PNIPAM- poly ethyl

For monomethoxy terminated poly(ethyl-ene glycol) as reductant it was shown that during the polymerization of N-isopropyl acrylamide (NIPAm) the formation of primary poly(ethylene glycol) radicals stops after about five minutes whereas the growing poly(ethylene glycol)-l>-PNIPAm radicals survive many hours. 

Several polymers have been characterized for their ability to form PM and PICM and are presented in Table 4.1. The hydrophilic segment can consist of polysaccharides, such as chitosan. and pullulan, or synthetic polymers, such as poly(ethylene glycol) (PEG), poly(N-vinylpyrrolidone) (PVP), poly(N-isopropylacrylamide) (PNIPAM), poly(2-ethyl-2-oxazoline) and poly(acrylic acid). Of all hydrophilic polymers, PEG (with a molecular weight of 1-20 kD) is undoubtedly the most widely used shell forming component of both PM and PICM. The neutrality, hydrophilicity and flexibility of PEG diminish the possibility of undesirable electrostatic interactions with plasma proteins. Furthermore, the presence of reactive groups at both chain ends... 

Since 2000, hving radical polymerization has allowed the synthesis of block copolymers with controlled molecular weight and a narrow MWD using many monomer combinations, as shown in Figs. 4 and 5 [71]. Block copolymerization with hydrophilic or thermoresponsive acrylamide derivatives 11,12 has been examined [72-77]. Block copolymers having hydrophiUc segments such as PNlPAM-poly[(meth)acrylic acid] (13) [78-80], PNIPAM-poly(sulfonic acid) (14) [81,82], PNIPAM-poly(2-hydroxyethylacrylate) U5) [83], and PNIPAM- poly](2-dimethylamino)ethyl methacrylate]-co-poly(2-hydroxyethyl methacrylate) (16) [84] were prepared. These formed polymer micelles in response to variation of the temperature. For example, Muller et al. have synthesized PNIPAM-poly(acrylic acid) with low polydis-... 

PELLys PGEA PGEMA Phe, F PHPMA PIAA PIC PMMA PNIPAM PS Poly(A -[2-(2-(methoxyethoxy)ethoxy)]acetyl-L-lysine) Poly(2-(P-D-glucopyranosyloxy)ethyl acrylate) Poly(2-glucosyloxyethyl methacrylate) Phenylalanine Poly(A-(2-hydroxypropyl)methacrylamide) Polyisocyanodipeptide Polyion complex Poly(methyl methacrylate) Pol v (/V-i s o p r o p y 1 aery 1 am idc) Polystyrene Radius of gyration Hydrodynamic radius... 

By polymerizing poly(A -isopropylacrylamide) (PNIPAM) [55] or poly (2-(diethylamino)ethyl methacrylate) (PDEAEMA) [56] as a stimuli responsive polymer/hydrogel layer around a colored nanoparticle of PS-co-PMMA, the local refractive index and consequently the color intensity of the latex could be switched by the temperature [55] or pH [56]. 

Liu and coworkers employed this method to study the micellization kinetics of a double hydrophilic diblock poly(W-isopropyIacrylamide)-poly(2-diethylamino ethyl methacrylate) (PNIPAM-PDEA) in aqueous solution [172]. The results obtained after a temperature jump from 20°C (unimers) to different final temperatures are shown in Fig. 33. 

Fig. 33 Time evolution of the scattered intensity upon different temperature jumps of the poly (A -isopropylacrylamide)-poly(2-diethylamino ethyl methacrylate) (PNIPAM-PDEA) block copolymers undergoing micelhzation in water. The temperatures shown indicate the final temperature after a jump from 20°C. Reprinted with permission from [172]. Copyright (2007) WILEY-VCH Verlag GmbH Co. KGaA, Weinheim...

The most widely investigated temperature-responsive biomedical polymer is poly(A-isopropyl acrylamide) (pNIPAM). This polymer is the focus of Chapter 1 in this book, and therefore it will not be discussed in depth here. However, pNIPAM has been paired with polyampholyte copolymers and applied to nanoparticle separations (Das et al., 2008), drug delivery (Bradley, Liu, Keddie, Vincent, Burnett, 2009 Bradley, Vincent, Burnett, 2009), and tissue engineering applications (Xu et al., 2008). In a related system, latridi et al. (2011) also used the LCST-responsive properties of polyethylene glycol methacrylate (PEGMA) copolymerized with methac-rylic acid and 2-(diethylamino) ethyl methacrylate in a temperature- and pH-sensitive doxorubicin drug delivery system. However, the primary focus of this study was to demonstrate the pH-dependent release properties as discussed earlier. 

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. 

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