CHAPTER 3
CHARACTERIZATION
OF MONOMERS AND
RESINS
Characterization…
69
CHAPTER 3
Characterization of monomers and resins
3.1 IR spectral characterization
Infrared spectroscopy is an essential and crucial characterization
technique to elucidate the structure of matter at the molecular scale. The
chemical composition and the bonding arrangement of constituents in a
homopolymer, copolymer, polymer composite and polymeric materials in
general can be obtained using Infrared spectroscopy [1]
The FT-IR spectrometers obtain the IR spectrum by Fourier
transformation of the signal from an interferometer with a moving mirror to
produce an optical transform of the infrared signal. Numerical Fourier analysis
gives the relation of intensity and frequency, that is, the IR spectrum. The FT-
IR technique can be used to analyze gases, liquids, and solids with minimal
preparation [2].
The absorption versus frequency characteristics of light transmitted
through a specimen irradiated with a beam of infrared radiation provides a
fingerprint of molecular structure. Infrared radiation is absorbed when a dipole
vibrates naturally at the same frequency in the absorber. The pattern of
vibrations is unique for a given molecule, and the intensity of absorption is
related to the quantity of absorber. In the IR region, each group has several
and different patterns of vibration such as: stretching, bending, rocking, etc.
Thus, infrared spectroscopy permits the determination of components
or groups of atoms that absorb in the infrared at specific frequencies,
permitting identification of the molecular structure. These techniques are not
limited to chemical analysis. In addition, the tacticity, crystallinity, and
molecular strain can also be measured.
1. R. Bhargava, S. Wang, and J. L. Koening, FTIR Microspectroscopy of
polymeric systems, Adv. Polym. Sci., 163, 137-191, 2003.
2. L. H. Lee, Characterization of Metal and Polymer Surfaces: Polymer
Surfaces Academic Press, ISBN-10: 0124421016, New York, USA,
1977.
Characterization…
70
The IR spectra of monomers and polymers were scanned on a
Shimadzu-8400 FT-IR spectrometer over the frequency range from 4000-400
cm-1.
3.1.1 2,4,6-Tris(4-hydroxyphenyl)-1,3,5-triazine(TP)
IR spectrum of TP is presented in Fig. 3.1. and absorption frequencies
in Table 3.1. The characteristic IR absorption frequencies (cm-1) are 3547 (-
OH str.), 3126 & 2827 (Ar-C-H str.), 1599 (-C=N str.), 1508 (-C=C Ar.str.),
1365(-C-N str.), 812 (para substitution) besides normal modes of aromatic
groups.
3.1.2 Epoxy resin of 2,4,6-tris(4-hydroxyphenyl)-1,3,5-triazine(ETP)
IR spectrum of ETP is presented in Fig. 3.2. and absorption
frequencies in Table 3.1.Observed characteristic absorption peaks (cm-1) are
3599 (-OH str.), 1246 (C-O-C str.) and 912 (terminal epoxy ring str.) besides
normal modes of alkyl, alicyclic and aromatic groups.
Characterization…
71
Fig. 3.1. IR spectrum of TP.
Fig. 3.2. IR spectrum of ETP.
Characterization…
72
Table 3.1: The characteristic IR absorption frequencies of TP and ETP
Types
Group
vibration
mode
Observed IR
frequencies, (cm-1)
Expected
frequencies, (cm-1)
TP ETP
Alkane
-CH3
and
-CH2-
C-H (υas) - 2928.04 2975-2950
C-H def, -CH2- - 1417.73 1485-1445
Twistiing &
Wagging - 1246.06 ~1250
-OH -O-H (str.) 3547.21 3599.29 3600-3200
C-O (str.) 1153.47 1168.90 1230-1140
Arom-
atic
C-H (i.p.d.) 1107.18 1168.90 1258±11, 1175±6,
1117±7
C-H (o.o.p.d.) 854.49 856.42 900-860, 850-800
(1,2,4 sub.)
