragmentation of VE network into highly volatile low-molecular-weight products (Rosu et al. 2008).

10 Chemical resistance and water absorption

VERs are used to handle most hot, highly chlorinated, and acid mixtures even at a high temperature due to the better chemical and solvent resistance of VERs compared with other thermoset resins (Jacob 2003). The excellent acid base resistance of epoxy-based methacrylated VERs is due to their low ester content and protection of the ester linkages by the methyl shield of the methacrylate group.

Table 2 Polybutadiene end capped with various chain ends [Pham and Burchill 1995].

PB1 HTPB end capped with MDI, i.e., bis(4-isocyanatophenyl) methane. Free isocyanate.(MDI-PB-MDI)

PB2 HTPB end capped with MDI. Excess isocyanate was neutralized with hydroxylpropylmethacrylate (HPM).(HPM-MDI-PB-MDI-HPM)

PB3 HTPB end capped with MDI. Excess isocyanate was neutralized with triethylene glycol (TG).(TG-MDI-PB-MDI-TG)

PB4 HTPB end capped with CRM (MDI terminated-terminated polypropylene glycol). Excess of isocyanate was neutralized with methanol (Me).(Me-CRM-PB-CRM-Me)

PB5 HTPB end capped with MDI. Excess isocyanate was neutralized with TG-MDI-TG.(TG-MDI-TG-MDI-PB-MDI-TG-MDI-TG)




The VERs are found to be the most resistant in acidic envi-ronments and distilled water, with better retention of the mechanical properties (Lee et al. 1992, Ghorbel and Val-entin 1993, Valea et al. 1999, Kumosa et al. 2001). The VER samples copolymerized with styrene (45 wt%) at room temperature absorbed less water (0.8 wt%) than did the samples without styrene. The amount of water absorbed also increased with the increase in temperature. Karbhari and Wang (2004) used DMTA to observe that the exposure of glass-fiber-reinforced VE composites to water initially caused plasticization, resulting in a decrease in the inten-sity of the loss tangent (tan δ) peak as well as a decrease in the glass transition temperature. Subsequent to this, lower-molecular-weight species gets leached out, result-ing in an increase in the glass transition temperature and a change in the loss tangent profile. This phenomenon could be termed as antiplasticization effect. The response of these resins to an alkaline solution showed an initial increase in brittleness due to moisture induced after curing, followed by the effect of plasticization. Rubber-modified VER is shown to have property retention similar to that of standard BPA-based VER except for the lower solvent resistance to low-molecular-weight solvents such as ethanol and toluene (Kardenetz et al. 1985). The cure schedule also influences the resistance of the resin toward different solvents. It is observed that the resin samples that are not subjected to post curing are more easily attacked by solvents brought in contact with them (Valea et al. 1998).

11 Applications

11.1 VERs as coatings and adhesives

The use of VERs as coating material has gained increasing popularity since the 1990s. Nowadays, VERs are being used as new-generation self-healing coatings. These coatings

have a self-protective ability to smartly resist mechani-cal and chemical damages caused by external aggressive environment. VERs containing TiO2 particles have been reported as a self-healing coating material for aluminum alloy 5083, which guard the metal surface. In case of abra-sion to the coating, the aluminum is said to react with BPA, which is a chemical precursor of VER, and forms a barrier at the damaged part, where these rutile particles serve as receptacles for the BPA. This diminishes the damage by the external hostile conditions on the surface (Stankie-wicz et al. 2013). Although the same coating was not found to be effective in inhibiting the corrosion of carbon steel, a three-layered coating consisting of super absorbent polymer mixed with VER sandwiched in between the top and base layers consisting of pure VER showed better polarizing resistance (Yabuki and Okumura 2012). Modi-fication in the base resin by reaction of the secondary hydroxyl group of triglycidyl ether of m-amino-phenol-based VERs with isocyanurate to obtain urethane linkages resulted in a coating that showed superior adhesion to the steel panels and exhibited good chemical resistance to various acids, alkalies, water, and organic solvent as compared with that of triacrylated derivatives (Patel et al. 1999). VER composites with different types of fillers have also been explored as high-performance coatings. Ehsani et al. (2013) has reported the use of glass flakes (GFs) as reinforcement fillers to enhance the physical properties (i.e., modulus, thermal expansion, thermal and electrical conductivity, and magnetic recording) of VER composite used for coating applications. A study of GF-reinforced polymer composite using DMTA in the temperature range of 25–180°C showed that in increasing the GF content from 5 parts per hundred resin (phr) to 15 phr, there was an increase in storage modulus, whereas higher thermal sta-bility was obtained with 25 phr GF content due to thicker GF-enriched char layer build up on the surface of the com-posite. As the filler content was increased from 0 phr to 15 phr, a decrease in reaction enthalpy and glass transition temperature of the composite system was observed.

Table 3 Mechanical test results for VERs toughened with modified polybutadiene (Pham and Burchill 1995).

