Single-chain Level Decoding of the Conformational Distribution in Bisphenol A Polycarbonate

Abstract

Bisphenol A polycarbonate (PC) exhibits cis and trans conformations depending on the relative orientation of the phenyl groups to the carbonate moiety, which critically influences its mechanical and thermal properties. Previous ensemble-averaged studies suggest that the trans conformation accounts for approximately 30% of the repeating units in PC. Nevertheless, the chain-level distribution of these trans units remains unresolved, obscuring the origin of ensemble-averaged conformational statistics and their link to macroscopic properties. Herein, the single-chain elasticity and conformational distributions of PC were investigated by combining single-molecule force spectroscopy with quantum mechanical calculations. The results reveal that individual PC chains exist in two discrete conformational populations, i.e., chains with a cis content exceeding 90%, and chains with a trans content in the range of 65±5%. The ratio of the two chain types is approximately 1:1, yielding an overall trans conformation fraction of ~30%, broadly consistent with previous reports. These findings demonstrate that the macroscopic trans fraction arises from a heterogeneous population of distinct single-chain conformations rather than a random distribution of cis and trans units over each chain. This work presents the first chain-level conformational map of PC and provides a molecular perspective for understanding the macroscopic mechanical properties of PC.