Chain-ramification polymerization

Scheme 12. First, quantitative addition of to-furan functionalized PIB (A ), obtained from a simple reaction between living PIB and 2-BusSnFu, to living PIB (A) could be achieved in Hex/CH2Cl2 (40/60 v/v) at -80 °C in conjunction with TiCl4. The resulting living coupled PIB-Fu+-PIB was successfully employed for the subsequent chain ramification polymerization of MeVE. This technique has its unique ability to control A and A block length independently. Pure poly(IB-s-IB -s-MeVE) three-arm star-block copolymer was obtained upon purification of the crude product by column chromatography [87].

As a proof of the concept, an amphiphilic A2B2 star-block copolymer (A = PIB and B = PMeVE) has been prepared by the living coupling reaction of living PIB followed by the chain ramification polymerization of MeVE at the junction of the living coupled PIB as shown in Scheme 26.5 [136]. 

In contrast to ionic chain polymerizations, free radical polymerizations offer a facile route to copolymers ([9] p. 459). The ability of monomers to undergo copolymerization is described by the reactivity ratios, which have been tabulated for many monomer systems for a tabulation of reactivity ratios, see Section 11/154 in Brandrup and Immergut [14]. These tabulations must be used with care, however, as reactivity ratios are not always calculated in an optimum manner [15]. Systems in which one reactivity ratio is much greater than one (1) and the other is much less than one indicate poor copolymerization. Such systems form a mixture of homopolymers rather than a copolymer. Uncontrolled phase separation may take place, and mechanical properties can suffer. An important ramification of the ease of forming copolymers will be discussed in Section 3.1. 

Bamford43,59 63 has proposed a general treatment for solving polymerization kinetics with chain length dependent kt and considered in some detail the ramifications with respect to molecular weight distributions and the kinetics of chain transfer, retardation, etc. 

The first unequivocal proof of feasibility of homogeneous polymerization free of termination and chain-transfer was reported in 1956, and the concept of living polymers and its ramifications were fully developed in those publications 2). Although the initial work dealt with anionic polymerization of styrene and the dienes, the underlying ideas were soon applied by other workers to a great variety of polymeric systems, as shown by the brief review of some of those developed recently. 

We shall not attempt to review and compare critically various theories of liquid crystallinity in this chapter. Inasmuch as theory based on a lattice model has proved most successful in the treatment of liquid crystallinity in polymeric systems, we shall present an abbreviated account of that theory confined to its essential aspects. The versatility of this theory has permitted its extension to polydisperse systems, to mixtures of rodlike polymers with random coils and to some of the many kinds of semirigid chains. These ramifications of the theory will be discussed in this chapter... 

The living nature of ethylene oxide polymerization was recognized by Flory21, who conceived the ramifications of such a situation. However, the earlier studies of this reaction involved chain-transfer. The investigators added alcohol to the polymerizing solutions to solubilize the otherwise insoluble alkoxides and thus, the reaction... 

Polyoses are also polysaccharides, but with lateral chains and ramifications. Between 50 and 200 saccharide molecules are polymerized. Galactoglucomannan or 4-0-methylglucuronoxylan is the main constituent. The polyoses connect the polysaccharides with the lignin in the cell wall. They determine the swelling and shrinkage of wood. 

A new imidazole-based ionic polymer was synthesized by co-polymerization of alkyl-bis(imidazole)s and diiodoalkyls. The resultant polymer chains consisted of alkyl-imidazolium salts. The polymerization can be carried out in situ, and a DSSC prepared with this material presented efficiency of 1.3% under 100 mW cm of irradiation. Different ionic polymers containing the imidazolium cation in the main polymer chain,or as ramifications, have also been synthesized. Other ionic polymers based on different materials which can also be prepared by in situ polymerization have been applied in DSSC, presenting interesting results. ... 

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