Samples KIci KIca GIci GIca Ksen E

Derakane 411-15 (BPA-based VE resin) 0.72 0.63 157 122 1.12 2.825 wt% HTPB 1.20 0.65 560 163 1.02 2.245 wt% PB1 1.86 0.89 1369 314 1.46 2.085 wt% PB2 1.67 0.82 1051 253 1.44 2.325 wt% PB3 1.91 0.82 1390 258 1.44 2.3610 wt% PB3 2.36 2.36 2571 2571 1.63 1.955 wt% PB4 2.22 2.22 1948 1948 1.56 2.105 wt% PB5 2.04 2.04 1751 1751 1.61 2.135 wt% PB3 2.59 2.59 3749 3749 1.75 1.33




VER is a promising class of thermosetting matrices used as adhesives with high strength and toughness, enduring service at high temperatures and chemical con-frontation for structural bonding applications as well as in repair applications. It has been reported that liquid crystalline VER synthesized from p-(2,3-epoxypropoxy)-α-methylstilbene as epoxy monomer showed excellent adhesive strength for aluminum substrate (Ambrogi et al. 2002). The methacrylate group of the resin acts like Lewis acid and interacts with aluminum oxide that acts as a Lewis base, both through the carbon-carbon double bond and through carbon-oxygen double bond present on the resin. It is believed that the resin shows adhesion to the oxide layer immediately before the curing reaction occurs and thus provides a stable structure after cure.

11.2 VERs as matrix for composite materials

Polymer matrix composites and especially FRPs are widely utilized in construction applications, including industrial and agricultural buildings, due to their high mechanical strength, tailored design through controlled anisotropy, chemical and thermal stability, acoustical characteristics, light transmission and translucency, electromagnetic transparency, electrical nonconduc-tivity, etc. (Taranu 2009). VERs, which are the leading candidate among thermosetting polymers, can serve as matrix material for producing fiber-reinforced compos-ites, short fiber-reinforced composites, as well as par-ticulate composites. These thermoset resins are shown to have very good adhesion to glass fibers, aramid fibers, as well as carbon fibers. Composites based on VERs are used in a variety of engineering applications and espe-cially for wear-sensitive applications. A comparison of the tribological properties of the composite produced by using glass fiber and carbon fiber, respectively, showed that carbon-reinforced VER composites show supe-rior wear resistance and lower coefficient of friction as compared with glass-fiber-reinforced VER composites (Suresha et al. 2010). The influence of aluminum ceramic particulate on the tribological characteristics of E-glass-fiber-based VER composites has also been studied by Chauhan et al. (2013). The minimization of erosion or wear performance was also observed in hybrid VER com-posites consisting of short glass and carbon fiber (1:1) with different fiber weight fractions (from 20 wt% to 50 wt%) (Kumar et al. 2012). Ku et al. (2007) were able to reduce the shrinkage of the VE composite contain-ing flyash as particulate filler by curing the composite sample in the presence of microwave. Microwave curing

not only showed lesser shrinkage but also gave the com-posite better fracture toughness.

E-glass and Kevlar-49 fiber-reinforced VE laminates have been reported to be used in ballistic applications (Panda et al. 1994). It has also been described that by optimization of loading of short aramid fibers and exter-nal variables (standoff resistance, impingement angle, erodent size, impact velocity, etc.), erosion or wear perfor-mance enhancement of short aramid-fiber-reinforced VER composite can be successfully achieved (Kumar et al. 2011)

A comparative study of the chemical and thermal behavior of two main types of thermosetting polymers, i.e., polyester resin and VER, showed that the VER cure reaction proceeded more slowly, because of which it was able to form a more compact structure; as a result, the VE/glass fiber composite gave better chemical resist-ance against seawater (Visco et al. 2011). In order to use these resins as matrix for preparing composites with high dielectric strength, hollow glass microballoons were used as fillers to obtain syntactic foams in order to develop inte-grated circuit boards having good mechanical strength (Shunmugasamy et al. 2013).

In the present era, the use of natural fiber reinforce-ments has also gained substantial attention in composite technology as a low-cost, lightweight, and environmental-friendly alternative to other synthetic fibers. The mechani-cal, chemical, and thermal properties of VER composites unified with naturally obtained cellulose, cotton, and luffa cylindrical fibers have also been investigated. Cellulose fabricated VER composites showed a gradual increase in water uptake, tensile modulus, and flexural strength with an increase in cellulose fiber volume fraction in composites (Alhuthali and Low 2013a). The thermal and mechanical behaviors of alkali-treated and -untreated cotton-fiber-reinforced VE composites have also been reported by Shahedefar and Rezadoust (2013). It was observed that the use of alkali-treated cotton fiber to reinforce VER improved the tensile strength and elongation-at-break of composites by 5% and 25%, respectively, as compared with that of untreated cotton fiber composites due to increased surface roughness by the removal of wax and oil from the surface of the fibers. Attempts have also been made by Siqueira and Botaro (2013) to replace synthetic fibers by fibrous mat of Luffa cylindrica ripe fruit as reinforcement and alu-minum hydroxide as polymer additive to prepare VER com-posites. These fibers of L. cylindrica were modified with 1,2,4,5-benzenetetracarboxylic dianhydride and NaOH (mercerization) to increase the interfacial compatibility, adhesiveness, and wettability between L. cylindrica fibers and VE matrix. These composites obtained also showed improved thermal and mechanical properties.




