Synthesis and characterization of urethane-acrylate graft copolymers

[摘要] Polyurethanes (PUs) are finding increasing application and use in many industries dueto their advantageous properties, such as a wide range of flexibility combined withtoughness, high chemical resistance, excellent weatherability, and very low temperaturecure. PUs do however have some disadvantages, for instance, PU is considered anexpensive polymer, especially when considered for solvent based adhesives. Amotivation for this study was to consider a largely unstudied area of PU chemistry bycombining PUs with polyacrylates. Polyacrylates are well known adhesives and cancarry specific functionality, but have the disadvantage that their flexible backbonesimpart limited thermal stability and mechanical strength. In this study PU wasincorporated into acrylates in an effort to obtain acrylate-g-urethanes with goodproperties. The mode of incorporation chosen was urethane macromonomers (UMs), ahardly mentioned substance in literature, yet one deserving investigation.UMs having different urethane chain lengths (X) were synthesized by the polyadditionpolymerization of toluene diisocyanate (TDI) and ethylene glycol (EG) by the prepolymermethod, which was terminated by 2-hydroxy ethyl methacrylate (HEMA) andisopropanol. The UMs were characterized by Fourier-transform infrared spectroscopy(FTIR), proton NMR (1H NMR), carbon NMR (13C NMR), gel permeation chromatography(GPC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA).Various percentages of the respective UMs (0-40 wt % according to acrylate monomers)were then incorporated into methyl methacrylate (MMA) and into normal butylmethacrylate (n-BMA) backbones via solution free radical copolymerization. Theresulting methyl methacrylate-urethane graft copolymers (PMMA-g-urethane) andnormal butyl methacrylate-urethane graft copolymers (n-PBMA-g-urethane) werecharacterized by GPC, 1H NMR and 13C NMR, FTIR, TGA, and DMA. Phase separationbetween the urethane segment and acrylate segment in the yield of graftcopolymerization products was investigated by DMA and transmission electronmicroscopy (TEM).As the concentration of the UMs in the free radical copolymerization feed increased,lower yields of both graft copolymers PMMA-g-urethane and n-PBMA-g-urethane were observed and more UM was incorporated into the PMMA and n-PBMA backbones. Italso was found that the thermal stability of the PMMA-g-urethane and n-PBMA-gurethanecopolymers increased with increasing UM concentration.DMA results showed that in most graft copolymer products the two respectivecomponent parts of PMMA-g-urethane or n-PBMA-g-urethane were completelycompatible as only one Tg was observed. Two glass transitions, at temperatures of 22.0and 76.0 oC, corresponding to the n-PBMA and urethane moieties, were observed whenthe chain length of the UMs was increased from X=4 to X=32 [the amount of this UMused in the copolymerization feed was increased to 40%, and microphase separationwas indicated].

[发布机构] Stellenbosch University