Polyurethane interpenetrating polymer networks synthesized under high pressure

Abstract

Interpenetrating polymer networks (IPN``s) of polyurethane-poly(methyl methacrylate) and polyurethane-polystyrene were synthesized under high pressure (up to $20,000 kg/cm^2$). The polyurethane network (based on poly(tetramethylene ether) glycol and 4,4,``-dephenyl-methane diisocyanate) was crosslinked with tri-methylolpropane, the poly(methyl methacrylate) network with ethylene glycol dimethacrylate, and polystyrene with divinyl benzene. The theoretical crosslink density of the networks were 3,200 and 2,000 molecular weight between crosslink sites ($\mbox{\overline{M}}$c). Polyurethane-polystyrene semi-IPN``s (one of the component polymer is linear) and linear blend (both of the component polymers are linear) were also prepared. The morphology via transmission electron microscopy, the glass transition behavior via differential scanning calorimetry, dynamic mechanical analysis, and the density behavior were analyzed to determine the effect of synthesis pressure and the effect of interlocking on the degree of intermixing of the component polymers. The domain sizes decreased with increasing synthesis pressure. The polyurethane domain sizes of the polyurethane-poly(methyl methacrylate) IPN``s decreased exponentially from about 300 to $30 \mbox{\AA}$ with increasing synthesis pressure from 1,250 to $20,000 kg/cm^2$. The domain sizes of polyurethane-poly (methyl methacrylate) and polyurethane-polystyrene IPN``s synthesized at high pressure ($20,000 kg/cm^2$ and $10,000 kg/cm^2$, respectively) were very small with sizes of about tens of angstroms which could be considered as a molecular level mixing, and they were optically transparent. The phase continuity changed also with pressure, the polyurethane phase became more continuous at low pressure, while the poly (methyl methacrylate) and polystyrene phase showed continuity at high pressure. The glass transition behavior of the polyurethane-poly (methyl methacrylate) and polyurethane-polystyrene IPN``s show...