Synthesis Of Polyisoprene And Polyisoprene-polystyrene Block Copolymer By Atom Transfer Radical Polymerization

Isoprene rubber has advantages of good elasticity,high mechanical strength,good binding properties,excellent water resistance and extraordinary electrical insulation.It has a wide range of applications in all areas of thenational economy.Anionic polymerization and coordination polymerization are two major traditional methods for synthesis of isoprene rubber.However,these two approaches are sensitive to air and humidity and require monomers of very high purity and extremely low reaction temperatures.Atom transfer radical polymerization(ATRP)is a transition metal complex-mediated controlled/"living" radical polymerization at mild reaction conditions.A lot of vinyl monomers have been polymerized by ATRP and this method has been extensively used to prepare a large variety of random,block,graft,cyclic,hyper branched,dendritical and crosslinked(co)polymers with predetermined molecular weights,narrow polydispersities and well-defined architectures.Isoprene intrinsically has a quite low chain propagation constant,and consequently the reactivity of isoprene is low and the polymerization rate of isoprene is very slow.For example,a previous research indicated that the ATRP of isoprene only obtained less than 5%conversion in 24 h.The aims of this work are to develop an appropriate ATRP system including a fast initiator,an efficecnt catalyst,and an effective promotion agent to increase the polymerization rate and improve the isoprene conversion.The discipline of co-polymerizaion of isoprene with styrene to synthsize polyisoprene-co-polystyrene block copolymer was also investigated in this study.The accomplishments of this work and the major achievements of this study are as follows:1.A lot of catalysts such as CuBr or CuCl complexed with N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine(TPEN),tris[2-(dimethyl-amino)ethylamine](Me6TREN),N,N,N ',N',N "-pentamethyl-diethylenetriamine(PMDETA),2,2-bipyridine(Bpy),tetramethyl ethylene diamine(TMEDA)as well as 4,4'-dinonyl-2,2-bipyridine(dNbpy)and many initiators,e.g.,ethyl 2-bromoisobutyrate(EBiB),ethy 2-bromophenylacetate(EBPA),ethyl-2-bromopropionate(EBP),bromoacetonitrile(BrAN),and ethyl-2-chloropropionate(ECP)have been explored for ATRP of isoprene.It was found that the polymerization mediated by CuBr/Bpy as a catalyst and EBP as an initiator produced polyisoprene with a narrowest molecular weight distribution.2.The concentrations of monomer,CuBr/Bpy and EBP as well as the reaction temperature were found to have a great influence on monomer conversion and molecular weight distribution of polyisoprene.It was conclude that the monomer could reach the highest conversion of 71.2%in 96 h at 130? when the initial concentration of isoprene,initiator and catalyst was 7.26 mol/L,0.07mmol/L and 0.14 mol/L respectively.The isoprene even achieved 70.1%conversion in 72 h at 150 ?.1H NMR spectroscopy results revealed that the polyisoprene had a 1,4-addition structure.3.One-pot ATRP and two-step ATRP were used to synthesize polyisoprene-co-polystyrene block copolymer.The one-pot method was found to have advantages of simple and easy operation,accurate molecular weight control,and elimination of intermediate disposal.