Determination of relative reactivity ratios (copolymerization parameters) for styrene and acrylamidostearic acid
Clougherty, Edward V
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Acrylamidosteric acid is both a monomer and (as its potassium salt) a soap. This problem was undertaken in order to establish fundamental copolymerization parameters for the system styrene, M1, and acrylamidostearic acid, M2. The propagation steps in the copolymerization of two monomers M1 and M2 are illustrated by the four equations: Equation: M1' + M1 ---> M1', Rate Constant: k11 Equation: M2' + M2 ---> M2', Rate Constant: k12 Equation: M2' + M2 ---> M2', Rate Constant: k22 Equation: M2' + M2 ---> M1', Rate Constant: k21 where M1' and M2' represent chain radicals having monomers M1 and M2 respectively, as their terminal, free-radical-bearing units. The fundamental parameters are defined as r1 = (k11/k12) and r2= (k22/k21). The polymerizations were run in tubes which had a side arm viscometer so that it was possible to determine whether any conversion had taken place during the experiment. After polymerization had produced evidence of some conversion (as indicated by the attached viscometer), the reaction tubes were cooled in a Dry Ice acetone bath. The contents of the tube were then subjected to a purifying procedure which for this system required that the mixture of monomer and polymer be precipitated four times from a dioxane solution by a four fold excess of ligroin. This procedure was deduced from preliminary solubility studies of monomer and polymer. The purifying procedure was tested by preparing synthetic mixtures of both monomers and polymers in proportions which amounted to a ten percent conversion of monomer to polymer. From the results of the test of the purification procedure a correction factor was calculated by which the experimentally determined values of the polymer composition were corrected. The calibration factors were determined by analyzing known mixtures of the two homopolymers. Five copolymerization runs were made in bulk at 65° with 0.5--0.6 mole percent initiator (dibenzoyl peroxide) to low conversion. The values for the relative reactivity ratios are as follows: r1 = 2.12, r2 = 0.36. These were determined by plotting the data according to the equations of Fineman and Ross: F(f-1)/f = r2*(F2/f)-r2 (f-1)/F= -r2*(f/F2) + r1 where F=F1/F2 (F1 and F2 are the initial mole fractions of monomers in the charge) f=f1/f2 (f1 and f2 are the mole fractions of the polymers). In order to visualize the accuracy of the results a theoretical curve of incremental polymer composition as a function of monomer composition was constructed using the above values of r1 and r2. The experimental points were then placed on the same curve. All the points fell close to the curve thus indicating acceptable results.
Thesis (M.A.)--Boston University