Study On Enhancement Of Fe(?) And Co(?) Catalysts Contain Fluorine-pyridine Imine Ligand In Isoprene Polymerization Process

Our country is the the largest consumer and importer of global natural rubber.As a strategic resource,natural rubber's stable supply is closely related to defense,transportation,medicine health care and many other areas of development.Too low self-support ratio,market risk and labor constraints and challenges make the development of natural rubber industry in our country being passive.Synthetic rubber is regarded as a substitute for natural rubber,which has been widely used in many fields.To a certain extent,it eases the shortages resulted from the shortage of natural rubber.Since Williams got isoprene from natural rubber in 1860,many researchers had been working on the research of synthetic natural rubber.Today,the synthesis of polyisoprene has got rapid development,according to the synthetic route of the catalytic system,we can mainly divided into lithium catalysts,titanium catalysts and rare earth catalysts.In recent years,the late transition metal complexes such as iron,cobalt complexes,represented as a new type of catalyst on polymerization,were getting more and more attention.This kind of catalyst is easy to synthesize and shows low cost,high activity,selectivity on polymerization.In this paper,we synthesized six kinds of iminepyridine Fe(?),Co(?)complexes containing fluoride substituent group,employed methyl alumina alkanes(MAO)and diethyl aluminium chloride as cocatalyst,and got polymers with different stereoselectivity and molecular weight efficiently.Compared with four Fe(?),Co(?)catalysts reported in literatures containing aryl and alkyl substituted iminopyridine,we found that the Fe(?),Co(?)catalysts containing fluoride contributed to the polymerization of isoprene.1)When employed Fe(?)complexes as catalysts,methyl alumina alkanes(MAO)as cocatalyst in isoprene polymerization,the polymers including cis-1,4-units and 3,4-units(about 55:45)were obtained.The catalytic systems showed good reactivity,high polymer molecular weight(around 100000)and broad molecular weight distribution(PDI=2?3),which helps to polymer modification.It is worth noting that iminopyridine Fe(?)complexes la showed a great activity on polymerization,only ten minutes the reaction can be completely transformed,a very high activity and high molecular weight polyisoprene was obtained.The amount of catalyst and cocatalyst has greater influence on polymerization,when reducing the amount of catalyst or cocatalyst,polymerization activity decreases subsequently.As for iminopyridine Fe(?)catalyst 2a and 3a,when increasing the amount of catalyst,the yield can be improved.Especially increased MAO to double amount,the molecular weight of 2a catalyzed polymer could increased more than 100000,which has a good application prospect.2)When employed Co(?)complexes as catalysts,diethyl aluminium chloride(AlEt2CI)as cocatalyst in isoprene polymerization,the polymers including cis-1,4 units and 3,4-units(about 70:30)were obtained.The catalytic system showed high polymer molecular weight(around 100000)and a narrow molecular weight distribution(PDI is about 2).The catalytic selectivities were less related to iminepyridine skeleton space steric hindrance and electrical effect,even with employed rich electrical alkyl substituted iminopyridine Co(?)complexes 4b or larger steric triphenyl benzene substituted iminopyridine Co(?)complexes 5b as catalyst,the polymer still remained similar chemoselectivity.It is important that in this polymerization the amount of catalyst is very low(80 ?mol),which reduces the cost of reaction,and the post-processing is convenient and environmentally friendly,contributing to the concept of green chemistry3)when introduced alkyl reagent[Ph3C][B(C6F5)4]to the catalytic system,under the condition of MAO as cocatalyst both Fe(?)complexes and Co(?)complexes are effective in catalysing isoprene polymerization,a high ratio trans-1,4 polymerization(>95%)was obtained as viscosity polymer.By introducing to alkyl boron reagents,the polymers showed low molecular weight(<2000)and a narrow molecular weight distribution(PDI=1?2).However,this kind of polymer were test that there were miscellaneous peak on balmy area through 1H NMR spectrum and suggested friedel-crafts alkylation reaction involving toluene may be happened in the process of polymerization.