N-isopropylacrylamide, NIPAAm

Grafting can also provide the monolithic polymers with rather unexpected properties. For example, the two-step grafting procedure summarized in Fig. 7, which involves the vinylization of the pore surface by reaction of the epoxide moiety with allyl amine, and a subsequent in situ radical polymerization of N-isopropylacrylamide (NIPAAm) initiated by azobisisobutyronitrile within these pores leads to a composite that changes its properties in response to external temperature [76]. 

The atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAAm) conducted in pure water at low temperature (4 °C) proceeds in a controlled fashion (Mn/Mw < 1.2) to near quantitative conversion. Different initiators, hgands, copper halides and ratios of copper (1) to copper (11) were investigated to enhance the control and rednce the termination. The reaction proceeds with a very fast kinetics and a high amount of Cu(ll) is needed to slow down the polymerization. The generated polymers were successfully chain extended suggesting that well defined and complex architectnres can be obtained. 

With the purpose of conferring thermosensitivity to chitosan-based hydrogels. Park et al. proposed the grafting of carboxylic acid-terminated poly(ethylene oxide-h-propylene oxide) block copolymer (Pluronic) onto the primary amine of chitosan, mediated by EDC coupling agent [102]. With the same purpose, Wang et al. grafted poly(N-isopropyl acrylamide) (NiPAM) chains onto chitosan by the copolymerization of acrylic acid-derivatized chitosan and N-isopropylacrylamide (NIPAAm) in aqueous solution [103]. 

PNIPAAm has been synthesized from N-isopropylacrylamide (NIPAAm) by a variety of techniques, the most widely used being free-radical initiation of organic solutions [147] and redox initiation in aqueous media [148]. Redox polymerization of NIPAAm in aqueous media typically uses ammonium persulfate or potassium persulfate as the initiator and either sodium metabisulfite or N,N,N N -tetramethylethylenediamine (TEMED) as the accelerator. In addition, the solutions are usually buffered to constant pH since in the absence of buffer much greater polydispersity is obtained. Whether one polymerizes NIPAAm in organic or aqueous solution also affects polymer properties [149]. 

The principles of RAFT polymerization were applied to the polymerization of N-isopropylacrylamide (NIPAAm), carried out in the presence of the dithiocarbamates benzyl 1-pyrrolecarbodithioate or cumyl 1-pyrrolecarbodithioate as chain transfer agents in 1,4-dioxane at 60°C. A kinetic investigation using in situ FT-NIR spectroscopy showed very long induction periods, which depended on the nature and concentration of the chain transfer agent. The resulting polymers had polydispersity indices Mw/Mn <1.3 and were analyzed by MALDI-TOF mass spectrometry, GPC, NMR, and UV spectroscopy [111]. 

It is our objective to review the intelligent pH/temperature-sensitive membrane by grafting acrylic acid (AAc) and N-isopropylacrylamide (NIPAAm)... 

In an analogous manner, copolymers were produced by RAFT polymerization using monomer 7 as comonomer with N-isopropylacrylamide (NIPAAM) (Scheme 12). Thiolactone contents of the final polymers were determined via H-NMR spectroscopy and elemental analysis. The polymers used for the PPM exhibited thiolactone contents between 23 and 32 mol%, with molar masses in the range of 10-20 kDa and low dispersities (D= 1.2-1.3) [52]. 

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