Precursor polymers, living polymerization

A potential drawback of all the routes discussed thus far is that there is little control over polydispersity and molecular weight of the resultant polymer. Ringopening metathesis polymerization (ROMP) is a living polymerization method and, in theory, affords materials with low polydispersities and predictable molecular weights. This methodology has been applied to the synthesis of polyacctylcne by Feast [23], and has recently been exploited in the synthesis of PPV. Bicyclic monomer 12 [24] and cyclophane 13 [25) afford well-defined precursor polymers which may be converted into PPV 1 by thermal elimination as described in Scheme 1-4. 

This technique is based on the use of a linear polymer with pendant functional groups that can be activated to initiate the polymerization of a second monomer. Based on this definition, the linear precursor polymer can be considered as a multifunctional macromolecular initiator. The importance of the grafting from technique by cationic polymerization of the second monomer increased considerably with the advent of living cationic polymerization. The advantage is the virtual absence of homopolymer formation via chain transfer to monomer. 

The counter radical method can also be used for graft copolymer synthesis. Solomon et al. propose two routes [51]. The first one involves copolymerization with a functional monomer such as methacrylate containing pendant al-koxyamine. In the second route, the alkoxyamine is grafted onto a polymer precursor used in a second step to initiate the living polymerization of a second monomer. PBd-g-PMA is prepared this way from PBd. 

The dormant polymer is living in the sense that it grows until the monomer is depleted, and that it can grow on after additional monomer feed as in an ionic living polymerization.3 The final degree of polymerization is determined by the initial concentrations of the monomer and of the radical precursor Ro Y, and the formation of block copolymers is possible. 

Poly(para-phenylene) (PPP, 64) is insoluble and infusible and so films of PPP must be made by precursor routes (Scheme 6.19) [105]. The first of these, which was developed at ICI [106, 107], utilizes a radical polymerization of the diacetate 82 to produce a precursor polymer 83 that is thermally converted to PPP. This method produces PPP containing about 15% 1,2-linkages. A totally para-polymer can be made by the method of Grubbs involving the stereoregular nickel-catalyzed living polymerization of the bis(silyl ether) 84 to 85, and then its conversion to 83 [108-110],... 

In order to synthesize homopolymers by polymer analogous reactions, the reaction must go to 100% conversion. Hydrosila-tions of mesogenic olefins are the most common polymer analogous reactions used to prepare SCLCPs [199]. However, the precursor poly(methyl siloxane)s are generally not prepared by living polymerizations, nor do the hydrosilations readily go to comple-... 

SCLCPs have also been prepared by alkylation and/or quatemization of linear poly (ethylene imine)s [215, 216] and po-ly(4-vinylpyridine)s [217-223] with meso-genic alkyl halides or carboxylic acids. Although these precursor polymers can be prepared by controlled cationic [224] and anionic [225, 226] polymerizations, respectively, living polymerizations were either not used to prepare the SCLCPs, or the mo-... 

In another arm-first strategy, it is possible to use a precursor bearing multiple complementary functions (X) to those (Y) of the living chains (Scheme 27.3) [6, 12-14]. Representative multifunctional agents employed in such an arm-first star polymer synthesis by the different controlled living polymerization (CLP) techniques are shown in Figure 27.4. 

Similarly, stable macroanions obtained by the subsequent metalation of the proper end groups such as diphenylvinyl and diphenylmethoxy were used in the living polymerization of tBMA yielding PIB-l7-PtBMA block copolymers with almost quantitative efficiency (Scheme 35). Moreover, amphiphilic polymeric materials can be prepared by hydrolysis of ester moieties of the polymers obtained by this method for instance, amphiphilic PIB-I7-PMAA diblock was prepared by the hydrolysis of the acrylate segment of the suitable precursor copolymer. A series of linear and star copolymers consisting of PIB and PMMA were also prepared. ... 

The polydispersity index for precursor polymers prepared via the Durham route was only in the range of 1.8-2.8 [88]. Krouse and Schrock were able to improve on the metathesis ROMP method and prepared a series of acetylene block copolymers with success both in controlling the molecular weight and in achieving low polydispersity [82]. Compared to a living polymerization process, the well-controlled ROMP precursor polymers can be grown continuously... 

As in the case of anionic living polymerization, the ATRP polymerization allows the synthesis of polymer networks by the end linking process [303]. A difunctional initiator (bis(2-bromopropionyloxy)ethane) allowed the preparation of difunctional polymer precursors that can be used to prepare polymer networks with divinylbenzene-end linking. Divinylbenzene also gives access to a self condensing TEMPO functionalized AB monomer [304]. 

In conclusion, by overcoming the disadvantage of the previous synthetic methods for the preparation of hyperbranched polymers, we designed an all-new Seesaw-type macromonomer strategy to construct perfect hyperbranched model samples with uniform subchains. In onr stndy, we successfully prepared various kinds of Seesaw-type macromonomers, snch as homopolymers, triblock copolymers and diblock copolymers. Using these maCTomonomers as precursors, we have further prepared a series of perfect hyperbranched homopolymers, block copolymers, graft copolymers and hetero-snbchain copolymers by a combination of controlled/ living polymerization and click chemistry. Various solution properties of these novel hyperbranched (co) polymers in dilnte and semidilute solntions have been studied in detail. More specifically, the main achievements of this work are as follows ... 

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