3 years ago

Optically Active Elastomers from Liquid Crystalline Comb Copolymers with Dual Physical and Chemical Cross-Links

Optically Active Elastomers from Liquid Crystalline Comb Copolymers with Dual Physical and Chemical Cross-Links
Chinedum O. Osuji, Xiayu Peng, Prashant Deshmukh, Dennis Ndaya, Rajeswari M. Kasi, Manesh Gopinadhan, Lalit H. Mahajan
We report on the synthesis and properties of cholesteric liquid crystalline random terpolymers with comblike architecture as a modular platform for preparation of stimuli-responsive photonic elastomers. Ring-opening metathesis of norbornene monomers bearing n-alkyloxy cholesteryl (Ch9), n-alkoxy cyanobiphenyl (CB6 or CB12), and poly(ethylene glycol) (PEG) side chains is efficient and quantitatively yields low polydispersity random terpolymers. This terpolymer scaffold self-assembles to form cholesteric mesophases (N*) in which microphase-segregated domains of PEG side chains are randomly embedded. The cholesteric mesophase provides a 1D photonic band gap structure at optical wavelengths, which is maintained during chemical cross-linking of the norbornene backbone to form elastomers. The presence of cyanobiphenyl mesogens leads to an increase in the helical pitch of the cholesteric mesophase, resulting in a red-shift of the reflectivity relative to the pure cholesteric mesophase. By contrast, the presence of PEG blue-shifts the reflectivity, such that the overall optical properties can be readily tailored by the composition of the terpolymer. Furthermore, the mechanical properties of the materials are enhanced by the presence of the microphase-separated PEG domains which act as physical cross-links and also provide plasticization of the system. The terpolymers described here provide a modular and versatile platform for the realization of photopatternable materials that exhibit shape memory and thermochromic properties.

Publisher URL: http://dx.doi.org/10.1021/acs.macromol.7b01157

DOI: 10.1021/acs.macromol.7b01157

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