Iranian polymer journal
Volume:15 Issue: 11, 2006

Epoxies are generally cross-linked by the addition of a hardener, most of the time a diamine such as diamine diphenyl sulphone, oxydianiline or methylene diamine, and then thermocured. These formulations are quite often used, particularly in the aerospace industry for making structural materials, prepregs or composites. In this paper we have investigated the cross-linking reactions of a difunctional cycloaliphatic epoxide monomer 3,4-epoxycyclohexylmethyl-3'', 4''-epoxycyclohexane carboxylate initiated by UV-irradiation and compared the kinetics with N,N-diglycidyl- 4-glycidyloxyaniline (a nitrogen-containing monomer with a functionality of three) and 4,4''-methylenebis (N,N-diglycidylaniline) (another nitrogen-containing monomer with a functionality of four). Kinetics is followed using a differential photocalorimetry (DPC) technique. Upon UV irradiation in the presence of cationic photoinitiator, the difunctional cycloaliphatic epoxide monomer shows an exotherm peak whereas for the latter two monomers, no exotherm peaks were observed from the sample as a result of exposure to the UV source. To explain the phenomenon observed, the effect of addition of two amines with wide difference in the basicity of p-nitroaniline and pyridine, has been studied on the UV-curing of epoxy resins. It has been found that the presence of amines does retard the rate of photopolymerization and the extent of retardation is dependent on the basicity of the amine. Of the two amines used, pyridine and p-nitroaniline, the former is a stronger inhibitor, because of the ready availability of the lone pair of electrons. The results explain the non-reactivity of nitrogencontaining epoxy monomers N,N-diglycidyl-4-glycidyloxyaniline and 4,4''-methylenebis (N,N-diglycidylaniline) to cationic polymerization upon exposure to UV-radiation.

The compatibilization effect of a hyperbranched poly(amide-ester) (HBP) on poly(acrylonitrile-butadiene-styrene)/poly(vinylchloride) (ABS/PVC) blends was examined. The effects of the amounts of HBP on mechanical properties of ABS/PVC (80/20, mass ratio) blends were investigated. The results showed that a small quantity of HBP had a significant effect on mechanical properties and can improve the compatibility of the ABS/PVC blends; the tensile strength of the ABS/PVC (80/20) blends reached to a maximum value when HBP content increased to 2 phr and then dropped quickly by adding more HBP, the impact strength of the ABS/PVC (80/20) blend decreased with incorporation of HBP, the higher HBP added, the greater impact strength of ABS/PVC blend decreased. The scanning electron microscopy indicated that the surfaces of ABS/PVC blends were mainly composed of separate tiny droplets and some cavities. When HBP was introduced into ABS/PVC (80/20) blends, the asperity of the surface decreased, and shear band began to form either partially or completely. DSC Analysis also confirmed that HBP could improve the compatibility of the ABS/PVC blends.

The synthesis of an epoxy vinyl ester resin was carried out using a bisphenol-A based epoxy resin and methacrylic acid in the presence of triethylamine as a catalyst. The reaction was performed in the temperature range of 90-120ºC and epoxy to carboxyl group ratio of 1. In all conditions a conversion of more than 95% was achieved. The reaction time (for conversions more than 95%) was different from 1.5 h at 120ºC to more than 8 h at 90ºC. The results indicated that reaction followed a first-order kinetics. The order of reaction with respect to methacrylic acid was also investigated by using excess method. It was found that in the reaction conditions, the reaction rate was independent of carboxyl group concentration. The specific rate constant, calculated by the regression analysis, was found to obey Arrhenius expression. The activation energy and frequency factor were found to be 82.61 kJ/mol and 5.43×109 min-1, respectively. FTIR Analysis of vinyl ester resin revealed that addition esterification reaction between carboxyl and epoxy groups took place and no side reactions (i.e., etherification reaction between epoxy and hydroxyl groups) occurred during the synthesis.

Polymeric additives include dispersants and binders which play a key role in processing of colloidal ceramic suspensions. In this work, the dispersion behaviour of colloidal Al2O3 suspensions in the presence of polymeric binder (polyethylene glycol) and dispersant (ammonium salt of polyacrylic acid) was investigated by sedimentation technique, viscosity measurement and FTIR method. The effects of polymeric binder molecular weight and concentration and its interaction with polymeric dispersant were investigated. The results showed that PEG 6000 can be used as a suitable polymeric binder in colloidal processing of alumina suspensions. The optimum concentration of polymeric binder which results in optimum stability conditions was obtained 5 wt% PEG 6000 based on the dry powder weight. Further increasing of binder concentration causes instability of the alumina suspensions via depletion mechanism. In the optimum range of the dispersant concentration (0.2-0.3 mL/100 g powder), suspensions with optimum binder concentration have lower stability compared to those with only dispersant as a polymeric additive. This behaviour is confirmed by FTIR spectra analysis of the polymeric species remained in supernatant liquid. The stability behaviour of the colloidal alumina suspensions with different contents of polymeric binder and dispersant was also evidenced by scanning electron microscopy imaging of the sediment layers after 3 weeks.

