SYNTHESIS AND THERMAL PROPERTIES OF CARBON DIOXIDE-CYCLOHEXENE OXIDE COPOLYMERS
二氧化碳-氧化环己烯共聚物的合成和热性能研究

Cyclohexene oxide copolymer (PCHC) with high molecular weight was synthesized using ternary rare earth metal coordinate catalyst(Y( Cl_3COO)_3-ZnEt_2-glycerine). The catalytic activity reached 11.8 kg polymer/mole Zn under optimal condition,the obtained PCHC showed number average molecular weight (M_n) of 7.0 × 10~4 , with carbonate unit over 95%. The glass transition temperature ( T_g) of PCHC was between ll0℃ and 120℃ ,it increased with increasing M_n when M_n was below 8.5 × 10~4 ,and leveled between 119℃ and 120℃ when M_n was over 8.5 × 10~4. The highest T_g may be reached as 120℃ if the M_n of PCHC is high enough,and the characteristic free volume constant K is 1.91 × 10~5. The influence of molecular weight on thermal stability of PCHC was investigated, raising molecular weight was beneficial for improving thermal stability of PCHC,and a 60℃ increase of the onset degradation temperature was observed when M_n increased from 39.9×10~3 to 93.1×10~3. Since the rare earth ternary catalyst changed to metal oxide ( mainly ZnO) after polymerization and post-polymerization treatments, the influence of Zn content on thermal stability of PCHC was studied based on Kissinger method,PCHC with Zn content below 5 × 10~6 showed surface activation energy for thermal decomposition of 199. 9 kJ/mol, whereas it decreased to 143. 9 kJ/mol for PCHC with Zn content of 4400 × 10~(-6). Therefore,reducing Zn content could improve the thermal stability of PCHC.