High impact polystyrene HIPS graft copolymer

The term graft copolymer is used to describe copolymers with long sequences of another monomer (comonomer) as branches on the main polymer chain. Most commercial varieties of high-impact polystyrene (HIP) and copolymers of acrylonitrile, butadiene, and styrene (ABS) are graft copolymen in which the main polymer chain is polybutadiene and the branches are styrene, or styrene and acrylonitrile. Figure 1.12 shows various types of copolymers. 

Rubber is incorporated into polystyrene primarily to impart toughness. The resulting materials consist of a polystyrene matrix with small inclusions of the rubber (usually 5-10wt% polybutadiene or copolymer rubber). They are termed high-impact polystyrene (HIPS). Grafting of the rubber to the polystyr-... 

Although this method yields a mixture of homopolymer and graft copolymer, and probably also ungrafted backbone polymer, some of the systems have commercial utility. These are high-impact polystyrene (HIPS) [styrene polymerized in the presence of poly(l,3-buta-diene)], ABS and MBS [styrene-acrylonitrile and methyl methacrylate-styrene, respectively, copolymerized in the presence of either poly(l,3-butadiene) or SBR] (Sec. 6-8a). 

High Impact Polystyrene (HIPS) HIPS is a heterogeneous material produced by continuous bulk or bulk-suspension processes, in which a butadiene-based elastomer (polybutadiene (PB), or a block copolymer of styrene-butadiene) is first dissolved in styrene monomer (St) and the resulting mixture is then heated so that the polymerization proceeds either thermally or with the aid of a chemical initiator. At the molecular level, the product is a mixture of free polystyrene (PSt) chains and elastomer chains grafted with PSt side chains. The process yields a continuous (free) PSt matrix containing... 

High impact polystyrene (HIPS) is an opaque material that has added butadiene rubber, partially as a blend and partially as a graft copolymer, to improve impact resistance. 

A graft polymer chain (Fig. 4c) has a linear backbone and randomly distributed side chains. The side chains (which can be very long) are structurally distinct from the main chain but can be homopolymers or copolymers. A well-known example of a graft polymer is high-impact polystyrene (HIPS), where polybutadiene (PB) side chains are grafted to the PS backbone. 

High-impact polystyrene (HIPS) is a graft copolymer. It is a PS backbone with chains of polybutadiene grafted onto the backbone. PS gives the material strength, but the rubbery polybutadiene chains give resilience to make it less brittle. 

Acrylonitrile is also commonly found in impact modifiers, such as the acrylonitrile-butadiene-styrene (ABS) type, produced by emulsion polymerisation. Polybutadiene seed latex particles are grafted onto styrene and acrylonitrile in a seeded emulsion polymerisation process. As the styrene-acrylonitrile copolymer shell forms, polybutadiene domains are spontaneously separated within. The resulting impact modifier particles are subsequently compounded with polystyrene to product high impact polystyrene (HIPS). The impact modification properties of the latex particles may be optimised through varying the butadiene content, the particle size and structure, and the shell molecular weight. A basic formulation for an ABS impact modifier is given in Table 6. 

These structures are illustrated in Figure 1.3. Through the leadership of Amos and others, polymer blends and grafts found uses as rubber-toughened plastics, which include high-impact polystyrene (HiPS) and acrylonitrile-butadiene-styrene (ABS) plastics. As further illustrated in Table 1.1, block copolymers containing a water-soluble block and an oil soluble block became important as surfactants through the work of Lunsted, while other block copolymers, composed of elastomer and plastic blocks, were useful as thermoplastic elastomers. 

Atactic polystyrene is sometimes known as general-purpose polystyrene (GPPS). There are other commercial grades of polystyrene, such as medium-impact polystyrene (MIPS) and high-impact polystyrene (HIPS). These impact-resistant forms of polystyrene are specially formulated by grafting to a rubber, such as polybutadiene or a styrene-butadiene copolymer, and dispersed in the base polystyrene. The inclusion and detection of small amounts of butadiene-based materials into the base polystyrene has been discussed. 

Butadiene (CH2=CH—CH=CH2) and styrene, two monomers listed in Table 25.1, can form a block copolymer called poly(styrene-butadiene-styrene) or SBS rubber [Figure 25.6(a)], in which there are alternating blocks of polybutadiene and polystyrene. They also form a graft polymer known as high-impact polystyrene (HIPS) [Figure 25.6(b)], in which chains of polybutadiene branch off of the main polystyrene chain. 

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