Reaction Kinetics and Reactivity Ratio Effects on Graft Copolymerization of 4-Vinylpyridine/1-Vinylimidazole Mixtures onto ETFE Film for Enhanced Basic Properties

Graft copolymerization of 4-vinylpyridine (4-VP) and 1-vinylimidazole (1-VIm) mixtures onto electron beam (EB)-irradiated poly(ethylene- co -tetrafluoroethylene) (ETFE) films was investigated to form a membrane precursor with a basic nature. The influence of grafting parameters, including absorbed dose, monomer concentration, and temperature at different times, on the degree of grafting (DG) was studied. The kinetics of the grafting reaction were quantitatively investigated with respect to initial polymerization rate ( r p 0 ), characteristic radical recombination rate ( γ ), and delay time ( t 0 ). The effect of variation of monomer reactivity ratios in 4-VP/1-VIm comonomer mixtures on the composition of the copolymerized monomer pair in the grafted films and the run number was studied using Mayo–Lewis model. The experimental data were fitted to 3-D geometrical space from which a new regression model was developed to enable predicting the content of 4-VP in the grafted films based on the reactivity ratios of 4-VP and 1-VIm using the quotient ( r m 1 / r m 2 ), which stands for the reactivity ratios of 4-VP and 1-VIm, respectively. The quadratic molar fraction of 4-VP (F 4-VP ) in the grafted film affected the run number ( R ) significantly and was found to be less than its content in the feed mixture ( f 4 -VP ) when a threshold at f4-VP 0.13[67.61+R] f 4 - V P ≅ 0.13 67.61 + R was reached. The composition of the basic grafted copolymer films was primarily influenced by kinetic parameters and reactivity ratios, resulting in a dominance of 4-VP units, irrespective of its feed ratio. Furthermore, the presence of 1-VIm led to a reduction in DG.