11.3 Nanostructured VER composites

Polymer nanocomposites are polymer matrix composites in which the reinforcement has at least one of its dimen-sions in the nanometer range. These composites show superior mechanical, thermal, electrical, optical, and other properties at relatively low reinforcement volume fractions. The transition from microparticles to nano-particles yields dramatic changes in physical properties. Nanoscale materials have a large surface area for a given volume, and many properties (chemical and physical) are governed by surfaces and surface properties (Luo and Daniel 2003, Thostenson et al. 2005). The use of organic or inorganic nanofillers such as carbon nanofibers, cel-lulose fibers, titanium oxide nanoparticles, etc., has become ubiquitous in the present-day matrix materials for developing nanocomposites. Efforts are always being made in order to develop material with better macro-scale properties. Jang et al. (2012) has studied the inter-facial interactions between the surfaces of oxidized vapor grown carbon nanofiber (VGCNF) and VE monomer and reported the formation of 5–10 Å stiffer interphase, which affected the interfacial adhesive bonding. This bonding could be increased by increasing the polar interactions between the matrix and oxidized VGCNFs. Nanocompos-ites developed by Shahrajabian et al. (2013) using TiO2 nanoparticles showed excellent mechanical and thermal properties, which were seen to increase after the compos-ites were exposed to electron beam. Recycled cellulose fiber sheet based VE-containing nanoclay filler eco-nano-composites were developed and were further investigated for water uptake and mechanical and thermal proper-ties. Nanoclay addition to the polymer matrix decreased water uptake and increased thermal stability, mechanical strength, and fire-resisting properties due to better inter-facial interactions between fiber and matrix, although it was observed that the addition made the nanocomposite brittle (Alhuthali et al. 2012). Chaturvedi et al. (2013) has described the development of graphene-reinforced VE nanocomposites. Graphene sheets can be used to resolve the serious concerns related to the use of carbon nano-tubes, primarily the cost and limited production. Multi-walled carbon nanotube unified VER nanostructures can become an emerging electrically conductive polymeric system (Yurdakul et al. 2010). Multiwalled carbon nano-tube-VE cross-linking nanostructures have also been used for bipolar plates in proton exchange membrane fuel cells. This unique system showed significant enhancement in performance of the fuel cell due to better dispersion of carbon nanotubes into the matrix, higher mechanical strength, and superior electrical conductivity. Thostenson

et al. (2009) has reported that due to the low electrical percolation threshold of VER as matrix, high aspect ratios of carbon nanotubes were maintained during nanocom-posite formation and an electrically conductive network was formed throughout the laminate, which in turn led to the utilization of carbon nanotubes as in situ sensors for detecting deformation and damage in advance naval com-posite structures.

Halloysite nanotubes (HNTs), which originate from naturally deposited alumiosilicate [Al2Si2O5 (OH)4.H2O] and have chemical analogy to kaolin, have been unified with VERs to reduce water uptake and amplify thermal and mechanical properties. HNTs have also been found to be effective in increasing the toughness of the material. It has also been reported that this nanocomposite attains good thermal stability and flame retardancy due to the hollow tubular structure of HNTs as well as the presence of Fe2O3 as impurity (Alhuthali and Low 2013b). Improved toughness properties of VER nanocomposites containing polypropylene mesofibers have been reported by Liang et al. (2011).

12 ConclusionVERs either in the pure form or in compounded form with fillers have use in a wide range of applications. The growth of VERs has also been boosted because of their excellent handling characteristics and easy cure. These are the prime candidates for composites in transporta-tion and infrastructure applications for construction of parts of automobiles, polymer concretes, reinforcements for bridges, etc., due to their excellent thermal perfor-mance and mechanical properties. Because of their inherent resistance to chloride attack and long service life, composites of VERs are adopted by the paper and pulp industries as well. VERs based on epoxy novolacs are used for chemical storage tanks, pipes and ducting, fume extraction system, and gas cleaning units, as these resins show superior chemical resistance at high tem-peratures. These have high tensile elongation along with superior corrosion resistance, which makes them a promising material for producing lining and coating with outstanding adhesion to other types of plastics and conventional materials such as steel and concrete. VERs also have a variety of applications in optical fiber coating, topcoats for metal containers, UV curing inks, as well as printed circuit boards (Radhakrishnan and Pethrick 1994, Bajpai et al. 2004, Chattopadhyay et al. 2005).




ReferencesAbadie MJM, Mekhissi K, Burchill PJ. Effects of processing

conditions on the curing of a vinyl ester resin. J Appl Polym Sci 2002; 84: 1146–1154.

Achary PS, Joseph D, Ramaswamy R. Study on a vinyl ester/methyl methacrylate based reactive acrylic adhesive toughened by hydroxyl terminated polybutadiene. J Adhes 1991; 34: 121.

Aggarwal S, Singhal R, Rai JSP. Curing and rheological behaviour of vinyl ester resins prepared in the presence of tertiary amines. J Macromol Sci Pure Appl Chem 1999; 36: 741–757.

Agarwal S, Srivastava D, Mishra A, Rai JSP. Decomposition behaviour of vinyl ester resins prepared in presence of tertiary amines. Polym Plast Technol Eng 2002; 41: 327–340.

Agarwal S, Mishra A, Rai JSP. Effect of diluents on the decomposition behaviour of vinyl ester resin. J Appl Polym Sci 2003; 87: 1952–1956.

Alhuthali A, Low IM. Mechanical properties of cellulose fibre reinforced vinyl-ester composites in wet conditions. J Mater Sci 2013a; 48: 6331–6340.

Alhuthali A, Low IM. Water absorption, mechanical and thermal properties of halloysite nanotube reinforced vinyl-ester nanocomposites. J Mater Sci 2013b; 48: 4260–4273.

Alhuthali A, Low IM, Dong C. Characterization of the water absorption, mechanical and thermal properties of recycled cellulose fibre reinforced vinyl-ester eco-nanocomposites. Composites Part B 2012; 43: 2772–2781.

