Molecular brush

Figure 22 represents a theoretical phase diagram obtained from a scaling analysis for a stiff backbone with flexible side chains taking into accoimt elastic and surface contributions to the free energy [82]. The diagram considers the states of a molecular brush under poor solvent conditions (x = h z = j rj) as a... 

Fig. 21. Microphase segregation and axial contraction of molecular brushes [82]...

Fig. 22. Diagram of states of a molecular brush as function of solvent quality z = (r( and...

The dry molecular brushes adsorbed on mica appear to exhibit undulations along the molecular contour (Fig. 23b). 

Although the observed undulations are consistent with the scaling picture, it is somewhat in contradiction to the axial contraction. On the other hand, axial contraction in molecular brushes can be limited, first because the backbone segments have limited flexibility and second because of hard core repulsion near the backbone or cylinder axis. In contrast to loose comb-Hke polymers [153], an... 

Yoshizawa, M. and Ohno, H., Molecular brush having molten salt domain for fast ion conduction, Chem. Lett., 889,1999. 

Gutowski, W. V. 2003. Interface/interphase engineering of polymers for adhesion enhancement Review of micromechanical aspects of polymer interface reinforcement through surface grafted molecular brushes. Journal of Adhesion 79 445-82. 

Physical chemists established a process called self-organization in which water-insoluble amphiphiles firstly form a molecular brush on the water surface and then assemble to spherical droplets or bladders in bulk water if a threshold concentration (cmc, critical micellar concentration) is surpassed. It was also shown that the self-organization of molecular mono- and bilayers is commonly not followed by crystal growth which would normally be favoured as it diminishes surface energies. Repulsive hydration and undulation effects were held responsible for preventing the growth of the delicate bilayer structures to 3D crystals. 

Figure 10. (a) Molecular brushes with poly(methyl methacrylate) side chains were adsorbed on mica and annealed above the glass transition temperature T= 105 °C for 24 h. (b) The undulated structures in higher magnification images demonstrate the tendency of the brush molecules to contraction via the buckling mechanism. The height of the molecules was determined to be 2 nm and the width 16 2 nm. 

Figure 14. Molecular brushes with poly(/j-butyl acrylate) side chains of different degrees of polymerization (a) n= 52 and (b) n = 10.

Figure 18. (Left) SFM images of poly(r -butylacrylate) brushes with varying degree of polymerization, n, of the polyfn-butylacrylate) side chains on mica (spin cast samples). (Right) Persistence length of a molecular brush as a function of the side chain length n. The continuous line describes the power function lp

When a linear polymer is grafted with a large number of much shorter side chains, cylindrical polymer brushes are formed [33, 108-111]. They are also denoted as bottlebrushes or molecular brushes. Although most cylindrical polymer brushes contain linear side chains, dendritic or even hyperbranched space demanding grafts can also render cylindrical shapes, which leads to the so-called dendronized [112-116] andhypergrafted[117, 118] polymers, respectively. In this review, we will focus on cylindrical brushes with linear side chains. Due to their anisotropic nature in topology, they have attracted more and more research interest in their synthesis, bulk, or solution properties, as well as applications. 

The authors [228, 236] synthesized polymers of the type of so-called molecular brushes-poly(sodiumoxi) methylsylseskvioxanes (PSMSO). Molecular brushes one names comb-like polynners with high density of grafted side chains. They found anomalous low values of solutions viscosity of molecular brushes PSMSO and on this basis supposed, that at side branch length growth the qualitative changes of polymer macromolecule in solution and block occurred [228,236,237], which consisted oftran-... 

Sheiko, S.S. Sumerlin, B.S. Matyjaszewski, K. Cylindrical molecular brushes Synthesis, characterization, and properties. Prog. Polym. Sci. 2008,33 (7), 759-785. 

Sheiko SS, Sumerlin BS, Matyjaszewski K (2008) Cylindrical molecular brushes synthesis, characterization, and properties. Prog Polym Sd 33 759... 

Panyukov S, Zhulina EB, Sheiko SS, Randall GC, Brock J, Rubinstein M (2009) Xension amplification in molecular brushes in solutirais and rm substrates. J Phys Chcan B 113 3750... 

Wang M, Zou S, Gutain G, Shen L, Deng K, Jones M, Walker GC, Scholes GD, Winnik MA (2008) A water-soluble pH-responsive molecular brush of poly(NJ4-dimethylaminoethyl methacrylate) grafted polythiophtaie. Macromolecules 41 6993... 

The localization of counterions in the intramolecular volume is a common feature manifested in dilute salt-free solutions of branched polyions of different topologies, including dendritic (star-burst), randomly (hyper)branched PEs, PE molecular brushes, etc. The physical reason for this phenomena is the same as outlined for PE stars a strongly charged, branched, macroion creates a high electrostatic potential, which attracts counterions and retains them in the intramolecular volume, in spite of a significant loss in the translational entropy. The effect is most pronounced in a dilute solution, where the concentration of counterions in the bulk is extremely low. 

Fig. 4 Branched polyions of different topologies star-bm (a), randomly blanched or hyper-branched (b), molecular brush (c)...

Molecular brushes are polymers composed of a long main chain (backbone), onto which side chains (grafts) are attached at regular intervals. See Fig. 4c for a graphic illustration. The graft-copolymers are classified as molecular brushes, provided the... 

The characteristic branching parameter (grafting density), n/m = specifies the onset of counterion localization inside the molecular brush. Note that in the osmotic regime, the spacers get fully extended, /t m. It is therefore not surprising, that the counterion localization in a cylindrical molecular brush coincides (in scaling terms) with the Manning condensation threshold [25] for a charged cylinder, qh = 1. 

Molecular brushes composed of biopolymers, are typically more complex than their synthetic analogs. They may comprise different types of biomacromolecules, and involve self-assembly mechanisms. For example, in aggrecanes [108] and... 

Recent advances in polymer chemistry, in particular, in controlled radical polymerization, have enabled the synthesis of complex macromolecular architectures with controlled topology, which comprise chemically different (functional) blocks of controlled length in well-defined positions. Block co- and terpolymers, molecular and colloidal polymer brushes, and star-like polymers present just a few typical examples. Furthermore, miktoarm stars, core-shell stars and molecular brushes, etc. exemplify structures where chemical and topological complexity are combined in one macromolecule. 

Yan Q, Yuan JY, Zhang FB, Sui XF, Xie XM, Yin YW, Wang SF, Wei Y (2009) Cellulose-based dual graft molecular brushes as potential drug nanocarriers stimulus-responsive micelles, self-assembled phase transition behavior, and tunable crystalline morphologies. Biomacromolecules 10 2033-2042... 

P2VP) molecular brushes via the free radical polymerization of methacryloyl-terminated P2VP macromonomers [14]. (Reprinted with permission of Wiley-VCH.)... 

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