Novel Copolyesters Containing Naphthalene Structure .2. Copolyesters Prepared From 2,6-Dimethyl Naphtha Late, 1,4-Dimethyl Terephthalate And Ethylene-glycol

8/2/2019 Novel Copolyesters Containing Naphthalene Structure .2. Copolyesters Prepared From 2,6-Dimethyl Naphtha Late,

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Novel Copolyesters Containing Naphthalene Structure, II.Copolyesters Prepared from 2,6-Dimethyl Naphthalate,1,4-Dimethyl Terephthalate, and Ethylene GlycolTSU-SHANG LU,' YIH-MIN SUN? and CHUN-SHAN WANG',*'Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan, Republic of China;'Department of industrial Safety and Hygiene, China Jun ior College of Medi cal Technology, Tainan, Taiwan 701,Republic of China

SYNOPSISCopolyesters containing rigid segments (naphthal ene and terephthalene) an d flexible seg-ments (al iphatic diol) struct ure were synthesized from DMN/D MT/EG (2,6-dimethylnaphthalate/l,4-dimethyl erephthalate/ethylene glycol) ternary monomers with variousmole ratios. Copolyesters having intri nsic viscosities of 0.52-0.65 dL/g were obtained bymelt polycondensation in the presence of metallic catalysts. T he effect of reaction tem-perature and time on the formation of the copolyesters was investigated to obtain an op-timum condi tion for copolyester manufacturing. The optimum condition for PN T (poly-ethylene naphthalate terephthalate) copolyester manufacturing is the transesterificationunder nitrogen a tmosphere for 4 h a t a temperature of 185 k C followed by polymerizationunder 2 mm Hg for 2 h at a temperature of 280C. Most copolyesters have bett er solubilitiesthan poly(ethy1ene naphthalate) (P EN ) and poly(ethy1ene terephtha late) (P ET ) in varioussolvents. Th e effect of the starting mole ratio of DMN , DMT, and EG on t he thermalproperties of the resulted copolyesters was also investigated using differential scanningcalorimetry (DSC) a nd thermal gravimetric analysis ( TGA ) .Glass transition temperaturesof copolyesters were in the range of 70.7-115.2OC, and 10% weight loss in nitrogen wereall above 426C. 0 995 John Wiley & Sons, Inc.Keywords: aromat ic copolyesters poly(ethy1ene tereph thalat e) poly(ethy1ene naph tha-late) * melt polycondensation * physical proper ties

INTRODUCTIONDue to its good thermal and mechanical properties,poly(ethy1ene terephthalate) (P ET ) is one of th emost widely used engineering plastics. Structurallyrelated poly(ethy1ene naphthalate) (P EN )has beenobtained from 2,6-dimethyl naphthalate and eth-ylene Th is newly developed high-perfor-mance polymer containing a rigid naphthalene ringhas exhibited superior physical and mechanicalproperties than widely used P E T s . ~ uch attentionhas been focused recently on the preparation andapplications of PEN. Due to it s enhanced physicaland mechanical properties, PEN has found many

* To whom al l correspondence should be addressed.Journal of Polymer Science:PartA Polymer Chemistry, Vol. 33,2841-2850 (1995)0 995John Wiley & Sons, Inc. CCC OSS7-624X/95/162841-10

applications: Yamamoto et aL4reported PEN bottleswith good gas-barrier property, transparency, andthermal resistance (up to 110C).High-quality fibersfrom PE N with flexibility, toughness, and resistanceto heat and abrasion have been p r~ d u c e d .~n ori-ented multilayer polyester film for magnetic record-ing tape with good machine direction st rength andheat resistance was reported by Tahoda e t aL6PENfilm is particularly well-suited for electronic andelectrical application^,^ such as flexible prin ted cir-cuits, class "F" insulation, wiring applications, toughmembrane switches, and flexible heaters. Althoughpoly(ethy1ene naphthalate) has superior physicaland mechanical properties than PET, however itsrelative low production volume and high price willlimit its applications in the near future.

We have already reported on the preparationand characterization of PE N and copolyesters

2841


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2842 LU , SUN, AND WANG

derived from bis(hydroxyethy1)naphthalatewithbis[4-(2-hydroxyethoxy)phenyl] ompounds.' Thephysical properties of PEN (such as solubility,mechanical properties, and thermal stability) weresuccessfully improved by the introduction of thearyl ether linkage and the bulky pendan t group,while the raw material cost can be reduced bychoosing an inexpensive comonomer, such a s bis-phenol A.

