The bulk polymerization reaction of isocyanate terminated polyurethane prepolymer and 1,4-butanediol under high pressure were analyzed in the temperature range between 30 and 80℃ and at pressure up to 3000 atm. The isocyanate terminated polyurethane prepolymer was prepared by reacting 1 equiv. of the poly(tetramethylene ether)glycol with 2 equiv. of 4,4-diphenylmethane dilsocyanate at 55℃. The conversion of the reaction was determined by titrating the residual isocyanate group with time. Molecular weight distribution of the polyurethanes synthesized under different conditions were analyzed by the gel permeation chromatography. Phase separation of the soft segment and the hard segment of the polyurethane was studied by measuring the dynamic mechanical properties of the soft segment and the melting behavior of the hard segment by DMA and DSC.
The polymerization rate increased with increasing synthesis pressure. The frequency factor in the reaction equation increased exponentially with synthesis pressure, but the activation energy was not particularly affected.
As the synthesis pressure was increased, tan δ increased and the soft segment Tg was shifted toward high temperature, and the hard segment Tm was shifted toward lower temperature. Therefore the phase separation of the soft segment and the hard segment was somewhat suppressed with increasing synthesis pressure due to the reduction of the chain mobility during the polymerization and the phase separation process.
Molecular weight and molecular weight distribution were not influenced by the synthesis pressure.