C=C (str.) 1599.04 1595.18 1600±6, 1579±6
Epoxy
CH2-O-CH
epoxy, bend - 912.36 900-920
C-H stretching - 3064.99 ~3050
Ar 1,4 substit. 812.06 813.99 800–860
CN
-C=N (str.) 1599.04 1600-1700
-C-N (str.) 1365.85 1369.50 1300-1400
Characterization…
73
3.1.3 Vinyl ester resins of 2,4,6-tris(4-hydroxyphenyl)-1,3,5-triazine
(ETPAA, ETPMA)
IR spectra of ETPAA and ETPMA are presented in Figs. 3.3 and 3.4.,
respectively and absorption frequencies in Table 3.2. The characteristic IR
frequencies (cm-1) are 3342-3288 (-OH str.), 1719-1701 (C=O str., ester),
1246 (C-O-C str.) and 1037-1034 (C-O str.) besides normal modes of
aromatic and aliphatic groups.
3.1.4 Unsaturated epoxy polyester polyol (ETPUP)
IR spectrum of ETPUP is presented in Fig. 3.5. and absorption
frequencies in Table 3.2. The characteristic IR frequencies (cm-1) are
3302.24-OH str., 1722.5 C=O str. (ester), 1417.7 C-H ipd (-CH=CH), 1247.9
aryl (C-O-C str.) and 1037.7 alkyl (C-O str.) besides normal modes of
aromatic and aliphatic groups.
Fig.3.3. IR spectrum of ETPAA.
Characterization…
74
Fig.3.4. IR Spectrum of ETPMA.
Fig.3.5. IR spectrum of ETPUP.
Characterization…
75
Table 3.2: The characteristic IR absorption frequencies of ETPAA, ETPMA
and ETPUP
Types
Group
vibration
mode
Observed IR frequencies,
(cm-1)
Expected
frequencies,
(cm-1)
ETPAA ETPMA ETPUP
Alkane
-CH3
and
-CH2-
C-H (υas) 2944.19 2941.54 - 2975-2950
C-H (υs) 2880.54 2883.68 2879.82 2880-2860
C-H def, -CH3 - 1425.44 - 1470-1435
C-H def, -
CH2- 1509.11 1516.10 1508.38 1500-1445
Twistiing &
Wagging 1246.78 1246.06 1247.99 ~1250
-OH O-H (str.) 3324.18 3288.74 3302.24 3600-3200
C-O (str.) 1173.48 1172.76 1172.76 1230-1140
Arom-
atic
C-H (i.p.d.) 1146.48 - 1147.68
1258±11,
1175±6,
1117±7,
C-H (o.o.p.d.) 859.07 854.49 858.35 900-860, 860-
800 (1,2,4 sub.)
C=C (str.) 1603.62 1597.11 1604.83 1600±6, 1579±6
Ester C=O (str.) 1719.35 1701.27 1722.49 1780-1710
C-O(str.) 1246.78 1246.06 1248 1300-1250
Ar 1,4 substit. ring
816.14 815.92 817.58 800–860
CN -C=N (str.) 1603.62 1597.11 1604.83 1600-1700
-C-N (str.) 1366.60 1365.65 1367.58 1300-1400
Alkenes
-C-H (str.) 3075.36 3072.71 3068.85 3010-3095
-C=C- (str.) 1603.62 1597.11 1604.83 1600-1680
=CH (i.p.d) 1418.15 1425.44 1417.83 ~1416
Characterization…
76
3.1.5 Epoxy polyester polyols
IR spectra of polyester polyols (ETPRA, ETPLA, ETPOA and ETPR)
are presented in Figs. 3.6-3.9, respectively and absorption frequencies in
Table 3.3. Polyester polyols showed characteristic IR absorption frequencies
(cm-1) at 3306-3302 (-OH str.), 1736-1709 (ester -C=O str.), 1298-1246 (C-O-
C str.) and 1041-1036 (C-OH def) besides normal modes of aliphatic, alicyclic
and aromatic groups. Thus, IR spectra supported formation of polyols.
3.1.6 Polyurethanes
IR spectra of polyurethanes of polyester polyols (ETPRAPU,
ETPLAPU, ETPOAPU and ETPRPU) are presented in Figs. 3.10-3.13,
respectively and absorption frequencies in Table 3.4. PUs showed
characteristic IR absorption frequencies (cm-1) at 3585-3639 (-N-H str), 1734-
1674 (ester and urethane str.) and 1215-1244 (C-O-C str.) besides normal
modes of aliphatic, alicyclic and aromatic groups. Urethane formation resulted
into lowering in the absorption frequencies of OH, ester and ether groups.