In the present study, a series of polyethylenenaphthalate terephthalate copolymers (PNT ) withvarious compositions were synthesized from DMN/DMT/EG ternary monomers with the objectives ofimproving the solubility and processability of PEN,

reducing the cost of PEN, while improving physicaland mechanical properties of PET.

Transesterification is generally the preferredprocess for the manufacture of PEN.1,2,9 he re aretwo steps in the preparation of PNT . The first stepis the formation of 2,6-bis(hydroxyethyl)naphthalate(BHEN) and 2,6-bis(hydroxyethyl)terephthalate(B HET) , respectively, from the transesterificationof 2,6-dimethyl naphthalate (DMN) or 2,6-dimethylterephthalate (DMT) with ethylene glycol (EG). Thesecond step is the PNT formation from the poly-condensation of BHEN and BH ET mixture at ele-vated temperature and reduced pressure. The re-action schemes are shown below:

0&-OCH,

mH,CO-C \II0+0

@-OCH,nH,CO-C \I1

0+

2(m+ n )HOCH,CH,OH c 0~ - o C H , C H ~ o Hrn HOH,CH,CO-C \II0+ 0@-oCH,cH,OHn HOH,CH,CO-C \I10+2( m+ n) CH,OHPolycondensation:0 0

~ o C H , c H ~ O Hm HOH,CH,COC \

0II0(2)I(m + n - 2) HOCH,CH,OH

T-T type N-N type N-T ype

EXPERIMENTALRaw Materials

termination of solubility, N-methyl-2-pyrrolidone(NM P), N,N-dimethylformamide (DMF), and pyr-idine, were purified by distillation under reducedpressure over calcium hydride and stored over 4 A

2,g-Dimethyl naphthalate (Amoco) is a commercial molecular sieves. Zinc acetate and antimony trioxideproduct and w as used without further purification. were commercial products (guaranteed reagent1,4-Dimethyl terephthalate (Janssen) and ethylene grade) and were used without further purification.glycol (Ferak) were reagent grade and used without Th e solvents, phenol (Ferak) and tetrachloroethanefurther purification. The solvents used for th e de- (Merck),used for the determination of solubility and


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NOVEL COPOLYESTERS CONTAINING NAPHTHALENE STRUCTURE. I1 2843

Table I. Characterization of BHEN and BHETSample Bis(hydroxyethy1)naphthalate Bis(hydroxyethy1)terephthalate

Formula C16H1606mp ("C) 129-1 31Elemental analysis (%): found (calcd) C: 63.16 (63.76)H: 5.26 (5.22)0: 31.58 (31.02)M+(304)3.12M - 61'243'100M - 88('16'42.97M - 105'199'46.31M - 133'17'' 28.35M - 178'126'13.493450 (0-H)3050 (Ar: C- )2900 (Alkyl: C- )1720 (C=O)1600 (Ar: C- )1240 ( C - 0 )1160 (C-OH)

M S (rile): (relative intensity, %)

IR (cm-')

C12HI406108-109C: 56.64 (56.70)H: 5.52 (5.51)0: 37.84 (37.79)M+(254'8.11M - 61'193' 100M - 88"66'46.27M - 105"49' 50.29M - 133'121'32.133450 (0-H)3045 (Ar: C -H)2900 (Alkyl: C- )1700 ( C = )1600 (Ar : C-C)1150 (C-OH)

intrinsic viscosity measurement of the polymer werealso used without purification.

InstrumentationElemental analyses were performed by the HeraeusCHN-0-Ra pid elemental analyzer. FTIR spectrawere recorded with a Nicolet 5DX-B spectropho-tometer. Mass spectra were recorded by the VG 70-250s GC/MS. Intr ins ic viscosities were obtained us-ing a Ubbelohde capillary viscometer (Schott-AVS310). Melting points of BHE N and BHET weredetermined in a polarizing microscope (LaboratoryDevices ME L-TEMPII) . DSC data were obtainedfrom 8-10 mg samples in a nitrogen atmosphere a ta 20C min-' heating rate using a Du Po nt 910 dif-ferential scanning calorimeter. Thermal gravimetricanalysis (TGA) was measured with a Du P on t 945a t a heating rate of 20C min-' in a nitrogen at -mosphere. The wide-angle x-ray measurements wereperformed at room temperature with powderedspecimens with a Rigaku Geiger Flex D-Max/IIIax-ray diffractograms, using Ni-filtered Cuka radia-tion (40 kV, 15 mA). The scanning rate was 2" min-'.

