The kinetics of a methyl methacrylate polymerization initiated by the stable free radicals in irradiated polytetrafluoroethylene and properties of the resultant graft polymer
The kinetics of the polymerization of methyl methacrylate(MMA)initiated by the stable free radicals in commercially available irradiated polytetrafluoroethylene micropowder and the rheological,thermal, chemical, and mechanical properties of the resultant graft polymer are described. Test tube runs using different ratios of MMA to PTFE were made to determine the feasibility of the reaction and optimum reaction conditions. The amount of graft produced was equal to the weight gain of the solids after removal of the adventitious homopolymer by extraction in acetone. Test quantities of material were produced in a 500 milliliter agitated reactor. A higher ratio of PTFE to excess MMA and longer reaction times result in higher conversion in test tubes, Higher temperatures decrease conversion if freshly irradiated PTFE is used, due to the thermally induced decay of free radicals. In a scaled-up reactor, the inhibiting effects of oxygen, which are exacerbated by the agitation, require that a nitrogen purge be used. A kinetics model relates the original concentration of PTFE free radicals. Graft polymer containing PTFE micropowder, PMMA graft, and PMMA homopolymer in a ratio of 18:5:1 was used for property characterization. Rheology experiments using a die with an L/D of 20 and included angle of 120° were made with the graft, PMMA homopolymer, and PTFE micropowder. Differential Scanning Calorimetry was used to study themal transitions. Exposure of the graft to solvents detrimental to PMMA was done to determine the graft's chemical resistance. Dynamic mechanical analysis was used to obtain the tensile and shear moduli. The graft material extrudes well at 513K and has a viscosity comparable to that of PMMA homopolymer. The material is stable upon re-extrusion. DSC thermograms show that the heat of transition of the PTFE melting peak is proportional to the amount of PTFE in the sample. Good solvents for PMMA are detrimental to the structural integrity of the graft extrudate; heat treatment improves the chemical resistance. The PTFE block controls the mechanical properties of the graft.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:kinetics methyl methacrylate polymerization graph polymer stable radicals
Date of Publication:01/01/1987