Polyphenylenes blending with other polymers

Polystyrene is one of the most widely used thermoplastic materials ranking behind polyolefins and PVC. Owing to their special property profile, styrene polymers are placed between commodity and speciality polymers. Since its commercial introduction in the 1930s until the present day, polystyrene has been subjected to numerous improvements. The main development directions were aimed at copolymerization of styrene with polar comonomers such as acrylonitrile, (meth)acrylates or maleic anhydride, at impact modification with different rubbers or styrene-butadiene block copolymers and at blending with other polymers such as polyphenylene ether (PPE) or polyolefins. 

The general motivation for blending styrenic resins with other polymers, particularly with the higher priced engineering resins, such as polycarbonate or polyphenylene ether, is primarily to lower the cost and improve the processability of the latter resins. As far as styrenic resins are concerned, some of the reasons for blending stem from the need to improve their property deficiencies, viz. solvent resistance, impact strength, heat resistance and flame resistance. 

During the last 40 years, ABS blends with most polymers have been patented. For example, wdth PVC in 1951, PC (introduced in 1958) in 1960, polyamide (PA-6) a year later [Grabowski, 1961a], polysulfone (PSF) in 1964, CPE in 1965, PET in 1968, polyarylether sulfone (PAES) and styrene-maleic anhydride (SMA) in 1969 (the blend is one of two resins called high heat ABS — the other being ABS in which at least a part of styrene was replaced with p-methylstyrene), polyethersulfone (PES) in 1970, polyarylates (PAr) in 1971, polyurethane in 1976, polyarylether (PPE or PAE) in 1982, with polyphenylene sulfide (PPS) in 1991, etc. 

In polymers such as polystyrene that do not readily undergo charring, phosphoms-based flame retardants tend to be less effective, and such polymers are often flame retarded by antimony—halogen combinations (see Styrene). However, even in such noncharring polymers, phosphoms additives exhibit some activity that suggests at least one other mode of action. Phosphoms compounds may produce a barrier layer of polyphosphoric acid on the burning polymer (4,5). Phosphoms-based flame retardants are more effective in styrenic polymers blended with a char-forming polymer such as polyphenylene oxide or polycarbonate. 

An efficient flame retardant effect was demonstrated with 2-mil zinc coatings on polyphenylene oxide-polystyrene blends (Notyl) by Nelson (21). The action may relate to enhanced char formation by chemistry specific to this blend. However, other metal coatings on some other polymers also appeared to contribute a measurable flame retardant effect. 

Polymer blends can be subdivided into two kinds those of compatible and those of incompatible polymers. Real compatibility is an exception (see 9.1) an example is PS with PPE (polyphenylene ether, also called PPO, polyphenylene oxide). These two polymers can be blended with each other on such a small scale that it really looks like molecular miscibility. This blend shows, therefore, only one single glass transition. 

As discussed by Dr. A. S. Hay, polyphenylene oxide was extremely difficult to mold but a chance discovery of blends with polystyrene, made the commercialization of this Important polymer feasible. The development of heat resistant polysulfones and polyaryletherketones are excellent examples of the application of good Industrial research chemistry. Fortunately, the stories of these and other developments are told by the clever scientists who were responsible for these dramatic breakthroughs in polymer science. 

The advances in polymer blending and alloying technology have occurred through three routes (1) similar-rheology polymer pairs, (2) miscible polymers such as polyphenylene oxide and polystyrene, or (3) interpenetrating polymer networks (IPNs). All these systems were limited to specific polymer combinations that have an inherent physical affinity for each other. However with... 

Several flexible polymers, such as natural rubber (NR) synthetic rubber (SR) polyalkyl acrylates copolymers of acrylonitrile, butadiene, and styrene, (ABS) and polyvinyl alkyl ethers, have been used to improve the impact resistance of PS and PVC. PS and copolymers of ethylene and propylene have been used to increase the ductility of polyphenylene oxide (PPO) and nylon 66, respectively. The mechanical properties of several other engineering plastics have been improved by blending them with thermoplastics. 

To the range of engineering plastics were added polyethylene and polybutylene tereph-thalates (PET and PBT), as well as General Electric s polyethers, the PPO (polyphenylene oxide) produced through polymerization of 2,6-xylenol and the Noryl plastic produced by blending PPO with polystyrene. Other special polymers, derived like the polycarbonates from bisphenol A, were added to this range polyarylates, polysul-fones, polyetherimides. 

Polymer Blends. Blending of polymers with each other accounts for approximately 40 percent of the present plastics market, and the practice is growing continually, because it permits the development of improved properties without the cost of inventing new polymers. When polymers are fairly miscible, as in the polyethylenes, and in polyphenylene ether plus polystyrene, blending can be used to produce intermediate properties and balance of properties. Most polymer blends... 

Sometimes certain materials need some properties from one polymer and some from another polymer. Rather than synthesizing a brand-new polymer with aU of the desired properties, two polymers can be melted together to form a blend polymer that possesses some of the properties of each constituent. Polystyrene and polyphenylene oxide that actually mixes well is one example of a blended polymer. Other examples are PET with polybutylene terephthalate and poly(methyl methacrylate) withpolyvinylidene fluoride. 

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