Liquid-crystalline polymers containing heterocycloalkanediyl groups as mesogens. 8. Morphological evidence for microphase separation in poly(methylsiloxane-co-dimethylsiloxane)s containing 2-[4-(2(S)-methyl-1-butoxy)phenyl]-5-(11-undecanyl)-1,3,2-dioxaborinane side groups

Composition-dependent phase transformation in side-chain liquid crystalline copolymers with mesogenic groups at different substituent positions

Copolymerization is an effective approach to tailor the thermal and structural properties of liquid crystalline polymer materials, which is essential for various applications. In this work, two series of polynorbornene copolymers, A-r-B and A-r-C, with the biphenyl mesogenic side group at different substituent positions were synthesized via ring-opening metathesis polymerization in various compositions. The corresponding homopolymers A and C are liquid crystalline polymers, exhibiting an oblique columnar structure (Colob/p2) and lamellar structure, respectively, while homopolymer B is amorphous. The composition-dependent phase behaviors of copolymers were systematically studied with the combination of SAXS, GISAXS, AFM, DSC and POM techniques. With increasing molar content of A (xA), the self-organzied structure of copolymer A-r-B follows the sequence from amorphous to lamellar, undulated lamellar, and Colob/p2 structures, and that of A-r-C follows the sequence of lamellar, undulated lamellar, and Colob/p2 structures. Then, copolymers with undulated lamellar or Colob/p2 structures tend to enter lamellar phase first at higher temperature and then change to the isotropic state during heating. The composition-induced transition from lamellar to supramolecular columnar organization is somewhat reminiscent of block copolymers and other soft matter systems that can form ordered structures. Furthermore, the subsitituent number and position of rigid mesogenic units in the side chain can further modify the morphologies of self-organized phases.

Polysiloxane-Based Side Chain Liquid Crystal Polymers: From Synthesis to Structure⁻Phase Transition Behavior Relationships

Organosilicon polymer materials play an important role in certain applications due to characteristics of much lower glass transition temperatures (Tg), viscosities, surface energy, as well as good mechanical, thermal stabilities, and insulation performance stemming from the higher bond energy and the larger bond angles of the adjacent silicon-oxygen bond. This critical review highlights developments in the synthesis, structure, and phase transition behaviors of polysiloxane-based side chain liquid crystal polymers (PSCLCPs) of linear and cyclic polysiloxanes containing homopolymers and copolymers. Detailed synthetic strategies are elaborated, and the relationship between molecular structures and liquid crystalline phase transition behaviors is systematically discussed, providing theoretical guidance on the molecular design of the materials.

Side-chain liquid crystalline polymer networks: exploiting nanoscale smectic polymorphism to design shape-memory polymers

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.