Date of Award
Doctor of Philosophy
Dr. George Lowry
Dr. James Howell
Dr. Robert E. Harmon
In this study the comparison of the methods used to calculate monomer reactivity ratios from experimental copolymer composition data is targeted.
For this purpose, nine samples of each of nine different concentrations of styrene-methyl methacrylate monomer mixtures were prepared. These mixtures were then polymerized for different times ranging from one to nine hours and the percent conversion to copolymer was determined.
The compositions of these copolymers were determined by their refractive index increments measured in two different solvents. Ultraviolet absorption spectroscopy was also studied as a possible method to find copolymer compositions. Though this method has been used previously, UV absorption by copolymers appears to be related to monomer sequence so that a simple application of Beer's Law is not valid.
As the best method to calculate r1 and r2 values, the Maximum Likelihood Method was taken. This method gave r1=0.495 and r2=0.467 where styrene is monomer 1. These values were then compared to the r1 and r2 values obtained from a Nonlinear Least Squares Method, Intersection Method, Fineman-Ross Method and the Kelen-Tudos Method. From this comparison it was seen that the Nonlinear Least Squares Method gave the best results. The Intersection Method gave better results than the Kelen-Tudos Method which in turn was better than the Fineman-Ross Method. Also it was observed that the calculation method of Fineman-Ross led to inconsistent monomer reactivity ratios.
This study is concluded with recommendations for further research in the area of penultimate effect in propagation, copolymers using monomers that will give a larger composition drift, and studies on the method of UV analysis of copolymer compositions taking the absorption of methyl methacrylate into consideration.
Erhan, Sevim Zeynep, "Effect of Polymerization Conversion on the Experimental Determination of Monomer Reactivity Ratios in Copolymerization" (1987). Dissertations. 3438.