Apolymer gel is a cross-linked polymer which undergoes a reversible volume and/or sol-gel phase transition in response to physiological (temperature, pH and presence of ion in organism fluids) or other external (electric field, light) stimuli. In structurally soft gels, the motion of polymer network and the diffusion of ions easily take place by an external stimulus. A typical function of gel containing ionic groups is to swell under the influence of an electric field, making it useful for wide biomedical applications. In this study, poly(acrylic acid) (PAA) hydrogel network was prepared by free radical polymerization whose average molecular weight between crosslinkes was calculated as 18500 g/mol and its homogeneity assessment evaluated by comparing 30 samples swelling ratios after 48 h soaking in distilled deionized water. The swelling behaviour of PAA under an electric field application was also investigated as a function of cross-linking agent and electric field intensity variation. It is seen that equilibrium swelling ratio of PAA gel increases from 16 (no electric field) to 30 (by application of 300 V/m electric field), however this variation is dependent on the sample location relative to electrodes. The normalized swelling ratio of sample changes by 4.8 to 0.9 relative to its distance from positive electrode. Increasing the concentration of cross-linking agent (EGDMA) from 0.14 to 0.71 molar percent of monomer resulted in 45% decrease of gel volume fraction. It is proven that applying an external electric field can make an improvement in the time-response of the hydrogel expansion phase and swelling behaviour.

Particle size distribution determines the major end-use properties of latex produced by emulsion. Therefore simulation and control of particle size distribution are important in emulsion polymerization. The investigated system is styrene polymerization. The model for determination of particle size distribution is based on population balance, accounting for nucleation and growth phenomena. The population balance equation (PBE) is discretized respect to particle radius. The ordinary differential equations obtained from discretization of PBE, initiator and monomers mass balances and algebraic thermodynamic equations are solved simultaneously via MATLAB programme. The accuracy of the model has been determined by the experimental results. The open-loop optimal surfactant feed profile for achieving a desired bimodal particle size distribution in a semi-batch reactor is obtained. The genetic algorithm is employed for the optimization.

Three different novel sorbents were prepared by cross-linking polypropylene grafted styrene-divinylbenzene (PP-ST-DVB) fibre with monochloromethylether or p-xylylenedichloride or 1,4-bis-chloromethyldiphenyl according to Friedel- Crafts reaction. A series of synthesis tests were made and the effects of several important factors including reaction temperature, time, catalyst, and material ratio on the Friedel-Crafts reaction were investigated in detail. The optimal synthetic conditions of sorbents were obtained. Compared with PP-ST-DVB fibre, the sorbents have larger specific surface area, pore volume, pore radius and higher adsorption capacities for organic vapours. The adsorption capacities for organic vapours on the hypercrosslinked sorbents were increased about 10 times. The adsorption capacities on the sorbents were related with the molecular length of cross-linking agents. The amounts absorbed on the sorbent 1, sorbent 2 and sorbent 3 can be reached to 428.6 mg/g for methanol, 471.9 mg/g for benzene, and 491.1 mg/g for toluene, respectively.

The kinetics of melt polyesterification of adipic acid with hexamethylene glycol in an equimolar ratio has been studied over a temperature range of 120ºC to 150ºC in the absence and presence of p-toluene sulphonic acid (PTSA) or diphenylammonium triflate (DPAT) as catalyst. The rate equations for polymerizations fit the rate equations proposed by Tang-Yao for 80-480 min. For acid-catalyzed and non-catalyzed polyesterifications at various temperatures, plots of 1/(1-p) and 1/(1-p)3/2 have been made against time, respectively. The fits test accuracy was also ensured by the least squares method. The experimental results show that reaction orders are 2.5 and 2 for uncatalyzed and acid-catalyzed reactions, respectively, with up to 97% conversion. The rate constants and activation energies for uncatalyzed and acid-catalyzed reactions were calculated. The activation energies are 45.01 kJ/mol for the self-catalyzed system, 35.32 kJ/mol for DPAT catalyzed system and 31.55 kJ/mol for PTSA catalyzed system. Activation energies are compared to literature data for polyesterification reactions of adipic acid with hexamethylene glycol in equimolar quantities. We found that the catalytic activity of DPAT in polycondensation is similar to that of PTSA.