Thus, IR spectra supported formation of polyurethanes.
Characterization…
77
Fig. 3.6. IR spectrum of ETPRA.
Fig. 3.7. IR spectrum of ETPLA.
Characterization…
78
Fig. 3.8. IR spectrum of ETPOA.
Fig. 3.9. IR spectrum of ETPR.
Characterization…
79
Fig. 3.10. IR spectrum of ETPRAPU.
Fig. 3.11. IR spectrum of ETPLAPU.
Characterization…
80
Fig. 3.12. IR spectrum of ETPOAPU.
Fig. 3.13. IR spectrum of ETPRPU.
Characterization…
81
Table 3.3: The characteristic IR absorption frequencies of polyols ETPRA,
ETPLA, ETPOA and ETPR.
Types Group
vibration mode
Observed IR frequencies, (cm-1) Expected
frequencies,
(cm-1) ETPRA ETPLA ETPOA ETPR
Alkane
-CH3
and
-CH2-
C-H (υas) 2928.4 2922.2 2920.3 2930.0 2975-2950
C-H (υs) 2854.7 2852.8 2850.8 2872.1 2880-2860
C-H def, -CH3 1419.6 1423.5 1421.5 1415.8 1470-1435
C-H def, -CH2- - 1462.1 1421.5 1466.1 1485-1445
Twistiing &
Wagging 1248 1246.1 1248 1248 ~1250
Skeletal CH2 4
or > 723.3 719.5 721.4 - 750-720
-OH O-H (str.) 3302.2 3306.1 3306.1 3002.2 3600-3200
C-O (str.) 1170.8 1172.1 1172.7 1172.7 1230-1140
Arom-
atic
C-H (i.p.d.) 1145.7 1147.7 1145.7 1145.7
1258±11,
1175±6,
1117±7,
C-H (o.o.p.d.) 860.2 856.4 858.4 858.35
900-860, 860-
800 (1,2,4
sub.)
C=C (str.) 1604.8 1577.8 1572.0 1606.7 1600±6,
1579±6
Ester C=O (str.) 1734.1 1736.0 1728.3 1709.0 1780-1710
C-O(str.) 1248 1246.1 1248 1298.1 1300-1250
Ar 1,4 substit.
Ring 819.7 815.9 821.7 817.8 800–860
CN -C=N (str.) 1604.8 1577.8 1572.0 1606.7 1600-1700
-C-N (str.) 1365.6 1367.6 1371.6 1367.6 1300-1400
Alkenes
-C-H (str.) 3009.1 3009.0 3007.1 3070.8 3010-3095
-C=C- (str.) 1604.8 1577.8 1572.0 1606.7 1600-1680
=CH (i.p.d) 1419.6 1423.5 1421.6 1415.8 ~1416
Characterization…
82
Table 3.4: The characteristic IR absorption frequencies of polyurethanes
ETPRAPU, ETPLAPU, ETPOAPU and ETPRPU.
Types
Group
vibration
mode
Observed IR frequencies, (cm-1) Expected
freq, (cm-1) ETPRAPU ETPLAPU ETPOAPU ETPRPU
Alkan
e
-CH3
and
-CH2-
C-H (υas) 2935.7 2922.2 2918.4 2949.2 2975-2950
C-H (υs) 2854.7 2850.8 2852.8 2868.2 2880-2860
C-H def 1450.5 - - - 1470-1435
Skeletal
CH2 4 or > 719.4 752.2 754.19 - 750-720
-OH O-H (str.) 3308 3306.1 3308 3308 3600-3200
C-O (str.) 1197.8 1215.9 1203.6 1209.4 1230-1140
Arom-
atic
C-H
(o.o.p.d.) 860.2 856.4 856.4 858.3
860-800
(1,2,4 sub.)
