Preparation and analysis of cross-linking copolymers

Copolymerization of ST (styrene) with EDM (ethylene glycol dimethacrylate) gives nonlinear polymers. The average molecular weight and polydispersity o f copolymers composed of ST and EDM were measured using the GPC (gel permea tion chromatography) technique, and an exponential increase in both quantit ies with reaction time was observed. H-1 and C-13 NMR spectra of the copoly mers were taken to prove the structure and purity of the products and to ca lculate the composition and pendant content of the copolymers. The ratio of the pendant double bonds of the copolymers was determined from the 1H NMR spectra. A remarkable increase in the ratio of the pendant double bonds wit h reaction time was observed. The mechanism for the chain propagation was s tudied and found to follow the terminal model. Reacitvity ratios were found to be r(1) = 0.452 +/- 0.031 for monomer ST and r(2) = 0.297 +/- 0.027 for monomer EDM. According to the size distribution of the copolymers measured by DLS (dynamic light scattering) and the average radii of gyration measur ed by SLS (static light scattering) techniques, the samples showed strong p olydispersity and an increase in molecular size with reaction time. Unusual ly high molecular weight values were observed after a certain reaction time .