Polymers comb-shaped

Anionic grafting methods (vide infra) can be applied to the synthesis of comb-shaped polymers. As an example, a polystyrene backbone is partially chloromethylated (under mild conditions) and used as an electrophilic deactivator for a living polystyrene 89). The grafting onto process yields well defined species that have been characterized accurately. The branches are distributed randomly along the backbone 90). 

Graft copolymers are comb-shaped polymers consisting of a backbone and two or more branches which differ chemically from the backbone. Branches are usually distributed randomly along the backbone, although recent advances in synthetic methods have allowed for the preparation of better-... 

Chowdhury, M.A.J., Ihara, H., Sagawa, T., and Hirayama, C., Retention versatility of silica-supported comb-shaped crystalline and non-crystalline phases in high-performance liquid chromatography, J. Chromatogr. A, 877, 71, 2000. Chowdhury, M.A., Ihara, H., Sagawa, T., and Hirayama, C., Retention behaviors of polycyclic aromatic hydrocarbons on comb-shaped polymer immobilized-silica in RPLC, J. Liq. Chromatogr. Relat. TechnoL, 23, 2289, 2000. 

Shundo, A., Nakashima, R., Fukui, M., Takafuji, M., Nagaoka, S., and Ihara, H., Enhancement of molecular-shape selectivity in high-performance liquid chromatography through multi-anchoring of comb-shaped polymer on silica, J. Chromatogr. A, 1119, 115,2006. 

N. A. Plate and V. P. Shibaev. Comb-Shaped Polymers and Liquid Crystals, Plenum, New York (1988). 

Special interest has been devoted in recent years to comb shaped polymers. This architecture consists of a backbone carrying p randomly distributed grafts of known length. 

Experimental data on branched polystyrenes were used to test the theory. There are some discrepancies in particular the parameter A varies from one polymer to another, especially for comb-shaped polymers y> also varies. It is suggested that the reason for the discrepancies in A may be the failure of the assumption of a Gaussian distribution of segment density. 

It has been hypothesized by Graessley (30) and others (3, 31) that the g1/2 rule is applicable to star-shaped and slightly branched polymers whereas the g372 rule describes the behavior of highly branched "comb-shaped polymers for which [rj] B/ [y] l < 0.5. The results of this study indicate that the g1/2 rule in combination with Equation 11 adequately represents the random trifunctionally and tetrafunctionally branched... 

Benns, J.M., Choi, J.S., Mahato, R.I., Park, J.S. and Kim, S.W. (2000) pH-sensitive cationic polymer gene delivery vehicle V-Ac-poly(l- histidine)-graft-poly(l- lysine) comb shaped polymer. Bioconjug. Chem., 11, 637-645. 

Homopolymerization of macromonomer provides regular star- or comb-shaped polymers with a very high branch density as shown in Fig. 1 a,c,e. Such polymacromonomers, therefore, are considered to be one of the best models for understanding of branched architecture-property relationships. Their properties are expected to be very different from the corresponding linear polymers of the same MW both in solution and the bulk state. Indeed, during the past decade, remarkable progress has been accomplished in the field of static, dynamic, and hydrodynamic properties of the polymacromonomers in dilute and concentrated solutions, as well as by direct observation of the polymers in bulk. 

In the next section, therefore, we review recent studies of simpler cases, i.e., homopoly(macromonomers), star- and comb-shaped polymers, followed by some interesting properties of the graft copolymers to be used as polymeric surfactants, surface modifiers, and compatibilizers for blends. 

Gnanou and coworkers [15,22,23] prepared several types of regular star- and comb-shaped polymers by living, ROMP of co-norbornenyl macromonomers, 8, 15 and 16. Some of them were characterized by means of the universal calibration in SEC to discuss the chain density, radius of gyration, and shrinking factor [63]. 

To improve mechanical and some other specific properties, one might find interesting the synthesis of comb-shaped polymers with a uni- and bidirectional molecular structure ... 

Plate NA and Shibaev VP "Comb-Shaped Polymers and Liquid Crystals" Plenum Press, New York, 1987. 

Shibae%, V. R, Kostromin, S. G., and Ivanov, S. A. Photoregulation of the optical properties of comb-shaped polymers with mesogenic side groups and the problems of data recording. Po/ym. Scf. 39, 118 (1997). 

The branching sites can be introduced onto the backbone either by postpolymerization reactions or by copolymerization of the main backbone monomer ) with a suitable comonomer, with the desired functional group (unprotected or in a protected form if this functional group interferes with the polymerization reaction). Branches of comb-shaped polymers are commonly prepared by anionic polymerization, and backbones with electrophilic functionalities such as anhydrides, esters, pyridine, or benzylic halide groups are employed.88 The actual average number of branches in the final copolymer can be found by the determination of the overall molecular weight of the copolymer and the known molecular weights of the backbone and the branches. 

Randomly branched comb-shaped polymers can be prepared by three general synthetic methods the grafting onto , the grafting from , and the grafting through or macromonomer method.88... 

PS, PS- -PI, and PS- PMMA comb-shaped polymers with well-defined molecular characteristics (Scheme 61). The PS- -PMMA graft copolymers were found to decompose in proton-containing media, while they were stable in organic solvents. 

Amphiphilic polymers can have a strong impact on the phase behaviour of microemulsions already at very low concentrations. The most drastic consequence is that on the emulsification capacity of surfactants. A first work in this respect was carried out using hydrophobically modified ethyl hydroxyethyl cellulose [ 1 ]. This is a comb-shaped polymer, having a water-soluble backbone functionalised with low molecular weight hydrophobic... 

---