Ambrogi V, Carfagna C, Giamberini M, Amendola E, Douglas EP. Liquid crystalline vinyl ester resins for structural adhesives. J Adhes Sci Technol 2002; 16: 15–32.

Atta AM, El-Saeed SM, Farag RK. New vinyl ester resins based on rosin for coating applications. React Funct Polym 2006; 66: 1596–1608.

Auad ML, Aranguren MI, Elicabe G, Borrajo J. Curing kinetics of divinyl ester resins with styrene. J Appl Polym Sci 1999; 74: 1044–1053.

Auad ML, Frontini PM, Borrajo J, Aranguren MI. Liquid rubber modified vinyl ester resins: fracture and mechanical behavior. Polymer 2001; 42: 3723–3730.

Auad ML, Proia M, Borrajo J, Aranguren MIJ. Rubber modified vinyl ester resins of different molecular weights. Mater Sci 2002; 37: 4117–4126.

Auad ML, Borrajo J, Aranguren MI. Morphology of rubber-modified vinyl ester resins cured at different temperatures. J Appl Polym Sci 2003; 89: 274–283.

Baikerikar KK, Scranton AB. Photopolymerizable liquid encapsulants for microelectronic devices. Polymer 2001; 42: 431–441.

Bajpai M, Shukla V, Kumar A. Film performance and UV curing of epoxy acrylate resins. Prog Org Coat 2004; 44: 271–278.

Bhatnagar R, Varma IK. Effect of α-methylstyrene off the curing behaviour of vinyl ester resin. J Therm Anal Calorim 1989; 35: 1241–1249.

Boutevin B, Parisi JP, Robin JJ, Roume C. Synthesis and properties of multiacrylic resins from epoxy resins. J Appl Polym Sci 1993; 50: 2065–2073.

Brill RP, Palmese GR. A investigation of vinyl ester-styrene bulk copolymerization cure kinetics using Fourier transform infrared spectroscopy. J Appl Polym Sci 2000; 76: 1572–1582.

Brill RP, Mccullough RL, Palmese GR. Effect of resin formulation and reaction temperature on the curing kinetics of vinyl ester resins. GR Am Soc Comp Conf Proc 1996; 576–583.

Brody JC, Gillespie JW. The effects of a thermoplastic polyester preform binder on vinyl ester resin. J Thermoplast Compos Mater 2005; 18: 157–179.

Brown JR, Mathys Z. Reinforcement and matrix effects on the combustion properties of glass fibre reinforced polymer composites. Composites Part A 1997; 28: 675–681.

Bucknall CB, Davies P, Partridge IK. Phase separation in styrenated polyester resin containing a poly(vinyl acetate) low-profile additive. Polymer 1985; 26: 109–112.

Bucknall CB, Partridge IK, Phillips MJ. Mechanism of shrinkage control in polyester resins containing low-profile additives. Polymer 1991a; 32: 636–640.

Bucknall CB, Partridge IK, Phillips MJ. Morphology and properties of thermoset blends made from unsaturated polyester resin, poly(vinyl acetate) and styrene. Polymer 1991b; 32: 786–790.

Burchill PJ, Kootsookos A, Lau M. Benefits of toughening a vinyl ester resin matrix on structural materials. J Mater Sci 2001; 36: 4239–4247.

Cao X, Lee LJ. Control of shrinkage and final conversion of vinyl ester resins cured in low-temperature molding processes. J Appl Polym Sci 2003; 90: 1486–1496.

Cassis FA, Talbot RC. Polyester and vinyl ester resins. In: Peters ST, editor. Handbook of composites. London: Chapman & Hall, 1998: 34–47.

Chang SS. Glass transition temperature of vinyl ester resin/styrene mixture as a function of composition and curing history. Polymer Preprints, Division of polymer chemistry. Am Chem Soc 1992; 33: 260–261.

Chattopadhyay DK, Panda SS, Raju KVSN. Thermal and mechanical properties of epoxy acrylate/methacrylates UV cured coatings. Prog Org Coat 2005; 54: 10–19.

Chaturvedi A, Tiwari A, Tiwari A. Spectroscopic and morphological analysis of grapheme vinylester nanocomposites. Adv Mater Lett 2013; 4: 656–661.

Chauhan SR, Gaur B, Dass K. Effect of microsize particulates on tribological characteristics of vinylester composites under dry and lubricated conditions. J Mater Sci Eng 2013; 2: 1. DOI:10.4172/2169-0022.1000117.

Chen JS, Yu TL. Microgelation of unsaturated polyester resins by static and dynamic light scattering. J Appl Polym Sci 1998; 69: 871–878.

Cheremisinoff PN, Cheremisinoff NP. Fibreglass reinforced plastics: manufacturing techniques and application. Norwich: William Andew Inc., 1995: 44–48.

Chiu YY, Lee LJ. Microgel formation in the free radical crosslinking polymerization of ethylene glycol dimethacrylate. J Polym Sci Part A Polym Chem 1995; 33: 269–283.

Choudhary MS, Varma IK. Effect of ethyl methacrylate on thermal and mechanical properties. Die Angew Macromole Chem 1993; 209: 33.

Cook WD. Thermal aspects of the kinetics of dimethacrylate photopolymerization. Polymer 1992; 33: 2152–2161.