Syntheses of BHET and BHEN CompoundsBHET [bis(hydroxyethyl) terephthalate] was pre-pared from dimethyl terephthala te (DM T) and eth-ylene glycol (EG) by the modified method (modifi-cation in catalyst and reaction condition) of Ba1iga.l'BHEN [bis(hydroxyethyl) naphthalate] was syn-thesized from corresponding dimethyl naphthalate

(DMN) and ethylene glycol (EG) following themethod described in a previous report." Th e purifiedBHET, BHEN monomers were identified by ele-mental analyses, mass spectra, IR spectra, andmelting points which are listed in Table I.Preparationof CopolyestersTransesterificafionTh e reactor for transesterification of DMN/DMTwith EG was the same as the one previously re-ported." To the reaction vessel, 1 mol of DMN/DM T mixture (various mol % ratios of DMN/D MTwere prepared: 100/0, 85/15, 70/30, 50/50, 30/70,15/85, and 0/100), 2 mol EG and zinc acetate (15X mol/mol ester group) were introduced. Thereaction was carried out with stir ring under a nitro-gen atmosphere. The temperature of the reactionmixture was measured with a thermocouple detectoran d w as maintained at 185* 2C. The temperatureof the distillation column was maintained at 100k 3C. The reaction w as considered to have s tarte dwhen the first drop of the methanol formed in theacceptor. The transesterification reaction w as fol-lowed by measuring the volume of methanol col-lected in the acceptor.PolycondensationThe monomers (BHEN and BHET) synthesizedabove were mixed in various mole ratios for the co-polymerization reaction. Besides th e esterificationbetween BHEN and BHET, the polycondensation


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2844 LU, SUN, AND WANG

0

Table 11. Solubilities of PET-PE N Copolyestersa

,'d

Solventb PEN 80 :20 60 : 40 50 : 50 40 : 60 20 :80 PETDMACDMFDMSONM Pm-cresolPyridineCHCI,CZHZCI4

----h-h-h--h

+h--++++-h-f h

+h+h-h+++++h++-

+h+h

+++++h++

-

-

-h--+h+h-h+h-

a (++) Soluble a t room temperature, ( +h ) soluble on heating, (-h) partially soluble on heating, (-) insoluble.DMAC: N,N-dimethy lacetamide, DMF: N,N-d imethylform amide, DMSO: dimethyl sulfoxide, NMP: N-methyl-2-pyrolidone.

of BHEN (or BHET ) itself could occur a t the sametime and a random copolymer would be generated.Th e reaction equation and product are indicated ineq. (2). A mixture of BHE N/B HET (0.4 mol), zincacetate, and antimony trioxide (8 X mol) wereintroduced into a 250 mL four-neck flask fitted witha reflux condenser, a thermometer, a gas inlet, a gasoutlet, and a mechanical stirrer. The reaction mix-ture was heated to 240 * 2C and maintained atthat temperature for 90 min under dry nitrogen. T hetemperature was raised to 250C and stirring wascontinued for 30 min. T he pressure of the reactionsystem was gradually reduced first to 180-200 mmHg over the course of 20 min. Over the course ofanother 10 min, the pressure was further reduced to1-3 mm Hg an d the reaction temper ature was raisedto t he final operating temperature ( - 280C). Th epolymerization was done isothermally at the finaltemperature for the required period of time with si-multaneous removal of ethylene glycol and othervolatiles by distillation. Finally, the pressure wasreturned to normal atmospheric pressure using ni-

I00

75h@

z50

825

0 0 I0 0 ?OO 30 0 400Time ( m i n )

Figure 1. Time-conversion curve of the transesterifi-cation of DMT and DMN with EG a t 1 :1 : 4 mole ratio.

trogen to prevent degradation by oxidation, and lightamber-colored, amorphous copolymers were ob-tained. In search of the optimum conditions for var-ious compositions for the polycondensation step,various mol 5% ratios of BHEN/BHET were pre-pared (100/0, 75/25, 50/50, 25/75, 0/100) and thefinal operation temperatures were varied from 250to 295C.

