Influence of main ingredients on properties of latex and latex film in polysiloxane modification of styrene-butyl acrylate copolymers

Water borne latexes of styrene (St) and butyl acrylate (BA) copolymer, modified with octamethylcyclotetrasiloxane (D-4) were prepared through a semi-continuous emulsion polymerization with dodecylbenzene sulfonic acid (DBSA) as the catalyst for D-4 ring-opening and ammonium persulfate (APS) as the initiator for St-BA polymerization. To enhance the compatibility of the silicone with St-BA copolymer by establishing chemical bonds between the two components, 3-(methacryloxy) propyl trimethoxysilane (MPTS) or hydroxyethyl acrylate (HEA) was employed as the coupling agents. The effect of DBSA location at start of emulsion polymerization was studied. It was found that more stable latex was obtained when DBSA was initially added in the reactor in comparison with its addition to the preemulsion followed by slow feeding to the reactor. HEA was also an effective coupling agent to improve the properties of the latex and the latex film. In addition, the influences of the amounts of APS, the catalyst DBSA, and D-4 on the latex properties were studied. The process was optimized with regard to the ingredients used in the polymerization. To achieve stable latex with good latex film properties, APS amount should be kept between 0.18 and 0.28 wt.%, D-4 monomer no more than 8 wt.% relative to the mass of all vinyl monomers, and the molar ratio of MPTS/D-4 is recommended to be 1/4. With HEA as the coupling agent, its amount should be 6.6 wt.% relative to the mass of D-4. The mechanical property of the latex film and its water absorption were also characterized.