Studies On The Interpenetrating Polymer Networks Based On Polyurethane

A kind of -NCO terminated polyurethane prepolymer (CO-TDI) were synthesized by reacting of 2,4-Toluene diisocyanate (TDI) with castor oil in this paper. The prepolymers were mixed with cross-linkers (phenylethylene, Acrylonitrile, methyl methacrylate and epoxy resin E-44, E-51), and formed interpenetrating polymer networks (IPN). The effect of reaction Conditions on the CO-TDI was studied by the measure of isocyanate content, the double bond and relative viscosity.Effects of the system composition on the mechanical properties of IPNs were studied by testing tensile strength. Fourier transform infrared spectrascopy (FTIR) was used to monitor during moisture curing process of polyurethane systems, the effect of reaction conditions on the polyurethane systems and the curing kinetics. The results showed with the increasing of the ratio n-NCO/OH in CO-TDI the content -NCO increased, whereas the content of double bond decreased and the viscosity decreased; With the temperature increased, the content of -NCO was decreased; With the increased of keeping time, the viscosity of CO-TDI increased;CO-TDI can be dissolved in benzene, toluene, xylene, acetone, ethyl acetate, but in ethanol insoluble.The tensile strength of IPN increased with the curing time. The tensile strength of IPNs prepared from vinyl monomers was better than that of epoxy resin, while tensile strength among vinyl monomers showing little differences. The tensile strength of IPNs increased with the increasing n-NCO/OH ratio in the prepolymer at first and decreased later, the maximal tensile strength at the ratio of 2.25. The experiments also showed the mechanical properties had little affected with the addition of antioxidant 1010,ultraviolet absorbent UV-327 and light stability agent 292. The tensile strength of IPNs increased with the increasing ininiators(BPO or AIBN) and catalyst in the prepolymer at first and decreased later, the maximal tensile strength at the of 0.5%,0.8% and 0.2%.The moisture of CO-TDI/S IPN was a slow process. The rate of moisture curing was related to the temperature of curing and relative humidity, which was activated with the increase of temperature and humidity. Furthermore, the curing kinetics of these circumstances was deducted according to the track scanning results obtained by Fourier transfer infra spectrophotometer, the result show that the moisture of two kinds IPNs are both first-order reaction;the activation energy was 34.45 kJ·mol^-1.The results revealed that IPNs had three perks, which respectively appeared at 240℃～330℃, 340℃～390℃and 390℃～500℃,namely degeneration of the polyurethane network, degeneration of the polyolefine network and the melting of the segment. The moisture curing of-NCO at 156℃was exothermic prosess and gave out CO₂.All the CO-TDI/St,CO-TDI/AN CO-TDI/MMA IPNs had experienced three endothermic steps,among which CO-TDI/AN had the least enthalpy value(AH), the differences between CO-TDI/St and CO-TDI/MMA being no significant; .The urethane from the epoxy resin reacting with CO-TDI had considerable impact on the heat properties of IPNS, on the contrast,there was little difference between the three series of IPNs,namely CO-TDI/St,CO-TDI/AN and CO-TDI/MMA.The three steps of decomposition were all one-order reactions,the activation energe respectively being 18.998k J·mol^-1,74.302 kJ·mol^-1 and 197.663kJ·mol^-1.