Bottlebrush Side Chain Isomers: Spherical Self-Assembly Eliminates PEG Crystallinity at Room Temperature

Bottlebrush block copolymer (BBCP) self-assembly provides opportunities to create a range of nanostructures exceeding the domain sizes traditionally found in linear copolymer systems. The same architecture that provides them with their unique self-assembly, however, makes exploring their structure-property relationships more complex. Here, we introduce the concept of side chain isomers: BBCPs with the same volume fractions and molecular weights, but differing side chain lengths. In this work we report the self-assembly of PEG-PDMS BBCPs that exhibit drastically different self-assembly and crystallinity behavior despite having the same molecular weight, volume fraction of each respective block, and identical PDMS block. Side chain asymmetry plays an important role in defining the self-assembled structure. Notably, the strong segregation strength and side chain asymmetry caused these samples to form highly curved morphologies at equal volume fractions, and which domain formed the core domain depended on the domains side chain length. Additionally, when PEG formed the core of the self-assembled structure, crystallinity of the PEG side chains was entirely suppressed at room temperature. We attribute this result to the soft confinement of the PEG domain within the PDMS matrix.