Cook WD, Simon GP, Burchill PJ, Lau M, Fitch TJ. Curing kinetics and thermal properties of vinyl ester resins. J Appl Polym Sci 1997; 64: 769–781.




Cook CD, Zipper MD, Chung ACH. PVAc phase precipitation in vinyl ester and polyester resins. Polymer 1998; 39: 5431–5439.

Dhulipala R, Krieg G, Hawley MC. Kinetic modeling of vinyl ester polymerization. Polym Mater Sci Eng 1993; 68: 175–176.

Dreeman E, Narkis M, Siegmann A, Joseph R, Dodiuk H, Dibenedetto AT. Mechanical behavior and structure of rubber modified vinyl ester resin. J Appl Polym Sci 1999; 72: 647–657.

Dua S, Mccullough RL, Palmese GR. Copolymerization kinetics of styrene/vinyl-ester systems: low temperature reactions. Polym Compos 1999; 20: 379–391.

Dusek K, Spevacek J. Cyclization in vinyl-divinyl copolymerization. Polymer 1980; 21: 750–756.

Ehsani M, Khonakdar HA, Ghadami A. Assessment of morphological, thermal and viscoelastic properties of epoxy vinyl ester coating composites: role of glass flake and mixing method. Prog Org Coat 2013; 76: 238–243.

Ganem N, Mortaigne B. Influence of the styrene ratio on the copolymerization kinetics of dimethacrylate of diglycidyl ether of bisphenol A vinyl ester resins crosslinked with styrene. J Macromole Sci Part A Pure Appl Chem 1993; 30: 829–848.

Ganem M, Lafontaine E, Mortaigne B, Bellenger V, Verdu J. Structure of vinylester networks: a rubber elasticity study. J Macromol Sci Part B Phys 1994; 33: 155–172.

Ganglani M, Carr SH, Torkelson JM. Influence of cure via network structure on mechanical properties of a free-radical polymerizing thermoset. Polymer 2002; 43: 2747–2760.

Gaur B, Rai JSP. Curing and decomposition behaviour of vinyl ester resins. Polymer 1992a; 33: 4210.

Gaur B, Rai JSP. Rheological and thermal behaviour of vinyl ester resin. Eur Polym J 1992b; 29: 1149–1153.

Gawdzik B, Matynia T. Synthesis and modification of epoxy-based divinyl ester resin. J Appl Polym Sci 2001; 81: 2062.

Ghorbel I, Valentin D. Hydrothermal effects on the physico-chemical properties of pure and glass fiber reinforced polyester and vinyl ester resins. Polym Comp 1993; 14: 324–334.

Han CD, Lem KW. Rheology of unsaturated polyester resin. I. effects of filler and low-profile additive on the rheological behavior of unsaturated polyester resin. J Appl Polym Sci 1983; 28: 743–762.

Han CD, Lem KW. Chemorheology of thermosetting resins. IV. The chemorheology and curing kinetics of vinyl ester resin. J Appl Polym Sci 1984; 29: 1879–1902.

Hsu CP, Lee LJ. Free-radical crosslinking copolymerization of styrene/unsaturated polyester resins: kinetics-gelation mechanism. Polymer 1993a; 34: 4496–4504.

Hsu CP, Lee LJ. Free-radical crosslinking copolymerization of styrene/unsaturated polyester resins: 1. Phase separation and microgel formation. Polymer 1993b; 34: 4516–4523.

Jackson RJ. Thickenable thermosetting vinyl ester resins, US Patent 4197390, USA, 1980.

Jacob A. Vinyl esters lead the corrosion challenge. Reinforced Plastics 2003; 47: 32–35.

Jang C, Nouranian S, Lacy TE, Gwaltney SR, Toghiani H, Pittman Jr CU. Molecular dynamics simulations of oxidized vapor-grown carbon nanofibre surface interactions with vinyl ester resin monomers. Carbon 2012; 50: 748–760.

Juska TD, Puckett PM. In: Mallick PK, editor. Composites engineering handbook. New York: Marcel Dekker, Inc., 1997: 101–166.

Kamal MR, Sourour S. Kinetics and thermal characterization of thermoset cure. Polym Eng Sci 1973; 13: 59–64.

Karbhari VM, Wang Q. Multi-frequency dynamic mechanical thermal analysis of moisture uptake in E-glass/vinyl ester composites. Composites Part B 2004; 35: 299–304.

Kardenetz PD, Messick VB, Craigie IJ. Unique vinyl ester resins: versatile resins for composites. Proceedings of SPI Composite Institute, 40th Annual Conference, 1985, 6-C.

Kinkelaar M, Wang B, Lee LJ. Shrinkage behavior of low profile unsaturated polyester resins. Polymer 1994; 35: 3011–3022.

Ku H, Chan WL, Trada M, Baddeley D. An evaluation of fracture toughness of vinyl ester composites cured under microwave conditions. J Mater Eng Perform 2007; 16: 741–745.

Kumar S, Satapathy BK, Patnaik A. Viscoelastic interpretations of erosion performance of short aramid fibre reinforced vinyl ester resin composites. J Mater Sci 2011; 46: 7489–7500.

Kumar S, Satapathy BK, Patnaik A. Thermo-mechanical correlations to erosion performance of short glass/carbon fiber reinforced vinyl ester resin hybrid composites. Comput Mater Sci 2012; 60: 250–260.

