Reversible-Deactivation Radical Polymerization Of Methyl Methacrylate Catalyzed By Organic Catalysts

Reversible deactivation radical polymerization(RDRP)has the characteristics of controllable molecular weight,narrow distribution,and the ability to produce a variety of topologically structured polymers with well-defined structures.It was widely used in the fields of block polymer synthesis,nanofine structure preparation,medical material,and photoelectric information technology.The RDRP by organic catalysts in the presence of iodine compounds has attracted wide attention because of its mild polymerization conditions,simple method,and excellent controllability.In this paper,the RDRP of methyl methacrylate(MMA)catalyzed by phosphoramide and carbodiimide in the presence of in situ alkyl iodide was developed,the types of organic catalysts were extended,and the polymerization method was optimized.The main work is as follows.1.Hexamethylphosphoramide(HMPA)has been found to be a novel and highly efficient organic catalyst for the RDRP of MMA.Firstly,the influence of the amount of catalyst,polymerization temperature,and different solvents on the solution polymerization was examined in detail.The results show that HMPA can effectively control the polymerization reaction.With the increase of the amount of catalyst,the induction period was shortened,the polymerization rate was accelerated.In the range of catalysts studied,the number average molecular weight of the polymer showed a linear growth relationship with the conversion rate,the molecular weight polydispersity index(PDI = Mw/Mn)was less than 1.25.The results of the effect of different temperatures(60 ℃,65 ℃ and 70 ℃)on the polymerization showed that the optimum polymerization temperature was 65 ℃,the molecular weight polydispersity index of the polymer was within 1.20.The polymer molecular weight polydispersity index was within 1.30 at low temperature(60 ℃)and high temperature(70 ℃)conditions.Good controllability can be achieved in several solvents such as toluene,benzene,tetrahydrofuran and anisole.The structure and the iodine-end-capped structure of the obtained PMMA was demonstrated by 1 H-NMR spectrum and GPC,and the fraction of iodine chain end of the PMMA chains was up to 98.8%.Then,the iodine terminus could be efficiently reactivated for chain extension and block reaction.Notably,high-molecular-weight PMMA with a narrow molecular weight distribution were successfully obtained(Mn up to 104 000,Mw/Mn =1.34).Finally,the UV detection and free radical capture experiments verified that the mechanism of polymerization catalyzed HMPA is reversible complexation mediated polymerization mechanism.2.The RDRP of MMA was carried out utilizing an alkyl iodide in situ formed as initiator and dicyclohexylcarbodiimide(DCC)or N,N’-diisopropylcarbodiimide(DIC)as highly efficient organic catalysts for the first time.Firstly,the catalytic activity of the two catalysts was demonstrated and compared.Then the influence of the polymerization temperature,the amount of catalyst DCC,the amount of traditional initiators and the type of solvents on the polymerization was investigated in detail.The results show that the polymerization has best controllability when[MMA]0:[I2]0:[ABVN]0:[DCC]0 = 200:1:1.7:4 at 65 0C.The measured molecular weight is consistent with the theoretical molecular weight and the molecular weight increases linearly with the increase of conversion rate.Both DCC and DIC can achieve excellent controllable effects in benzene,toluene,tetrahydrofuran and anisole.And found that a small amount of DMF in toluene solvent can increase the reaction rate without affecting the polymer molecular weight polydispersity index.Then the structure and the iodine-end-capped structure of the obtained PMMA was demonstrated by 1H-NMR spectrum and GPC,and the fraction of iodine chain end of the PMMA chains was up to 97.5%,and the chain extension reaction of MMA was successfully achieved.Finally,it was verified that both DCC and DIC can complex with iodine and activate alkyl iodine.It was proved that the polymerization mechanism of MMA in the presence of carbodiimide was reversible complexation mechanism.3.With HMPA as the catalyst and 2-iodo-2-methylpropanenitrile as the initiator,the reversible-deactivation radical polymerization of MMA was achieved under visible light conditions.The effects of light sources and oxygen on the photopolymerization of MMA were investigated.The results show that the photopolymerization catalyzed by HMAP has good controllability,the measured molecular weight is consistent with the theoretical molecular weight,and the molecular weight polydispersity index is lower(PDI<1.26).In the sunlight,the polymerization rate is the fastest,followed by blue and green light.The control of polymerization under these three light sources is good.When there is a small amount of oxygen,the polymerization rate is slowed,but the molecular weight dispersion index can reach about 1.10.