High glass transition temperatures of poly(methyl methacrylate) prepared by free radical initiators

High glass transition temperatures of poly(methyl methacrylate) (PMMA) prepared by free radical initiators was investigated. Di-tert-butyl peroxy oxalate was prepared by the reaction of oxalyl chloride and tert-butyl hydroperoxide, and was kept at -30°C. Other radical initiators and chemicals were purified by standard procedures. The 'H NMR spectra were recorded by a Bruker Advance DPX 300 (300 MHz) spectrometer. The differential scanning calorimetry (DSC) measurement was performed on a DSC 2920 module in conjunction with the TA Instruments 5100 system at a scan rate of 10°C/min under a nitrogen atmosphere. The instrument was calibrated using indium and zinc as calibration standards for the temperature and enthalpy changes. The results show that the lower PMMA obtained has higher viscosity than that of the higher PMMA with the same molecular weight.