The impact of architecture and block lengths of poly(trimethylene carbonate-b-sarcosine) copolymers on their self-assembly behavior

The chemical composition and macromolecular architecture of amphiphilic block copolymers govern their self-assembly behavior in aqueous solution. Although a wide range of block chemistries and polymer architectures has been investigated, the influence of architecture on key properties of self-assembled structures, including polymersome membrane thickness, remains insufficiently understood. The increasing availability of well-defined block copolymers with diverse architectures provides an opportunity to systematically evaluate architectural effects by direct comparison with linear analogues of comparable composition. In this study, poly(trimethylene carbonate- b -sarcosine) (P(TMC- b -Sar)) copolymers with AB linear diblock, ABA linear triblock, and AB 2 miktoarm star architectures were synthesized by ring-opening polymerization, and their self-assembly in aqueous solution was characterized using electron microscopy and light scattering techniques. Copolymer architecture was found to significantly influence the morphology and size distribution of the resulting self-assembled structures. In particular, AB 2 miktoarm star copolymers formed polymersomes over a broader range of hydrophilic PSar weight fractions and hydrophobic PTMC block lengths than their AB linear counterparts. Furthermore, AB 2 -derived polymersomes were more abundant in the smaller size range and exhibited measurably thinner membranes than AB-derived polymersomes with similar PTMC block lengths. We also demonstrate that residual PTMC homopolymer impurities generated during synthesis of certain AB 2 copolymers substantially alter vesicle morphology by promoting the aggregation of smaller vesicles. These findings demonstrate that both block copolymer architecture and the controlled presence of homopolymer impurities play important roles in governing block copolymer self-assembly and should be carefully considered in the design of polymersome-forming materials.