The structure and physical properties of in situ composites based on semiflexible thermotropic liquid crystalline copolyesteramide and poly(butylene terephthalate)

Liquid crystalline polymer-poly(butylene terephthalate) (LCP/PBT) blends we re prepared by melt mixing. The LCP employed was a thermotropic copolyester amide based on 30 mol % of p-amino benzoic acid (ABA) and 70 mol % of poly( ethylene terephthalate) (PET). The thermal, dynamic mechanical and rheologi cal properties, morphology, and crystal structure of LCP/PBT blends were st udied. The results showed that the semiflexible ABA30/PET LCP is miscible i n the melt state with PET, and they are partial miscible in the solid state . Differential scanning calorimetric measurements showed that the introduct ion of the semiflexible LCP into LCP/PBT blends retards the crystallization rate of PBT. However, the LCP dispersed phase acted as the sites for the n ucleation of spherulites and enhance the degree of crystallinity of PET. Ho t-stage optical microscopy examination revealed that the LCP microfibers wi th random orientation are dispersed in the PET matrix of compression molded LCP/PBT blends. Under the application of a shearing force, the LCP domains in the PET matrix tended to deform into microfibers, and to orient themsel ves along the flow direction. The formation of microfibers resulted in an i ncrease of the storage modulus. The torque measurements indicated that the melting viscosity of the LCP/PBT blends is much lower than that of the pure PET. Finally, the wide-angle X-ray diffraction patterns indicated that PET shows no structural change with the incorporation of LCP, but the apparent crystal sizes of several diffraction planes change significantly. (C) 2000 John Wiley & Sons, Inc.