Unravelling Intrinsic Thermal Conduction Mechanism through Phonon Transport Pathway Engineering of Long-Range Ordered Block Copolymers

Abstract

Highly thermally conductive polymers are playing essential roles in various electronics-related fields. However, the mechanism underlying thermal conduction remains hitherto elusive. Herein, the intrinsic thermal conduction mechanism of polymers was disclosed by rational molecular structural design and precise synthesis through reversible addition-fragmentation chain transfer (RAFT) polymerization. By precisely controlling the spatial distribution and sequence of cyanobiphenyl-based liquid crystalline (LCx) monomer and glycidyl methacrylate (GMA, epoxy-containing unit), as well as length of flexible segment (-CH₂-)x in LCx, block copolymers PLCxm-b-PGMAn with multi-level long-range ordered structures were generated. Specifically, microstructurs of hexagonally packed cylinder-like (HEX-like), lamellar-like (LAM-like), and inverted hexagonally packed cylinder-like (Inverted HEX-like) were effectively constructed as the flexible segment of -CH₂- was increassed to 11 ((-CH₂-)11, LC11). It is noteworthy that increasing the ratio of LC11 is highly beneficial for enhancing thermal conductivity. Moreover, compared with HEX-like and inverted HEX-like morphologies, which exhibited numerous thermal interfaces, the LAM-like morphology was able to construct long-range phonon transport pathways and reduce phonon scattering through the synergistic effect of microphase separation-driven confined assembly with semicrystalline structure and supramolecular assembly, thereby exhibiting higher thermal conductivity. This study elucidates the thermal transport mechanism at molecular levels by experiments and simulations, highlighting the crucial role of multiscale chain alignment and long-range ordered structures synergistically enhancing phonon propagation in polymers.