Main Chain Hydrogen-Bonded Polymers

The pure bulk-phase behavior was studied on blends consisting of poly(acryhc acidj/hydroxypropyl cellulose [44], poly(2-vinylpyridine)/end-sufonic acid poly(styrene) [45], and poly(acryHc acid)/poly(N,N-dimethyl-acrylamide) [46]. Goh et al. [47,48] and others [49] have studied an interesting example of [60]fullerenated poly(2-hydroxyethyl methacrylate) with poly(l-vinylimidazole) or poly(4-vinylpyridine) or poly(styrene-co-4- 

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As pointed out by Griffin and coworkers, the production of main-chain, hydrogen-bonded polymers can be considered a step-growth process [49], with the number-average DP defined by the... 

At this point, it is worth mentioning that the possibility exists to assemble main-chain, hydrogen-bonded polymers from covalent polymers with sticky ends, that is, hydrogen-bonding telechelic polymers. For example, Lenz and coworkers have proposed that the liquid-crystalline behavior of... 

Shimizu LS. Perspectives on main-chain hydrogen bonded supramolecular polymers. Polym... 

Dynamic polymers containing main-chain hydrogen bonds have been studied extensively, among others thanks to their peculiar, but outstanding material properties. However, as the ultimate goal in DCC comprises temptation and isolation of particular sequences or conformations, we focus here on the kinetically more stable main-chain covalent polymers. 

Figure 8 Representative examples of main-chain, hydrogen-bonded, liquid-crystalline polymers [41,49-53].

When a chiral ansa-type zirconocene/MAO system was used as the catalyst precursor for polymerization of 1,5-hexadiene, an main-chain optically active polymer (68% trans rings) was obtained84-86. The enantioselectivity for this cyclopolymerization can be explained by the fact that the same prochiral face of the olefins was selected by the chiral zirconium center (Eq. 12) [209-211]. Asymmetric hydrogenation, as well as C-C bond formation catalyzed by chiral ansa-metallocene 144, has recently been developed to achieve high enantioselectivity88-90. This parallels to the high stereoselectivity in the polymerization. 

Alexander C, Jariwala CP, Lee CM, Griffin AC. Hydrogen-bonded main chain hquid crystalline polymers. Polym Prepr (Am Chem Soc Div Polym Chem) 1993 34 168-169. 

Cho et al. described the synthesis and polymerization of 4,8-cyclododeca-dien-l-yl-(4 -methoxy-4-biphenyl) terephthalate VIII [54,55]. Polymerization was carried out with WCl4(OAr)2/PbEt4. The double bonds in the polymer backbone were subsequently hydrogenated with H2/Pd(C), leading to a SCLCP with a fully saturated hydrocarbon backbone. This polymer system had a very flexible polymer backbone but a stiff connection between the main chain and the mesogenic unit. The distance between two adjacent side chains was about 12 methylene units. This very flexible main chain allowed the polymer to organize into a LC mesophase. Both polymers - the unsaturated and the saturated -showed smectic liquid crystalline mesophases with almost the same transition temperatures (see Table 5). 

Conjugated polymers differ from saturated polymers in that each carbon of the main chain is bonded to only three other atoms. The classic example is polyacetylene, (CH) , in which each carbon is cr-bonded to only two neighboring carbons and one hydrogen atom. The chemical structures of polyacetylene and some of the other most commonly studied conjugated polymers are shown in Fig. 

Binder W, Zirbs R (2007) Supramolecular polymers and networkswith hydrogen bonds in the main- and side-chain. In Binder W (ed) Hydrogen bonded polymers, vol 207. Springer, Berlin, pp 1-78... 

The same design principles used to describe hydrogen-bonded, liquid-crystalline polymers, may also be used to classify hydrogen-bonded polymers in isotropic solution. The first examples described herein are main-chain polymers constructed from ditopic monomers (Figure 7). 

Chain transfer reactions mostly proceed by abstraction of a monovalent atom such as hydrogen or a halogen. The scission of a bond carbon - oligovalent (e.g., H) atom is of interest for the introduction of endgroups into a polymer produced in a free radical reaction. Radically induced vinyl monomer polymerization with the possibility of chain transfer to a polymer of different chemical structure present in the reaction mixture leads to graft copolymers if bond scission occurs outside the main chain, no matter whether a single atom or a grouping is abstracted. Quite a different result is obtained if a radical attack involves a bond in the main chain of the polymer, if this bond scission occurs at a monovalent atom, which must be at the chain end, there is block copolymer formation. If bond scission occurs inside the polymer backbone, either block or random copolymers are produced [63]. 

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