Temperature-responsive brushes

PNIPAAM, is a well-known temperature-responsive polymer [47] that has been used in the preparation of thermoresponsive membranes [48,49]. The colloidal nanopores were modified with PNIPAAM brushes (Scheme 8.4) [50], and the... 

Laloyaux, X. Fauire, E. Blin, T. Purohit, V. Leprince, J. Jouenne, T. Jonas, A. M. Glinel, K. Temperature-responsive polymer brushes switching from bactericidal to ceU-repeUenL Adv. Mater. 2010,22,5024-5028. 

Idota, N., Ebara, M., Kotsuchibashi, Y., Narain, R., Aoyagi, T. (2012). Novel temperature-responsive polymer brushes with carbohydrate residues facilitate selective adhesion and collection of hepatocytes. Science and Technology of Advanced Materials, 13, 064206. 

Polyethylene glycol-based temperature-responsive polymer were also applicable to the preparation of polymer brush-based TRCS, as reported by Kessel et al. (2010) and Wischerhoff et al. (2008). 

This technology has been expanded to prepare intelligent nanocapsules with temperature-responsive cross-linked shells and pH-responsive brushes on their inner walls. These nanocapsules have been prepared by the surface-initiated atom transfer radical polymerization (SI-ATRP) technique with sihca NP as the sacrificial templates. The two-step, sequential SI-ATRP procedure provided the poly(tert-butyl acrylate) (PtBA) brushes on the inner walls of the temperature-responsive cross-linked poly(A-isopropylacryl-amide) (PNIPAA) shells. Then the ester groups in the nanocapsules were transformed chemically into carboxyl groups after etching the silica templates with HF (Mu and Liu, 2012). 

Metal nanoparticles embedded inside temperature-responsive polymer brushes (Lu et al., 2006) or cross-linked pNlPAM shell (Lu dai,2009a) were tested for the oxidation of alcohols to corresponding aldehydes or ketones (Lu et al., 2009a). The nanoparticles were fully accessible to the reactants at the temperature below the LCST of pNIPAM. Swelling-shrinking could be... 

Lee, H.-i., Pietrasik, J. and Matyjaszewski, K. (2006a) Phototunable temperature-responsive molecular brushes prepared by ATRP , Macromolecules, 39, 3914-3920. 

Zhang et al. controlled the size of nanoparticles by exploiting the pH and temperature responsiveness ofa poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brush [68]. Briefly, a PDMAEMA bmsh was synthesized onto a polystyrene latex nanoparticle via atom transfer radical polymerization (ATRP). Dynamic light-scattering events indicated that pH changes led to temperature changes in solution, which resulted in an alteration in particle size. This approach could be useful in enzyme immobilization or protein separation. 

Stenzel MH, Zhang L, Huck WTS (2006) Temperature-responsive glycopolymer brushes synthesized via RAFT polymerization using the Z-group approach. Macromol Rapid Commun 27(14) 1121-1126... 

Mittal, V., Matsko, N.B., Butte, A., and MorbideUi, M. 2007. Synthesis of temperature responsive polymer brushes from polystyrene latex particles functionalized with ATRP initiator. Eur. Polym. J. 43 4868-81. 

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). 

Fig. 5 Smart UV-responsive coating on silica nanoparticles with PNIPAM brushes functionalized with FRET donors, 4-(2-acryloyloxyethylamino)-7-nitro-2,l,3-benzoxadiazole (NBDAE), and photoswitchable acceptors, l -(2-methacryloxyethyl)-3, 3 -dimethyl-6-nitro-spiro(2//-l-benzo-pyran-2,2 -indoline) (SPMA). The UV radiation induces the change from colorless spiropyran derivatives in the outer part of the coating (7) to the fluorescent merocyanine form (2). Thus, FRET with the benzoxadiazole moieties in the inner part of the coating is enabled and the fluorescence color changes from green to red. By variation of the temperature and induction of a collapse of the PNIPAM chains (3), the FRET efficiency can be tuned (4). Reprinted, with permission, from [70], Copyright (2009) American Chemical Society...

Thermally responsive polymers, such as poly( V-isopropyl acrylamide) (NI-PAm), have also been studied extensively for applications related to those previously discussed [112], De las Heras et al. described the synthesis and patterning of NIPAm brushes on SAMs and their subsequent performance during temperature-dependent adhesion assays of BSA and Streptococcus mutans (Fig. 7). The authors employed p.CP to pattern features of hydrophobic hexadecanethiol and backfilled the surface with an initiator-functionalized alkanethiol. Polymer brushes were grown via surface-initiated atom transfer radical polymerization (ATRP). FITC-BSA was then... 

On the basis of our experimental results presented so far, the overall viscoelastic behavior of these triblock copolymers shows an elasticity-dominance over the viscosity. After reaching the critical mass density, where the static elasticity es reaches the maximum, these triblock copolymers collapse into the subphase and form hydrated brushes and these anchored brushes may be responsible for the result that the surface viscosities drop to around the 0 value at r. A distinctive difference between two types of polymers, sample I (PEO-PPO-PEO) and sample II (PPO-PEO-PPO), is the temperature dependence of r where both static elasticity and dilational viscosity show kinds of transitions. V of sample I increases with increasing temperature while that of sample II does not change with temperature. 

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