Solubility TestThe solubilities of these polymer were determinedby adding polymer (1-2% by weight) to the desiredsolvent in a tes t tube. T he tube was left to stand for24 h to observe whether the polymer dissolved.When the polymer did n ot completely dissolve a troom temperature, the test tube was heated andcooled. Th e polymer was defined to be soluble whenno polymer has precipitated after thecooled.

1 6

1 2

0x x>.

4

P

tube was


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i n n .

0 100 200 300 40 0 5 0 0Time ( m i n i

Figure 3. Time-conversion curve of the transesterifi-cation of DMT and DMN with EG at various composi-tions.

Intrinsic Viscosity DeterminationIntrinsic viscosity of the polymer was measu red us-ing an Ubbelohde viscometer. T he polymer sample(0.06 g) was accurately weighed (+.0.001 g) an d dis-solved in 25 mL of symmetric tetrachloroethane-phenol (2 : 3 w/w). T he solution was maintained a t120C for 20-25 min t o achieve a complete solutionof the polymer in the solvent. The solution was the ncooled to room temperature and filtered through a0.45 pm disposable membrane filter (cellulose ace-tate). Using the viscometer at 30C, the intrinsicviscosity was calculated from the relative viscosityby th e Ram Mohan Rao equation.13

Determination of the Moisture Absorptionof CopolyestersDisk samples [ 3 mm (T )X 20 mm (D)] were driedunder vacuum a t 120C until moisture had been ex-

0 0.2 0.4 0.6 0.8 1composition DMT/(DMT+DMN)

Figure 4.various compositions.

Relative initial transesterification rate for

BHET/BHEN = 2511.5

0.110 ,0 100 200 300 400

REACTION TIME ( m i n )Figure 5.condensation of BHET-BHEN (25 :75).

Time-intrinsic viscosity curve for the poly-

pelled. T hen , the samples were put inside a dry boxfor cooling. After being weighed, the samples wereplaced in the boiling water (100C) for 24 h an dthen weighed again. The moisture absorption wascalculated as: Percen t weight gain = [ (W/Wo) 11X 10096, where W = weight of copolymer sampleafter standing a t 100C water for 24 h, and Wo=weight of copolymer sample after dried undervacuum a t 120C.

RESULTS AND DISCUSSIONCharacterization of BHET and BHENBoth hydroxyethyl monomers were synthesizedunder th e mos t preferable conditions, and resultsare summarized in Table 11. A polarized micro-scope was used to determine th e melting point ofBHET and BHEN. The sharp melting point ofmonomers was indicative tha t th e monomers werepure. Th e synthesized BH ET ha s a melting tem-

0.60.5

>. 0.4$ 0.3> 0.2

0.C

tz

BHET/BHEN=SO/SO - sooc........0 . ... 2650c.... ... 2800c.__--.-. 9.50c

0 so 100 IS0 200 2.50 300REACTION TIME ( m i n )

Figure 6.condensation of BHET-BHEN (50 : 50).



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2846 LU, U N , AND WANG

perature of 109-llOC which is the same as re-ported value."

The results of elemental analyses of these mono-mers are shown in Table I1 which agree well withthe assigned structures. Electron impact inducedfragmentation patterns of these monomers at 30 eVhave been obtained. The common features observedin the mass spectra and the infrared spectra ofbis(hydroxyethy1) monomers are also shown in Ta-ble 11.From these results, it can be concluded thatthe products were in good agreement with the as-signed structures.

Searching for the Optimum ConditionsforSyntheses of CopolyestersThe ester-exchange polymerization (alcoholysis) ofaromatic diester with aliphatic diol using zinc acetateor antimony trioxide as a catalyst used by the authors''is a convenient method for the preparation of copo-

0

0

lyesters on the laboratory scale. The same techniquewas applied here to prepare copolyesters from DMN/DMT/EG ternary monomers in various mole ratios.The extent of the transesterification reaction was fol-lowed by measuring the quantity of methanol collected.Figure 1 shows how the transesterification reactionproceeds with zinc acetate as catalyst. Using theDMN/DMT mole ratio of 1 1and the catalyst con-centration of 15 X mol/mol ester group, the timerequired for 90% completion of the reaction was ca. 5h. Application of previously derived kinetic equation12to these data, and plotting the Yvalues" thus obtainedagainst time, the points in Figure 2 were obtained. Itis obvious that the copolymerization reaction does notfit into the reaction model as previously reported."An explanation for the deviation may be attributed tothe different reactivity of the naphthalate ester andthe terephthalate ester. The reaction is a competitionreaction for ethylene glycol between DMN and DMT.This competition reaction can be represented as:

