High Impact Poly styrene

Poly(styrene) (PS) belongs to the largest volume thermoplastic resins (1). Unmodified PS is well suited to applications, where its brittleness is acceptable. In contrast, certain engineering plastics have been used in applications, where less brittleness is required. 

However, such alternative polymers are often too expensive or they have too superior properties, e.g., other than less brittleness that are not needed for the particular application. For these reasons, a good solution is to start with styrene-based copolymers, and to modify them accordingly (2). 

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On the other hand, high impact poly(styrene) (HIPS), ABS, acrylonitrile-ethylene-propylene-based rubber/styrene copolymer resin (AES), acrylonitrile/acryl-based rubber/styrene copolymer resin (AAS) show excellent impact strengths, but these resins are inferior in chemical resistance and abrasion resistance. 

High impact poly(styrene) (HIPS) is sometimes also accessed as TPS, which stands for toughened PS. 

Various patents on the homopolymerization of BD in the presence of styrene are available [581-590]. According to these patents, St is used as a solvent in which BD is selectively polymerized by the application of NdV/DIBAH/EASC. At the end of the polymerization a solution of BR in St is obtained. In subsequent reaction steps the unreacted styrene monomer is either polymerized radically, or acrylonitrile is added prior to radical initiation. During the subsequent radical polymerization styrene or styrene/acrylonitrile, respectively, are polymerized and ris-l,4-BR is grafted and partially crosslinked. In this way BR modified (or impact modified) thermoplast blends are obtained. In these blends BR particles are dispersed either in poly(styrene) (yielding HIPS = high impact poly(styrene) or in styrene-acrylonitrile-copolymers (yielding ABS = acrylonitrile/butadiene/ styrene-terpolymers). In comparison with the classical bulk processes for HIPS and ABS, this new technology allows for considerable cost reductions... 

As mentioned extensively, PPE is not mainly used as such, but in polymeric blends and copolymers to faciUtate the fabrication. Some of these copolymers act also as impact modifiers for example, block copolymers built from styrene, ethylene, butylene, and propylene. Naturally, the impact can be improved by using high impact poly(styrene) (HIPS) instead of ordinary PS in blends. Other impact modifiers include rubbery materials, such as poly(octenylene), and ethylene propylene diene monomer rubber. 

Figure 11-10. Bagley plot of a high-impact poly(styrene) at 189° C at shear gradients of 10, 100, 1000, and 4000 s" from measurements with capillaries of / = 1 mm in diameter ( ) ox R = 0.6 mm (O) and different lengths L. (After BASF.)...

Considerable quantities of styrene are used in producing copolymerisates and blends, as, for example, in the production of copolymers with acrylonitrile (SAN), terpolymers from styrene/acrylonitrile/butadiene (ABS polymers) or acrylonitrile/styrene/acrylic ester (ASA), etc. The glass transition temperature of poly (styrene), 100 C, can be increased by copolymerization with a-methyl styrene. What are known as high impact poly (styrenes) are incompatible blends with poly(butadiene) or EPDM, which are consequently not transparent, but translucent. For this reason, pure poly (styrenes) are occasionally called crystal poly (styrenes). 

Figure 35 4. Loss modulus, C, as a function of temperature for a poly(buta-diene) elastomer produced by emulsion polymerization, E>BR, an E>BR grafted with styrene E-Br-g-S, a poly(styrene), PS, and a high-impact poly(styrene) produced by in situ polymerization of styrene in a solution of E-BR in styrene, HIPS. The peaks give the dynamic glass transition temperatures. (After data by H. Willersinn.)...

Figure 35-9. Multiphase systems in the in situ production of high-impact poly(styrene) by the free radical polymerization of a styrene>c/5-poly(butadiene) solution. (After S. L. Aggarwal and R. A. Livigni.)...

Figure 35-12. Tensile stress-strain curves for poly(styrene), PS, and high-impact poly(styrene), HIPS, at 20 C. The arrows indicate the onset of a whitish coloration. (After C. B. Bucknall.)...

The commercial names of polymers do not always fulfill what they promise. Not only more or less branched homopolymers of various molar masses are encountered under the name, poly(ethylene), but also copolymers of ethylene with propylene, butene-1, etc. Commercially, not only the homopolymers of styrene are included under the poly(styrene) designation, but also copolymers with acrylonitrile (SAN), blends of poly(styrene) with various elastomers (HIPS = high impact poly(styrene)) and graft copoly-mers-blends of acrylonitrile, butadiene, and sytrene. The styrene monomeric unit is the main component in all of these polymers thus, these polymers are all included in the poly(styrene) family, although their properties can differ from each other (Table 36-4). 

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