Kumosa L, Armentrout D, Kumosa M. An evaluation of the critical conditions for the initiation of stree corrosion cracking in unidirectional E-glass/polymer composites. Compos Sci Technol 2001; 61: 615–623.

La Scala JJ, Orlicki JA, Sands JM, Palmese GR. Fatty acid-based monomers as styrene replacements for liquid molding resins. Composites 2004; Convention and Trade Show, American Composites Manufacturers Association, Tampa, FL, USA, Oct. 6–8, 2004a.

La Scala JJ, Sands JM, Orlicki JA, Robinette EJ, Palmese GR. Fatty acid-based monomers as styrene replacements for liquid molding resins. Polymer 2004b; 45: 7729–7737.

La Scala JJ, Sands JM, Palmese GR. Liquid resins with low VOC emissions. 24th Army Science Conference Proceedings, GP-07, Orlando, Florida, USA, Nov. 29–Dec. 2, 2004c.

La Scala JJ, Orlicki JA, Winston C, Robinette EJ, Sands JM, Palmese GR. The use of bimodal blends of vinyl ester monomers to improve resin processing and toughen polymer properties. Polymer 2005; 46: 2908–2921.

Launikitis MB. In: Luben G, editors. Handbook of composites. New York: Van Nostrand, Reinhold Co., 1982: 38.

Lee JH, Lee JW. Kinetics parameters estimation for cure reaction of epoxy based vinyl ester resin. Polym Eng Sci 1994; 34: 742–749.

Lee SB, Rockett TJ, Hoffman RD. Interaction of water with unsaturated polyester, vinyl ester and acrylic resins. Polymer 1992; 33: 3691–3697.

Lem KW, Han CD. Thermo-kinetics of unsaturated polyester and vinyl ester resins. Polym Eng Sci 1984; 24: 175–184.

Li L, Sun X, Lee LJ. Low temperature cure of vinyl ester resins. Polym Eng Sci 1999; 39: 646–661.

Li P, Yang X, Yu Y, Yu D. Cure kinetics microheterogeneity, and mechanical properties of the high-temperature cure of vinyl ester resin. J Appl Polym Sci 2004; 92: 1124–1133.

Li S, Xia J, Li M, Huang K. New vinyl ester bio-copolymers derived from dimer fatty acids: preparation, characterization and properties. J Am Oil Chem Soc 2013; 90: 695–706.

Liang Y, Jensen RE, Pappas DD, Palmese GR. Toughening vinyl ester networks with polypropylene meso-fibres: interface modification and composite properties. Polymer 2011; 52: 510–518.

Lucas JC, Borrago J, Williams JJ. Cure of unsaturated polyester resins: 2. Influence of low-profile additives and fillers on the




polymerization reaction, mechanical properties and surface rugosities. Polymer 1993; 34: 1886–1890.

Luo JJ, Daniel IM. Characterization and modeling of mechanical behavior of polymer/clay nanocomposites. Compos Sci Technol 2003; 63: 607–1616.

Malik M, Chaudhary V, Varma IK. Current status of unsaturated polyester resins. J Macromol Sci Polymer Rev 2000; 40: 2–3.

Malik M, Choudhary V, Varma IK. Effect of oxirane groups on curing behavior and thermal stability of vinyl ester resin. J Appl Polym Sci 2001; 82: 416.

Mallision JH. Corrosion-resistant plastic composites in chemical plant design. New York: Marcel Dekker Inc., 1987: 39.

Martin JS, Laza JM, Morras ML, Rodriguez M, Leon LM. Study of the curing process of vinyl ester resin by means of TSR and DMTA. Polymer 2000; 41: 4203–4211.

Mortaigne B, Feltz B, Laurens P. Study of unsaturated polyester and vinylester morphologies using excimer laser surface treatment. J Appl Polym Sci 1997; 66: 1703–1714.

Mouritz AP, Mathys Z. Post-fire mechanical properties of marine polymer composites. Compos Struct 1999; 47: 643–653.

Mousa A, Karger-Kocsis J. Cure characteristics of a vinyl ester resin as assessed by FTIR and DSC techniques. Polym Compos 2000; 8: 455–460.

Oprea S, Vlad S, Stanciu A, Macoveanu M. Epoxy urethane acrylate. Eur Polym J 2000; 36: 373–378.

Pal N, Srivastava A, Rai JSP. Synthesis of vinyl ester resins in the presence of monoepoxies: a kinetic study. Polym Plast Technol Eng 2003; 42: 105–122.

Panda SP, Navale NG, Saraf MN, Gupta RK, Goel RA. Ballistic applications of glass and Kevlar fibre vinyl ester composites. Defence Sci J 1994; 44: 341–343.

Pantano V, Compston P, Stachurski ZH. Effect of matrix toughness on the shear strength of brittle rubber-modified glass-fibre/vinyl ester composites. J Mater Sci Lett 2002; 21: 771–773.

Patel SV, Thakkar JR, Patel HA. Novel vinyl ester resin and its urethane derivatives. High Perform Polym 1999; 11: 177.

Peter M, Barbara S, Ramona S, Heike B. Catalysts for preparation of addition products of epoxide oligomers and methacrylic acid. Ger. off. DE 4,004,091, 1991. Chem Abstr 1991; 115: 233095d.

Pham S, Burchill PJ. Toughening of vinyl ester resins with modified polybutadienes. Polymer 1995; 36: 3279–3285.

