Emulsifier-free emulsion polymerization of acrylonitrile-butadiene-carboxylic acid monomers: a kinetic study based on polymerization pressure profile

摘要

Emulsion polymerization of acrylonitrile-butadiene-carboxylic acid monomers (XNBR latexes) in the absence of emulsifier is associated with thermodynamic and kinetic complexities and is very sensitive to colloidal stability. In this paper, polymerization pressure profiles were utilized for kinetic studies of emulsifier-free emulsion terpolymerization of acrylonitrile, butadiene and two carboxylic acid monomers (i.e., acrylic acid and methacrylic acid). It was found that the type and amount of acidic monomer have a great impact on the nucleation rate as well as particle size distribution and carboxyl group distribution of XNBR latexes. Also, the type of the acidic monomer affects the rates of entry and exit of radicals to and from particles and consequently the average number of radicals per particle, where a higher rate of polymerization was observed for methacrylic acid latexes. The reaction temperature has profound effects on polymerization rate, particle size distribution and colloidal stability of the latex. Partitioning of pressure profiles into four distinct regions in accordance with well-established intervals of Harkins model and analyzing particle size distribution and carboxyl group distribution, established a conceptual framework for kinetic studies in emulsion polymerization of XNBR latexes.