Neodymium-Based Catalyst For The Synthesis Of A Novel Polybutadieneelastomer

Coordination polymerization of1,3-butadiene with the catalytic system composed of neodymium tricarboxylate (RE), cocatalyst Al(i-Bu)3(AL), chlorinating agent (CF) and a modifier (OCT) was carried out in hexane. The influence of the amount of OCT, addition order and ageing conditions of the catalyst on catalytic activity, molecular weight and their distributions of the resultant polymers were initially investigated. The monomer conversion was determined by gravimetric method. The molecular weight and molecular weight distribution were determined by GPC. The microstructure of the polymer was characterized by13C-NMR. The following conclusions can be obtained.1. When OCT was used as a modifier, two modified catalyst systems with high catalytic activity were obtained by using CF and ETCA as chlorinating agents. Solid foundation was provided by the differences in catalytic activity between the two catalysts for the synthesis of bimodal polybutadiene. 2. The results show that in the presence of OCT, the catalytic activity was improved as much as twice over that of the ternary catalyst (ND+AL+RX). The number-average molecular weight (Mn) of polybutadiene was increased from2.7×105to1.2×106and molecular weight distributions were narrowed from3.63to2.11when the molar ratio of OCT/ND was increased from0to5.0.The contents of cis-1,4units of polybutadiene were high (ca.98.6%) on the basis of13C-NMR characterization. Both the monomer conversion and molecular weight of polybutadiene were increased with the increase of ageing time. The catalyst system presented higher activity but less stability at high ageing temperature.3. In the catalyst system of (RE+OCT)+(CF+A1),the molar ratio of CF/RE show great effect on the catalytic activity and the molecular weight of the resultant polymer, kpA is as high as3.43×10-3min-1when the molar ratio of CF/RE equals to20. While in the catalyst system of (RE+OCT)+(ETCA+A1), the catalytic activity is much higher than the above catalysts, kpA is as high as7.4×10-3min-1when the molar ratio of ETCA/RE is1.5.4. The two active centers were mixed in the polymerization system: when the two catalyst system (RE+OCT)+(CF+Al) and (RE+OCT)+(ETCA+Al)were both introduced into the polymerization in the different molar ratios, the polybutadienes with bimodal distribution were synthesized. GPC characterization showed that the fraction of higher molecular weight polymers was increased with the increasing of the amount of ETCA. When the percentage of ETCA is90%, the bimodal distributions can be detected obviously.5. One active center was obtained first and the other active center was formed by in-situ method:After the active center A was obtained by the catalyst (RE+OCT)+CF+A1,(ETCA+AL) was introduced into the above catalytic system or the polymerization solution, then the other active center was formed thereby, two said active centers in the system initiated the polymerization of butadiene simultaneously, when the molar ratio of ETC A/RE in the range of0～5, the fraction of higher molecular weight of the resultant polymer was also increased.6. Two active centers were both formed by in-situ method:by introduction of two chlorinating agents CF and ETCA, the dual active centers can be obtained which can be used in the synthesis of bimodal polybutadiene in the same catalytic system. When the molar ratio of the chlorinating agents is in the range of6-14, bimodal distributions can also be detected by GPC clearly.7. The ageing process of ETCA+Al in advance is an important factor affecting the molecular weight of polybutadiene. The broad molecular weight distribution can be obtained by mixing the two catalyst systems aged at0℃and50℃respectively.