Radhakrishnan S, Pethrick RA. Continuous UV cure monitoring and dielectric properties of photocross-linked-lined epoxy-acrylate resins. J Appl Polym Sci 1994; 51: 863–871.

Rao BS, Madec PJ, Marechael E. Synthesis of vinyl ester resins evidence of secondary reactions by 13C NMR. Polym Bull 1986; 16: 153–157.

Rao BS, Madec PJ, Marechal E. Chemical modification of a vinyl ester resin by acid anhydrides and characterization of the products by 13C NMR. J Macromol Sci Chem 1987; 24: 19–733.

Rey L, Galy J, Sauterea H. Reaction kinetics and morphological changes during isothermal cure of vinyl/dimethacrylate networks. Macromolecules 2000; 33: 6780–6786.

Robinette EJ, Ziaee S, Palmese GR. Toughening of vinyl ester resin using butadiene-acrylonitrile rubber modifiers. Polymer 2004; 45: 6143–6154.

Rosu L, Cascaval CN, Rosu D. Effect of ultraviolet radiation on vinyl ester network based on bisphenol A. J Photochem Photobiol A: Chem 2008; 194: 275–282.

Rosu L, Cascaval CN, Rosu D. Effect of UV radiation on some polymeric networks based on vinyl ester resin and modified lignin. Polym Test 2009; 28: 296–300.

Sadler JM, Nguyen APT, Toulan FR, Szabo JP, Palmese GR, Scheck C, Lutgen S, La Scala JJ. Isosorbide – methacrylate as a bio-based low viscosity resin for high performance thermosetting resins. J Mater Chem 2013; 1: 12579–12586. DOI:10.1039/c3ta12918g.

Sandner B, Schreiber R. Synthesis and polymerization of epoxymethacrylates, 1 catalysis and kinetics of the addition reaction of methacrylic acid and 2,2-bis[4-(2,3-epoxypropoxy)phenyl]propane. Macromol Chem 1992; 193: 2763–2770.

Saunders KJ. Organic polymer chemistry, 2nd ed., New York: Chapman and Hall, 1973.

Scott TF, Cook WD, Forsythe JS. Kinetics and network structure of thermally cured vinyl ester resins. Eur Polym J 2002a; 38: 705–716.

Scott TF, Cook WD, Forsynthe JS. Photo-DSC cure kinetics of vinyl ester resins. I. Influence of temperature. Polymer 2002b; 43: 5839–5845.

Scott TF, Cook WD, Forsynthe JS. Photo-DSC cure kinetics of vinyl ester resins II: influence of diluent concentration. Polymer 2003a; 44: 671–680.

Scott TF, Cook WD, Forsynthe JS, Bowman CN, Berchtold KA. FTIR and ESR Spectroscopic studies of the photopolymerization of vinyl ester resins. Macromolecules 2003b; 36: 6066–6074.

Shahedefar V, Rezadoust AM. Thermal and mechanical behavior of cotton/vinylester composites: effects of some flame retardants and fibre treatment. J Reinf Plast Compos 2013; 32: 681.

Shahrajabian H, Brooghani SYA, Ahmadi SJ. Characterization of mechanical and thermal properties of vinyl-ester/TiO2 nanocomposites exposure to electron beam. J Inorg Organomet Polym 2013; 23: 1282–1288. DOI:10.1007/s10904-013-9920-z.

Shunmugasamy VC, Pinisetty D, Gupta N. Electrical properties of hollow glass particle filled vinyl ester matrix syntactic foams. J Mater Sci 2013; 49: 180–190. DOI: 10.1007/s10853-013-7691-0.

Siebert AR, Guiley CD, Kinloch AJ, Fernando M, Heijnsbrock EPL. Toughened plastics II: novel approaches in science and engineering. In: Keith Riew C and Kinloch AJ, editors. Advances in chemistry series 252. Washington: American Chemical Society 1996: 151–160.

Siqueira EJ, Botaro VR. Luffa cylindrica fibres/vinylester matrix composites: effects of 1,2,4,5-benzenetetracarboxylic dianhydride surface modification of the fibres and aluminum hydroxide addition on the properties of the composites. Compos Sci Technol 2013; 82: 76–83.

Sitzmann EV, Wostratzky DA, Bramer DA, Jankauskas J, Al-Akhdar W, Evers H, Jung T, Megert S. Composites 2001, Convention and Trade Show, Composites Fabricators Association, Tampa, FL, USA, Oct. 3–6, 2001.

Srivastava A, Aggarwal S, Rai JSP. Kinetics of esterification of cycloaliphatic epoxies with methacrylic acid. J Appl Polym Sci 2002; 86: 3197–3204.

Stankiewicz A, Szczygiel I, Szczygiel B. Self-healing coating in anti-corrosion applications. J Mater Sci 2013; 48: 8041–8051.

Starr B, Burts E, Upson JR, Riffle JS. Polyester dimethyacrylate oligomers and networks. Polymer 2001; 42: 8727–8736.

Stone MA, Fink BK, Bogeti TA, Gillespie JW. Thermo-chemical response of vinyl-ester resin. Polym Eng Sci 2000; 40: 2489–2497.

Sultania M, Rai JSP, Srivastava D. Studies on the synthesis and curing epoxidized novolac vinyl ester resin from renewable resources. Eur Polym J 2010; 46: 2019–2032.




Suresha B, Kumar KS, Seetharamu S, Kumaran PS. Friction and dry sliding wear behavior of carbon and glass fabric reinforced vinyl ester composites. Tribol Int 2010; 43: 602–609.

