二氧化碳-氧化环己烯共聚物的合成和热性能研究

采用三元催化剂(Y(Cl3COO)3-ZnEt2-glycerin)催化二氧化碳与氧化环己烯共聚反应,制备了高分子量二氧化碳与氧化环己烯共聚物(PCHC).8 h内催化剂平均活性达到11.8 kg polymer/mol Zn,PCHC主链上碳酸酯单元含量大于95%,数均分子量达到7.0×104.研究了PCHC的玻璃化转变温度和分子量的关系,当PCHC的数均分子量(Mn)低于8.5×104时,玻璃化转变温度(Tg)随Mn增加而升高;Mn高于8.5×104时,Tg对Mn的依赖性不大.当PCHC的分子量充分高时,其玻璃化转变温度可以达到120℃,PCHC的自由体积特征常数K=1.91×105.研究了聚合物分子量对其热稳定性的影响,结果表明提高分子量有利于提高PCHC的热分解温度.通过实施聚合反应和后处理,三元催化剂转化为相应的金属氧化物(主要为氧化锌)残留在聚合物中,采用Kissinger方法得到纯PCHC(除去金属氧化物)的热分解表观活化能约为199.9 kJ/mol,含金属氧化物(Zn含量4400×10-6)PCHC的热分解表观活化能下降为143.9 kJ/mol.因此氧化锌能够促进PCHC的热降解,减少PCHC中氧化锌的含量有利于改善PCHC的耐热性能.

SYNTHESIS AND THERMAL PROPERTIES OF CARBON DIOXIDE-CYCLOHEXENE OXIDE COPOLYMERS

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.