Crystallization of molecular bottlebrushes bearing single- and double-crystalline side chains

Molecular bottlebrushes (mBBs) are an important polymer system for studying the architecture dependence of various phenomena, such as self-assembly and mechanical response. In this work, mBBs are employed as the model system to study the molecular structure and architectural effects on polymer crystallization. A grafting-to method was used to syntheisze mBBs bearing poly(ethylene oxide) (PEO) side chains, with grafting density ranging from 0.19-0.91. The effect of side chain grafting density on the nucleation and growth of PEO was decoupled in a series of non-isothermal and isothermal crystallization measurements. This system is compared with a 3-arm star bottlebrush synthesized from a 3-arm star PMA backbone to reveal the architectural effect. Furthermore, mixed mBBs with double crystalline side groups were synthesized to understand confined crystallization in mBBs. Poly(caprolactone) side chains are grafted alongside PEO side chains to achieve a random graft copolymer with high grafting density and varying side chain composition. Our study shows that the grafting density increases the melt-memory effect of side chains, backbone architecture reduces the growth rate of crystals grown from the melt, and that mixed grafted bottlebrushes follow some trends shown in block copolymer systems in nucleation order and confined crystallization. These three systems illustrate the broad range of properties attainable through architecture control in bottlebrush copolymers.