Rubber-modified Polystyrene HIPS and SAN Copolymers ABS

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- 

Like HIPS, acrylonitrile-styrene-butadiene (ABS) polymers have polybutadiene rubber incorporated into styrene-acrylonitrile copolymer (SAN), giving a resin consisting of a two-phase system with inclusions of rubber in a continuous glassy matrix. Again, development of the best properties requires grafting between the glassy and rubbery phases. 

In rubber-modified polystyrenes, the rubber is dispersed in the polystyrene matrix in the form of discrete particles. The two-phase nature of rubber-modified polystyrene was first suggested by Buchdahl and Nielsen [47] based on data on dynamic mechanical properties obtained with a torsion pendulum. The existence of two prominent loss peaks led to this conclusion, one at low temperatures which is due to the a relaxation of the rubber (e.g. 193 K for polybutadiene) and one at high temperatures which is due to the a relaxation of the matrix (e.g. 373 K for polystyrene). Later, microscopy provided proof of the existence of the rubber phase as a discrete dispersed phase in polystyrene [48]. 

The morphology of the rubber-modified polystyrenes system involves some complex aspects, such as particle size, size distribution, occlusions of polystyrene inside the rubber phase, interfacial bonding between the rubbery particles and the brittle matrix, etc. Many authors have observed that some of the most important factors in controlling the mechanical properties of HIPS and ABS are rubber particle size [49], volume fraction of the rubbery phase (rubber + occluded polystyrene) [50,51] and the degree of graft [52]. Grafting occurs during the polymerization of styrene when some of the free radicals react with the rubber 

There is a relatively sharp drop in storage modulus corresponding to the a relaxation of the rubber phase. At temperature above the Tg of the rubber, the storage modulus of the rubber becomes negligible compared with that of the rigid matrix, and the modulus of the composite is due solely to the matrix. Under these conditions, the system can be described by the modified Kerner equation [12,53]  

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