Synthesis Of High Cis-1,4Polyisoprene And Butadiene And Isoprene Copolymer Using Rare Earth Catalyst System

The rare earth catalyst is highly efficient on polymerization of conjugated dienes. The polymer obtained is highly stereoselective (cis-1,4content is over95%). Mostly, rubber products with high cis-1,4content have excellent tensile properties, outstanding wear resistance, good flexibility, and little permanent deformation. Polymer with narrow molecular weight distribution shows better mechanical performances. Homogeneous rare earth catalyst is preferred to prepare polymer with high cis-1,4content and narrow molecular weight distribution. In this work, through injecting isoprene monomer into the catalyst and aging at high temperature, homogeneous phosphate neodymium catalyst were prepared to obtain high cis-1,4content polyisoprene and isoprene-butadiene copolymer with narrow molecular weight distribution.Firstly, polyisoprene was synthesized in cyclohexane using Nd(P507)3/AlH(i-Bu)2/AlEt2Cl catalyst. The catalyst aging at60℃for2h showed high activity at low [Al]/[Nd] ratio of10to give polyisoprene having high cis-1,4stereoregularity (>96%), a high number-average molecular weight (Mn～105), and relative narrow molecular weight distributions (Mw/Mn=2.1). The effects of aging and polymerization conditions were examined. The catalyst activity increased with the increase of aging time and aging temperature. The unimodal GPC curves of the polymers and relatively narrow distribution indicate that the polymerization proceed a single active site. Regardless of reaction conditions such as [Al]/[Nd] ratio and polymerization temperature, the cis-1,4contents of the produced polymers stayed in the range of96%～97%, indicating the high stability of stereospecificity of the catalyst.Butadiene and isoprene copolymerization was carried out in hexane using the same catalyst system. The catalyst showed high activity in the same aging condition. The copolymer was of high cis-1,4stereoregularity in both polyisoprene unit (cis-1,4=96.5%) and polybutadiene unit(cis-1,4=97.4%) with Mn=7.17×104and Mw/Mn=2.45.The unimodal GPC curves of the copolymer indicated that the polymerization proceeds a single active site. The DSC curve of the copolymer showed single glass transition temperature which proved random copolymerization. The reactivity rate of the copolymer was calculated with Kelen-Tudos method. It turned out that the reactivity rates of butadiene (r1) and isoprene (r2) were respectively1.21and0.73. The product of r1and r2was close to1, which proved its random structure. The13C-NMR spectrum was used to determine the sequence distribution of the copolymer. The peak position in the aliphatic carbon part shows no difference while the composition changed in the copolymer. The data are analyzed and examined in use of the statistical formula under Bernoullian model and Markov model. It turns out that all the data accord with Markov model. Moreover, the copolymer chains with higher Bd content contain longer polybutadiene segments, and the copolymer chains with higher Ip content contain longer polyisoprene segments.