C=C (str.) 1593.2 1579.7 1595.1 1589.4 1600±6,
1579±6
Ureth
anes
-NH (str.) 3587.7 3639.8 3616.6 3585.7 3500-3650
C=O (str.) 1710.9 1674.3 1734.0 1722.5 1780-1710
C-O(str.) 1244.1 1215.1 1234.4 1236.4 1200-1300
Ar 1,4
substit. 819.7 817.8 817.8 821.7 800–860
Alkenes
-C-H (str.) 3070.7 - 3072.7 - 3010-3095
-C=C-
(str.) 1593.2 1579.7 1595.1 589.4 1600-1680
=CH
(i.p.d) 1415.8 1413.8 1413.8 1415.8 ~1416
Characterization…
83
3.2 1H NMR spectral characterization
Nuclear Magnetic Resonance (NMR) is a spectrometric technique for
determining chemical structures. When an atomic nucleus with a magnetic
moment is placed in a magnetic field, it tends to align with the applied field.
The energy required to reverse this alignment depends on the strength of the
magnetic field and to a minor extent on the environment of the nucleus, i.e.,
the nature of the chemical bonds between the atom of interest and its
immediate vicinity in the molecule. This reversal is a resonant process and
occurs only under select conditions. By determining the energy levels of
transition for all of the atoms in a molecule, it is possible to determine many
important features of its structure. The energy levels can be expressed in
terms of frequency of electromagnetic radiation, and typically fall in the range
of 5-600 MHz for high magnetic fields. The minor spectral shifts due to
chemical environment are the essential features for interpreting structure and
are normally expressed in terms of part-per-million shifts from the reference
frequency of a standard such as tetramethyl silane.
In general, the resonant frequencies can be used to determine
molecular structures. 1H resonances are fairly specific for the types of carbon
they are attached to, and to a lesser extent to the adjacent carbons. These
resonances may be split into multiples, as hydrogen nuclei can couple to
other nearby hydrogen nuclei. The magnitude of the splittings, and the
multiplicity, can be used to better determine the chemical structure in the
vicinity of given hydrogen. It often provides the best characterization of
compound structure, and may provide absolute identification of specific
isomers in simple mixtures. It may also provide a general characterization by
functional groups which cannot be obtained by any other technique. As is
typical with many spectroscopic methods, adding data from other techniques
(such as mass or infrared spectrometry) can often provide greatly improved
characterizations.
3. N. P. Cheremisinoff, Polymer Characterization Laboratory Techniques
and Analysis, Noyes Publications, New Jerssy, U.S.A., pp-61-62, 1996.
Characterization…
84
The NMR spectra of all samples were scanned on a Bruker AVANCE II
(400MHz) spectrometer by using CDCl3/DMSO-d6 as a solvent and TMS as
an internal standard.
3.2.1 2,4,6-Tris(4-hydroxyphenyl)-1,3,5-triazine (TP) 1H NMR (DMSO-d6) spectrum of TP is shown in Fig. 3.14. The
observed chemical shifts (ppm) and types of protons are assigned as follows:
9.940 [s, -OH(a)], 6.946-6.967 [dd, -ArH(b)], 8.546-8.567 [dd, -ArH(c)].
3.2.2 Epoxy resin of 2,4,6-tris(4-hydroxyphenyl)-1,3,5-triazine (ETP) 1H NMR (CDCl3) spectrum of ETP is presented in Fig.3.15. Chemical
shifts (ppm) and multiplicities of different types of protons are assigned as
follows: 8.67-8.64[dd, ArH(a)], 7.02-7.00[dd, ArH(b)], 4.34-4.27[m, 2H(c)],
4.01-4.06[m, H(d)], 3.42[s, OH(f)], 2.80-2.96[d, 2H(e)].
3.2.3 Vinyl ester resins of 2,4,6-tris(4-hydroxyphenyl)-1,3,5-triazine
(ETPAA, ETPMA) 1H NMR (DMSO-d6) spectra of vinyl ester resins are presented in
Figs.3.16 and 3.17. Different types of protons, their chemical shifts (ppm) and
multiplicities are assigned as follows:
ETPMA: 1.906 [s, -CH3(g)], 4.13-4.19 [m, -O-CH2(c), & -OH(e)], 4.198-4.30
[m, -O-CO-CH2(f)& -CH2-CH(d)], 5.713 and 6.107 [s, =CH2(h), j=1.9], 7.206-
6.79[m, Ar H ortho to –CH2-O-(b)], 8.650-8.544[m, Ar H ortho to s-triazine ring
(a)]. Residual DMSO-d6 at 2.5 and water in DMSO-d6 a broad peak at 3.5
were observed.
