Polymer main-chain

Recently, several groups have focused on the preparation of water-soluble Ceo-star polymers as potential photochemotherapeutic agents for the photodynamic therapy of cancer [45]. 

Owing to the low control of the double-addition to C ) that leads to eight possible isomers, and the difficult preparation of pure bis-adducts, this class of compounds has been perhaps the least explored among all the polyfullerenes (Chapter 2). 

Nevertheless, a series of water-soluble poly(fullerocyclodextrin)s has been prepared that shows good performances as a DNA-cleaving agent [46]. 

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Fig. 14. Main-chain polymer Hquid crystal phases (a) nematic, (b) smectic.

Dobb, M. G. and McIntyre, J. E. Properties and Applications of Liquid-Crystalline Main-Chain Polymers. Vol. 60/61, pp. 61—98. 

Liquid crystalline main chain polymers with siloxane spacer groups were obtained by the hydrosilation of (Si—H) terminated polydimethylsiloxane oligomers and mesogenic groups with terminal double bonds as shown in Reaction Scheme XVII-(a). Reactions were usually carried out in THF with the Wacker Oil catalyst 255). Completion of the reactions was followed by the disappearance of the strong (Si—H) absorption band at 2140 cm-1 using IR spectroscopy. 

Bis-o-quinodimethanes have also been used to functionalize [60]-fullerene by Diels Alder reaction. An example is the preparation of main-chain polymers with incorporated [60]-fullerene units [48] illustrated in Scheme 2.20. Cycloaddition of bis-diene 50 generated in situ from bis-sulfone 49 with [60]-fullerene leads to an oligomer mixture 51. Another type of functionalization is based on the... 

The steric frustrations have also been detected in LC polymers [66-68]. For example, the smectic A phase with a local two-dimensional lattice was found by Endres et al. [67] for combined main chain/side chain polymers containing no terminal dipoles, but with repeating units of laterally branched mesogens. A frustrated bilayer smectic phase was observed by Watanabe et al. [68] in main-chain polymers with two odd numbered spacers sufficiently differing in their length (Fig. 7). 

Fig. 7. Two-dimensional packing observed for the main-chain polymer with two odd numbered spacers of different length. Solid lines and arrows indicate the two-dimensional rectangular lattice and macroscopic polarization, respectively (Watanabe et al. [68])...

We note that the bilayer smectic phase which may be formed in main-chain polymers with two odd numbered spacers of different length (Fig. 7), should also be polar even in an achiral system [68]. This bilayer structure belongs to the same polar symmetry group mm2 as the chevron structure depicted in Fig. 17b, and macroscopic polarization might exist in the tilt direction of molecules in the layer. From this point of view, the formation of two-dimensional structure of the type shown in Fig. 7, where the polarization directions in neighbouring areas have opposite signs, is a unique example of a two dimensional antiferroelectric structure. 

In one of their notable examples, the hydroboration polymerization of low molecular weight allyl-telechelic polyisobutylene with tripylborane (trip = 2,4,6-triisopropylphenyl) was found to yield air-stable organoboron segmented block copolymers. These boron main-chain polymers (8) (Fig. 8), unlike the general ones, were stable to air. The stability was due to the steric hindrance of the bulky tripyl groups preventing oxygen attack of the borons.28... 

Hydroboration polymerization between diene monomers and 2,4,6-trimethylphenylborane (mesitylborane)6 or 2,4,6-triisopropylphenylborane (tripyl-borane)7 gave organoboron main-chain polymers (scheme 3). The polymerization was... 

The conformational mobility of a chromophoric main-chain polymer is often connected to its electronic structure. Therefore, changes in the UV-visible absorption spectra and/or chiroptical properties are spectroscopically observable as thermo-, solvato-, piezo-, or electrochromisms. It is widely reported that o-conjugating polysilanes exhibit these phenomena remarkably clearly.34 However, their structural origins were controversial until recently, since limited information was available on the correlation between the conformational properties of the main chain, electronic state, and (chir)optical characteristics. In 1996, we reported that in various polysilanes in tetrahydrofuran (THF) at 30°C, the main-chain peak intensity per silicon repeat unit, e (Si repeat unit)-1 dm3 cm-1, increases exponentially as the viscosity index, a, increases.41 Although conventional viscometric measurements often requires a wide range of low-dispersity molecular-weight polymer samples, a size exclusion chromatography (SEC) machine equipped with a viscometric detector can afford... 

A. Iraqi and I. Wataru, Preparation and properties of 2,7-linked A-alkyl-9JL-carbazole main-chain polymers, Chem. Mater., 16 442M48, 2004. 

Aromatic polyesters were particularly good candidates for this new field of thermotropic main-chain polymers, since the relatively low energy of association of the ester groups led to low inter-chain forces. Further research led to the discovery that incorporation of 2,6-naphthylene or of 4,4 -biphenylyl groups, in addition to p-phenylene groups, as components of aromatic polyesters, introduced a useful new degree of randomness. Particularly useful, and the basis of the commercial products Vectra (polymer) and Vectran (fibre) from Hoechst-Celanese and Kuraray, are the copolymers formed by polymerisation of mixtures of p-acetoxybenzoic acid and 6-acetoxy-2-naphthoic acid. Within a range of... 

Below Tg, in the glassy state the main dynamic process is the secondary relaxation or the )0-process, also called Johari-Goldstein relaxation [116]. Again, this process has been well known for many years in polymer physics [111], and its features have been estabhshed from studies using relaxation techniques. This relaxation occurs independently of the existence of side groups in the polymer. It has traditionally been attributed to local relaxation of flexible parts (e.g. side groups) and, in main chain polymers, to twisting or crankshaft motion in the main chain [116]. Two well-estabhshed features characterize the secondary relaxation. 

Fig. 33. Examples of main-chain polymer liquid crystals I - mesogenic group, II - spacer.

Muller and co-workers have prepared the first reported tetrathiafulvalene (TTF) main chain polymer which they suggest may improve metallic and redox properties of the material due to improved through-bond and through-space interactions in the solid state <1999CC1407>. They also report a simple synthesis of the polymeric material via a novel oxidative polymerisation sequence as outlined in Scheme 18. 

Deuterium NMR measurements are performed for main-chain polymer liquid crystals having structures such as-[Ph-0-C0-Ph-O-(CH2)n-0-Ph-C0-O-Ph-0-(CH2)n-0lx- with n = 9 and 10. The general profiles of the spectra are found to be similar to those of the corresponding dimer. The results of the RIS analysis suggest that the spatial configurations of the spacer are nearly identical between the dimer and the polymer. 

Properties and Applications of Liquid-Crystalline Main-Chain Polymers... 

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