Molecular engineering of side-chain liquid crystalline polymers by living polymerizations

Abstract

Living" anionic, cationic, metalloporphyrin and ring-opening metathesis polymer izations have been used to prepare well-defined side-chain liquid crystalline homopolymers, block and graft copolymers and statistical copolymers. This paper analyzes their successes and failures by reviewing the mechanistic aspects and experimental conditions of each type of polymerization, and identifies other classes of mesogenic monomers that could be polymerized in a controlled manner in the future. The emerging structure/property relationships are then identified using well defined SCLCPs in which only one structural feature is varied while all others remain constant. The the:rmal transitions of liquid crystalline polymethacrylates, polynorbomenes and poly(vinyl ether)s reach their limiting values at less than 50 repeat units, which are generally equal to those of the corresponding infinite molecular weight polymers:Increasing spacer length depresses the glass transition of SCLCPs, and consequently often uncovers mesophases that are not observed without a spacer. The crystalline melting of tactic SCLCPs also tends to decrease (with odd-even alternation) with increasing spacer length. Without additional order within the polymer backbone due to high tacticity, mesogenic side-chains generally do not crystallize until the spacer contains at least nine carbon atoms. As the flexibility of the polymer backbone increases, the glass transition temperature decreases, and the side chains are able to crystallize at shorter spacer lengths and form more

Tailored Phase Transitions via Mixed-Mesogen Liquid Crystalline Polymers with Silicon-Based Spacers

“…The yield after distillation was measured to be around 52%. 1 Synthesis of M2 by Route I. This synthetic route is similar to that reported by Shiota and Ober, 12 yet with different compounds and purification procedures.…”

“…The polymers (PMiSj, where i ) 1, 2 and j ) 1, 2, 3; see materials and methods, above) and copolymers (P(x′M1-co-y′M2)) were dried overnight at 40°C under vacuum before further characterization. 1 H NMR of the homopolymers were run, confirming the structure and good purity of the final polymers. For comparison purposes, a cross-linked, mesogen-free analogue of the copolymers was prepared by polymerizing S3 with higher molecular weight R,ω-divinyl-terminated poly(dimethylsiloxane) and 12.5 mol % of CL.…”

“…We present the synthesis of two chemically similar mesogens, namely, 1,4-bis-[4-(4-pentenyloxy)benzoyl]hydroquinone 10,11 (M 1 ) and 2-tert-butyl-1,4-bis[4-(4-pentenyloxy)benzoyl]hydroquinone (M 2 ), that, although chemically similar, differ drastically in their phase transition temperatures. Indeed, we will show that substituting the slender mesogen, M 1 , with a tert-butyl group (M 2 ) results in a 140°C drop in the nematic-isotropic transition, thus suggesting that one could tune the thermal properties of the resulting materials upon mixing of these mesogens; i.e., "mixedmesogen" LCPs. We thus describe the synthesis and characterization of silicon-based main-chain liquid crystalline homopolymers, blends, and copolymers using both M 1 and M 2 as mesogens.…”

“…After removal of solvent by evaporation, the raw product (a waxlike brown solid) was collected and purified by column chromatography using silica gel as the stationary phase and a mixture of ethyl acetate and hexanes (1:7 v/v) as eluent. 1 proceeded and was continuously stirred for 48 h. At the end of the reaction, a white solid as a byproduct was removed by filtration, resulting into a clear brown solution of the desired product in dichloromethane. After the removal of CH2Cl2 by evaporation, the waxlike, brown raw product was collected.…”

Synthesis of novel acetylene monomers with mesogenic moieties and their polymerization using Schrock-type molybdenum carbenes

“…Furthermore, this effect in the NMR spectrum suggests that the resulting polymers are predominantly trans-configured. With respect to the interesting membrane properties of both liquid crystalline and polyacetylene-based gas separation membranes [63][64][65], these new polymers are fundamentally interesting for membrane materials. The thermal behavior and liquid crystalline properties of the polymers will be subject to detailed discussion in another paper [66].…”