The purpose of this research is to use polytetrafluoroethylene (PTFE) free radicals, as formed by irradiation, to initiate a methyl methacrylate (MMA) polymerization. This results in the formation of a block copolymer of PTFE and PMMA. The kinetics of this system are of special interest, since the steady state assumption in the theory of free radical polymerization does not apply.
To carry out this reaction, samples of irradiated PTFE were weighed in test tubes and methyl methacrylate was added volumetrically. The mixture was placed in a constant temperature bath and the reaction was carried out for a specified amount of time. At the end of the time limit, hydroquinone at approximately one weight per cent of the total reacting mixture was added to the test tube to quench the reaction.
All reactions were performed in air at atmospheric pressure. Various temperatures and ratios of PTFE to MMA were used.
The contents of the test tubes were removed to dried preweighed extraction thimbles. Extractions in acetone were carried out in a Soxleht extraction column until the thimbles and their contents reached a constant weight. The amount of poly(methyl methacrylate) grafted onto the polytetrafluoroethylene free radicals was found by subtracting the mass of the thimble and amount of PTFE used from the total mass of the thimble and its contents. Conversion was defined as the amount of graft formed divided by the initial mass of MMA used. DSC, ESR, and FTIR were used to substantiate the gravimetric analysis.
The amount of conversion of MMA to a graft onto the PTFE free radicals is a function of concentration, time, and temperature. Given a set amount of MMA, more conversion to PMMA graft occurs if more PTFE free radicals are available to initiate the polymerization. Various grades of PTFE formed by different radiation doses result in different conversions because they do not contain the same amount of free radicals. Higher reaction temperature and longer times result in more conversion.
Initiation in this system is very fast, and the PTFE free radicals are used up almost immediately. Steady state assumptions do not apply to this system since no more PTFE free radical initiators can be produced. Propagation is assumed to follow the same scheme as for a methyl methacrylate homopolymerization in a solvent. Termination is more difficult in this case than in a solvent system since the MMA chains are restricted by being attached to the PTFE matrix and must grow far enough away from this matrix to find another chain with which to terminate.
In order to satisfy the kinetics of this system, an equation is derived that relates the natural logarithm of the ratio of the initial to the final quantity of MMA to the natural logarithm of time. This straight line has a slope of k p/k t, the ratio of the rate.