Tuning Thermal Properties of Copolymers via Monomer Sequence and Interactions

Controlling the glass transition temperature (T_g) is a primary objective in developing functional polymeric materials, and copolymerization is a common strategy. The Fox equation is often employed to predict T_g, but it does not consider the influence of monomer sequence or interactions between dissimilar monomers. To understand experimental deviations from the Fox equation, we prepared and analyzed polymers with identical compositions but different sequences. Initially, we synthesized poly(methyl methacrylate-co-4-tert-butylstyrene) (PMMA-PtBS) with varied compositions through free radical polymerization at low conversion. The T_g of each copolymer, as measured by DSC, was consistently lower than the value predicted by the Fox equation, with a maximum deviation of 10 °C at 29 wt% MMA. We also prepared PMMA-PtBS using atom transfer radical polymerization, yielding a down-chain gradient in composition, which exhibited an even more pronounced negative deviation from the Fox equation. We have also prepared and analyzed PMMA-b-PtBS and PMMA-b-(PMMA-PtBS) block copolymers. For the study of monomer interaction effects, poly(methyl methacrylate-co-9-vinylcarbazole) (PMMA-P9VC) was also investigated. When the content of 9VC was relatively low, a positive deviation from the Fox equation was observed, but at high 9VC content, a negative deviation was observed.