Semibatch Seeded Emulsion Polymerization of Acrylic Monomers: Bimodal Particle Size Distribution

• Published in: Journal of macromolecular science. Part A, Pure and applied chemistry Pure and applied chemistry, 1997-07, Vol.34 (7), p.1221-1236
• Main Authors: Chern, Chorng-Shyan, Chen, Tseng-Jung, Wu, Shinn-Yih, Chu, Horng-Bin, Huang, Chun-Fu
• Format: Article
• Language: English
• ISSN: 1060-1325; 1520-5738
• DOI: 10.1080/10601329708009381

Injecting sodium dodecyl sulfate (SDS) into the reaction medium induces a second crop of tiny primary particles (i.e., secondary nucleation) in semibatch seeded emulsion polymerization. Secondary nucleation may thus result in latex products with a bimodal particle size distribution (BPSD-Latices). The concentration of seed particles ([Seed]) is the most important variable for controlling the particle-size-distribution-related parameter (P), followed by the time when the surfactant is injected into the reactor (t s ). The resultant latex particle size (d p ) is not sensitive to changes in the concentration of injected SDS ([SDS]). Parameter P decreases with increasing [Seed] or t s . This implies retarded secondary nucleation during monomer addition when [Seed] or t s increases. An experiment with smaller values of [Seed] and t s favors formation of BPSD-Latices. The data clearly show a bimodal particle size distribution when P is greater than approximate 70%. Parameter P correlates well with the total seed particle surface area (A s ) regardless of the seed particle size, and P (%) is proportional to A s (cm 2 ) to the -0.319 power. Thus, A s is a very useful parameter for manipulation of the resultant latex particle size and particle size distribution.