The rates of reactions are represented by:

cco - ccand p2=CL30 cco

CB O - CBP1 =where p1and p2are the extents of reaction (3) and(4); A ,C,, and Cc are the concentration terms forreactant A ,B,and C; CAo,CBo, nd Ccoare the initialconcentration terms for reactant A, B, and C; and

BHET/BHEN =75/250.7 I 1

0 100 200 300 400REACTION T I M E (min)

Figure 7 .condensation of BHET-BHEN (75 : 2 5 ) .

Time-intrinsic viscosity curve for th e poly-


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28OOC0.6-

0.5-

8 0.4->GG 0.3-

aBHET:BHEN+ M):o

........+..... 7 y 25----0---o:so

0.2#fmt I I I I0 100 200 300 400

TIME (min)Figure 8.condensation of PN T copolymers at 280C.


k l and k2 are apparent rate constants for reactions(5) and (6).

As discussed above, the reactivity difference be-tween benzene ring and naphthalene ring makestheir reaction rate constants ( k , and k2 ,respectively)different. To explain the effects of DMN/D MT mol% ratio on the transesterification reaction, the initialrate was simply used in the following discussions.

The dependence of transesterification rates onthe composition of reactants in the region 0/100-100/0 (DMN/DMT) have been investigated. Figure3 is a representation of the results as plots of theextent of the reaction against time at various mol% ratios of DMN/DMT. It can be seen that whenthe DMT amount was increased, the rate of thetransesterification was increased, especially in theinitial stage of the reaction. Figure4 hows the initialrates of transesterification reaction versus compo-sition of reactants. As shown in Figure 4, he reac-tion rate increases with increasing amounts of DMT.

Thus, it requires different lengths of reaction timefor various mole ratios of reactants (DMT/DMN)to achieve the same conversion. For example,at 100/0 or 85/15 ratio (D MT/D MN), the time requiredfor 95% conversion was about 4 h, whereas for 70/30 or 50/50 ratio, i t required 5 h for 90% conversion.When the DMN became dominant component(DMT/DMN = 30/70, 15/85, 0/100), the time re-quired for 85% conversion became 5.5 h. Sincetransesterification has to be close to completion(> 80%)before the polycondensation can be start edto guarantee an expected composition of copolymer,the reaction temperature at the final stage oftransesterification can be slightly increased to in-crease the reaction rate an d shorten t he operationtime.

Because of the very low solubility of these ho-mopolymers and copolymers in common solvents for

the determination of their MW, an assumption wasmade that the copolymers all have the same hydro-dynamic volume and using intrinsic viscosity as acriteria in comparing the growth of molecularweight. Figures 5-7 show the plots of the intrinsicviscosities of copolymers vs time a t various reactiontemperatures. Three BHET/BHEN ratios wereprepared 25/75, 50/50, and 75/25. The results in-dicated that an increase in intrinsic viscosity withan increase in reaction temperature at t he beginning.We also found tha t when the BHE T component wasdominant, the reaction rate increased faster withthe increase in the reaction temperature. With amixture of BHET and BHEN, three type of con-densations, namely BHET and BHET (T-T),BHET and BHEN (T-N), B HEN and BHEN (N-N) , could take place simultaneously an d a randompolymer would be formed. The relative rates of th ethree condensation models can be obtained from theinitial rates in Figure 8 and approximated as T-T> T-N > N-N. So the polycondensation of T-Tmodel was mostly affected by temperature. Th e rea-son for difference in polycondensation rates (T-T> T-N > N-N) may be attributed to that the sterichindrance of benzene ring is less than tha t of naph-thalene ring.

Another interesting phenomenon is observedfrom these figures, the degradation reactions dependgreatly on the proportion of BHEN in the reactants.This may be explained as follows: the heat resistanceof naphthalene ring is much better than that of ben-zene ring, so the polymerization with excess ofBHET monomers degrade faster than copolymerswith excess of BHEN monomers at high reactiontemperature. It was also observed th at th e high ratioof BHET always ended in the formation of deeplycolored products a t high reaction temperatures.

