Glass transition temperature and architecture of branched poly(methyl methacrylates)

It has been shown that, for a number of MMA-based copolymers prepared through the copolymerization of MMA with a bifunctional comonomer in the presence of a chain-transfer agent, an increase in the concentration of the comonomer (the branching agent) is accompanied by a rise in the molecular mass of the copolymers and a reduction in their glass transition temperature T _g by 30–40°C. This phenomenon provides evidence for the presence of branches in the copolymers and the incorporation of the chain-transfer agent into the branches. The value of T _g linearly declines with an increase in the between the concentration of the branching agent and the molecular mass of the copolymer, that is, with an increase in the number of branches (and end groups) in a macromolecule. A correlation between the glass transition temperature and the rheological and diffusion-sorption characteristics of the branched copolymers has been established. The number of end groups in the copolymers under study has been calculated in accordance with the previously advanced model for the formation of branched macromolecules. The experimental dependences of T _g on the content of the branching agent, the number of end groups, and the molecular mass of the copolymers confirm this model.