Atom Transfer Radical Suspension Polymerization Of Polymer Beads For Lost Foam Casting And Modification Of The Beads' Pyrolysis Properties

Pattern materials used in lost foam casting have a significant effect on casting formation in the lost foam process. Generally, pattern materials are some expandable polymers which include polystyrene, polymethyl methacrylate and styrene-methyl methacrylate copolymer. According to the requirements based on craft in evaporative pattern casting, these polymers must be provided with high average molecule weight and narrow molecule weight distribution;Further more, they have to possess the desired pyrolysis properties. In this thesis, atom transfer radical suspension polymerizations were carried out to synthesize these pattern polymers beads which showed high average molecule weight and norranow molecule weight distribution. Thermal degradation of the pattern polymers in the presence of the additive ammonium chloride or dicumyl peroxide was also studied.Results of FT-IR and ¹H-NMR have proved that polystyrene, polymethyl methacrylate and styrene-methyl methacrylate copolymer were synthesized. Analysis by GPCV measurement showed that the number average molecule weight (M_n) of polystyrene beads was as high as 185210, M_w was 281520, and the molecule weight distribution was narrow (M_w/M_n=1.52). The molecule weight and polydispersity indexes had reached to the requirements employed in lost foam casting. Effects of hydroxyl anion added to the water phase on the atom transfer radical suspension copolymerization were studied.The results indicate that atom transfer radical suspension polymerization displayed controlled/living character as evidenced by the plot of㏑[M]₀/[M] versus time was linear. The first order reaction kinetics of atom transfer radical polymerization was not altered by hydroxyl anion. Both monomer conversion and reaction rate increased with an increase of hydroxyl anion concentration ranged from 0 to 3% at water phase. And the apparent activation energy of the polymerization was reduced because of hydroxyl anion. Hydroxyl anion promoted the polymerization. It was due to that hydroxyl anion induced double bond of monomer to dissociate at polymerization.Thermal behaviors of polystyrene, polymethyl methacrylate and styrene -methyl methacrylate copolymer were investigated by differential scanning calorimetry. The thermal decomposition temperature of polystyrene was the highest. Thermal degradation temperature of styrene-methyl methacrylate copolymer beads was lower than that of polystyrene; however, it was also relatively high. Thermal degradation of styrene-methyl methacrylate copolymer in the presence of the additive ammonium chloride or dicumyl peroxide was studied with thermogravimetry. Thermogravimetry results showed that both ammonium chloride and dicumyl peroxide made thermal decomposition temperature of styrene-methyl methacrylate copolymer to decrease. Ammonium chloride accelerated thermal degradation of copolymer in nitrogen, and the residue at 500℃after thermal treatment was only 0.0015% of the total weight, it had brought styrene-methyl methacrylate copolymer to completely degrade. Dicumyl peroxide promoted degradation of copolymer in initial thermal degradation, but at the evening of thermal degradation suppressed degradation and the residue reached to 0.96% of sample.