The physico-chemical characterization of poly (2-hydroxyethyl methacrylate-co-methacrylic acid): 1. Effect of PEG 400 on the tacticity and reactivity ratios

Abstract

A series of copolymers of 2-hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAA) were selected as possible carrier systems for controlled drug delivery. The tacticity of these copolymers averaged 60% syndiotacticity and 40% heterotacticity when prepared with 2,2,azobisisobutyronitrile (AIBN) at 70°C (pH c. 3.5). The presence of poly(ethylene glycol)400 (PEG 400) in the reaction mixture seemed to have only a minimal effect (at a low pH) on the polymerization reaction. In contrast, an increase in the pH gave a tendency towards heterotacticity and had an enormous effect on the reactivity ratios. The r values change from r(1) 1.50 and r(2) 0.67 to r(1) 13.8 and r(2) 0.07 for HEMA and MAA respectively. These changes affect the copolymer composition and thus the rate of drug release from the polymeric drug delivery systems made from these copolymers.