Study On MMA Radical Polymerization Regulated By Carbon-based Materials

In this paper,using carbon-based multi-walled carbon nanotubes(MWCNTs)and graphene(GR)as regulators of methyl methacrylate(MMA)radical polymerization system,a series of polymethyl methacrylate(PMMA)were synthesized via the bulk polymerization and interfacial polymerization at low temperature(<50?).The molecular structures of the polymerization products were characterized by fourier transform infrared spectroscopy,nuclear magnetic resonance spectroscopy and Raman spectroscopy.The molecular weights and its distribution widths of the polymerization products were measured by gel permeation chromatography and viscosity method.The glass transition temperatures(T_g)of the polymerization products were measured by differential scanning calorimeter.The effects of the composition of carbon-based materials,initiator concentration and polymerization temperature on the reaction rate,molecular structure,T_g and molecular weight distribution width were investigated.The main conclusions are as follows:(1)The low temperature bulk polymerization of BPO-MMA regulated by MWCNTs was studied.MWCNTs can shorten the polymerization time,accelerate the polymerization rate,and effectively control the molecular weight and its distribution width of the polymer at low temperature.The maximum number average molecular weight(Mn)of the product is0.96×10⁶ g/mol,the weight average molecular weights(Mw)are more than 1.00×10⁶ g/mol,and the minimum polydispersity index(Mw/Mn)is 1.32.The percentage of syndiotactic structure(rr)of the product is 60.9%-66.0%,and the percentage of random structure(mr)is29.9%-35.2%.The rr/mr ratios of the polymerization products are similar to that of PMMA,and MWCNTs does not change the stereoregularity of the polymer.The T_g of the polymerization product with the introduction of MWCNTs is improved accordingly.(2)The low temperature bulk polymerization of BPO-MMA regulated by GR was studied.The defect degree of GR-2(I_D/I_G=1.98)is higher than that of GR-1(I_D/I_G=0.29).The polymerization rate of the system with GR-2 is faster than that of GR-1.GR can also effectively control the molecular weight distribution width of the product.The maximum M?of the product is 3.49×10⁶ g/mol,the maximum Mn is 0.83×10⁶ g/mol,the maximum Mw is 1.27×10⁶ g/mol,and the minimum Mw/Mn is 1.39.The percentage of rr of the product is 55.3%-62.8%,and the percentage of mr is 33.2%-37.0%.The rr/mr ratios of the polymerization products are similar to that of PMMA.With the introduction of GR,the tereoregularity of the polymer is not changed,but the T_g is changed.(3)The low temperature interfacial polymerization of(NH₄)₂S₂O₈-MMA in aqueous phase regulated by MWCNTs and GR-1 respectively was studied.In this polymerization system,both MWCNTs and GR-1 can significantly increase the polymerization rate and control the molecular weight distribution width of the product.The minimum Mw/Mn of the polymer with MWCNTs is 1.94,and the minimum Mw/Mn of the polymer with GR-1 is1.79.The polymerization products are all PMMA polymers,and the percentages of rr,mr and mm of each products are almost the same.MWCNTs and GR-1 do not change the stereoregularity of the polymer.With the addition of MWCNTs and GR-1,the T_g of the polymer is changed.(4)The related mechanism is proposed that carbon-based materials regulate the controlled free radical polymerization of olefin monomers.The introduction of MWCNTs/GR accelerates the decomposition of the initiator,then the initiator initiates the MMA polymerization to produce chain free radicals at low temperature rapidly.Based on the interaction between chain free radicals and delocalized?electrons of MWCNTs/GR in high viscosity polymerization system,the diffusion of active chains becomes difficult,which reduces the probability of termination of double radical chains and forms polymers with narrow molecular weight distribution.Thus,controlled free radical polymerization of MMA is realized at low temperature.