Patent ID: 7649067

Claim:
An emulsion polymerization process for producing a vinyl ester based polymer latex in an aqueous medium, said polymer comprising polymerized units of: (a) 40-95.3 wt. % vinyl ester monomer (b) 5-30 wt. % ethylene monomer (c) 1-10 wt. % post-crosslinking monomer, (d) 0.2-2 wt. % vinyl sulfonate monomer, and (e) 0.5-2 wt. % unsaturated carboxylic acid monomer, based on the total weight of monomers, wherein the process is carried out substantially in the absence of any added protective colloid and in the presence of from 0 to 1.0 wt. % of surfactant, based on the total weight of the monomers, wherein the process comprises (i) a first stage of providing an initial reactor charge comprising an aqueous phase comprising a) 10-30 wt. % of the vinyl ester monomer, based on total weight of vinyl ester monomer, b) at least 50 wt. % of the ethylene monomer, based on total weight of ethylene monomer, c) 5-25 wt. % of the post-crosslinking monomer, based on the total weight of post-crosslinking monomer, and d) 50-100 wt. % of the vinyl sulfonate monomer, based on total weight of vinyl sulfonate monomer, and (ii) a second stage of feeding any remaining monomers and optionally a polymerization initiator system in one or more feeds to the initial charge, wherein the vinyl ester polymer latex has a solids content of at least 20 wt. %.