A new in situ polymerization method is discussed wherein monomers of the major component are polymerized in the presence of a preformed thermotropic liquid crystalline polymer (LCP) . Poly (p-oxybenzoate-co-p-phenyleneisophthalate) (HIQ) was chosen for this study.HIQ is well known to have a narrow process window and to be difficult to process reproducibly, both drawbacks for a commercial product. An in situ polymerization of the HIQ monomers in the presence of a fully polymerized LCP, such as poly (4-oxybenzoate-co-6-oxy-2-naphthoate) (CO) results in the "CO-HIQ" in situ blend. The in situ blend exhibited reduced biphasic morphology and was more homogeneous than was HIQ. The glass fiberfilled CO-HIQ resin also featured improved melt flow and more reproducible mechanical properties than those of HIQ. The in situ blends were characterized by optical microscopy, 'H-NMR, and melt rheology. The effect of the LCP level on the morphology of the in situ blend is discussed. 0 1994 John Wiley & Sons, Inc.
I NTRO DUCT10 NThe copolyester, poly (p -0xybenzoate-co-p -phenyleneisophthalate ) ( HIQ ) was originally synthesized by Cottis et al.' HIQ is a copolyester of para-hydroxybenzoic acid (HBA) , isophthalic acid (JA) , and hydroquinone (HQ) . The 4-oxybenzoate segments, resulting from HBA, impart nematogenicity, causing the copolyester to be liquid crystalline in the temperature range of 280-400°C. At the same time, the IA and HQ form 1,4-phenyleneisophthalate segments that are known to form a crystalline structure similar to that of a flexible chain polymer such as poly (ethylene terephthalate) .2-3 Thus, when the composition of HIQ contains an equal level of these two ester linkages, it exhibits biphasic morphology, coexistent liquid crystalline, and crystalline phases. A particular composition of interest is HIQ at HBA/IA/HQ 35/32.5/32.5 (HIQ35), which has almost an equimolar ratio of both ester linkages and, thus, features pronounced biphasic morphology. It should be noted that both homopolymers of HBA and IA/HQ melt at higher than 4OO0C and, thus, are intractable. Also, HIQs with greater than 50% HBA or less than 25% HBA have melting points at or above 400°C and, thus, cannot be melt-proc e s~e d .~.~ Studies within Hoechst Celanese and by others3 concluded that due to the biphasic nature of HIQ it is extremely difficult to obtain reproducible results from melt polymerization and subsequent melt pro~essing.~ In recent years, several workers attempted to modify HIQ to suppress the biphasic nature and to take advantage of its liquid crystalline properties and low cost. The most striking example is from MacDonald and Ryan,5 who were successful in modifying the morphology of HIQ by including an additional component: small amounts of 6-hydroxy-2-naphthoic acid (HNA) . Their composition was made by a novel dispersion polymerization that exhibits uniform morphology and is claimed to have superior properties. Siemionko6 disclosed compo-
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