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