Polystyrene latex by dispersion polymerization: real time SAXS measurements

The purpose of this work was the characterization of polystyrene and poly(styrene-co-Boc-aminostyrene) latex particles obtained by dispersion polymerization as a function of reaction time. Small angle scattering of X-rays (SAXS) using synchrotron radiation was the main technique used to describe the system, by means of real time experiments (in situ) and in samples prepared from extracts of the polymerization reaction taken at several times during the polymerization process (ex situ). Complementary measurements of light scattering were performed on these extracted samples in order to estimate the average particle size at different times during the polymerization reaction. Analysis of the SAXS data gave information on the characteristics of the surface of the latex particles by means of the fractal dimension. The time evolution of the integrated intensity was related to changes in electron density contrast and the volume fraction of the solid polymer phase for both the styrene (ST) homopolymerization and styrene/Boc-aminostyrene (ST/Boc-AMST) copolymerization experiments performed in this work. The results indicated that there is a slight difference in these polymerization reactions taking into account the growth of the macromolecular chains that seems to be faster for the homopolymerization reaction. In the case of copolymerization, the Boc-AMST monomer competes with styrene in the insertion in the growing polymer chains, thus leading to a slow-down of the conversion rate. In both cases, the end product of the reaction is a polydisperse system of micron sized spherical particles with fractally rough surface.