Revisit the crystallization mechanism of vectra,? a liquid crystal polymer

Abstract

ABSTRACT:We have studied isothermal transition kinetics and crystallization mechanisms of the Hoechst Celanese liquid crystal polymer Vectra™ A-950 using a differential scanning calorimetry. This material is a random copolymer with a composition made of 73 mol %/27 mol % of HBA (1,4-dihydroxybenzoic acid)/HNA (2,6-dihydroxynaphthoic acid). When comparing our results to previous work on 75/25 HBA/ HNA, we found some similarities as well as dissimilarities. In the case of similarities, both polymers show two types of transition processes in the low-temperature region (below 495 K). One is a fast process, which can be regarded as liquid crystal transition, and is characterized by a heat of fusion that does not vary significantly with annealing time. The other transition is a slow process related to crystal perfection and shows increases in the heat of transition and the transition temperature with increasing annealing time. However, the apparently slight difference in polymer composition also leads to a few surprising results. For example, previous work on 75/25 HBA/HNA two transition peaks (slow and fast processes) were observed after annealing it at 505 K, while in the current work only one transition peak in the case of 73/27 HBA/HNA was observed. In addition, based on the relationship between heat of fusion and annealing time, the LCP made from 73/27 HBA/HNA may perfect faster (in the time scale we study); hence, its posttreatment processes may be accomplished more efficiently than that of 75/25 HBA/HNA. This result also suggests that the former may have a better sequence or a better matching of molecular dimensions for crystallization than that of the latter.

Fracture behavior of heat treated liquid crystalline polymers

“…The thermal treatment also produces a second endotherm for B-N and RD1000. Previously, Chung et al and Romo-Uribe et al had reported the production of a second endotherm in B-N [11][12][13].…”

High-Performance Segmented Liquid Crystalline Copolyesters

“…Despite the characteristic high‐melting temperature, LC polyesters are often melt processable with enhanced shear thinning, resulting from anisotropy that reduces the viscosity of the melt at typical processing temperatures . This feature renders LC polyesters excellent candidates for a variety of commercial applications, including but not limited to protective coatings, displays, electronic devices, composites, substrates, and flame‐resistant structures …”

SALS, WAXS and mechanical properties of heat‐treated thermotropic polymers

“…Manipulating the orientation of the anisotropic macromolecules optimizes mechanical properties of LCP fibers . Molecular alignment and microstructure are controlled through processing conditions during fiber spinning and heat treatment . At the molecular level, the degree of straightness in the molecular architecture of the polymers studied here (Fig.…”

“…The double aromatic ring in the N monomer acts as a parallel offset thereby disturbing the regularity of molecular packing, thus lowering the solid‐to‐nematic transition temperature . Despite the evident importance and striking physical properties of commercial thermotropic LCPs, there are to date few studies addressing the influence of thermal treatment on their mechanical properties …”