STRUCTURAL MORPHOLOGY OF POLY(STYRENE)-POLY(BUTYL ACRYLATE) POLYMER-POLYMER COMPOSITES STUDIED BY DYNAMIC MECHANICAL MEASUREMENTS

The emulsion polymerization process allows production of polymer particles with different structural morphologies. Films obtained after coalescence keep some memory of this morphology, but large modifications can occur during coalescence. In the present case, one of the polymers, polystyrene (PS), exhibits a glass temperature (Tg) much higher than the filmification temperature (close to room temperature), while the other one, poly(butyl acrylate) (PBA), has a much lower Tg. Furthermore, it is well known that dynamic mechanical measurements can be very helpful in providing information on the morphology of polymer materials, i.e., on geometrical and topological arrangement of homopolymer domains. At first, this method was used for comparison of two types of films: i) the first one obtained from structured-core (PS)-shell (PBA) particles, ii) the second one obtained from a blend of homopolymer particles (PS and PBA). It appears that the expected core-shell particles lost their geometric structure in the second film. Second, comparison of the predicted dynamic modulus and experimental data shows that i) strong interactions exist between PS nodules unless their coalescence has occured, leading to an abnormally high modulus at room temperature, ii) after achieving their coalescence, PS forms a more or less continuous phase. Both phenomena strongly depend on the particle size and their respective volume fractions.