Self-organization induced sequence regulation in step-growth copolymers

The sequence of a copolymer is important to its properties and functions. Biopolymers, such as proteins or DNAs, can have almost perfect sequence control. However, for synthetic copolymers, sequence control is currently very limited. Understanding the effects that can influence copolymer sequence is of great interest. Here we devise and implement a model of a simple, coarse-grained, A,B copolymerization process, where a step-growth polymerization occurs irreversibly in solution. Holding the energetic reaction barriers between all monomers constant, we study the other effects that could influence copolymer sequence - effects arising from interactions among the monomers and oligomers and between the nascent chains and other environmental features. We find that, at modest attraction differences of just 1 kT between different monomer pairs, a spontaneous micro-phase separation can emerge during the reaction as the nascent chains lengthen. This phase separation can then change the local environment of the reactive ends, leading to a breakdown in Flory's equal reactivity principle. These micro-phase separations can also yield long range ordering in the polymer sequence. When polymerization results in relatively stiff chains, crystallites can be formed during the reaction, which can self-template additional growth, resulting in a low polydispersity and relatively narrow single-monomer block length distributions. We also study other simple templating effects that provide insights on the physics of surface templating and self-replication. Our studies here provide a better understanding of the potential influence of self-assembly processes during copolymerization and suggest new potential synthetic approaches to control copolymer sequence.