The Interplay Between Liquid–Liquid Phase Equilibria, Sequence, and T g in Copolymers

Copolymerization is commonly employed to tune polymers’ glass formation and improve properties such as ion conductivity and adhesion. Classically, mixing rules such as the Fox equation are employed to explain glass transition temperature ( T g ) variations with copolymer composition. However, many copolymers deviate from these mixing rules in a manner that is monomer-sequence sensitive. We perform molecular dynamics simulations to probe the interplay between copolymer sequence, liquid–liquid phase equilibria, and T g . We find that the direction and sequence-dependence of T g shift are predicted by the liquid–liquid phase behavior of the comonomers. Systems tending toward Upper Critical Solution Temperature behavior exhibit negative T g deviations, while systems tending toward Lower Critical Solution Temperature behavior exhibit positive T g deviations. In both cases, this effect is strengthened with increasing alternation─a consequence of bond-induced forced mixing. These results inform strategies for rationally varying copolymer T g, at fixed composition, via the design of polymer chain sequence.