ETPAA: 3.991-4.127 [m, -O-CH2(c), & -OH(e)], 4.227-4.299 [m, -O-CO-
CH2(f)& -CH2-CH(d)], 6.954-7.211[m, Ar H ortho to –CH2-O-(b)], 8.530-
8.643[m, Ar H ortho to s-triazine ring (a)]. Protons g and h appeared to be
merged with the e and f protons hence no clear signal could be obtained.
Residual DMSO-d6 at 2.5 and water in DMSO-d6 a broad peak at 3.5 were
observed.
Characterization…
85
Fig. 3.14. 1H NMR(DMSO-d6) spectrum of TP.
Fig. 3.15. 1H NMR (CDCl3) spectrum of ETP.
Characterization…
86
Fig. 3.16. 1H NMR (DMSO-d6) spectra of ETPMA.
Fig. 3.17. 1H NMR (DMSO-d6) spectra of ETPAA.
Characterization…
87
3.2.4 Unsaturated epoxy polyester polyol (ETPUP) 1HNMR (DMSO-d6) spectrum of ETPUP is presented in Fig.3.18 from
which it is observed that the spectrum is highly complex. Different types of
protons, their chemical shifts (ppm) and multiplicities are assigned as follows:
1.19-1.18 [d, -CH-CH3(j)], 2.90-2.77 [m, -CH2-CH(OH)-CH2-(d)], 3.74-3.71[d, -
CH-OH (e)], 3.86-3.79 [m, -OCH2-(c)], 4.74-3.97 [m, -CH2-O-CO-(f,k)], 5.66-
5.04 [m,-CH2-CH(CH3)-O-(i)], 7.23-6.97[m, Ar H ortho to –CH2-O-(b)and
CH=CH(g,h)], 8.65-8.54[m, Ar H ortho to s-triazine ring(a)] and 10.30-10.28
[d, -COOH(l)]. Residual DMSO and moisture appeared at about 2.50 and
3.40. Side spinning bands are also observed around intense peaks.
Fig. 3.18. 1H NMR (DMSO-d6) spectrum of ETPUP.
Characterization…
88
3.2.5 Epoxy polyester polyols 1H NMR (DMSO-d6) spectra of ETPOA, ETPLA, ETPR and ETPRA are
presented in Fig.3.19-3.22 respectively from which it is observed that the
spectrum is highly complex. Different types of protons, their chemical shifts
(ppm) and multiplicities are assigned as follows:
ETPOA: 0.836-0.863 [t, 3H(1)], 1.153-1.263 [m, H(2-7, 12-15)], 1.35-1.45 [m,
H(16)], 1.964-1.978 [m, H(8,11)], 2.093 [m, H(17)], 4.0-4.2 [m, -CH-OH(20)& -
OCH2-(21)], 4.2-4.4 [m, -CH2-CH(OH) (19) & -CH2-OCO-(18)] 6.958-7.201[m,
Ar H ortho to –CH2-O-(22)], 8.533-8.653 [m, Ar H ortho to s-triazine ring(23)].
ETPLA: 0.921-0.950 [t, 3H(1)], 1.102-1.227 [m, H(2-4, 12-15)], 1.442-1.500
[m, H(16)],1.993-2.049 [m, H(5, 11)], 2.422-2.437 [m, H(17)], 2.716-2.900 [m,
H(8)], 4.0-4.2 [m, -CH-OH(20)& -OCH2-(21)], 4.230-4.277 [m, -CH2-CH(OH)
(19) & -CH2-OCO-(18)], 6.96-7.187 [m, Ar H ortho to –CH2-O-(22)], 8.538-
8.649 [m, Ar H ortho to s-triazine ring(23)].
