FT-IR spectrum of the neat resin sample between KBr discs was obtained with a Thermo-Nicolet Nexus-870-FTIR spectrometer.

¹H-NMR spectrum was recorded on a Bruker AC 200 spectrometer. Sample was dissolved in deuterated chloroform and TMS was used as the internal standard.

Viscosity measurements were carried out with TA instruments (model AR1000, Newcastle, DE, USA) in a parallel plate configuration (40 mm diameter, 1 mm gap) at various shear rates at 30°C for AFCFC and at different temperatures from 30 to 80°C for BCCOMB.

Mole of primary and secondary amine per gram of AFCFC was determined by potentiometric titration (Siggia, 1979). In this method, a small amount (500 mg) of AFCFC was taken into a 100 ml beaker and dissolved in 1:1 ethylene glycol-isopropanol mixture (25 ml). Then, the resulting solution was titrated with 1 N hydrochloric acid prepared in the 1:1 ethylene glycol-isopropanol mixture. The neutralisation point was determined by plotting the apparent pH against millilitres of acid. The total moles of amine/gram was calculated via the following equation 1:

Equation 1 To determine secondary amine moles only, the same method (equation 1) was employed after addition of salicylaldehyde (2.5 ml) in the sample solution. The mole was calculated by equation 2:

Equation 2 The primary amine mole was calculated by subtracting the secondary amine moles from the total amine moles.

The term epoxide equivalent or EEW is defined as the weight of the resin in grams, which contains one-gram equivalent of epoxy. The EEW was determined by hydrogen bromide method (Lee and Neville, 1967) and is calculated from the following equation 3: Equation 3 Where, w, weight of the sample; S, ml of HBr used in titrating the sample; B, ml of HBr used in titrating the blank, and N, normality of HBr.

DSC studies were conducted on a Mettler DSC 25 module attached to a Mettler TC 114000 thermal analyzer, adopting the method of the variable peak exotherm to determine the kinetic parameters of different resin formulations. All measurements were carried out under nitrogen flow (100 ml/min) keeping a constant heating rate and using an alumina crucible with a pinhole. The dynamic scans were conducted at 5, 10, 15, and 20°C/min heating rates. AFCFC (20 phr) was added to BCCOMB resin and mixed thoroughly for 15 min. The clear viscous solution was then subjected to DSC study.

The FT-IR spectrum of AFCFC is shown in Figure 6. For AFCFC, peaks at 3,420 cm⁻¹ and 3,380 cm⁻¹ are due to primary N-H stretching. Peak at 3,208 cm⁻¹ is due to secondary N-H stretching. Peaks at 3,061 cm⁻¹ and 2,855 cm⁻¹ are due to aromatic and aliphatic C-H stretch, respectively. The C-H stretching in formaldehyde generally comes at 2,850 cm⁻¹. It confirms the presence of –CH₂ moiety in AFCFC introduced from formaldehyde unit. Peaks at 619 cm⁻¹ and 785 cm⁻¹ are due to the C-Cl stretching. Peaks at 1,479 cm⁻¹ and 1,260 cm⁻¹ are for N-H bending and C-N aromatic stretching, respectively, confirming the presence of primary and secondary amine moiety. The peak at 1,607 cm⁻¹ is due to aromatic C = C ring stretching which also supports the probable structure of AFCFC as shown in Figure 2.

¹H-NMR spectrum of AFCFC is shown in Figure 7. In proton NMR of AFCFC, one singlet signal at 6.6 ppm and two doublet signals at 6.9 and 6.7 ppm are for aromatic protons. There is also a triplet at 7.2 ppm for secondary amine proton, which couples with aliphatic –CH₂ proton. The singlet at 3.6 ppm is for –CH₂ protons and the singlet at 3.9 ppm is due to primary -NH₂ proton. All these confirm the structure of AFCFC. The formation of AFCFC was also justified from NMR by matching the peak area ratio of aliphatic and aromatic protons with that of number ratio of aliphatic and aromatic protons. The peak area ratio of aliphatic and aromatic protons (2.1/4.5, i.e. 0.46:1) was almost the same with that of aliphatic and aromatic protons number ratio (4/9, i.e. 0.44:1). Owing to this reason, the reaction did not proceed further.

Mole of primary and secondary amine per gram AFCFC has been calculated from the results of potentiometric titration (Aniline was used as the internal standard). The results confirmed the presence of both primary and secondary amine in AFCFC. The mole of total amine, the mole of secondary amine and the mole of primary amine per gram of AFCFC were 0.0072, 0.0048 and 0.0024, respectively. From the mole of primary amine per gram of AFCFC, molecular weight of AFCFC was also calculated. There was a small difference between the molecular weight calculated from the molecular structure (405) and potentiometric titration (416). The small difference comes from the approximation of mole of primary amine calculation in potentiometric titration.

Epoxy equivalent of BCCOMB was 147.5. The actual number of epoxy groups in the reaction product of AFCFC and ECH (BCCOMB) was expected to be five and EEW value should be 135.7. However, the epoxy equivalent value (147.5) indicated incomplete epoxidation, which was also proved by the presence of an unreacted primary –NH group in the resin (FT-IR spectrum of BCCOMB). So the actual degree of epoxidation was 4.6 which was obtained from the epoxy equivalent value (147.5) and molecular weight (678.5) calculated from structure having molecular formula C₃₄H₄₂N₃O₅Cl₃ (Figure 4).

In the FT-IR spectrum (Figure 8), the characteristic absorption band due to the epoxide group was observed at 982 cm⁻¹. A broad absorption band was observed around 3,409 cm⁻¹, which may be due to the primary –NH stretch. As the epoxy equivalent in BCCOMB was lower than 5, the lower functionality may, therefore, arise due to the presence of an unreacted primary –NH group in this resin. The presence of the –NH group is further confirmed by the appearance of a strong absorption band at 1,492 cm⁻¹ due to –NH bending. The secondary -NH stretching is almost absent in the FT-IR of BCCOMB.

The viscosity results of AFCFC are shown in Table I. It appears that AFCFC shows nearly Newtonian behaviour with an average viscosity of 30.34 cP.

The viscosity of BCCOMB at different temperatures is shown in Figure 9. From Figure 9, it is clear that the product is highly viscous with respect to AFCFC. The viscosity of AFCFC is given in Table I at 30°C confirming the reaction of amine and ECH. The resin also shows Newtonian behaviour at each temperature. It is also evident from Figure 10 where the viscosities of BCCOMB at a constant shear rate (49.99 s⁻¹) have been plotted against temperatures that the viscosity decreases with increase in temperatures. This temperature-dependence shows Arrhenius dependence, which is shown in Figure 11, following equation (Doremus, 2003): Equation 4 where η is the viscosity, R the gas constant, T the absolute temperature, A, a constant and Q the activation energy. The Q was calculated from the slope of the graph of log η versus 1,000/T (Figure 11) at a constant shear rate (49.99 s⁻¹) and fitted to a straight line. The activation energy (Q) calculated from equation is 69.45 kJ mol⁻¹.