Phosphorus-Modified Polymers

In commercial practice, the introduction of relatively small quantities of phosphorus into established polymers is at present of much greater importance than the synthesis of new polymers with high P content. The properties of conventional polymeric materials such as polyethylene, polystyrene and polyurethane may all be modified with advantage. 

The most important properties developed by many phosphorus-modified polymers are increased flame resistance and thermal stability (see below). Other claimed improvements include crease resistance, better uptake of dyestuffs, and rotproofing. 

Phosphorus-modified polymers may be achieved by the introduction of P-containing groups into the side chains by a phosphorylation reaction with a pre-formed polymer. Reaction of polyethylene or polypropylene with phosphorus trichloride and oxygen, for example, results in phosphorylation 

Side chain polyphosphonate polymers can be obtained from polystyrene by reaction with PCI3 and AICI3 (12.194) and from polyvinyl chloride by reaction with a trialkyl phosphite (12.195). Reaction with cross-linked varieties of polystyrene in (12.186) leads to the production of resins with cation exchange properties [24]. 

Esterifled phosphonate groups can be added to natural rubber by the action of dialkyl phospho-nates (12.196). Butadiene rubber will undergo free radical polymerisation in the presence of an organic peroxide in a reaction of type (12.197). Cross-linking can be induced by the action of P4S10, or R = allyl in the case of (12.198). 

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Per Perez, R. M., Sandler, J. K. W., Altstadt, V., Hoffmann, T., Pospiech, D., Ciesielski, M., Doring, M., Braun, U., Balabanovich, A. 1., Schartel, B. Novel phosphorus-modified polysul-fone as a combined flame retardant and toughness modifier for epoxy resins. Polymer 48 (2007) 778-790. 

Surface Characterization. Several analytical methods were used in characterizing the modified polymer surfaces. Energy Dispersive X-ray (EDX) spectra and electron micrographs of the surfaces were obtained using a JEOL JSM-IC848 scanning electron microscope in order to confirm the presence of phosphorus and chlorine. 

Modified polymer Maximum phosphorus content (wt%) Phosphorus group Thermal stability Charring increase Ref ... 

Introducing phosphorus-containing groups into the structure of polysulfone (either into backbone or main chain) the new modified polymers display high thermal stability with inherent flame retardant quality and could also be used as high temperature matrix resins and toughness modifiers in curable high performance epoxy resins. 

Synthetic resins, such as phenolic and cresylic resins (see PHENOLIC RESINS), are the most commonly used friction material binders, and are usually modified with drying oils, elastomer, cardanol [37330-39-5], an epoxy, phosphorus- or boron-based compounds, or even combinations of two. They are prepared by the addition of the appropriate phenol and formaldehyde [50-00-0] in the presence of an acidic or basic catalyst. Polymerization takes place at elevated temperatures. Other resin systems are based on elastomers (see Elastomers, synthetic), drying oils, or combinations of the above or other polymers. 

Price, D., Pyrah, K., Hull, T. R., Milnes, G. J., Ebdon, J. R., Hunt, B. J., and Joseph. P., Flame retardance of poly(methyl methacrylate) modified with phosphorus-containing compounds, Polym. Degrad. Stab., 2002, 77, 227-233. 

Moreover, the development of new strategies for surface modifications of nanoparticles with compounds having FR activity could provide a new field of research on FR systems. The use of novel phosphorus-, nitrogen-, or halogen-containing modifiers, instead of alkylammonium ions, for layered silicates seems promising. FR action conferred by the surface modifier can be combined with action due to composite morphology, particularly when the host polymer is a polymer blend instead of a pure polymer. 

Phosphorus FR compounds cover a wide range of chemical structures not only as additives incorporated in the molten state in thermoplastics but also as reactive components introduced as monomers in thermoset polymers phosphates, phosphonates, phosphinates, phosphine oxides, phosphites, red phosphorus, etc. They can be also used as layered silicate modifiers. Organic phosphates and red phosphorus are among the most frequent additive FRs used in various non-polyolefinic polymers. 

G. Chigwada and C.A. Wilkie, Synergy between conventional phosphorus fire retardants and organically-modified clays can lead to fire retardancy of styrenics, Polym. Degrad. Stabil., 2003, 80 551-557. 

B. Schartel, U. Knoll, A. Hartwig, and D. Ptttz, Phosphonium-modified layered silicate epoxy resins nanocomposites and their combinations with ATH and organo-phosphorus fire retardants, Polym. Adv. Technol., 2006, 17 281-293. 

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