ETPR: 0.851-0.873 [m, H (1, 6, 10)], 1.40-1.60 [m, H (4, 7, 8, 9)], 2.0-2.1 [m,
H (5,11,12)], 2.2-2.3 [m, H(2)], 2.3-2.4 [m, H(3)], 4.0-4.2 [m, -CH-OH(17)& -
OCH2-(18)], 4.20-4.35 [m, -CH2-CH(OH) (16) & -CH2-OCO-(15)], 6.985-7.201
[m, Ar H ortho to –CH2-O-(19)], 8.547-8.653 [m, Ar H ortho to s-triazine
ring(20)].
ETPRA: 0.8-0.9 [t, H(1)], 1.2-1.3 [m, H(2-5, 12-15)], 1.45-1.55 [m, H(6, 16)],
1.966 [m, H(8,11)], 2.047-2.175 [m, H(17)], 3.481-3.503 [m, H(7)], 4.0-4.15
[m, -CH-OH(20)& -OCH2-(21), -OH(24)], 4.15-4.3 [m, -CH2-CH(OH) (19) & -
CH2-OCO-(18)], 6.9-7.3 [m, Ar H ortho to –CH2-O-(22)], 8.5-8.7 [m, Ar H ortho
to s-triazine ring(23)].
Characterization…
89
Fig. 3.19. 1H NMR (DMSO-d6) spectrum of ETPOA.
Fig. 3.20. 1H NMR (DMSO-d6) spectrum of ETPLA.
Characterization…
90
Fig. 3.21. 1H NMR (DMSO-d6) spectrum of ETPR.
Fig. 3.22. 1H NMR (DMSO-d6) spectra of ETPRA.
Characterization…
3.3 Determination of epoxy equivalent of the epoxy resins
Epoxy content is reported in terms of “epoxide equivalent” or “epoxy
equivalent weight” and is defined as the weight of
contains one gram equivalent of epoxy. The term “epoxy value” represents
the fractional number of epoxy groups contained in 100 grams of resins.
Epoxy equivalent may be determined by infrared analysis. The
characteristic absorption ba1 for terminal epoxy groups; from 847.45 to 775.2
groups; and from 769.2 to 751.8 cm
The epoxide equivalent may be determined from changes in
related to change in molecular weight using the
group at 912.4 or 862.1 cm
Greenlee [5] has
epoxide content of the
1 g sample of the epoxide composition with an excess of pyridine containing
pyridine hydrochloride at the boiling point for 20 min and back titrating the
excess pyridine hydrochloride with 0.1 N sodium hy
phenolphthalein as an indicator and considering that 1 HCl is equal to 1
epoxide group.
Jungnickel et al [6
hydrohalogenation methods with bisphenol
containing sample. They recommended the use of a stronger reagent (1 N
pyridinium chloride in pyridine), larger sample sizes and a stronger
4. J. Bomstein. Infrared spectra of oxirane compounds. correlations with
structure. Anal. Chem., 30, 544
5. S. O. Greenlee. (Devoe & Raynolds Co. New York) Phenol aldehyde and
epoxide resin compositions. U.S. Pat. 2,502,145 1949; C.A. 44, 5
1950.
Determination of epoxy equivalent of the epoxy resins
Epoxy content is reported in terms of “epoxide equivalent” or “epoxy
equivalent weight” and is defined as the weight of resin in grams, which
contains one gram equivalent of epoxy. The term “epoxy value” represents
the fractional number of epoxy groups contained in 100 grams of resins.
Epoxy equivalent may be determined by infrared analysis. The
characteristic absorption band for the epoxy group is from 877.2 to 806.45 cm
for terminal epoxy groups; from 847.45 to 775.2 cm-1for internal epoxy
groups; and from 769.2 to 751.8 cm-1 for triply substituted epoxy group
The epoxide equivalent may be determined from changes in
related to change in molecular weight using the absorption band of the epoxy
group at 912.4 or 862.1 cm-1 in comparison to aromatic bands at 1610.3 cm
] has described the method for epoxy equivalent. The
epoxide content of the complex epoxide resins were determined by heating a
1 g sample of the epoxide composition with an excess of pyridine containing
pyridine hydrochloride at the boiling point for 20 min and back titrating the
excess pyridine hydrochloride with 0.1 N sodium hydroxide by using
phenolphthalein as an indicator and considering that 1 HCl is equal to 1
et al [6] have reported somewhat better results than other
hydrohalogenation methods with bisphenol-A epoxy resins and with water
containing sample. They recommended the use of a stronger reagent (1 N
pyridinium chloride in pyridine), larger sample sizes and a stronger
J. Bomstein. Infrared spectra of oxirane compounds. correlations with
structure. Anal. Chem., 30, 544-546, 1958.
