Cross-linkers, temperature-responsive

A cleavable, temperature-responsive polymeric cross-linker was utilized by Xu and cowoikers [111] to stabilize micelles from PEO-b-PAPMA-b-poly((Af,Af-diisopropylamino)ethyl methacrylate) triblock copolymer. The PNIPAm cross-linker contained activated ester end groups that were reacted with the primary amines on the PAPMA middle block. The trithiocarbonate moiety located at the middle of PNIPAm cross-linker could then be degraded by aminolysis to break the cross-links. Temperature-responsive micelles and vesicles from diblock and triblock copolymers were shell cross-linked via interpolyelectrolyte complexation [108, 112]. The cross-links formed by the electrostatic interactions of oppositely charged polyelectrolytes could be disrupted by the addition of SME. 

DVB were valid in this system as well. These concern the dependence of surface area and pore volume on the amount of diluent and cross-linker. The surface area increases with the amount of EDMA and goes through a maximum with increasing amount of diluent. Using cyclohexanol-dodecanol as a solvent-non-solvent pair, the factors of importance for the structure and morphology of the polymers were studied by experimental design [34]. In these experiments the concentration of the diluent mixture was varied between 20 and 77% (volume/total volume), the concentration of EDMA between 25 and 100% (volume/monomer volume), the concentration of initiator (AIBN) between 0.2 and 4% (w/w), the concentration of non-solvent (dodecanol), between 0 and 15% (v/v) and the polymerisation temperature between 70° and 90°C. The surface area (determined by nitrogen sorption), pore volume (determined by mercury porosimetry) (see Section 2.11.6.) and the mechanical properties were chosen as responses. 

This chapter covers the preparation, characterization, and biomedical application of thermally sensitive particles. Thermosensitive hydrogel is prepared by precipitation polymerization of A-alkylacrylamide or A-alkylmethacrylamide as a principal water-soluble monomer, a water-soluble cross-linker (for instance, A-methylenebisacrylamide), and an initiator (such as Azobis-amidinopropane derivatives, potassium persulfate, or basically any charged initiator). The core-shell latexes are produced by a combination of emulsion and precipitation polymerization, such as the preparation of polystyrene core and poly(A-isopropylacrylamide) shell or encapsulation of coUoidal seed using alkylacrylamide derivatives. During the elaboration of such stimuli-responsive particles, various aspects should be considered (1) a water-soluble cross-linker is needed, (2) the polymerization temperature should be higher than the LCST of the corresponding linear polymer, and (3) the production of water-soluble polymer (which can be controlled by monitoring the polymerization conditions). The polymerization mechanism has been clearly discussed and well illustrated, but the nucleation step remains questionable and requires further work. 

Fig. 18.5 Chemical composition of the different nematic LSCEs EAZO-n (a), opto-mechanical experiments for the different elastomers under UV-irradiation (Xirrad = 380 nm) at 333 K (b), schematic model of the photo-active cross-linker binding points within the elastomeric network (c), evolution of the maximum opto-mechanical response, with the temperature (d), and...

In 2000, Benaglia and coworkers reported preparation of MeO-PEG supported quaternary ammonium salt (10) and examined the catalytic efficiency in a series of phase-transfer reactions (Fig. 5.3) [69]. The reactions occurred at lower temperatures and with shorter reaction times than with comparable insoluble 2% cross-linked polystyrene-supported quaternary ammonium salts, although yields varied with respect to classical solution phase quaternary ammonium salt catalyzed reactions. It was observed that yields dropped with a shorter linker, and that PEG alone was not responsible for the extent of phase-transfer catalysis. While the catalyst was recovered in good yield by precipitation, it contained an undetermined amount of sodium hydroxide, although the presence of this byproduct was found to have no effect on the recyclability of the catalyst... 

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