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Advances have been made in understanding the interactions of composition

molecular weight

liquid crystallinity

orientation

and three-dimensional crystallinity on the properties of injection-molded and melt-spun liquid crystalline polyesters （LCP’s）. Two classes of potentially low-cost LCP’s were compared:（1） semiflexible LCP’s prepared from 1

6-hexanediol and the dimethyl ester of either trans-4

4’stilbenedicarboxylic acid or 4.4 ’ biphenyldicarboxylic acid and （2） all-aromatic LCP’s prepared from terephthalic acid

2

6-naphthalenedicarboxylic acid

the diacetate of hydroquinone

and the acetate of p-hydroxybenzoic acid. The effects of composition on the plastic properties of the 4-component all-aromatic LCP’s were determined with the aid of a 3 x 3 factorial statistically designed experiment

the generation of equations with a computer program

and the plotting of three-dimensional figures and contour diagrams. The effects of absolute molecular weight （M

w

） on the tensile strengths of the semiflexible LCP’s and one of the all-aromatic LCP’s having an excellent balance of plastic properties were also compared

and it was observed that the semiflexible LCP’s required M

w

’s about 4 times higher than the all-aromatic LCP to attain a given strength. Persistence lengths and molecular modeling were used to explain these differences.