Poly brushes temperature

Yamamoto, S Tsujii, Y. and Fukuda, T. (2002) Glass transition temperatures of high-density poly(methyl methacrylate) brushes. Macromolecules, 35, 6077-6079. 

Efremova NV, Sheth SR, Leckband DE (2001) Protein-induced changes in poly(ethylene glycol) brushes molecular weight and temperature dependence. Langmuir 17 7628-7636... 

Poly(methyl methacrylate) with a variable degree of polymerization anchored to silica surfaces was synthesized following the room temperature ATRP polymerization scheme described earlier [45,46]. In the main part of Fig. 25 we plot the variation of the PMMA brush thickness after drying (measured by SE) as a function of the position on the substrate. Thickness increases continuously from one end of the substrate to the other. Since the density of polymerization initiators is (estimated to be 0.5 chains/nm ) uniform on the substrate, we ascribe the observed change in thickness to different lengths of polymer chains grown at various positions. 

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). 

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... 

A. Roosjen, H. C. van der Mei, H. J. Busscher, and W. Norde, Microbial adhesion to poly (ethylene oxide) brushes influence of polymer chain length and temperature, Langmuir 20, 10949-10955 (2004). 

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... 

Figure 2 The height of a polymer brush as a function of temperature, as revealed by neutron reflectometry. The brush is composed of end-grafted deuterated polystyrene, and the environment ispoly(vinyl methyl ether). As the temperature is increased the interaction between polystyrene and poly( vinyl methyl ether) becomes increasingly unfavourable and the brush height decreases reversibly...

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. 

Poly(iV-isopropylacrylaniide) (PNIPAAm) is by far the most prominent example of a thermally responsive polymer. It undergoes a phase transition at the lower critical solution temperature (LCST), resulting in a strong decrease in hydration of the polymer. For polymer brushes, this behavior is reflected in a collapse of the structure above the LCST. Because of the proximity of the LCST (32°C) to the body temperature, PNIPAAm is considered an interesting candidate for drug release systems. 

Figure 77 (a) Isomerization within the locally confined side chains of the brushes and (b) possible modes of aggregation behaviors of poly-[BPEM-g-(DMAEMA-sfaf-MOAB)] in aqueous solution as a function of photochemical isomerization and temperature. Reprinted from Lee, H.-l. Pietrasik, J. Matyjaszewski, K. Macromolecules 2006, 39(11), 3914-3920, with permission from ACS. ... 

Due to the relative ease of control, temperature is one of the most widely used external stimuli for the synthesis of stimulus-responsive bmshes. In this case, thermoresponsive polymer bmshes from poly(N-isopropylacrylamide) (PNIPAM) are the most intensively studied responsive bmshes that display a lower critical solution temperature (LOST) in a suitable solvent. Below the critical point, the polymer chains interact preferentially with the solvent and adopt a swollen, extended conformation. Above the critical point, the polymer chains collapse as they become more solvophobic. Jayachandran et reported the synthesis of PNIPAM homopolymer and block copolymer brushes on the surface of latex particles by aqueous ATRP. Urey demonstrated that PNIPAM brushes were sensitive to temperature and salt concentration. Zhu et synthesized Au-NPs stabilized with thiol-terminated PNIPAM via the grafting to approach. These thermosensitive Au-NPs exhibit a sharp, reversible, dear opaque transition in solution between 25 and 30 °C. Shan et al. prepared PNIPAM-coated Au-NPs using both grafting to and graft from approaches. Lv et al. prepared dual-sensitive polymer by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide from trithiocarbonate groups linked to dextran and sucdnoylation of dextran after polymerization. Such dextran-based dual-sensitive polymer is employed to endow Au-NPs with stability and pH and temperature sensitivity. 

Free-radically produced poly(styrene) is atactic, having a glass transition temperature of 100°C. It is used mainly for injection-molded articles, e.g., household containers (flow temperature 140-160°C). A small quantity is used for highly oriented monofilaments for brush bristles and highly oriented films for insulation purposes. 

In order to address the question of whether or not the specific side chain conformation influences the main chain conformation, cylindrical brush polymers with poly-L-lysine (PLL) side chains were synthesized [88], Here, we will discussed in some detail the cylindrical brush sample CB-PLL55, which comprises 960 main chain repeat units and an average of 55 lysine repeat units in one side chain sample. Typically, PLL forms a random coil in aqueous solution In aqueous 0.5 M NaC104 solution, however, it is known to adopt one of the most prominent structures of polypeptides an a-helix (see also Sect 6.1) [89]. Upon reduction of the charge density by changing the pH to >9.8 and/or increasing the temperature or by addition of surfactant, a p-sheet structure is favored. Thus, cylindrical brushes with PLL side chains seemed to be ideal candidates for investigating the influence of a coil to a-helix to p-sheet transitimi of the side chains on the main chain conformation. Indeed, circular dichroism (CD) measurements confirmed that all three side chain conformations also occur in the side chains of cylindrical brush polymers (Fig. 18). 

FIGURE 12.12 Schematic of mouse embryonic stem cells (mESC) attachment (above LCST) and detachment (below LCST) to/from thermo-responsive polymer substrates. Poly(ME02MA-co-OEGMA) polymer brushes are shown as chain extended at temperatures below the LCST forming a cell-resistant surface, whereas collapse of the bmshes above the LCST results in a more favorable surface for cell attachment [192]. 

Room-Temperature, Aqueous-Phase Fabrication of Poly(methacrylic acid) Brushes by UV-LED-Induced, Controlled Radical Polymerization with High Selectivity for Surface-Bound Species... 

Poly(ester-Anhydrides) and Poly(ether-anhydrides). 4,4 -alkane-and oxa-alkanedioxydibenzoic acids were used for the s5mthesis of polyanhydrides. These polyanhydrides melted at a temperature range of 98-176°C and had Mw up to 12,900. Di- and triblock copolymers of poly(caprolactone) (PCL), poly(lactic acid) (PLA), and poly(hydroxybutyrate) (PHB) have been prepared from carboxylic acid terminated low M prepolymers copolymerized with SA prepolymers by melt condensation (49). Similarly, di-, tri-, and brush copolymers of poly(ethylene glycol) (PEG) with poly(sebacic anhydride) (PSA) have been prepared by melt copolymerization of carboxylic acid terminated PEG (50). 

---