Polymerisation charge-transfer

Fig. 20 Log EM for interaction of end-groups on polymer chains with average polymerisation degree 3c (i) pyridine-catalysed hydrolysis of the p-nitrophenyl ester group of [27] ( ) and [28] ( ) in aqueous solution (data from Sisido et at., 1976, 1978), (f i) intramolecular charge-transfer complexes of [29] in chloroform ( ) and in ethanol (O). (Data from Sisido et at., 1977 Takagi et at., 1977)...

Cochet M, Maser WK, Benitor A, Callejas A, Martinez MT, Benoit JM, Schreiber J, Chauvet O (2001). Synthesis of a new polyaniline/nanotube composite in-situ" polymerisation and charge transfer through site-selective interaction. Chem. Commun. 16 1450-1451. 

Another very instructive case concerns the alleged initiation of a cationic polymerisation by a charge-transfer complex formed by the compound chloranil (2,3,5,6-tetrachloroquinone) with the monomer N-vinyl-carb-azole. It was shown (Natsuume et al., 1969 1970) that this compound is not an initiator, but that the polymerisations were caused by a hydrolysis product, 2-hydroxy-3,5,6-trichloroquinone, which is a strong acid. One has learnt from this finding to be extremely suspicious of any claims for charge-transfer catalysis and to test one s suspicions by appropriate experiments involving progressive purification of the putative catalyst. 

The photolytic excitation of charge-transfer complexes is another recent addition to the available physical expedients to promote cationic polymerisation. The cation radicals generated by the photolysis have been characterised in some systems. More recent still is the use of ultraviolet radiation to induce the photolysis of substances whose photoproducts are initiators of cationic polymerisation. These processes will be discussed in Chap. Vin. 

The above survey does not include those systems in which polymerisation studies led the authors to conclude that complexes between the monomer and the Lewis acid must have formed prior to the appearencx of active species. We deliberately restricted our attention to investigations in which some direct evidence for complexation was offered. It can be concluded that while complexes between Lewis acids normally used in cationic polymerisation and aromatic hydrocarbons are common and readily observed, less information is available for simflar interactions with the olefinic double btMid because of the intrinsic difficulty arising from concurrent polymerisation. However, complexation (probably in the form of charge-transfer associations) seems to be the general behaviour rather than the exception, although its extent (relative strength of the complex) varies appreciably from system to system and is probably low for many olefins. 

Marek and Toman published a new brief study of the system VCI4-isobutene illuminated by visible monochromatic light (578 and 589 run) not absorbed by the Lewis acid on its own. Polymerisations occurred in bulk only when the system was illuminated. The authors concluded that initiation must have taken place following the exita-tion of the monomer-catalyst charge-transfer complex to give the isobutene radical-cation. 

Photoinitiated Addition Polymerisation Chromium (VI) ions undergo a photoredox process to give chromium (V) ions by a charge-transfer mechanism which involves the formation of active HCrO. ions that effectively initiate the photopolymerisation of acrylonitrile while 2,U,6-trimethylbenzoyldiphenylphosphine-... 

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. 

Radical polymerisation can be induced using the charge transfer complex formed between iV -ethoxy-p-cyanopyridinium hexafiuorophosphate and 1,2,4-... 

CTC decreases as polymerisation temperatures increase, furthermore, for the styrene-MA pair the charge-transfer complex should be non-existent above 130° C. However, alternating styrene-co-MA and other MA copolymers have been grafted on a variety of other polymeric materials (39,40,41). Our own results further confirm the contribution of CTC to general activation of the grafting reaction. It is important to note that the grafting efficiency... 

Iron-arene complexes are known to exhibit extremely high photoactivity as initiators. Quantum efficiencies have been found to be greater than I in the photopolymerisation of dicyanate esters. Phenylglycine derivatives have been found to be excellent co-synergists for the iron-arene complexes when used in conjunction with dyes and amines. Complexes of various types have also been proposed. Maleic anhydride-THF complexes have been used for the photopolymerisation of oligourethane acrylates while metal-ion complexes of spiropyran copolymers undergo reversible polymer precipitation. Azo and polyazo initiators have been used to make butadiene-isoprene block copolymers while charge-transfer complexes of morpholine-chlorine induce the radical polymerisation of methyl methacrylate. The presence of zinc chloride enhances the... 

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