Phase Structures, Transition Behaviors, and Surface Alignment in Polymers Containing Rigid-Rodlike Backbones with Flexible Side Chains. 1. Monotropic Phase Behavior in a Main-Chain/Side-Chain Liquid Crystalline Polyester

Abstract

A series of polyesters, which are comprised of aromatic main chain backbones and flexible aliphatic side chains with 4-cyanobiphenyl end groups, has been synthesized based on a polycondensation of 2,2‘-bis(trifluoromethyl)-4,4‘-biphenyldiyldicarbonyl chloride with 2,2‘-bis{ω-[(4-(4-cyanophenyl)phenoxy]-n-alkoxy)carbonyl]}-4,4‘-biphenyldiol (PEFBP). For a PEFBP polyester containing eleven methylene units in the side chains, PEFBP(n = 11), multiple phase transitions can be found via differential scanning calorimetry during cooling and heating at varying rates. Different phase structures are identified by wide-angle X-ray diffraction and electron diffraction experiments, while morphologies of these ordered states are observed by polarized light and transmission electron microscopy. During cooling, a high temperature nematic (N) phase is formed at 193 °C independent of the cooling rate due to the combined orientational order of the cyanobiphenyl groups in the side chains and the aromatic polyester backbones. At a temperature of 90 °C, a new ordered low-temperature phase with an orthorhombic lattice (KO) starts to form at a cooling rate equal to or slower than 10 °C/min. However, the formation temperature of this phase is too close to the glass transition temperature (60 °C) to proceed to completion. Only at very slow heating rates (e.g., 1 °C/min), can the KO phase further develop. This phase melts at around 120 °C during heating and returns to the N phase. A new crystalline phase with a triclinic lattice at high temperatures (KT1) appears at 130 °C. It then transfers to a second triclinic crystalline phase (KT2). This KT2 phase melts at around 180 °C and, again, returns to the N phase. At 193 °C, isotropization occurs. This complicated phase behavior can be explained by the monotropic origin of the KO and KT1 phases with respect to the KT2 phase, which are metastable in the whole temperature region.

Effect of side-chain asymmetry on the intermolecular structure and order-disorder transition in alkyl-substituted polyfluorenes

“…[35]. When assuming constant volume for the main chain we can estimate densities separately for main chain ρ mc = 1.118 g/cm 3 and side chains ρ sc = 0.917 g/cm 3 . On the other hand, crystallographic data shown provide the area of monomer A monomer ≈ 47.6Å 2 defined by the stacking distance and polymer repeat (5.8 × 8.2Å 2 ).…”

“…The size of an unperturbed coil R c is show for comparison. For PF6-PF9, H is calculated from the α crystalline unit cell parametersb andc and assumed side-chain density 0.95 g/cm 3 listed in Ref. [35].…”

“…Hairy-rod polymers consist of a stiff backbone and flexible side chains that organize into alternating backbone and side-chain layers and experience an order-disorder transition (ODT) on heating [1][2][3][4][5]. Phase behavior of alkyl-substituted conjugated polymers can be understood in similar terms, and this was illustrated early with polythiophenes [6,7].…”

Effect of flexible spacer length on the mesophase structures of main-chain/side-chain liquid crystalline polymers based on ethyl cellulose

“…[1][2][3][4][5][6][7][8][9] In the past, many MCSCLCPs have been synthesized, and the relationship between LC behavior and structural variations has been investigated. [10][11][12][13][14][15][16][17][18][19] Generally, MCSCLCPs can be classified into two kinds according to the constitution of the backbone: one is of a nonrigid nature containing some flexible spacers, 1,3,8,11,[20][21][22][23][24] and the other is of a rigid nature without any flexible spacers. 4,13,15,25,26 Recently, we reported novel MCSCLCPs based on mesogen-jacketed liquid crystalline polymers and ethyl cellulose (EC): these types of MCSCLCPs exhibit very interesting and versatile supramolecular structures.…”

“…[10][11][12][13][14][15][16][17][18][19] Generally, MCSCLCPs can be classified into two kinds according to the constitution of the backbone: one is of a nonrigid nature containing some flexible spacers, 1,3,8,11,[20][21][22][23][24] and the other is of a rigid nature without any flexible spacers. 4,13,15,25,26 Recently, we reported novel MCSCLCPs based on mesogen-jacketed liquid crystalline polymers and ethyl cellulose (EC): these types of MCSCLCPs exhibit very interesting and versatile supramolecular structures. 27,28 Cellulose, which is the main constituent of plant cell walls and is abundant in nature, is known for its excellent biocompatibility and thermal and mechanical properties.…”