Polymerization mass HIPS

The grafting is accomplished in the commercial mass polymerization process by polymerizing styrene in the presence of a dissolved rubber. Dissolving the elastomer in the styrene monomer before polymerization produces HIPS grades. Since the two polymer solutions are incompatible, the styrene-rubber system phase separates very early in conversion. Polystyrene forms the continuous phase, with the rubber phase existing as discrete particles having occlusions of polystyrene. Different production techniques and formulations allow the rubber phase to be tailored to a wide range of properties. Typically ... 

Table I provides an overview of general reactor designs used with PS and HIPS processes on the basis of reactor function. The polymer concentrations characterizing the mass polymerizations are approximate there could be some overlapping of agitator types with solids level beyond that shown in the tcd>le. Polymer concentration limits on HIPS will be lower because of increased viscosity. There are also additional applications. Tubular reactors, for example, in effect, often exist as the transfer lines between reactors and in external circulating loops associated with continuous reactors.

Various reactor combinations are used. For example, the product from a relatively low solids batch-mass reactor may be transferred to a suspension reactor (for HIPS), press (for PS), or unagitated batch tower (for PS) for finishing. In a similar fashion, the effluent from a continuous stirred tank reactor (CSTR) may be transferred to a tubular reactor or an unagitated or agitated tower for further polymerization before devolatilization. 

Because of the difficulties of presses with HIPS cited earlier, it is usual to transfer the syrup to a suspension reactor containing water and a suspending agent for the completion of polymerization. Design problems for suspension reactors will be discussed in the next section. Design problems for HIPS prepoly batch-mass reactors are analogous to HIPS continuous reactors as discussed in Section 2.3. 

Access to Practice. Publications and patents on the batch mass process are limited. Bishop s book CD contains the most detailed description of the polymerization press and mass-suspension processes for PS and HIPS. Fong (16) presents an economic analysis of the press process based on Bishop s description. Patent references are few for the batch-mass process the 1939 Bakelite patent on transfer of prepoly syrup to chambers or containers is of historical interest (17). 

Suspension Polymerization. Suspension polymerization probably remains the most widely practiced method of producing PS. It can also be used to produce HIPS. To improve quality of the latter, however, a batch-mass prepolymerization of the rubber syrup is normally carried out first the syrup is then suspension polymerized to completion. 

Because PS is brittle with little impact resistance under normal operating conditions, early work was done to impart impact resistance. The best known material from this work is called HIPS, which is produced by dispersing small particles of BR in with the styrene monomer. Bulk or mass polymerization of the styrene is begun producing what is referred to as... 

Through polymerization of a styrene rubber solution, one obtains SB mass (styrene-butadiene). SB forms a twophase system in which the styrene is the continuous phase and the rubber, usually a butadiene base, is the discontinuous phase. The rubber phase also contains pockets of styrene. The SB polymer, because of its properties, is also known as impact resistant or high impact PS (HIPS). 

A number of important commercial resins are manufactured by suspension polymerization, including poly(vinyl chloride) and copolymers, styrene resins [general purpose polystyrene, EPS, high impact polystyrene (HIPS), poly(styrene-acrylonitrile) (SAN), poly(acrylonitrile-butadiene-styrene) (ABS), styrenic ion-exchange resins], poly(methyl methacrylate) and copolymers, and poly(vinyl acetate). However, some of these polymers rather use a mass-suspension process, in which the polymerization starts as a bulk one and, at certain conversion, water and suspending agents are added to the reactor to form a suspension and continue the polymerization in this way up to high conversions. No continuous suspension polymerization process is known to be employed on a... 

As has been seen in Table 4.1, the polymer microstructure influences the application properties of the polymer, such as melt flow index (MFI). The MFI is the mass flow rate [in g (10 min) ] of a HIPS melt that flows through a capillary, when forced by a piston loaded by a constant weight. It indicates the processability of the polymer and it is an important quality control variable in the polymerization process. MFI mainly depends... 

Acrylonitrile-Butadiene-Styrene Polymer. The name acrylonitrile-butadiene-styrene (ABS) polymer is reserved for a family of thermoplastics with the SAN matrix containing dispersed elastomer particles.The oldest approach to the ABS preparation, similarly as in the case of HIPS, is mechanical blending of individual components. At present the graft polymerization of a mixture of styrene with acrylonitrile in the presence of a suitable rubber component is the current process of ABS polymer manufacture. Most producers employ some form of emulsion technology, but the mass or mass-emulsion polymerization is also technologically feasible (60,272). 

In the continuous mass polymerization of acrylonitrile butadiene styrene (ABS) and high impact polystyrene (HIPS), the thermal polymerization of styrene and alpham-ethyl-styrene is of increasing concern [3]. Scale-up issues remain, especially for the... 

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