Table 111. Time-Dependent Dissolution ofPoly(ethy1ene Naphthalate/terephthalate)Random Copolymers

Polymer Approximate TimeNeed for Solutionsa (h)

Feed Ratio vDMN:DMT (dL/g) 0.5% 1% 5%

100 : 0 0.528 > 6 > 6 > 680 : 20 0.523 5 > 6 > 660 : 40 0.567 1 2 450 : 50 0.547 0.5 0.6 140 : 60 0.583 0.6 1 220 : 80 0.657 3 5 > 60 : 100 0.574 > 6 > 6 > 6

a Measured a t 50C in m-cresol.


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2848 LU , S U N , A N D W A N G

It may be concluded that the polycondensationtemperature should not exceed 300C and eachcomposition has its own opt imum reaction condi-tion. For BHET(%) > 50, the optimum operationcondi tion was 265-270C an d 3 h. For BHET(%)< 50, th e optimum condition was 275-280C an d 2-2.5 h. Therefo re, a general operating condition forthe polycondensation step in P N T process was cho-sen to be 28O"C, 2 h a nd the resulted copolyestershad intrinsic viscosities of more than 0.52 dL/g.

Properties of CopolyestersStructures of the resultant copolymers were ana-lyzed by FTIR spectra: two strong aromatic absorp-tions appeared at 1600 and 1500 cm-' due to thenaphthalene and benzene ring; prominent absorp-tions owing to este r carbonyl group (C=0) a t 1680-1700 cm-l an d methylene group at 2950 cm-' werealso present. A stron g hydroxy (-OH) absorptiona t 3450 cm-' for th e starting monomers ( BH EN andBHET) weakened as the reaction proceeded. Un-fortunately, the nearly complete overlap of t hecharacteristic peaks for aromatic PE T/ PE N systemsin the F TIR spectra disqualified the use of this an -alytical tool for compositional analyses of these co-polymers. So, the initial feed ratios were used toapproximate the product composition of copolymers.

The solubilities of copolymers were determinedusing powdery specimens in various solvents a t am-bient temperature, and the results are summarizedin Table 11. Th e homopolyesters (P EN and PET)had the poorest solubility as they dissolved onlypartially in l,l,Z,Z-tetrachloroethane n heatingwhile the solubilities of the copolyesters improveddramatically as expected in various solvents, suchas, NMP, m-cresol, pyridine, and tetrachloroethane.Another interesting phenomenon observed fromTable I1 is that the enhanced solubility character of

2_u_?I

5.0 r0 15 20 25 30 35 40 452 8

Figure 9. WAXS diffractograms from poly(ethy1enenaphthalate): (1)product of' polycondensation; (2) meltannealing a t 200C , 10 min.

the resultant copolyesters depend greatly on thecompositions. Therefore, to prove the phenomenon,two different methods were used to study the solu-bility of the copolymers. F irst, t he t ime required fordissolution a t 80C and 1atm pressure was measured(Table 111). Next, solubility limits were approxi-mately determined (Table IV). Judgment of whethercomplete dissolution had occurred was based on th eoptical clarity of the system. Generally, it was foundth at the composition of PE N/ PE T in the copolymeraffected both the rat e of dissolution and the amountof polymer th at could be dissolved. From these datath e 50 : 50 copolymer had the best solubility in allsolvents tested. Th e enhanced solubilities of the co-polyesters may be attributed to the random copo-1ymeri~ation.l~he random blocks in the copolyesterchain could make it more difficult to form a crys-

Table IV. Concentration-Dependent Dissolution of Poly(ethy1ene naphthalate/terephthalate) Random CopolymersPolymer

Feed Ratio 9Approximate Concentration of Solutions" (% )

DMN :DMT (dL/g) 0.5 1 5 15 20 25100 :0 0.52880 :20 0.523 X X60 : 40 0.567 X X X X50 :50 0.547 X X X X X X40 :60 0.583 X X X X X X20 :80 0.657 X X X X X0 : 100 0.574 X X

a Time was held constant at 12 h in each case. solvent is rn-cresol.


