1. Field of the Invention
This invention relates to polymeric impact modifiers useful especially for PVC, to impact modified thermoplastics such as polyvinyl chloride (PVC), and to a process for preparing such modifiers.
2. Description of the Prior Art
U.S. Pat. No. 4,078,018 to Rhone-Progil teaches PVC impact modifier graft polymers having a butadiene-alkyl acrylate backbone polymer which is agglomerated. "This agglomeration operation consists of enlarging a certain quantity of particles by processes different from polymerization," according to the Rhone-Progil patent. The acrylic monomer and styrene monomer are successively grafted onto the backbone polymer in aqueous emulsion.
U.S. Pat. No. 3,842,144 to Kureha teaches PVC impact modifiers obtained by graft polymerizing upon a cross-linked butadiene-styrene rubber latex a first and then a second grafting component in a sequential two stage process.
U.S. Pat. No. 3,644,250 to Mitsubishi Rayon teaches PVC impact modifiers produced by grafting first styrene and then methyl methacrylate onto an elastomer of butadiene/n-butyl acrylate/styrene.
U.S. Pat. No. 4,173,596 to B. F. Goodrich teaches a seed polymer of cross-linked poly(n-butylacrylate), an intermediate layer derived from a monomer mixture containing n-butyl acrylate and an additional monomer, and an outer shell derived from a monomer mixture containing styrene and methyl methacrylate.
U.S. Pat. No. 3,264,373 to Union Carbide teaches low butadiene level impact modifiers for PVC, having up to 20% butadiene, preferably up to 12%, and the balance alkyl acrylate in the rubber stage, and a second stage free of styrene.
British Pat. No. 1,251,403 teaches impact modifier polymers having a butadiene based trunk polymer containing at least 60% butadiene and grafting polymers of first methyl methacrylate and cross-linking monomers then styrene, then methyl methacrylate and optional crosslinking monomer.