Structure Formation during Solution Copolymerization of p-Acetoxybenzoic Acid and p-Acetoxyphenylbenzoic Acid

Copolymers were prepared by solution polymerization of 4-acetoxybenzoic acid (ABA) and 4-acetoxyphenyl-benzoic acid (APBA) in Therm-S800 (a mixture of triethylbiphenyl isomers). Morphological changes of the copolymer crystals with molar ratio of the monomer mixture and their formation mechanism were investigated. In the range of 0-5 mol% of APBA, it was found that aspect ratios and yields of whiskers decrease with the increase of APBA. In the range of 70-100 mol% of APBA, the diameter of fibrillar crystals in the bundle-like aggregates increased with the increase of ABA. The yields decreased with the increase of ABA. Furthermore, in both ranges segregation of oligomers with many co-units occurred when oligomers crystallized, but the formation mechanism was fundamentally similar to that of each homopolymer. On the other hand, in the range of 10-60 mol% of APBA, sphere-like products were obtained and their yields increased. Only a single diffraction ring was observed in their wide-angle X-ray diffraction patterns, suggesting hexagonal packing of the copolymer chains. Molar ratios of monomer residues in the products were determined with high performance liquid chromatography, using the hydrolysates of the products. They were in good agreement with those in feed. From these exprerimental results, it was deduced that droplets are formed by liquid-liquid phase separation, in which the degree of polymerization of oligomers is increased to give rise to crystallization.