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

We have developed a novel thin-film polymerization technique to in situ exa mine and analyze polycondensation reactions and liquid crystal texture evol ution for wholly aromatic liquid crystal copolymers poly(p-oxybenzoate/2,6- oxynaphthoate) (P(OBA/ONA)) as well as homopolymers poly(p-oxybenzoate) (PO BA) and poly(2,6-oxynaphthoate) (PONA). The polycondensation reactions were conducted on the heating stage of a polarizing microscope at various tempe ratures and were characterized by FTIR. During the early stage of the react ion, 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 phy sical factor of reducing system energy. The rate of liquid crystal area inc reasing was much faster in the case of coalescence. The progress of crystal lization during the late stage of polymerization was found to be strongly d ependent on the system morphology. Crystallization occurred rapidly if ther e was no stripe texture. Otherwise, crystallization was retarded or suppres sed. For P(OBA/ONA) copolymers, the appearance of stripe texture was determ ined by monomer composition and reaction temperature. While for both POBA a nd 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. (C) 1999 Elsevier Science Ltd. All rights reserved.