Morphological Development in Alkyl-Substituted Semiflexible Polymers

Abstract

Nonsymmetrically substituted semiflexible polymers were synthesized by reacting (hydroxypropyl)cellulose (HPC) with hexyl, octyl, dodecyl, and octadecyl isocyanates. X-ray diffraction studies indicate that the polymer chains are assembled in regular, layered arrays. Polymers with six and eight carbons in the side chains (C6HPC and C8HPC) showed spherulitic structures typical of common crystalline polymers when examined by a polarized optical microscope (POM), whereas liquid crystalline (LC) textures were observed for C12HPC and C18HPC. When the polymers were slowly cooled from the melt, crystalline (C) textures could be obtained for C12HPC and C18HPC at preselected temperatures slightly higher than the corresponding (isotropic f LC) transition temperatures determined by DSC cooling scans. Upon further cooling, liquid crystalline structures appeared at temperatures 5-6°C lower. The unusual POM observations are in contrast to conventional thermal transitions reported for liquid crystalline polymers, where the isotropic f LC transition takes place at a temperature higher than that of the LC f C transition, but are consistent with Keller's studies on another liquid crystalline polymer.

Optical properties of guest host systems based on cellulose derivatives

“…In fact, layered structures of the type described above were found for several semi-flexible polymers. Lee et al [17] used a similar model to describe the structure of several derivatives of HPC with various side chain length, according to Wegners bilayer model for substituted aromatic polyesters. [18] Gray et al reported a parallel alignment of the polymer backbone in thermotropic cholesteric phases of HPC esters.…”

Thermally driven smoothening of molecular thin films: Structural transitions in n-alkane layers studied in real-time

“…Alkane molecules with their simple, rod-like molecular shape are a model system for more complex chainlike organic molecules [5][6][7] and are also important building blocks, e.g., as side chains of polymers and can dominate their crystallisation behavior. 8,9 Beyond its importance as a generic model system for fundamental molecular processes, tetratetracontane (TTC), in particular, is also of technological importance in organic electronics as an encapsulation material for transistors and biosensors in an aqueous environment, 10,11 where the active layer is completely wetted by TTC and therefore fully encapsulated.…”

Effect of synthetic pathways on the phase transition and side-chain crystallization behavior of alkyl-substituted cellulose ethers

“…Crystallization within the alkyl nanodomains of comb-like polymers occurs when the number of carbon atoms of the side chain is 12 or more, as in the cases of some alkyl-substituted rigid polymers, [23][24][25][26][27][28][29][30][31][32] exible polymers [33][34][35][36] and semi-exible polymers. 37,38 The crystallizable CH 2 units are usually packed into a hexagonal lattice, 39,40 but some other packing modes of the CH 2 units (for example, orthorhombic packing) have been reported for side chain polymers with long alkyl groups. [41][42][43][44] In addition, transitions between hexagonal and orthorhombic packing can also occur under certain conditions.…”