title: Side-chain liquid crystalline polymer networks: exploiting nanoscale smectic polymorphism to design shape-memory polymers.
abstract: Herein, we investigate the influence of nanoscale smectic polymorphism within end-on fixed side-chain liquid crystalline polymer networks (SCLCNs) on macroscopic shape-memory and actuation properties. We have synthesized a series of SCLC-type linear (TP-n) and cross-linked random terpolymers (XL-TP-n) with varying length of flexible methylene spacers (n = 5, 10, and 15) between polynorbornene main-chain and cholesteryl ester side-chains. Thermal and mechanical analyses by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) confirm a glass transition (T(g)), a clearing temperature (T(cl)), and a network structure in the XL-TP-n. Detailed structural investigation conducted using wide-angle and small-angle X-ray scattering (WAXS and SAXS) at room temperature proves self-assembled smectic A (SmA) polymorphism of the XL-TP-n which evolves from non-interdigitated bilayer (SmA(2)) for n = 5 to mixed layers of monolayer-like highly interdigitated layer (SmA(1)) and SmA(2) for n = 10 and to SmA(1) for n = 15. In addition, TP10 at temperatures above 60 °C interestingly shows transformation of SmA structure from mixed layer (SmA(1) + SmA(2)) to interdigitated structure (SmA(d)). The SmA polymorphism developed in TP-n during shape-memory cycles (SMCs) significantly impacts the ultimate strain responses. A mechanism for the unique interdigitation-based thermostrictive behavior is proposed. More importantly, this new actuation mechanism observed in these XL-TP-n can be exploited to develop intelligent thermal actuators.
authors.affiliation: Polymer Program, The Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269, USA.
authors.forename: Suk-kyun
authors.initials: SK
authors.lastname: Ahn
authors.forename: Prashant
authors.initials: P
authors.lastname: Deshmukh
authors.forename: Manesh
authors.initials: M
authors.lastname: Gopinadhan
authors.forename: Chinedum O
authors.initials: CO
authors.lastname: Osuji
authors.forename: Rajeswari M
authors.initials: RM
authors.lastname: Kasi