Phosphorous-acid monomer containing emulsion polymer modified urea-formaldehyde resin compositions for making fiberglass products

An aqueous urea formaldehyde resin (UF resin) binder composition comprising the UF resin and from 2 to 10 wt. %, based on the total solids of the binder composition, of at least one polymer modifier which is a multistage aqueous emulsion copolymer having two or more polymer stages and having one protuberant polymer stage which is a phosphorous acid group containing polymer that sticks out or protuberates from the one or more other polymer stages of the multistage emulsion copolymer, the protuberant polymer stage copolymer comprising, as copolymerized units, a) from 0.5 to 10 wt. % of one or more phosphorus acid monomers or salts thereof;

• b) from 0.2 to 20 wt. %, of one or more carboxylic acid monomers, sulfur acid monomers, salts thereof or combinations thereof;
• c) from 0.1 to 30 wt. % of one or more multiethylenically unsaturated monomers;
• and d) as the remainder of monomers at least one second monoethylenically unsaturated monomer, all monomer proportions based on the total weight of monomers used to make the emulsion copolymer, and the overall multistage aqueous emulsion copolymer comprising a copolymer having a measured glass transition temperature of from −60 to 25° C.