Graft polymers weather resistance

Whilst the ASA materials are of European origin, the AES polymers have been developed in Japan and the US. The rubber used is an ethylene-propylene terpolymer rubber of the EPDM type (see Chapter 11) which has a small amount of a diene monomer in the polymerisation recipe. The residual double bonds that exist in the polymer are important in enabling grafting with styrene and acrylonitrile. The blends are claimed to exhibit very good weathering resistance but to be otherwise similar to ABS. 

In order to produce a resin with excellent impact strength and at the same time excellent weather resistance and aging resistance, it is essential to eliminate the unsaturated ethylene polymer from the graft copolymer. Therefore, ASA polymers that are crosslinked with the alkyl acrylate rubber polymer are preferred (17). 

The first LDPE/HDPE blends were patented by du Pont de Nemours before Z-N polymers became available (Roedel 1961). The blend comprised an experimental HOPE (p = 0.939-1.096 g mL Tm 120 °C) obtained by polymerizing C2 in its own medium at T 0 °C and P 31 MPa, using, e.g., a hydroxy-cyclohexyl-L-hydroperoxide catalyzed by ferrous chloride tetrahydrate. The blend showed 50 % moisture permeabDity of that by LDPE. In 1958 Phillips Petroleum patented PE/PE blends, either cross-linked in electron accelerator or not (Canterino and Martinovich 1963 Nelson 1964). Mitsubishi disclosed PO blends comprising vinyl-trimethoxysUane-grafted polyolefin (PP, LDPE, EPR, or EVAc) and ethylene-acryloyloxy tetramethylpiperidine copolymer. These water-cross-linkable resins were used for the manufacture of weather-resistant cross-linked PO pipes in outdoor applications (Ohnishi and Fukuda 1993). Thermally reversible cross-links (based on ionic interaction between maleated- and glycidyl methacrylate-grafted polyolefins) were also proposed (Okada 1994 Okada and Masuyama 1994). 

Copolymer composition has a direct effect on the Tg of the polymer, which determines the minimum film forming temperature (MFFT) of the latex and the application. Thus, a 95/5 wt/wt butyl acrylate/methyl methacrylate is an adhesive, whereas a 50/50 copolymer of the same monomers is a binder for paints. Copolymer composition affects properties such as resistance to hydrolysis [4] and weatherability. In situ formed blends of random copolymers of different compositions may be beneficial for application properties [5]. Conventional free-radical polymerization, which is the process used to manufacture almost all commercial emulsion polymers, does not allow the production of block and gradient copolymers (accessible by means of controlled radical polymerization [6], Section 3.3). Nevertheless, graft copolymers are frequently formed, and the extension of grafting largely determines the application properties. Thus, grafting determines the size of the rubber domains in ABS polymers, and the toughness of these polymers increases with rubber size. 

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