Abstract:
This research has concerned a study on the effect of composition in methyl metliacrylate-styrene random copolymers on their K and a constants in the Mark-Houwink equation. The equation has been used to determine an average molecular weightof homopolymers based on their measured viscosity. In this work, the copolymers having various composition and chain length were prepared via a controlled free radical polymerization, using benzyl diethyldithiocarbamate (BDC) and tetraethylthiuram disulfide (TD) as iniferters. The synthesized products were aiialyzed by various techniques including FT-IR, 'H-NMR, GPC and Viscometry. By relating the determined K and a constants of various copolymers to their composition,it was found that the constants changed with the composition. The a constant of polystyrene decreased with increasing PMMA content in the copolymer molecules to 60% PMMA composition. After that, the constant increased with filrther increasing the PMMA content. On the contrary, the K constant increased with PMMA content in the copolymer molecules up to the composition of 60% PMMA. Beyond that composition, the constant decreased again. These results suggested that an average molecular weight ofthe known composition random copolymer cannot simply be approximated by using a linear equation, comprising the K and a constants of each relevant homopolymers.