S. O. Greenlee. (Devoe & Raynolds Co. New York) Phenol aldehyde and
epoxide resin compositions. U.S. Pat. 2,502,145 1949; C.A. 44, 5
91
Determination of epoxy equivalent of the epoxy resins
Epoxy content is reported in terms of “epoxide equivalent” or “epoxy
resin in grams, which
contains one gram equivalent of epoxy. The term “epoxy value” represents
the fractional number of epoxy groups contained in 100 grams of resins.
Epoxy equivalent may be determined by infrared analysis. The
nd for the epoxy group is from 877.2 to 806.45 cm-
for internal epoxy
for triply substituted epoxy group [4].
The epoxide equivalent may be determined from changes in intensity as
absorption band of the epoxy
in comparison to aromatic bands at 1610.3 cm-1.
described the method for epoxy equivalent. The
complex epoxide resins were determined by heating a
1 g sample of the epoxide composition with an excess of pyridine containing
pyridine hydrochloride at the boiling point for 20 min and back titrating the
droxide by using
phenolphthalein as an indicator and considering that 1 HCl is equal to 1
reported somewhat better results than other
A epoxy resins and with water
containing sample. They recommended the use of a stronger reagent (1 N
pyridinium chloride in pyridine), larger sample sizes and a stronger hydroxide
J. Bomstein. Infrared spectra of oxirane compounds. correlations with
S. O. Greenlee. (Devoe & Raynolds Co. New York) Phenol aldehyde and
epoxide resin compositions. U.S. Pat. 2,502,145 1949; C.A. 44, 5614,
Characterization…
92
solution (0.5 N) for samples of relatively low molecular weight. They have
developed a variation of the pyridinium chloride method in which pyridinium is
replaced by chloroform. The precision and accuracy are somewhat better, due
to the reduction of side reactions. The pyridinium chloride-chloroform method
even permits the determination of epoxides sensitive acids, such as styrene
and isobutylene oxides. However, the preparation of the reagent is
cumbersome, and reaction periods of 2 h are required. Especially time
consuming is the need for the exact equivalence of hydrogen chloride and
pyridine.
Burge and Geyer [7] have also described an extensive procedure for
the determination of epoxide equivalent. A weighed sample of an epoxide
compound containing 2-4 milliequivalents of epoxy group is placed into a 250
ml round bottomed flask, and 25 ml of 0.2 N pyridinium chloride in pyridine
was added. The solution was swirled and if necessary, heated gently until the
sample was dissolved completely and refluxed for 25 minutes, cooled and
then added 50 ml of methyl alcohol and 15 drops of phenolphthalein indicator
and titrated with 0.5 N methanolic NaOH till pink end point. The epoxide
equivalent was calculated according to following relationship:
sampleinoxygenoxiranegrams
gramsinweightSampleequivalentEpoxide
×= 16
3.1
Where gram oxirane oxygen in sample = (ml NaOH for blank-ml
NaOH for sample) x (Normality of NaOH) x (0.016)
The number 0.016 is the mili equivalent weight of oxygen in grams.
The epoxide equivalent of the epoxy resin of 2,4,6-tris(4-hydroxyphenyl)-
1,3,5-triazine (ETP) is 771.
6. J. L. Jungnickel, E. D. Peters, A. Polgar and F. T. Weiss. Organic
Analysis (J. Mitchell Jr., ed.). 1, 127, Interscience, New York, 1953.
7. R. E. Burge, Jr. and B. P. Geyer. Analytical Chemistry of Polymers. (G.
M. Hline, ed.) Vol. XII/1, Interscience New York, 1959.
Characterization…
93
3.4 Determination of acid values of the polyester polyols
Acid value is a measure of the free fatty acids content of oil and is
expressed as the number of milligrams of potassium hydroxide required to
neutralize the free acid in 1 gram of the sample. Acid values of polyester
polyols were determined according to standard reported method [8].
