反应挤出接枝共聚反应表观链增长常数的测量

Measurement of the Apparent Chain Propagation Rate Constantsfor Graft Copolymerization by Reactive Extrusion

以预辐照的LLDPE反应挤出接枝MAA作为研究对象,通过在双螺杆挤出机中的不同部位取样,用FTIR分析接枝物及均聚物的产量,并用ESR测试链增长自由基浓度,设计了测定接枝和均聚反应初始阶段的表观链增长常数的方法.结果表明,在本实验测试范围内表观接枝链增长常数不同于均聚链增长常数;所得的测量值符合理论预测值,证明测试方法适合高温熔融体系的研究.

In this work, the macromolecular peroxide - induced grafting of MAA onto LLDPE by reactive extrusion was chosen as model system to study the apparent chain propagation rate coefficients for both graft reaction （kp.g） and homopolymerization of grafting monomers（ kp,h ）. The time-evolution rates of graft copolymerization and homopolymerization both exhibited two stages, linear and flat stage, which were controlled by monomer solubility and diffusion. By measuring the concentration of free-radicals and initial polymerization rate, which were determined with electron spin resonance spectroscopy（ESR） and Fourier transform infrared spectroscopy（FTIR）, kp,g and kp,h were obtained. It was found that kp.g increased with increasing temperature, while kp,h decreased when the temperature was over 200 ℃, this has been attributed to the effect of ceiling temperature, That the value of kp,h Was always larger than kp,g was also observed, indicating that graft copolymerization was not dominant reaction in this grafting process. The measured data were in agreement with theoretical calculations, which showed that this technique reliably and directly provides individually apparent chain propagation rate coefficients.