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Table V. Thermal Properties of Poly(ethyle1e naphthalate/terephthalate) Copolyesters

PE N 100 :0 267.16 115.24 453.35 33 0.52880 : 20 102.17 450.45 30 0.52360 : 40 94.29 444.64 27 0.567PN T 50 : 50 91.89 444.64 27 0.54740 : 60 86.75 444.64 24 0.58320 :80 83.65 428.68 20 0.657

PET 0 : 100 253.38 70.69 426.10 18 0.574a A 10% weight-loss temperature observed by TGA at a 20"C/min heating rate in nitrogen.

Residual weight at 5.70C in nitrogen.

talline lattice structure and thu s enhanced the sol-ubility of the copolyesters. The x-ray diffractionpatterns of the copolymers verified that all co-polyesters synthesized are amorphus except for verylow copolymerization (< 8%).Another phenomenonwas observed in x-ray diffraction patte rns t ha t noneof the copolyesters could be induced to crystallizefrom the melt by annealing, however both homo-polymers gave crystalline x-ray patterns on meltannealing (see Fig. 9) .

Th e TGA curves of all polymers exhibited a 10%weight loss ( T d ) t 426-454C and residual weightat 530C (RW) of 18-33% in nitrogen. The TGAdata ar e listed in Table V. Their thermal stabilityincreased with the increase in DMN content inreactant monomers (Fig. 10).

The Tg f polymers evaluated by DSC are alsotabulated in Table V. Tg as 70.7"C for benzene-based homopolymer (PET).T he Tg f naphthalene-based homopolymer ( PE N) was 115.2"C, which is445C higher than that of PET. All copolymersshowed single Tg etween those of the two homo-polymers, which increased monotonously with the

5 0 3 8 00 2 0 4 0 6 0 8 0 I r ' o

DMN content i n mol%Figure 10. Glass transition temperature (T,) and a 10%weight-loss temperature (Td)versus DMN content inreactants.

increase in naphthalene content of polymers (Fig.10). The higher Tgsan d better thermal stability ofcopolyesters over those of PET, should be ascribedto th e existence of bulky, thermally, and thermoox-idatively stable naphthalene ring in the mainchain.15 Figure 11 is a plot of Tgand T,,, of the co-polymers against DM N content in reactants. It canbe found that the copolyesters still have meltingpoints when DMN or DMT component is smallerthan 8 mol %. However, in 20-80 mol % range, ran -dom copolymers were formed and they were amor-phous with single Tg nd no T,.

Disk samples [3 mm (T ) X 20 mm (D)]ere fab-ricated from copolyesters and placed into 100Cboiling water for 24 h. The weight gains from thismoisture absorption tests are shown in Figure 12.The ir mois ture absorption increased monotonouslywith the increase in DM T content in reactants.CONCLUSIONSA series of P N T copolyesters were synthesizedthrough melt polycondensation of DM N/ DM T/ EGternary monomers:

2 8 02 6 0 -

E.'v2 4 02 2 0

5 0 - 1 2 0 00 2 0 1 0 6 0 8 0 I 0 0

D M N Conlcnt in md %Figure 11. Glass transition temperature (T,) and crys-talline melt point (T,) versus DMN con tent in reactants.


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2850 LU , S U N , AND WANG

0 20 40 SO 60 80 100Composition (DMT/(DMT+DMN))

Figure 12.tions (lOO"C, 24 h in water).

Moisture absorption for various composi-

1. Each composition has its own optimum co-polymerization condition. Generally, a reac-tion condition of 4 h a t 185C for thetransesterification followed by 2 mm Hg for2 h a t 280C for polycondensation is sufficientto yield good copolymer.

2. The copolymers have higher solubility, lessmoisture absorption, higher Tgs, and arethermally more stable than PET and maycost less tha n PEN. Thus , these copolymerswould be expected to find various commercialapplications.

Financial support of this work by the National ScienceCouncil of Republic of China is gratefully appreciated(NSC83-0405-E006-145).

REFERENCES AND NOTES1. U.S. Pat. 3,436,376 ( 196 9); 3,842,040 (19 74) ;

5,294,695 ( 1994).2. T. Shima, H. Yamashiro, H. Aoki, and M. Shimoma

( to Teijin Ltd.), Jpn . Kokay 73-40,918 ( 1990);C h e m .

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Received Ap ril 26, 1995Accepted June 7, 1995

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