Homopolymerization Of Isoprene And Copolymerization Of Isoprene With Styrene Using Novel Rare Earth Catalysts

Rare earth catalysts have high catalytic activities on homopolymerization and copolymerization of conjugate dialkenes, such as butadiene (Bd) and isoprene (IP). The polymer or copolymer has high molecular weight and high cis content. Our group has done a lot of research works on this field, and has got some achievements.In this paper, we use novel rare earth catalysts and successfully prepared polyisoprene (PIP) with high molecular weight and high cis-1,4 content. Researches on copolymerization of IP and styrene (St) were also carried out by these catalysts. Random copolymer of IP and St(poly(IP-co-St)) was successfully obtained.PIP was obtained by a ternary rare earth catalytic system which do not contain halogen Nd(P204)3-Al(i-Bu)3-MAO. The catalytic system shows high catalytic acitivit under following polymerization conditions: Al/Nd=30, Al(i-Bu)3 /MAO20/80, IP/Nd=2500, aging for half an hour, toluene used as solvent, polymerized at 50C for 1 hour. The polymer yield was about 95%, and PIP obtained by it has a high molecular weight (Mv=56.7x104) and a high cis-1,4 content (about 95%).PIP was also obtained successfully by a novel binary rare earth catalytic system NdCl3-3HMPA-Al(i-Bu)3. The catalytic also shows high catalytic acitivit following porymerization conditions: Al/Nd=30, IP/Nd=1000, aging for half an hour, toluene used as solvent, polymerized at 50C for 6 hour. The polymer yield was about 92%. PIP obtained by it has a high molecular weight (Mw=6.9x105) and high cis-1,4 content (about 95.5%).Though the catalyst mentioned above can not catalyse the homopolymerization of St , random poly(IP-co-St) was obtained by it. The coporymer obtained following conditions: HMPA/Nd=3, Al/Nd=30, Monomer/Nd=1000, IP/St=7/3, aging for half an hour, toluene as solvent copolymerized at 50C for 6 hours) has conversion of 63%, 8 mol% St, a relatively high molecular weight ([ ]=1.73dL/g) and no gel content. The unique point of this catalyst is that the copolymer has high cis-1,4 content in Bd units(96%) in spite of the increase of molar pencentage of St in it, which is quite different from other catalyst for coporymerization of IP/St.Using MAO as a cocatlyst of NdCl3 3HMPA, a novel catalystic system NdCl33HMPA-MAO was found. This system has catalytic activity on polymerzaiton of IP. But the activity is not very high, and the MAO's dosage is large. PIP was obtained under following conditions: HMPA/Nd=3,Al/Nd=140, IP/Nd=500, aging for half an hour, polymerized for 6 hour, toluene as solvent. It is found that through GPC determination in polymerization system there are two activity centers C1 and C2*: C1* has higher activity and shorter life. On the other hand, C2* has lower activity and relatively longer life. And C2 shows the character of quasi living center.Considering that Nd(P204)3-Al(i-Bu)3-MAO and NdCl3 3HMPA-Al(i-Bu)3 are both good catalysts for homopolymerization of IP, it might be also good for copolymerization of IP and Bd. So experiments based on this idea were carried out. But we found that with the increase of Bd units' percentage in copolymer, gel content also increased. It is hard to examine the samples, so that we didn't go further on such copolymerization experiments.