Copolymers, comb shape

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-... 

Y. Kodera, R. Tanaka, A. Matsushima, and Y. Inada. Chemical modification of 1-asparaginase with a comb-shaped copolymer of polyethylene glycol and maleic anhydride. Btcckem. Biaphys. Res. Comnun. 1S4 144 (1992). 

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. 

Finally, we will consider briefly the formation of multilayer thin films by layer-by-layer deposition of hydrogen-bonded polymer pairs [51,52]. In this way a multilayer structure is obtained from potentially miscible polymer pairs. The stability of these films very much depends on the presence of hydrogen bonds, and pH may be used as an external trigger to erase the layered structure [53,54] and selectively dissolve one of the components [25-27]. This procedure allows for the preparation of microporous films not unlike the nanoporous films obtained by dissolution of the hydrogen-bonded side groups from self-assembled block copolymer-based comb-shaped supramo-lecules [15,17,18]. 

The concept where amphiphihc molecules are hydrogen bonded to one block of a block copolymer to form specific comb-shaped supramolecules allows the production of nanoporous materials in a straightforward way. The concept is illustrated in Fig. 24. The procedure was first applied to a polystyrene-bZocfc-poly(4-vinylpyridine) diblock copolymer with a stoichiometric amount of pentadecylphenol hydrogen bonded to the P4VP block. The relative block lengths were selected to render a lamellar-m-cylindrical morphology, where the P4VP(PDP) comb-shaped blocks form the cylinders... 

Besides hollow channels, porous lamellar structures have also been prepared via the comb-shaped supramolecules route. PS-fo-P4VP diblock copolymers were taken that, together with zinc dodecylbenzenesulfonate [187],... 

A macromonomer technique was employed by Ishizu and Kuwahara to prepare miktoarm star copolymers of the (PS) (PI)m type.128 PS and PI macromonomers were prepared by coupling the living chains with />chloromethylstyrene. The PS and PI macromonomers (vinyl end-capped chains) were copolymerized anionically in benzene using n-BuLi as initiator. The products are comb-shaped copolymers, but they behave as miktoarm stars of the type A Bm. The reaction sequence is given in Scheme 58. 

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. 

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. 

S. Ivanov, I. Yakovlev, S. Kostromin, V Shivaev, L. Lasker, J. Stumpe, and D. Kreysig, Laser-induced birefringence in homeotropic films of photochromic comb-shaped liquid-crystalline copolymers with azobenzene moieties at different temperatures, Makromol. Chem. Rapid... 

Although in controlled radical polymerisation, termination reactions cannot be excluded completely, they are limited in their extent and consequently the molecular weight is controlled, the polydispersity index is small and functionalities can be attached to the macromolecules. These features are indicative of the realisation of well-defined polymer architectures such as block copolymers, starshaped and comb-shaped copolymers. 

Kodera et al. [32] used a comb-shaped copolymer of polyethylene glycol derivative and maleic anhydride to abolish the enzyme s immunogenicity. Two different products were obtained—one having 85% of the original enzyme activity the other 46%. Following the modification process there was no longer demonstrable immunoreactivity toward anti-l-ASP antisera. In vivo studies have not been performed. 

Compared to block copolymers, there have been relatively fewer examples of using homopolymers for nanofabrication. Nevertheless, some polymers with amphiphilic properties were also used in the fabrication of nanostructures with various metal salts/complexes. For example, polyaniline (PANI) emeraldine base formed self-organized mesomorphic structures when mixed with Zn(DBS)2 by the coordination between Zn2+ and the imine nitrogen atoms on the polymer main chain.100 The resulting supramolecule PANI[Zn(DBS)2]0.5 had a comb-shaped... 

The copolymerization of the macromonomers produced comb-shaped copolymers but their solution and solid state properties were similar to those of miktoarm stars. The number of PS and PI arms incorporated in the final product... 

The sensitivity of vibrational spectroscopy allows interactions of polyelectrolytes and surfactants to be monitored in aqueous and nonaqueous solutions. The solubilization and conformational properties of a comb-shaped copolymer of 1-octadecane-co-maleic anhydride in aqueous solution in the presence and absence of SDS depend on the degree of ionization of the copolymer (2i). The C-H stretching region of the Raman spectrum is sensitive to such interactions. Figure 11 illustrates how the C-H stretching band shifts as a function of solvent (in this case water and heptane). 

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