Polymerisation free-radical addition

Free-Radical Addition. In free-radical addition polymerisation, the propagating species is a free radical. The free radicals, R-, ate most commonly generated by the thermal decomposition of a peroxide or aso initiator, 1 (see Initiators, free-RADICAl) ... 

Elementary Kinetics of Free-radical Addition Polymerisation... 

Elementary kinetics of free-radical addition polymerisation 29... 

Initiation reactions are usually started by an active free radical such as peroxide (-0-0-), e.g. benzoyl peroxide is a good inititator for the free radical addition polymerisation of styrene to produce polystyrene AICI3 is an initiator for the cationic addition polymerisation of isobutylene to form isobutyl synthetic rubber or azobisiso-butyronitrile compounds (-N=N-) (abbreviated to AIBN). Propagation reactions are the continuing process and, eventually, lead to the termination stage that occurs by combination or disproportionation. This usually occurs when the free radicals combine with themselves and signals the end of the polymerisation process. All polymers formed by this process are thermoplastics. Table 4.1 is a list of common polymers prepared by the addition process. 

As commercially available polymers have p = 1, the ratio of M /Mn = 2. There is no such simple theory for addition polymerisation. If there are a number of different types of polymerisation sites on a catalyst used for free radical addition polymerisation, the MWD can be very broad, while singlesite catalysts can produce narrow MWDs. 

Polymers can be formed from compounds containing a c=c double bond. Alkenes, such as ethene, can undergo addition polymerisation to form a polymer. A polymer is a compound consisting of very long chain molecules built up from smaller molecular units, called monomers. The polymerisation of ethene, to form poly(ethene), is a free radical addition reaction. 

This work describes a new type of monolithic support offering a highly interconnected permanent porosity possessing pendant double bond. This support may provide a better accessibility to active sites and allows the use of a wider range of solvents than classical gel type beads prepared by suspension polymerisation. The free radical addition of functional thiols led to the production of functional supports (acid, ester, alcohol, amine, thiol...). 

Conversely, when the rate of propagation is faster than chain transfer, products arising from telomerisation and polymerisation are formed in greater concentration. In this section, free-radical addition to fluoroalkenes will be dealt with first, in order to establish... 

Diethyl vinyl phosphate can be co-polymerised with styrene, methyl methacrylate or acrylonitrile monomers by free radical addition, using benzoyl peroxide (12.84). Alternating or block-type polymers are presumably possible. 

Free radical chain polymerisation is the method used to prepare the most common polymers. A free radical is generated and reacts with one molecule of monomer (initiation). Then monomer molecules react with this first species, leading to formation of a long chain by successive additions of monomer (propagation). Finally, chains are terminated by reaction of two chains bearing radicals (termination). As radicals are very reactive species, side reactions are likely to occur and modify the simple process (transfer). 

Interesting research on the dynamic mechanical and thermal properties of fire-retardant high-impact polystyrene (HIPS) is published by Chang and co-workers [19]. HIPS may be produced by the free-radical chain polymerisation of styrene in the presence of an unsaturated elastomer. The authors showed that the melting point of the additive in relation to the processing temperature of the thermoplastics and the compatibility of the additive with the polymer phases are the two important variables governing the interaction of additive with polymer matrix. 

Huang and co-workers [191] investigated the effects of a nonionic surfactant, Triton X-100, on the laccase-catalysed conversion of bisphenol A. It was found that the addition of Triton X-100 into the reaction system increased the conversion of bisphenol A (BPA), especially near the critical micelle concentration of Triton X-100. In addition, it was fonnd that the stability of laccase was greatly improved in the presence of Triton X-100 and the binding of Triton X-100 to the laccase surface also mitigated the inactivation effect cansed by the free radicals and polymerisation products. Under otherwise identical conditions, a lower dosage of laccase was needed for the higher conversion of BPA in the presence of Triton X-100. 

All these observations can be rationalised by assuming the mechanism of polymerisation to be similar to free-radical addition of thiols to olefins as outlined next. 

The subject of dispersion polymerisation in organic media has been comprehensively reviewed (Do This reference should be consulted for a detailed treatment of the theory of particle stabilisation and the kinetics and mechanism of free radical dispersion polymerisation in organic mediae In this paper, emphasis is placed on the more practical aspects of preparing polymer latexes and on useful empirical rules for newcomers to the field wishing to make their own latexeSc Processes for the preparation of latexes by addition and condensation polymerisation and by inverse emulsification of aqueous monomer solutions in organic liquids are reviewedo... 

The monomers are added to the solution of epoxy in order that a free radical initiated polymerisation can take place in the presence of the epoxy. The grafting of the addition polymer onto the aliphatic carbons of the epoxy, takes place during this polymerisation stage. 

ESBR and SSBR are made from two different addition polymerisation techniques one radical and one ionic. ESBR polymerisation is based on free radicals that attack the unsaturation of the monomers, causing addition of monomer units to the end of the polymer chain, whereas the basis for SSBR is by use of ionic initiators (qv). 

In a simple free-radical-initiated addition polymerisation the principal reactions involved are (assuming termination by combination for simplicity)... 

A certain free-radical polymerisation reaetion is described by the following sequence of initiation, addition and termination... 

The initiation of polymerisation takes place in two steps The decomposition of initiator to form the free radical and the addition of the radical to the monomer with the generation of another radical. If the radical produced by decomposition of the initiator, I, is designated as R, then the process of initiation could be shown as under ... 

When free radical initiation is because of the addition of the radical to one end of the double bond, then we may expect that the radical would be attached to the end of the Polymer chain. The presence of such end fragments of the initiator has been confirmed for radical polymerisations and with several monomers by endgroup analysis. 

The second common method of synthesising polymers (Fig. 5.3) is chain (addition) polymerisation. The most common type of addition polymer is based on ethene CH2 = CHj in which the monomer contains at least one double (tt) bond which on being activated, by free radical attack say, opens up to produce two single sigma bonds and the homopolymer poly(ethene). (Note in Fig. 5.3 the resultant polymer backbone is joined together by carbon-carbon bonds, unlike the condensation polymer systems (Fig. 5.1).)... 

In the presence of an organic peroxide Initiator, the alkenes and their derivatives undergo addition polymerisation or chain growth polymerisation through a free radical mechanism. Polythene, teflon, orlon, etc. are formed by addition polymerisation of an appropriate alkene or Its derivative. Condensation poiymerisation reactions are... 

Polymerisa- tn chain length or chain growth can take place through the formation of either free radicals or ionic species. However, the free radical governed addition or chain growth polymerisation is the most common mode. 

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