Effect of Ultrasound on Synthesis of a Polycarbonate [1

Abstract

Abstract Effects of ultrasound (US) on the synthesis of poly(p-xylylene carbonate) [1] by crown ether mediated reactions of a,a'-dibromo- and dichloro-p-xylenes with potassium carbonate at ambient temperatures for 12, 18 and 24 h in diglyme, DMF, chlorobenzene, and NMP solvents were compared with syntheses in the absence of US at elevated temperatures. No polymer was formed with the dibromide in 24 h at ambient temperature in the absence of US. With US, yields and Mn increased to a maximum with time and then decreased because of polymer chain fragmentation. A maximum yield of 56% with Mn = 2500 was obtained with US in DMF in 18 h. No polymer was formed in 60 h in DMF at 80 or 120 °C in the absence of US. The maximum Mn of 4300 was for polymer formed in 18 h in diglyme; however, the yield was only 2%. Results in other solvents (Tables 1–3) were intermediate. US reactions with the dibromo compound were much faster than with the dichloro anlong. Mechnisms for US-induced fragmentations are proposed.