Emulsion polymerization of styrene using a reactive surfactant.

摘要

Emulsion polymerizations of styrene using the reactive surfactant, sodium dodecyl allyl sulfosuccinate, TREM LF-40, its hydrogenated derivative, H-TREM, and its polymeric counterpart, poly(TREM), were studied. The critical micelle concentrations (cmc), adsorption isotherms and the presence of double bonds were determined for the three surfactants. The kinetics of emulsion polymerizations using TREM LF-40 were found to be unusual with varying TREM LF-40 concentrations ([E]) in that the reaction rate R_p was not found to be directly proportional to the number of particles, N_p (R_p ∝ N_p0.67). However, by varying the initiator concentration ([I]), the kinetics were found to be the same as for conventional surfactants (R_p ∝ N_p 1.0 ∝ [I]0.4). The kinetics using poly(TREM) were found to be as expected for different [E] and [I] (R_p ∝ N _p1.0 ∝ [E]0.2−0.5 and R _p ∝ N_p1.0 ∝ [I]0.4−0.8 ), where the lower dependence on [E] and higher dependence on [I] are due to the ionic strength and the longer nucleation period with poly(TREM).; The reasons for the unusual kinetics of the emulsion polymerization of styrene using TREM LF-40 were chain transfer and copolymerization, which take place primarily at the oil/water interface, but also in the aqueous and monomer phases. Both chemical reactions decreased the overall reaction rate. Latex characterization by serum replacement, conductometric titration, molecular weight, and AFM studies provided evidence that more than half of the TREM LF-40 and poly(TREM) were chemically bonded to the polymer particles. The fraction of chemically-bound TREM and poly(TREM) decreased with increasing [E] and increased with increasing [I]. The contact angle of water on films cast from the latexes showed that TREM LF40 and poly(TREM) did not migrate significantly to the surface of the film, which was consistent with latex surface characterization results.; Seeded emulsion polymerizations of styrene using the conventional surfactant SLS, TREM LF-40, and poly(TREM) were investigated and compared. The reaction rate decreased using TREM LF-40 and poly(TREM), compared to SLS. For TREM LF-40, it is explained by its participation in copolymerization and/or chain transfer reactions. For poly(TREM), the proposed reason is the formation of a ‘hairy’ adsorbed layer on the particles, which acts as a barrier decreasing the diffusion of the radicals into and out of the particles. Further, evidence was provided by the molecular weight of the polymer formed. A model for the seeded emulsion polymerization of styrene was developed and the modeling results are consistent with the experimental data using SLS, poly(TREM) and TREM LF-40. All the above results were found to be consistent with each other.