Temperature effect on epitaxial growth of poly(p-oxybenzoate)

Abstract

A series of epitaxial polymerizations of poly(p-oxybenzoate) (POBA) on substrates of single-crystal mica, potassium bromide (KBr), and uniaxially aligned poly(tetrafluoroethylene) (PTFE) was performed at temperatures from 200°C to 270°C. As the temperature rose, not only did the POBA domain dimension in the polymer chain direction and the thickness of the epitaxial layer increase, but also the domain morphology changed correspondingly. The POBA domains tended to grow more three dimensionally at low temperatures, accompanied by a decreased epitaxial order. Thus, a high temperature favored epitaxial crystallization of POBA onto crystalline substrates. The POBA film grown on KBr substrate at 220°C revealed a low density layer consisting of lamellaelike plates. Subsequent annealing at 320°C produced a fibrous morphology in which the POBA fibrils were aligned, forming a 90°C cross-hatched network. More interestingly, a POBA film on KBr substrate, prepared by melt condensation reaction at 180°C for 24 h followed by annealing at 280°C for 1 h and then at 320°C for 2 h, produced laminae with both square and rectangular patterns with domain boundaries that aligned with KBr crystal axes. The electron diffraction (ED) pattern showed a phase 1 crystal pattern with the POBA polymer chains perpendicular to the substrate surface with very high crystallinity.