Gradient and block side-chain liquid crystalline polyethers

Abstract

A set of gradient copolymers composed of liquid crystalline polyether and poly(butylene oxide) with narrow molecular weight distributions and well-defined, continuous growing composition profiles were synthesized via anionic ring-opening polymerization. For comparison, corresponding diblock copolymers without compositional gradient were also prepared. The thermal transitions, phase structures and their evolutions of these two sets of liquid crystalline copolymers with composition and temperature were systematically investigated. The compositional gradient copolymers were found to possess a remarkable sensitivity on the phase structures on multiple length scales. Compared with the corresponding liquid crystalline block copolymers, they exhibited a broad glass transition region and a large breadth of liquid crystalline phase transformation associated with disordered mesogenic packing and a thickness distribution of liquid crystalline layers. Ordered, nanophase separated structures were observed to gradually develop with increase of gradient length. They exhibited distinct ordering and evolution processes with continuous liquid crystalline melting, which are different from the reference samples of diblock copolymers. Those behaviors are speculated to originate from the heterogeneity intrinsic to liquid crystalline gradient copolymer. 51 The density of EOBC homopolymer at room temperature is 0.99; the density of its melt at 140 o C is 0.95, for example, which have been measured by a pycnometer.

Synthesis of gradient copolysiloxanes by simultaneous copolymerization of cyclotrisiloxanes and mechanism for kinetics inverse between anionic and cationic ring‐opening polymerization

“…Tetrahydrofuran (THF) was used as the eluent and the flow rate was set at 1 mL min 21 (30 8C). Samples were prepared in THF at 5-10 mg mL 21 and rapidly injected after preparation to avoid depolymerization. Molar mass and molar mass distributions of copolymers were determined from a calibration curve based on narrowly dispersed polystyrene standards.…”

“…The T g was determined by differential scanning calorimetry (DSC) using a SII EXTRA 6200 DS calorimeter at a heating rate of 20 K min 21 under a nitrogen flow rate of 10 mL min 21 . The optimized molecular configuration was simulated with density functional theory (DFT) calculations at the B3LYP/6-311G(d,p) level by using the Gauss 09 package.…”

“…This indicated that although the two monomers were not compatible prior to the polymerization, they resulted in the formation of the copolymers rather than the blends of the two types of homo-polysiloxanes after polymerization. Moreover, the number average molar mass (M n ) is 2.5 3 10 4 g mol 21 , and the molar mass distribution (M w /M n ) for the copolymer obtained from Ph 2 Si(OLi) 2 initiation is 1.3 [ Fig. 4(B)], the narrow M w /M n indicates that the copolymerization initiated by Ph 2 Si(OLi) 2 is a controlled process.…”

“…However, in recent years, gradient copolymers of different siloxane units have gradually produced extensive concern because of their potential unique properties which are significantly different compared with the properties of block and random copolymers . Gradient copolymers are a novel class of polymers that exhibit a gradual change in composition along the chain . They can potentially be used as polymer blend compatibilizers, surfactants, and environment‐sensitive materials …”

“…6,[17][18][19] Gradient copolymers are a novel class of polymers that exhibit a gradual change in composition along the chain. 17,[20][21][22][23][24][25][26][27][28] They can potentially be used as polymer blend compatibilizers, surfactants, and environment-sensitive materials. 12,24,[29][30][31][32] In general, copolysiloxanes are obtained from copolymerization of different monomers.…”