Suspene L, Fourquier D, Yang YS. Application of phase diagrams in the curing of unsaturated polyester resins with low-profile additives. Polymer 1991; 32: 1593–1604.

Swisher DH, Grams DC. Thermosetting vinyl ester resins reacted with dicarboxylic acid anhydride, US Patent 3564074, USA, 1971.

Taranu N. Composite materials-course notes. United Kingdom: The University of Sheffield Printing Office, 2009.

Thostenson ET, Li CY, Chou TW. Nanocomposites in context. Compos Sci Technol 2005; 65: 491–516.

Thostenson ET, Ziaee S, Chou TW. Processing and electrical properties of carbon nanotube/vinyl ester nanocomposites. Compos Sci Technol 2009; 69: 801–804.

Ullett JS, Chartoff RP. Toughening of unsaturated polyester and vinyl ester resins with liquid rubbers. Polym Eng Sci 1995; 35: 1086–1097.

Valea A, Martinez ML, Gonzalez ML, Eceiza A, Mondragon I. Influence of cure schedule and solvent exposure on the dynamic mechanical behavior of a vinyl ester resin containing glass fibers. J Appl Polym Sci 1998; 70: 2595–2602.

Valea A, Gonzalez ML, Mondragon I. Vinyl ester and unsaturated polyester resins in contact with different chemicals: dynamic mechanical behaviour. J Appl Polym Sci 1999; 71: 21–28.

Varma IK, Gupta VB. In: Kelly A and Zweben C, editors. Thermosetting resins – properties, comprehensive composite materials, vol. 2. Amsterdam: Elsevier, 2000: 18–21.

Varma IK, Rao BS, Choudhry MS, Choudhry V, Varma DS. Effect of styrene on the properties of vinyl ester resin. Angew Makromol Chem 1985; 130: 191–199.

Visco AM, Campo N, Cianciafara P. Comparison of seawater absorption properties of thermoset resins based composites. Composites Part A 2011; 42: 123–130.

Wang W. Synthesis and characterization of UV – curable polydimethylsiloxane epoxy acrylate. Eur Polym J 2003; 39: 1117–1123.

Wheelar RN. The properties and applications of epoxide resin ester. Paint Technol 1955; 19: 159–163.

Yabuki A, Okumura K. Self healing coatings using superabsorbent polymers for corrosion inhibition in carbon steel. Corros Sci 2012; 59: 258–262.

Yang H, Lee LJ. A kinetic model for free-radical crosslinking co-polymerization of styrene/vinylester resin. Polym Compos 2001; 22: 668–679.

Yang YS, Suspense L. Curing of unsaturated polyester resin: viscosity studies and simulations in pre-gel state. Polym Eng Sci 1991; 31: 321–332.

Yang X, Li S, Tang X, Xia J. Research on preparation, properties and UV curing behaviors of novel myrcene-based vinyl ester resin. Adv Mater Res 2013; 807–809: 2826–2830.

Young RE. In: Bruins PF, editor. Unsaturated polyester technology, New York: Gordon and Breach, 1976: 315–342.

Yu SH. Reactive modifier of elastomeric comb copolymer for thermosetting resins and process for making the same. U.S. Patent 5506320, USA, 1996.

Yurdakul H, Seyhan AT, Turan S, Tanoğlu M, Bauhofer W, Schulte K. Electric field effects on CNTs/vinyl ester suspensions and the resulting electrical and thermal composite properties. Compos Sci Technol 2010; 70: 2102–2110.

Zaske OC. Unsaturated polyester and vinyl ester resins. In: Goodman SH, editor. Handbook of thermoset plastics, New Jersey: William Andrew Inc., 1998: 122–168.

Zhang S, Ye L, Mai YW. A study on polymer composite strengthening systems for concrete columns. Appl Compos Mater 2000; 7: 125–138.

Ziaee S, Palmese GR. Effects of temperature on cure kinetics and mechanical properties of vinyl-ester resins. J Polym Sci Part B Polym Phys 1999; 37: 725–744.

Shipra Jaswal received her bachelor’s degree in 2006 and master’s degree in 2008 from Himachal Pardesh University, Shimla, Himachal Pradesh, India. She is currently pursuing her PhD on the synthesis of hyperbranched vinyl ester resins based on natural products from the National Institute of Technology, Hamirpur, Himachal Pradesh, India. She is also working in a project as women scientist under Women Scientist Scheme-A, approved by Depart-ment of Science and Technology, New Delhi, India. She has three publications in national and international conferences.

Bharti Gaur is an associate professor in the Department of Chemis-try, National Institute of Technology-Hamirpur, Himachal Pradesh, India. She received her BSc degree from St. Bedes College Shimla in 1986. She completed her postgraduate studies in organic chemistry from Sardar Patel University, Anand, Gujarat, India, in 1988. She obtained her PhD degree from HBTI Kanpur, India, in 1993. She has worked as a scientist in IIT Delhi for 2 years, where she filed two patents in the area of energetic binders for solid rocket propellants. She has taught in a number of undergraduate and postgraduate institutes before joining NIT Hamirpur as an assistant profes-sor in 2010. She has more than 25 research papers in national and international journals and conferences. Her current research interests include microbial fuel cell, synthesis of proton exchange membrane for fuel cells, nanocomposites, synthesis of adhesives, and coatings.



Documents

New trends in vinyl ester resins