TMXDI-based poly(ether urethane)/polystyrene interpenetrating polymer networks: 1. Morphology and thermal properties

In this, the first of two papers on the full composition series of simultaneous polyurethane (PUR)/polystyrene (PS) interpenetrating polymer networks (IPNs), the morphology and thermal properties are investigated. For the first time in IPN preparations, tertiary aliphatic m-tetramethylxylene diisocyanate (TMXDI) was used in the PUR hard segment. An investigation of the reaction kinetics of the 60:40 PUR/PS IPN composition by Fourier transform infrared (FTi.r.) spectroscopy, using a heated cell unit, confirmed that the PUR was the first network formed. Scanning (SEM) and transmission (TEM) electron microscopy indicated a grossly phase-separated morphology. The phase domain sizes at the outer composition ranges (90:10, 80:20, 70:30 and 10:90 PUR/PS IPNs) were smaller (20-300 nm) than at the mid-range compositions (300 nm-6 mu m). SEM and TEM showed phase inversion to occur at a composition between the 30:70 and 20:80 PUR/PS IPNs. Comparing the immiscible PUR/ PS IPN composition series with a similar semi-miscible PUR/PEMA IPN series revealed that in addition to phase domain sizes, the domain shape and the definition of the phase boundaries are of importance in assessing the miscibility of IPNs. No significant improvement in the thermal decomposition profile was observed for the IPN compared to the respective homonetworks. (C) 1998 Elsevier Science Ltd. All rights reserved.