As the reaction progresses acid is consumed to form ester, on
completion of reaction i.e. conversion of acid group to ester group the acid
value reaches minimum or practically zero.
Into a 250 ml stoppered flask, 1g ETPRA/ETPLA/ETPOA
/ETPR/ETPMA/ETPAA was dissolved in 50 ml THF and heated gently for
some time. The solution was cooled and 5-10 drops of phenolphthalein was
added as an indicator and titrated with standard 0.1 N alcoholic potassium
hydroxide solution.
The procedure was repeated for blank titration under similar condition.
The acid value of a given sample was determined according to following
relationship.
Acid Value =� .�∗ �∗ (���)
� 3.2
Where N = Normality of KOH
A = Sample burette reading
B = Blank burette reading
W = Weight of sample in grams
The average of three measurements of each of polyester polyols is reported
in Table 3.1. From Table 3.1 it is clear that 4h reaction time is sufficient to
achieve desired acid values.
8. ASTM D 1980-87, Standard method for acid value of fatty acids and
polymerized fatty acid,1998.
Characterization…
94
Table 3.1: Acid values of polyester polyols and vinyl ester resins
Time,
h
Acid value, mg KOH/g
ETPOA ETPRA ETPLA ETPRO ETPAA ETPMA
2 30.3 24.7 60.6 46.0 26.1 24.3
3 22.4 18.4 52.7 34.9 14.1 18.5
4 17.9 15.7 41.5 30.3 13.1 10.4
5 11.2 10.1 25.8 15.7 9.8 5.8
6 8.97 7.8 16.8 9.0 9.8 3.5
Characterization…
95
3.5 Determination of hydroxyl values of polyester polyols
Hydroxyl value is a measure of free hydroxyl groups present in the
polyester polyols (epoxy esters) and it is expressed as number of milligrams
of potassium hydroxide equivalent to the quantity of acetic acid that binds with
1 g of hydroxyl containing substances. The hydroxyl value gives information
about the number of free hydroxyl group present in a material. The
determination is carried out by acetylation with acetic anhydride in pyridine.
Aldehyde and primary and secondary amines interfere with the determination
and if present then phthalic anhydride is used in place of acetic anhydride.
+ N + NCCH3
O
Resin O C
O
CH3Resin OH CH3COOH+
+ +H2OCH3COOH KOH CH3COOK
Hydroxyl values of polyester polyols and epoxy esters were determined
according to standard reported method. Into a 250 ml round bottomed flask
equipped with a condenser and oil bath, was dissolved 1g
ETPRA/ETPLA/ETPOA /ETPR/ETPMA/ETPAA in 25 ml of acetylating mixture
of acetic anhydride and pydrine(1:7 v/v). The reaction mass was brought to
reflux for 40-45 min, cooled to room temperature and 10 ml cold water was
added slowly down to condenser and titrated with standard 1N alcoholic
potassium hydroxide using 10-15 phenolphthalein as an indicator. Hydroxyl
values were determined according to following relationship [8]:
Hydroxyl Value =� .�∗(���)∗�
��.�� !"#$% 3.3
Where N= Normality of alcoholic KOH,
B= Blank Reading
A= Sample burette reading
W= Wt of sample
The average of three measurements of each of polyester polyols is
reported in Table3.2. Low acid values and high hydroxyl values of the resins
confirmed almost conversion of epoxide groups into corresponding esters.
Characterization…
96
Table 3.2: Hydroxyl Values of polyester polyol and vinyl ester resins.
Time,
h
Hydroxyl value, mg KOH/g
ETPOA ETPRA ETPLA ETPRO ETPAA ETPMA
2 126.6 235.8 73.8 49.2 87.9 59.8
3 284.8 395.4 126.5 193.3 168.7 179.5
4 386.7 536.9 291.8 393.7 305.8 280.5
5 453.5 627.6 474.6 478.1 407.8 317.9
6 597.6 707.4 576.5 566.0 474.6 430.1