Gordon W. Calundann

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

We have studied isothermal transition kinetics and crystallization mecha- nisms of the Hoechst Celanese liquid crystal polymer Vectra™ A-950 using a differen- tial 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-dihy- droxynaphthoic 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.

Thermotropic Poly(Ester-Amides) Based on Naphthalene Monomers

Abstract The structure and properties of a range of thermotropic poly(ester-amides) derived from 2,6-naphthalene derivatives is described. Many of these polymers may be melt-processed into fibers, monofils, and molded structures having very attractive physical and mechanical properties. A variety of monomers has been used and structure/composition/property relationships are described along with details of synthesis and processing conditions. Both fibers and molded articles may be heat-treated to enhance their tensile properties. Molded articles and extruded rods have exceptional tensile moduli in the unfilled state.