单茂钛/甲基铝氧烷催化剂乙烯/丙烯共聚合研究

改性甲基铝氧烷(mMAO)激活五甲基茂基三氯化钛(Cp TiCl3)催化乙烯 丙烯共聚合,控制两种单体的进料配比,得到单元序列分布不同的共聚物.混合单体中含有少量丙烯,共聚合活性高于相同聚合条件下乙烯均聚合的活性.用1 3C -NMR测定共聚物分子链的微观结构和单元序列分布,计算出单体的竞聚率;结果表明共聚物分子链中两种单体的序列分布均匀.混合单体中丙烯含量较大时,共聚物为完全无规共聚物;而当丙烯含量少时,丙烯链节或短的聚丙烯链段均匀分布于聚乙烯链段之间.共聚物经DSC分析,也证明不存在长序列的聚乙烯链段;因此,即便在进料气体中丙烯含量很少的情况下,共聚物仍然没有明显的熔融温度和结晶性.

COPOLYMERIZATION OF ETHYLENE AND PROPENE WITH MONOTITANOCENE/METHYLALUMINOXANE AS CATALYST

Ethylene and propene were homo- and copolymerized with monotitanocene catalyst composed of η5-pentamethylcyclopentadienyltrichloride titanium (CpTiCl 3 ) activated by modified methylaluminoxane (mMAO).Influences of copolymerizati on conditions including ethylene/propene molar ratio in the feeding,polymerizati on te mperature and Al/Ti molar ratio on activity,propene content in copolymers and th e triad and tetrad sequence distributions were investigated.The monomer reactivity ratios r E and r P (E = ethylene,P = propene) for ethylene/propene co polymerizat ions were estimated from the 13C-NMR spectra.At high propene content in the fee ding,the CpTiCl 3/mMAO catalyst gave rise to r Er P≈1 in combina tion with a resultant random copolymer.Whereas,at low propene content in the feeding, the c opoly mer exhibits a tendency toward alternating comonomer distribution (r Er P<1),whi ch indicates that propene suquences are isolated in the copolymer.The thermal pr operti es of copolymers determined by DSC are mainly dependent on the propene content i n the copolymers.