Initiation styrene polymerisation

The styrene-diene triblocks, the main subject of this section, are made by sequential anionic polymerisation (see Chapter 2). In a typical system cc-butyl-lithium is used to initiate styrene polymerisation in a solvent such as cyclohexane. This is a specific reaction of the type... 

An alternative method of initiating styrene polymerisation depends on the addition of free radical generators. Various eatalysts are used at different temperatures depending on their rates of decomposition, but only peroxides are used extensively in industrial production processes. Other classes of initiators are usually either not readily available or not stable enough imder the conditions of st5rene polymerisation. 

Organic peroxides are used in the polymer industry as thermal sources of free radicals. They are used primarily to initiate the polymerisation and copolymerisation of vinyl and diene monomers, eg, ethylene, vinyl chloride, styrene, acryUc acid and esters, methacrylic acid and esters, vinyl acetate, acrylonitrile, and butadiene (see Initiators). They ate also used to cute or cross-link resins, eg, unsaturated polyester—styrene blends, thermoplastics such as polyethylene, elastomers such as ethylene—propylene copolymers and terpolymers and ethylene—vinyl acetate copolymer, and mbbets such as siUcone mbbet and styrene-butadiene mbbet. 

Another useful, and quite sensitive, test is the initiation of polymerisation (c/ p. 320). Polymerisation can be initiated, in suitable substrates, by cations and anions as well as by radicals, but the effect of these several species can be differentiated by using a 50/50 mixture of phenylethene (styrene), PhCH=CH2, and methyl 2-methyl-propenoate (methyl methacrylate), CH2=C(Me)C02Me, as substrate cationic initiators are found to produce polystyrene only, anions polymethyl methacrylate only, while radicals produce a copolymer containing equal amounts of the two monomers. 

List C contains peroxidisable monomers, where the presence of peroxide may initiate exothermic polymerisation of the bulk of material. Precautions and procedures for storage and use of monomers with or without the presence of inhibitors are discussed in detail. Examples cited are acrylic acid, acrylonitrile, butadiene, 2-chlorobutadiene, chlorotrifluoroethylene, methyl methacrylate, styrene, tetraflu-oroethylene, vinyl acetate, vinylacetylene, vinyl chloride, vinylidene chloride and vinylpyridine [1]. 

Technical Information, Polystyrene Initiators for Styrene Polymerisation, Akzo Chemie, Deventer, the Nethedands, Nov. 1985. 

Recently, Mengoli and Vidotto restudied these systems and obtained evidence for a direct addition reaction in the initiation of the polymerisation of isobutylvinyl ether by the radical cation perchlorate of 9,10-dijiienylanthracene. The kinetics of styrene polymerisations by the above initiator in nitrdienzene at 10°C were also studied. Important termination reactions giving indanyl-type cations were detected and attrSmt-ed to the perchlorate anion. This system was in fact found to display many similarities with that involving the same monomer and perchloric acid ... 

Hallensleben andMoller ) prepared block copolymers of styrene and polyesters by mixing the latter with monomeric styrene in methylene chloride and adding BF3 Et20. The authors claimed that growing polystyrene chains transferred to the polyesters to give dialkoxycarbenium ions capable of initiating the polymerisation of styrene to give block copolymers. 

It is well known that several monomers,such as styrene, < ( methylstyrene,isoprene,vinyl acetate (jj) have shown formation of oharge-transfer complexes in the presence of oxygen. Polystyrene peroxide is formed by photoirradiation of charge-transfer complex in the initial stage of polymerisation and the further photoinduced decomposition of the polystyrene peroxide initiates the polymerisation of styrene. On the other way,the reaction between excited state of styrene and oxygen may induce the formation of an alternating copolymer with peroxide groups -0-0- in-backbone. 

Details A gas, an initiator for polymerisations (ethylene, vinyl and styrene). 

The time-dependent evolution of the polymerisation and copolymerisation reactions of styrene/unsaturated polyester resin was characterised using optical levitation with Raman spectroscopy (135). The n-butyllithium-initiated anionic polymerisation of styrene in ethylbenzene was measured using Raman spectroscopy (214). 

Emulsion polymerisation is characterised by the fact that a free radical initiator (usually water-soluble) is used to polymerise free radically polymerisable monomers to give a water-insoluble polymer. The main ingredients of an emulsion polymerisation system include monomer, dispersant, emulsifier and initiator. Water is often used as the dispersant. A water-insoluble monomer can be dispersed in water by means of an oil-in-water emulsifier and polymerised with a water-soluble initiator. Styrene, MMA and VA are systems for which emulsion polymerisation are commonly used. 

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