Dendron-modified polymers

The photoisomerization of the azobenzene on polymer films has been also exploited to devise controlled release drug delivery systems. In this regard, researchers have recently directed their attention to the development of photo-controlled drug delivery platforms based on dendron-modified surfaces [274] and mesoporous coatings [274—276]. Mei et al. [276] tethered 6-CD to hollow MSNs via... 

The second method involves substitution reactions on a preformed polymer with a stiff backbone. The advantage of this method is that it provides better control over the MW of the starting polymer. However, the substitution may not be 100%. The first example involved the substitution on a poly( 1,1,1-propellane) copolymer [116]. A copolymer with 80% functionalizable units has been successfully modified with a [G-1]-Br poly(benzyl ether) dendron (see Scheme 13a). Further studies exploring the feasibility and steric limitations of the substitution route have been performed on poly(p-phenylene) [113, 116]. The Williamson substitution reaction on... 

The new regularly branched polymers on the basis of PS were synthesized recently [227]. Each repeated link of these polymers maeromol-eeules contains the Dendron s of Frechett5 e as a side ladieal. The study of this modified by Dendron s PS solutions has shown, that the generation number increase from 1 up to 4 results in hydro dynamical sizes and macromolecules equilibriiun rigidity enhancement in comparison with the initial PS (see Table 24). The similar results were obtained for other polymers as well, modified by Dendron s. These studies were performed within the framework of classical experimental methods, which are distinguished by both high complexity and united theoretical basis absence, taking into account macromolecule structure in solution. Therefore, the authors [240] performed the theoretical description within the framework... 

Hence, the perfonned within the framewoik of fractal approach analysis of behavior of polystirene, modified by Dendron s, in diluted solutions gave the same conclusions, as the analysis within the fiamewoik of classical approaches. The main distinction of the indicated approaches is the fact, that the structural model, allowing to describe quantitatively macromolecules structural state and conformation, was placed in the fractal approach base. Other characteristics (gyration radius, Kuhn segment length and so on) are the function of the indicated structural state of a macromolecule. The fractal analysis methods, used for the description of linear flexible-chain polymers behavior, can be applied successfiilly also in case of polymers with more complex macromolecular architecture. 

Kozlov, G. V Dolbin, I. V MU man, L. D. The Maik-Kuhn-Houwink equation fractal variant for polystirene, modified by dendrons. Proceedings of VIII International Sci.-Pract. Conf New Polymer Composite Materials. Nal chik, Publishers Print-Center , 2012, 124-127. 

The DB of branching can be modified by special synthetic approaches, as demonstrated by the NMR quantification of subunits. Copolymerization - for example, the addition of bifunctional monomers AB - resulted in an increase in linear units and, therefore, in a decrease of the DB [109-112]. An enhancement of DB was realized, for example, by employing a slow monomer addition technique [113], the polymerization of prefabricated dendron macromonomers [56, 114], and by a stepwise addition of the monomer mixture for the (A2 + B3) approach [92]. Whereas dendritic and terminal units are essential for a dendritic structure, in the case of hb polymers the content of the linear units can vary greatly. To date, few examples of AB2 hb polymerizations have been reported were the linear unit is a chemically labile structure that either breaks down to the initial educts, or reacts immediately with a further terminal unit to form the stabile dendritic unit. Thus, a hb polymer containing only T and D units is formed, with 100% DB [35,115-119]. 

Following A. D. Schliiter s question of whether one can create a molecular object, i.e., a molecular system that does not respond to its surrounding, by making a polymer thicker and thicker [93], shape-persistent dendronized polymers in solution were studied by advanced pulse EPR methods. As expected, DEER spectroscopy yields the size (thickness) of different generations of charged cylindrical dendronized polymers in solution [94]. Moreover, a combination of CW EPR and a modified isotopolog-specific DEER variant provides a better understanding of how amphiphilic molecules can be loaded into and released upon external stimulation from these thick polymers [95]. 

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