Novel thin-film polymerization and time evolution of liquid crystal texture during polymerization

Abstract

We have developed a novel thin-film polymerization technique to in situ examine and analyze polycondensation reactions and liquid crystal texture evolution for wholly aromatic liquid crystal copolymers poly(p-oxybenzoate/2,6-oxynaphthoate) (P(OBA/ONA)) as well as homopolymers poly(p-oxybenzoate) (POBA) and poly(2,6-oxynaphthoate) (PONA). The polycondensation reactions were conducted on the heating stage of a polarizing microscope atvarious temperatures and were characterized by FTIR. During the early stage of the reaction, liquid crystal areas increased through two mechanisms. One was domain growth of single droplet, and the other was coalescence by welding adjacent droplets. The former was mainly driven by chemical factor of chain growth, while the later was driven by both chemical factor of chain growth and physical factor of reducing system energy. The rate of liquid crystal area increasing was much faster in the case of coalescence. The progress of crystallization during the late stage of polymerization was found to be strongly dependent on the system morphology. Crystallization occurred rapidly if there was no stripe texture. Otherwise, crystallization was retarded or suppressed. For P(OBA/ONA) copolymers, the appearance of stripe texture was determined by monomer composition and reaction temperature. While for both POBA and PONA homopolymer systems, no stripe texture but only crystallization has ever been observed in the late stage of the reactions in our experimental temperature range.