Demystifying The Synthesis and Preparation of Protein-Mimicking Random Heteropolymers

Random heteropolymers (RHPs) with statistically distributed comonomers along the polymer chains are commonly used as functional materials for achieving biomimetic functionality. This is due to their capacity to replicate protein-like phase behavior and functions. However, unlike many branches of chemistry and biology where structures can be constructed precisely on the molecular level, the inherent stochastic nature of monomer sequences in RHPs raises concerns regarding their high material dispersity and difficulties in chemical characterization. Moreover, while extensive research has been conducted on synthesizing and understanding two-monomer systems, there have been limited studies and systematic guidance on the synthesis of multi-monomer copolymers such as RHPs, which involves complex, interdependent reaction kinetics among multiple comonomers. These knowledge gaps present barriers for researchers outside the polymer chemistry community who seek to create protein-mimicking RHPs with targetable structures and properties.<br/>Towards these prospects, here we conduct a comprehensive investigation into the sequence heterogeneity and compositional drift in a family of 4-monomer-based RHPs. We commenced with experimentally determining the relative reactivities of a repertoire of four methacrylate monomers in reversible addition-fragmentation chain-transfer (RAFT) copolymerization. These underlying kinetic factors dictate the sequence heterogeneity of as-synthesized RHPs.Combining with stochastic sequence simulation, we designed four new RHPs, with each ensemble designed to exhibit different levels of hydrophilicity. Of particular interest is our findings that the purification procedures used during RHPs preparation, including pentane precipitation and dialysis against water, can preferentially eliminate different RHP subpopulations. This selectivity can be attributed to the conformations and apparent solubilities exhibited by these subpopulations, which are due to their particular chemical compositions within the whole RHP ensembles. Additionally, we quantitatively mapped out the trajectory of monomer compositions during the whole RHP preparation process. The predicted RHP cumulative compositions are in close agreement with the experimental results. These results validate the fidelity of predictive modeling and multicomponent RHP copolymerization. There are potentially over 300 commodity methacrylate monomers that are available for synthesizing RHPs materials. These findings are readily applicable to study the structure and sequence of heteropolymers beyond those described in this work. Overall, this work provides critically needed information to design and understand RHPs as functional materials while addressing the concerns related to their sequence heterogeneities.