Advances in mathematical modelling of multicomponent free-radical polymerizations in bulk, solution and emulsion

Abstract

A computer package has been developed to simulate free-radical multicomponent polymerization in bulk, solution and emulsion. The simulation package consists of two models, one for bulk and solution polymerization, and the other for emulsion polymerization. Great emphasis has been placed on making both models general and reliable. This has been achieved through in-depth kinetic studies, critical model evaluation and extensive model testing. Models have been gradually enhanced and extended from a homopolymerization case to two comprehensive multicomponent bulk/solution/emulsion models. Databases of physicochemical parameter values for both models have been developed in parallel. The bulk/solution model's database includes 12 monomers and the database for the emulsion model consists of 5 monomers. Both databases also have many initiators, solvents (in bulk/solution model's database only), chain transfer agents and emulsifiers (in emulsion model's database only). Such extensive databases allow the models to simulate multicomponent polymerizations for a wide range of reaction recipes.

In the first stage of model development, the bulk/solution model was developed and extensively tested with a total of 15 copolymer systems. Several important aspects in copolymerization kinetics were discussed. In most model testing cases, model predictions turned out to be very satisfactory and this confirms the reliability of the package. The literature review on copolymerizaiton kinetics and model testing presented in this thesis are believed to be the most extensive so far in the literature.

In the second stage of model development, terpolymerization kinetics in bulk/solution over the entire conversion range were investigated in detail. The bulk/solution copolymerization model was extended to simulate terpolymerization in bulk/solution and testing over the entire conversion range. This is the first time that a terpolymer system is modelled over the entire conversion range. Testing has been performed with the very challenging (and widely used commercially) system of butyl acrylate/methyl methacrylate/vinyl acetate in bulk and solution (toluene). Due to the scarcity of available experimental data in the literature, we were not able to test the model more extensively with other terpolymerizations, however, the system in question was extremely challenging as a test case.

In the third stage of model development, a general and comprehensive emulsion model has been developed. This emulsion model is one of the very few that can simulate emulsion homopolymerization as well as copolymerization under a very wide range of reaction and operation conditions. The model can describe the most important physicochemical phenomena (micelle formation, particle nucleation, absorption and desorption of radicals, monomer partitioning, gel effect, etc.) occurring in emulsion polymerization. Difficult and challenging subjects in emulsion polymerization kinetics, such as monomer partitioning through thermodynamic equilibrium, particle nucleation, desorption, etc., have been solved satisfactorily in a general fashion. This model can predict important reaction characteristics (conversion profile and rate of polymerization) and polymer/latex properties (number of particles, particle size, molecular weight averages, copolymer composition and sequence, etc.).

The emulsion model has been tested with monomers of very different characteristics, like styrene (a "typical case 2" monomer with very low water solubility and no desorption), vinyl acetate (a typical "case I" monomer with high water solubility and significant desorption) and methyl methacrylate (a typical "case 3" monomer that exhibits strong gel effect). The model has also been tested for the copolymer system of styrene/methyl methacrylate. In most cases, simulation results are satisfactory compared to experimental data collected either from the literature or from this laboratory.

After this systematic effort in refining and testing our multicomponent simulation model/package/database, we strongly believe that the package can provide a very flexible and useful tool that could guide academic and industrial research and development, as extensively demonstrated in Gao and Penlidis (I 996, 1998) for homo- and copolymerizations, and in the present thesis for terpolymerizations and emulsion case.