ASA polymers

DR (Rohm and Haas) and Plex 8535-F (Rohm GmbH). Some typical properties of these materials compared with straight PMMA and with the competitive ABS and ASA polymers (discussed in Chapter 16) are given in Table 15.3. 

ASA polymers which utilise an acrylic ester rubber (see Chapter 15). 

Weather-resistant ASA polymers containing acrylic rubber in an SAN matrix (LURAN S, BASF). 

The earliest preparation on an acrylonitrile-styrene-acrylate (ASA) polymer is believed to have taken place in 1964 (1,2). ASA was first introduced to the market by BASF in around 1970 as Luran S, based on patents from the 1960s (3-6). 

ASA polymers are produced by introducing a grafted acrylic ester elastomer during the copolymerization reaction between styrene and acrylonitrile. 

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 properties and the methods of characterization of the of the ASA family are standardized (23). Some selected properties of an ASA polymer are shown in Table 12.4. 

Because of the enhanced weather resistance, ASA is used extensively in the automotive industries, and further in general for outdoor applications. In particular, ASA polymers have been widely applied to glossy colored outdoor products including (17) ... 

Acrylonitrile-butadiene-styrene (ABS) and acrylonitrile-styrene-acry- late (ASA) are rubber-toughened plastics based upon the styrene-acrylonitrile (SAN) copolymer matrix. The combination of the stiffness and toughness exhibited by these materials has made them increasingly attractive in engineering applications, and the activity of the patent literature testifies to a continuing interest in improving properties through modifications of structure. The aim of this paper is to discuss a quantitative approach to structure-property relationships in ABS and ASA polymers. 

Two ASA polymers were studied Luran S 757R and Luran S 776S both were made by BASF. The polymers have similar SAN matrices but respectively contain ca. 30 and 40% of the acrylic rubber-toughening agent. The ABS polymer (ABS 500) was made by the Dow Chemical Co. It contained SAN-filled rubber particles ca. 1.0 /an in diameter, suggesting that it was manufactured by bulk or suspension polymerization. 

ASA Polymers. Creep tests were performed on Luran S 757R at stresses from 19-26 MN/m2. Over this range, the time to reach 5% ex-... 

Figure 2. Creep and recovery of ASA polymer Luran S 757R stress = 20...

T is the absolute temperature. These plots are shown in Figure 4 for both ASA polymers. Both rate quantities give approximately the same value, ca. 3500A3, for the apparent activation volume yv for both polymers. 

A similar graph can be plotted for the maximum lateral strain rate d/dt (—ei) (see Figure 5) this gives an apparent activation volume of ca. 3000 A3 for the shear processes in both ASA polymers. 

Acrylonitrile-styrene-acrylate (ASA) polymers share obvious similarities with ABS but ASA was only developed in the 1960s. ASA polymers are essentially SAN polymers impact modified with an acrylate rubber. The earliest attempt to make ASA was by Herbig and Salyer of Monsanto [23] using butyl acrylate as the rubber phase. This work was then refined by Otto [24] and Siebel [25], both of BASF, who copolymerized butyl acrylate with butadiene to prepare the rubber phase. 

Fig. 1. Tensile creep and recovery of rubber-modified plastics, showing axial strain (x), lateral contraction ( ), and volume strain (o) for ASA polymer and polypropylene copolymer at 20 °C...

Styrene/acrylonitrile copolymers are used for crockery, machine components, and monofilaments. They are made less breakable by the addition of l,4-ci5-poly(butadiene) (ABS polymer). ABS polymers are sensitive to sunlight and acid (weathering in exterior use), so for these purposes ASA polymers are more suitable, i.e., terpolymers of acrylic ester, styrene, and acrylonitrile. Terpolymers of methyl methacrylate, butadiene, and styrene (MBS polymers) are transparent, in contrast to ABS polymers. 

Because of the above oxidative chain scission reaction in PBD phase, ABS gradually loses its impact strength upon exposure to sunlight. The ASA polymers, on the other hand, retain their impact strength and toughness even after prolonged outdoor/UV exposure, significantly better than ABS, due to the presence of the weatherable acrylic elastomer phase, which replaces the unstable PBD phase. The outdoor/UV resistance of ASA and ASA-PC blend vs. ABS is schematically illustrated in Fig. 19.9a. 

Poly(vinyl chloride) + Poly(vinylchloride-co-acrylate) PVC + VC/A, Poly(vinyl chloride) + chlorinated Polyethylene PVC + PE-C, Poly(vinyl chloride) + Poly(acrylonitrile-co-butadiene-co-acrylester) PVC + ASA Polymer Blends III... 

There are two major producers of SAN for the merchant market in the United States, Bayer Corp. and the Dow Chemical Co., which market these materials under the names of Lustran and Tyril, respectively. Bayer became a U.S. producer when it purchased Monsanto s styrenics business in December 1995 (332). Some typical physical properties of these SAN resins have been shown in Table 11. These two companies also captively consume the SAN for the production of ABS as well as SAN-containing weatherable polymers. The other two U.S. SAN producers, either mainly consume the resin captively for ABS and ASA polymers (GE Plastics) or toll produce for a single client (Zeon Chemicals). BASF is expected to become a more aggressive SAN supplier in the United States since its Altamira, Mexico, stryenics plant came on-line in early 1999. Overall, U.S. SAN consumption has been relatively stable for the last few years, ranging from 43 x 10 to 44.5 x 10 t (95-98 million poimds) between 1994 and 1996. Most markets for SAN are growing at only GDP rates. Consumption growth for SAN in 1996-2001 is expected... 

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