Processing of intractable polymers using reactive solvents. 6. A new reactive solvent concept based on reversible depolymerisation

The use of reactive solvents which reversibly (de)polymerise to facilitate the processing of poly(2,6-dimethyl-1,4-phenylene ether) (PPE) was explored. PPE can be dissolved at elevated temperatures in very low molecular weight thermoplastic poly(urethane) (TPU) fragments obtained via depolymerisation and these solutions can then be processed at the relatively low temperature of 250 °C. After processing and upon cooling, the TPU fragments repolymerise which induces a L–L phase separation between PPE and TPU followed by vitrification of the PPE matrix phase and at lower temperatures vitrification of the TPU dispersed phase. Since phase separation occurs during cooling, the phase separation is induced thermally as well as chemically, since the molecular weight of the ‘solvent’ increases upon lowering the temperature. The properties of the final materials, such as heat resistance, are dominated by the continuous PPE matrix. The starting molecular weight of TPU and the composition of the blend had pronounced effects on the phase separation, morphology and viscosity of the blends. Increasing the amount of TPU resulted in larger TPU particles but no effect on the Tg of the PPE-rich matrix was observed. Increasing the starting molecular weight of TPU resulted in higher phase separation temperatures and higher Tgs for the PPE-rich matrix. Possibilities for diminishing the residual TPU fractions were explored. The interference of vitrification with phase separation could be postponed and, consequently, the residual fraction of TPU in the PPE phase could be reduced either via an increase in the starting molecular weight of TPU or a decrease in cooling rate or Tg of the matrix.