Hydrophilic polymers, polymer brushes polymerization

Recently, core-shell type microgels, which contain a hydrophobic core and a hydrophilic thermosensitive shell, have become attractive for scientists because such systems can combine the properties characteristic of both the core and the shell [53], We have prepared core-shell microgel particles consisting of a poly(styrene) core onto which a shell of polyCA-isopropylacrylamide) (PS-PNIPA) has been affixed in a seeded emulsion polymerization [54-56], In this case, the ends of the crosslinked PNIPA chains are fixed to a solid core, which defines a solid boundary of the network. In this respect, these core-shell latex particles present crosslinked polymer brushes on defined spherical surfaces. The solvent quality can be changed from good solvent conditions at room temperature to poor solvent conditions at a temperature... 

Hydrophilic modification of the PTFE membranes is performed for treatment of potable water and waste water. Xu et al. reported the graft copolymerization of AAc and NaSS binary monomers from the high energy EB pre-irradiated PTFE microporous membrane [137]. The AAc/NaSS binary monomers exhibited synergistic effect and improved the graft polymerization reaction with the pre-irradiated PTFE membrane. The water flux decreased with the increase in NaSS concentration. The grafted polymer brushes on the PTFE membrane decreased the water contact angle and produced a stable hydrophilic surface. 

Besides ATRP, RAFT polymerization can also be employed to graft hydrophilic polymer brushes from the PVDF membrane surface. The PVDF membrane was firstly functionalized with hydroxyl groups, which can react with 4,4 -azobis(4-cyanopentanoic acid) (ACPA) to produce the activated PVDF membrane to allow the subsequent graft copolymerization of MMA or PEGMA in the presence of a CTA via RAFT polymerization [143]. The modified membrane can be further graft copolymerized with DMAEMA to produce the diblock copolymer brushes on the PVDF membrane surface. 

Mizutani, A., Nagase, K., Kikuchi, A., Kanazawa, H., Akiyama, Y, Kobayashi, J., Annaka, M., and Okano, T. 2010. Preparation of thermo-responsive polymer brushes on hydrophilic polymeric beads by surface-initiated atom transfer radical polymerization for a highly resolutive separation of peptides. Journal of... 

The synthesis of cylindrical polymer brushes with amphiphilic poly(acrylic acid)-block-poly(n-butyl acrylate) (PAA-b-PnBA) diblock copolymer side chains is shown in Fig. 13.14. The procedure includes several steps (i) synthesis of a well-defined macroinitiator, PBIEM, by esterification of poly(2-hydroxyethyl methacrylate) (PHEMA), which was synthesized via ATRP of 2-hydroxyethyl methacrylate (HEMA) or anionic polymerization of silyl-protected HEMA (ii) ATRP of t-butyl acrylate (tB A) initiated by the pendant a-bromoester groups of PBIEM, yielding cylindrical brushes with PtBA homopolymer side chains (iii) sequential ATRP of n-butyl acrylate (nBA) forming the cylindrical bmshes with diblock copolymer [poly(t-butyl acrylate)-block-poly(n-butyl acrylate) (PtBA-b-PnBA)] side chains and (iv) hydrolysis of the PtBA block to produce the hydrophilic poly(acrylic acid) (PAA) block forming the core of an amphiphilic core-shell cylinder brash [106]. By using this technique, other well-defined core-shell cylindrical polymer brashes with polystyrene (PS), PS-b-PAA or PAA-b-PS, as side chains have been successfully synthesized. 

Surface prop>erties can be modified by thin layers of grafted polymers on a surface (not only flat substrates, but also colloidal particles, fibers, etc). These layers can be fabricated by grafring-from (as radical polymerization at the interface) and grafring-to (as tethering of the polymer chains from solution) methods. Grafted surfaces using smart temperature-responsive polymers can modulate cell adhesion and detachment properties in dependence on the temprerature. Cells adhere and proliferate on hydrophobic surfaces rather than hydrophilic ones. They tend to adhere to the surface with appropriate hydrophobidty. Polymer brush systems can be used to control adsorption mechanism, for example, protein adsorption or adsorption of nanopartides. 

As with normal hydrocarbon-based surfactants, polymeric micelles have a core-shell structure in aqueous systems (Jones and Leroux, 1999). The shell is responsible for micelle stabilization and interactions with plasma proteins and cell membranes. It usually consists of chains of hydrophilic nonbiodegradable, biocompatible polymers such as PEO. The biodistribution of the carrier is mainly dictated by the nature of the hydrophilic shell (Yokoyama, 1998). PEO forms a dense brush around the micelle core preventing interaction between the micelle and proteins, for example, opsonins, which promote rapid circulatory clearance by the mononuclear phagocyte system (MPS) (Papisov, 1995). Other polymers such as pdty(sopropylacrylamide) (PNIPA) (Cammas etal., 1997 Chung etal., 1999) and poly(alkylacrylicacid) (Chen etal., 1995 Kwon and Kataoka, 1995 Kohorietal., 1998) can impart additional temperature or pH-sensitivity to the micelles, and may eventually be used to confer bioadhesive properties (Inoue et al., 1998). 

Tsarevsky has found that hypervalent iodine compounds can be used for the direct azidation of polystyrene and consecutive click-type functionalization [49]. In particular, polystyrene can be directly azidated in 1,2-dichloroethane or chlorobenzene using a combination of trimethylsilyl azide and (diacetoxyiodo)benzene. 2D NMR HMBC spectra indicate that the azido groups are attached to the polymer backbone and also possibly to the aryl pendant groups. Approximately one in every 11 styrene units can be modified by using a ratio of PhI(OAc)2 to trimethylsilyl azide to styrene units of 1 2.1 1 at 0 °C for 4 h followed by heating to 50 °C for 2 h in chlorobenzene. The azidated polymers have been further used as backbone precursors in the synthesis of polymeric brushes with hydrophilic side chains via a copper-catalyzed click reaction with poly(ethylene oxide) monomethyl ether 4-pentynoate [49],... 

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