EMULSION POLYMERIZATION PROCESS WITH DELAYED ADDITION OF CHAIN TRANSFER AGENT
Original Publication Date: 1997-Oct-31
Included in the Prior Art Database: 2004-Apr-08
Xerox Disclosure Journal
Disclosed is an improved emulsion-aggregation polymerization process wherein the addition of a chain transfer agent is delayed until after initiation has commenced. In a conventional batch emulsion aggregation polymerization process, the ingredients, including, monomer(s), initiators, surfactant(s), and chain transfer agent, are typically added at the start of the reaction, that is, prior to initiation of the polymerization reaction. In embodiments, the improved polymerization is accomplished under an inert atmosphere, such as nitrogen, and a chain transfer agent is added, preferably neat, to the reactor after the polymerization has been proceeding for a short time. The improved process eliminates the formation of sediments, which amounts to about 4 percent of the product in the conventional polymerization process. The improved process conducted under inert atmosphere is also safer than the reaction carried out in the presence of oxygen. The improved process allows control of the molecular weight (Mw) and the molecular weight distribution(MWD) of the polymer product and which latex product is free of disagreeable sediment. The improved process differs from known batch and semi-batch processes, or semicontinuous emulsion-polymerization processes. In an exemplary example, a conventional emulsion polymerization is conducted with the exceptions that a nitrogen purge and atmosphere are used, and the charge transfer agent, dodecanethiol, was added over about 15 minutes to the heated polymerization mixture at about 60 to 80°C and about 25 minutes after the polymerization had been initiated. Product polymers typically had a Mw = 25,000-30,000; Mn = 5,500-6,500; MWD = 3.75-4.25; and Tg = 55.5- 57.5"C. No sediment was observed. The present process is particularly useful in preparing low molecular weight polymers for use in high gloss, color toner applications.