Radical addition vinyl polymerisation

Additions to C=C are almost certainly the most important group of reactions involving radicals. This is due largely to the importance of addition (vinyl) polymerisation (p. 320), and the consequent extent to which its mechanism has been investigated but addition of halogens and of halogen hydracids is also of significance. 

Radical addition, 312-323 carbon tetrachloride, 320 halogens, 313 hydrogen bromide, 316 sulphenyl halides, 320 vinyl polymerisation, 320 Radical anions, 218 Radical rearrangements, 335 Radicals, 20, 30,299-339 acyl, 306, 330, 335 addition to 0==C, 313-323 alkoxyl, 303... 

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. 

Both the benzoyl and alkyl radicals initiate the polymerisation by addition to the monomer double bond. By contrast, the ketyl radical is inactive toward vinyl double bonds, so that initiation occurs through the H-donor radical. To be efficient, a photoinitiator must effectively absorb the radiation emitted by the light source... 

Water is the ideal solvent from the cost and pollution viewpoints, but it is a non-solvent for many surface coating polymers. It will ssolve a small number of homopolymers, notably those derived from acrylamide, acrylic acid, itaconic acid, vinyl methyl ether, vinyl pyrrolidone and vinyl sulphonic acid, but none of these homopolymers forms flexible films of use in the coatings industry. While copolymers of acrylic or methacrylic acids with acrylate esters are generally insoluble in water, their salts are soluble when the acid content is over 5% (for hydrophilic monomers) and 12% (for hydrophobic monomers). Such polymers can be prepared in solution, or in emulsion, but not in aqueous solution. This is because the acrylate esters are insoluble in water. The acid is copolymerised in the un-ionised form because the ion is unreactive to free radicals. In emulsion polymerisation, care has to be taken to avoid homopolymerisation of the acrylic or methacrylic acid in the water phase. Suppression of homopolymerisation requires a low concentration of acid throughout the polymerisation process. This can be achieved by using a long reaction period and slow addition of monomer mixture, or by careful pH buffer selection. 

Monomer addition under radical propagation conditions leads to mainly an atactic configuration. As a consequence, radical polymerisations of asymmetric vinyl polymers usually lead to amorphous materials. However, if the substituent is small enough to enter into the crystal cell, atactic vinyl polymers can crystallise (an example is poly(vinyl fluoride)). 

Several papers have appeared in the literature in recent years showing that certain metal acetylacetonates can function as initiators for the polymerisation of vinyl and diene monomers in bulk and solution (1 - 12). Results for the kinetics of bulk and solution polymerisation are consistent with the view that the reaction occurs by a free-radical mechanism. The usual free-radical kinetics are operative, but an unusual feature is that, in some cases, certain additives such as chlorinated hydrocarbons have an activating effect upon the reaction by inducing more rapid decomposition of the initiator (2,11,12,13). Other additives which have been reported as promotors for the polymerisation include pyridlne(14) and aldehydes and ketones(15). The complexity of the reaction in the presence of such additives is evident from the fact that chloroform has been reported to be an inhibitor for the poly-merlsatlon(3). 

The most important industrial applications of radical reaction to date are used for the manufacture of polymers. Around 108 tonnes (or 75%) of all polymers are prepared using radical processes. These are chain reactions in which an initial radical adds to the double bond of an alkene monomer and the resulting radical adds to another alkene monomer and so on. This addition polymerisation is used to make a number of important polymers, including poly(vinyl chloride) (PVC), polystyrene, polyethylene and poly(methyl methacrylate). Copolymers can also be easily prepared starting from a mixture of two or more monomers. These polymers have found widespread use as they possess a range of chemical and mechanical properties (such as strength and toughness). 

Why is radical polymerisation of vinyl chloride to give poly(vinyl chloride) described as showing a marked preference for head-to-tail addition ... 

One of the most common technologies for the synthesis of polymer polyols by a radical mechanism is based on the stepwise addition of a mixture of vinylic monomers (polyether polyol, initiator, transfer agent (mixture I)) to a second mixture (mixture II) of polyether polyol (identical with the polyether used for mixture I) and NAD (macromer or nonreactive NAD) under a nitrogen protective atmosphere, in the polymerisation reactor at 115-... 

Trapping Reactions with 2-t-Butylacrylic Acid Methylester XIV. This trapping reaction, which mimics the initiation step of the polymerisation process, has been used to obtain information on the reactivity of the primary radicals formed upon irradiation [ 1 ] [26]. Photolysis of BOMB in the presence of a threefold excess of XIV affords the benzoyl derivative XV in 87 % yield (Figure 9). Again VII was etlso isolated (64 %), whereas no stable addition product of -aminoalkyl radical could be identified. This result suggests that the benzoyl radical is mainly responsible for the polymerisation of vinylic monomers and is in agreement with previous studies on benzil ketals and benzoin ethers [ ]. But, as -aminoalkyl radicals have also been shown to initiate acrylate polymerization [ ], further investigations will be devoted to the elucidation of the role of this primary photoproduct in the overall polymerisation process. 

Near-IR spectroscopy (10000-4000/cm) was successfully used to monitor conversion dining conventional, anionic solution polymerisation of styrene and isoprene to homopolymers and block copolymers. The conversion of the vinyl protons in the monomer to methylene protons in the polymer was easily monitored under conventional (10-20% solids) solution polymerisation conditions. In addition to the need for an inert probe, high sampling frequencies were required since polymerisation times ranged from 5s in tetrahydrofuran to 20 minutes in cyclohexane. Preliminary data indicate that near IR is capable of detecting sequence distribution for tapered block copolymers, geometric isomer content, and reactivity ratios for free-radical copolymerisation. 20 refs. USA... 

Simal, F., Demonceau, A., Noels, A.F., Kharasch addition and controlled atom transfer radical polymerisation (ATRP) of vinyl monomers catalysed by Grubbs ruthenium-carbene complexes. Tetrahedron Lett. 1999, 40 5689-5693. 

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