The phase separation of block copolymers (BCPs) has been widely investigated in past few decades, not only because of fundamental science interests but also its broad applications. One key challenge that still remains is achieving ultra-small phase separation (sub-10 nm or even sub-5 nm), which is highly desirable to the microelectronics industry. One approach is to make a high χ-low N diblock copolymer. Due to strong immiscibility of two polymer components (high χ), these dibock copolymers are still phase separated even at low N, allowing for small phase separation behavior in the bulk state. However, in order to obtain a high χ-low N diblock copolymer, new polymer structures need to be designed (usually involving multi-step synthesis), making this approach impractical. Herein, we report a universal strategy to access ultra-small phase separation by using Janus bottlebrush copolymers (BBCPs). A series of branched macromonomers (BMMs) with different polymer combinations were polymerized by ring-opening metathesis polymerization (ROMP) to afford Janus BBCPs. These Janus BBCPs showed a very strong tendency to phase separate, compared to the corresponding BMMs. Different polymer combinations were applied including polydimethylsiloxane (PDMS), poly(lactic acid) (PLA), polystyrene (PS), poly(tert-butyl acrylate) (PtBA), and poly(ethylene glycol) (PEG). The simple synthetic procedure and incorporation of readily accessible polymers lend wide applicability to this method. Ultra-small phase separation (with the domain size as small as 2.8 nm) was demonstrated by a PDMS-branch-PLA Janus BBCP.

Janus bottlebrush copolymers: A universal strategy enabling access to ultra-small phase separation

255th National Meeting (2018)

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