Styrene iniferter polymerization

The Inifer technique enables us to fulfil some requirements of polymer architecture even in some radical processes. An amplified form may be applied, the Iniferter variant, where the radical initiator simultaneously acts as a transfer and terminating agent. Otsu et al. used sulphides and disulphides (tetraethylthiuram disulphide, PhSSPh, Ph2S, PhCH2SSCH2Ph) [96] and carbamates (benzyl-A,A-diethyldithiocarbamate, p-xylylene-A,7V-diethyl-dithiocarbamate) [97] in the photopolymerization of methyl methacrylate and styrene, and phenylazotriphenylmethane in the polymerization of methyl methacrylate [98]. Living radical polymerizations yield polymers with defined end groups or the required block copolymers. 

The free radical polymerization of styrene initialized by iniferter is influenced by chemical binding of iniferter on the surface of the silica." This reaction is used for grafting the polymer onto the surface of the silica. A similar approach is used when carbon whisker is incorporated during the graft-polymerization of methyl methacrylate. Depending on how the whisker is prepared, surface conversion can be increased up to twelve times compared to a polymerization with no whisker present. The addition of graphite to the poly esterification reaction doubles the molecular weight of the polymer. ... 

RAFT polymerizations with this iniferter of iV-butyl acrylate and styrene yielded polymers with M. / Mn equal to 1.15 and 1.16 respectively. Polymerization of methyl methacrylate, however, yielded a polymer with a broad Mw/M ratio. On the other hand, polymerization in the presence of CuBr/TMPA by ATRP exclusively through the bromine chain ends yielded a polymer with narrow ratio [282],... 

The transfer coefficients of disulfides are extremely low for styrene and methyl methacrylate (see Table 4), but are close to one for the vinyl acetate polymerization. In general the xanthogens and thiurams have higher chain transfer ability, which has been attributed to the iniferter mechanism described above. Monosulfides have lower transfer coefficients in comparison to disulfides. This may refiect steric factors and the relative strength of the C—S bond, which is significantly stronger than the S—S bond. 

Early attempts to realize the controlled radical polymerization of styrene involved the concept of reversible termination of growing polymer ehains by iniferters (initiation, trans/er, termination) [38]. These iniferters based on dithiocarbamates were the first species with photochemically labile C-S bonds. 

A broad spectrum of organic disulfldes has been employed as transfer agents. Among these are dialkyl, diaryl and diaroyl disulfides as well as xanthogens. For monomers such as styrene or methacrylates, transfer coefficients of disulfides are very low, but in the polymerization of vinyl esters they may come close to unity. For xanthogens and thiurams, transfer coefficients are usually higher than for disulfides, which is commonly explained by their iniferter capabilities. ... 

Thermal iniferters have been mainly used for the polymerization of methyl methacrylate. It was reported that polymerization of styrene with some thermal iniferters such as l,l,2,2-tetraphenyl-l,2-bis(phenoxy)ethane and tetraarylsc-cinonitriles proceeds via a dead-end polymerization mechanism, i.e., it does not follow living radical polymerization conditions. On the other hand, Jongh et al and Chernikova et al reported that some specially designed hexa-substituted-ethane derivatives can act as iniferters for styrene polymerization. 

Photolysis of (A, A -diethyldithiocarbamyl) methyl styrene leads to the initiating benzyl radical with the inactive diethyldithiocarbamate radical. This benzyl radical can add to the vinyl group of a second molecule of iniferter to produce a dimer. The dimer corresponds to an AB2 monomer with one polymerizable vinyl group and two initiating/propagating sites. By repeating these elementary reactions, this self-condensing vinyl polymerization system proceeds to form hyper-branched polymers (Scheme 3.10). 

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