Solution copolymerizations of butyl acrylate/methyl methacrylate in toluene were performed over an expanded temperature range (60 -140°C) compared to more typical ranges that do not exceed 80°C. From a large amount of data collected independently at two laboratories, reactivity ratios were estimated at five different temperatures. The reactivity ratios were estimated from low conversion copolymer composition data using both the error-in-variables model method and a nonlinear parameter estimation based on the integrated copolymer composition equation. Using all of the available data, temperature-dependent expressions were developed for the reactivity ratios and compared to previously published bulk copolymerization values. No significant differences appeared to exist between the bulk and solution polymerization reactivity ratios. Furthermore, the copolymer composition data conformed to the MayoLewis kinetic model over the entire temperature range.

The rheo‐kinetics of thermoplastic polyurethane (TPU) formation was investigated in a measurement kneader at high temperatures. The TPU was made of a polyester polyol, methyl‐propane‐diol and a 50/50 mixture of 2,4′‐ and 4,4′‐diphenylmethane diisocyanate (MDI). The reaction proceeded according to a second order reaction for which the kinetic constants were determined by size exclusion chromatography (SEC) analysis. The activation energy was found to be equal to 61.3 kJ/mol, and the pre‐exponential factor was equal to 2.18e6 mol/kg K. For the temperature range under investigation, the flow activation energy was equal to 42.7 kJ/mol, which is comparable to that of a linear polymer. This indicates that the hard segments are completely dissolved at the temperatures investigated. The initial part of the reaction was much faster than anticipated from the kinetic measurements. Diffusion limitations at higher conversions probably cause this decrease in reaction velocity. At longer reaction times, the molecular weight leveled off because of depolymerization. Therefore, additional experiments are necessary to describe the complete polymerization of thermoplastic polyurethane. Polym. Eng. Sci. 44:1648–1655, 2004. © 2004 Society of Plastics Engineers.

ABSTRACT:The effects of the reaction conditions on the kinetics of two different polyurethane systems were investigated. To do so, three different kinetic methods were compared: adiabatic temperature rise (ATR), measurement kneader, and high-temperature measurements. For the first polyurethane system, consisting of 4,4-diphenylmethane diisocyanate (4,4-MDI), butane diol, and a polyester polyol, the reaction conditions did not seem to matter; a kinetically controlled reaction was implicated for all reaction conditions. The reaction was second order in isocyanate concentration and 0.5th order in catalyst concentration and had an activation energy of 52 kJ/mol. The second polyurethane system consisted of a mixture of 2,4-diphenylmethane diisocyanate and 4,4-MDI, methyl propane diol, and a polyester polyol. For this system, each of the three measurement methods showed different behavior. Only at a low catalyst concentration did the ATR experiments show catalyst dependence; at higher catalyst levels and for the other two measurement methods, no catalyst dependence was present. Furthermore, the ATR experiments proceeded much faster. Presumably, for this system, the rapid diffusion interfacial of the species present was hindered by the presence of bulky oligomer molecules. The result was a diffusion limitation reaction at low conversions and an inhomogeneous distribution of species at higher conversions.

The reactive extrusion of thermoplastic polyurethane in a corotating twin-screw extruder was investigated. The polyurethane system consisted of a mixture of 2,4-diphenylmethane diisocyanate (2,4-MDI) and 4,4-MDI, methyl-propane-diol and a polyester polyol. An engineering extrusion model was designed and compared with experimental results. In this validation study the catalyst level, throughput, rotation speed and the barrel wall temperature was varied. A comparison of the experiments with the model showed that the model captured the polyurethane extrusion fairly well. Furthermore, the effect of the depolymerization reaction on the polyurethanes extrusion was investigated. It was found that the extruder operation is gravely affected by the depolymerization reaction: the depolymerization reaction limits the maximal obtainable conversion, stabilizes the extruder operation, and causes undesired post-extrusion curing of the polyurethane.