Poly(7-oxabicyclo[2.2.1]heptane-co-tetrahydrofuran): Polymerization, polymer characterization and spinning

Abstract A high-yield cationic copolymerization of 7-oxabicyclo[2.2.1]heptane (OBCH) and tetrahydrofuran (THF) was developed to yield high molecular weights, the mechanism being deduced from product and kinetic studies. The monomer ratios were varied to arrive at a range of products melting at various temperatures. The crystallization rate was influenced by copolymerizing minor amounts of a third monomer—ethylene oxide (EO). Spinning experiments were carried out mainly on a miniature spinning apparatus, enabling ram extrusion from an evacuated chamber heated only in the lower part. Polymers and yarns were characterized by solution viscosities, nuclear magnetic resonance (proton and carbon) spectra, gel permeation chromatography, wide-angle and small-angle X-ray scattering, hot-stage microscopy, interference microscopy and thermal scan wide-angle X-ray scattering. Rheology characterization was attempted using the miniature spinning device with wide ‘spinning holes’. Copolymerization proceeds in a truly random fashion; molecular weight is regulated almost exclusively by precipitation. The viscosity of the polymer melt, very high at rest, drops to a fairly low level upon shearing and the shear stress seems to be essentially independent of the shear rate. The OBCH/THE copolymers show thermotropic liquid-crystalline behaviour with as little as 30 wt% of the rigid monomer, OBCH. High molecular orientation is easily achieved in as-spun yarn. Poor drawdown ratios, no higher than 2.4, can be reached. No high-modulus or high-tenacity yarns are accessible with the present copolymer system. The poor extensibility of the spinning thread seems to point to extensive chain folding in the (imperfect) lamellae in the liquid-crystalline state.