NIPAAm copolymers

As observed for other copolymers that exhibit an LCST (3), sodium chloride depresses the LCST of NIPAAM copolymers (Figure 6). The difference appears to be very large for NIPAAM copolymers in 0.9 M sodium chloride versus PBS (15 to over 20 C). These studies indicated that the NIPAAM-AAM copolymer that precipitated most efficiently above 55 C and below 65 C in 0.9M NaCl contained 67% NIPAAM and 33% AAM. 

The ability to incubate a AAM-NIPAAM copolymer-antibody conjugate with the sample at 37 C should further improve this advantage. 

Synthesis and Characterization. The transition temperature (Tc) of NIPAAm copolymers can be modified by a hydrophilic or hydrophobic comonomer. This phenomenon has already been explained on the basis of inter-molecular and intramolecular hydrogen bond formation between the solvent (water) and polymer chains [6,7],... 

Incorporation of DMAAm increases the Tc of NIPAAm copolymers [18], It has previously been shown that the Tc and swelling of NIPAAm hydrogel layers is largely affected by varying the amount of chromophore [18,31], Terpolymers prepared from NIPAAm/DMAAm/DMLAAm were investigated by DSC, which is a convenient method to study the phase transition temperature of polymers. The phase transition temperature increases with the increase in the mol-% of hydrophilic DMAAm in NIPAAm terpolymers (Table 1). 

Polyvinylpyrrolidone/ Emulsion NIPAAM copolymer polymerization None n-Hexane used at processing [92]... 

Trialkyl-4-vinylbenzyl phosphonium chloride/ V-isopropylacrylamide (NIP AAm) copolymers. These types of crosslinked TRVB/NIPAAm copolymers were prepared by copolymerization of TRVB, NIP AAm, and MBAAm in dimethyl sulfoxide. Poly(NIPAAm) is a thermosensitive polymer, which has a lower critical solution temperature (LCST) at around 33°C. Therefore, the copolymers are crosslinked cationic polymers and thermosensitive polymers, which swell and deswell below and above the LCST (about 33°C) of poly(NIPAAm). 

In the researches performed by Tenhu and co-authors [19-21], it was shown that by means of chemical modification of the units with reactive pendant groups in thermoresponsive NiPAAm-containing copolymers one can prepare polymeric products, whose solution behaviour resemble in some aspects the behaviour predicted by the theory for protein-like copolymers. Scheme 1 presents the reaction used in these syntheses. 

Nonetheless, one cannot exclude the probability of a successful combination of these prerequisites (as was the case with poly[(NiPAAm-co-GMA)-g-PEO considered above]) that will allow us to obtain, using the chemical colouring approach, the protein-like HP-copolymers with a dense hydrophobic core wrapped by the hydrophilic shell. Such a shell should be capable of efficiently protecting the temperature-responsive macromolecules against pronounced interchain hydrophobic interactions and precipitation at temperatures significantly higher than those at which the copolymers of the same total monomer composition—but with a non-protein-like primary sequence of comonomer units—are in the soluble state. 

It was found that in spite of the large excess of modifying amine (N-isopropyl-, -diethyl, -dipropyl, -diisopropyl, -n-hexyl, -cyclohexyl, -n-octyl), the extent of substitution did not exceed 5-10 molar %. For the case of the N-isopropyl derivative, i.e. [poly(AAm-co-NiPAAm)], the authors connected such results with the temperature-induced conformational transformation of partially hydrophobized copolymer acquiring the contracted conformation, "... which made it difficult for N-isopropylamine to react further with the amide groups [22], Unfortunately, no data on the solution behaviour of these interesting copolymers have been reported to date, although there is a high probability that they would demonstrate certain properties of the protein-like macromolecules. At least, in favour of similar supposition is supported by the results of our studies [23] of somewhat different PAAm partially hydrophobized derivative, whose preparation method is depicted in Scheme 3. 

The polymers and some copolymers of NiPAAm are well-known [41,47-54] to possess a brightly-expressed LCST behaviour in aqueous media. In recent years this behaviour has attracted growing interest because of the possible applications of such macromolecular systems in diverse areas, especially in the... 

Unfortunately, data on the temperature-dependent solution behaviour of these fractions are not available to date, although it will be of considerable interest to compare, e.g., HS-DSC and NMR results for the bound and unbound fractions of poly(NiPAAm-co-NVIAz) over the temperature range characteristic of the conformational and phase transitions of NiPAAm homopolymers and copolymers. 

It was shown that the final copolymers synthesized at 30 °C from the feeds with molar comonomer ratios of 95 5 and 90 10 contained 4.8 and 11.4 mol % of NVP units and had molecular weights 4.2 x 106 and 7.9 x 106, respectively. Poly(NiPAAm-co-NVP)s that formed in the course of precipita-... 

The temperature-sensitive poly(A-isopropyl acrylamide) and pH-sensitive poly(methacrylic acid) were used as the two component networks in the IPN system. Since both A-isopropyl acrylamide (NIPAAm) (Fisher Scientific, Pittsburgh, PA) and methacrylic acid (MAA) (Aldrich, Milwaukee, Wl) react by the same polymerization mechanism, a sequential method was used to avoid the formation of a PNIPAAm/PMAA copolymer. A UV-initiated solution-polymerization technique offered a quick and convenient way to achieve the interpenetration of the networks. Polymer network I was prepared and purified before polymer network II was synthesized in the presence of network I. Figure I shows the typical IPN structure. 

Hydrogels synthesized from polymers and copolymers of N-isopropyl acrylamide (NIPAAm) shrink or swell as the temperature is raised or lowered through their lower critical solution temperature (LCST). 

We report here on copolymer hydrogels of N-isopropyl acrylamide (NIPAAm) and acrylamide (AAm) which are crosslinked with mediylene-bis-acrylamide (MBAAm) and which contain the enzyme asparaginase immobilized within the gel. 

Poly (NIPAAm) has been previously shown to have an LCST ca. 31-33 (21) while copolymers of NIPAAm and AAm have LCST s which rise as the AAm content increases (5, 7-9). At a sufficiently high content of AAm, the LCST phenomenon is no longer observed. Figure 2 illustrates the temperature dependence of relative gel water contents for copolymer gels of NIPAAm and AAm. The sharpest drop in water content with temperature is seen for the 100% NIPAAm gel. As the AAm content increases, the drop becomes flatter, and occurs at higher temperatures. 

Figures 3 and 4 show the kinetics of water deswelling of the NA-100 and NA-95 gels. It can be seen that as little as 5% AAm has a significant effect on both the rate and extent of deswelling at temperatures between ca. 34 and 40 . This is the region where collapse of the poly(NIPAAm) gel would be occurring due to the 31-33 LCST of poly(NIPAAm). The LCST of a copolymer of 95% NIPAAm/5% AAm has an LCST around 34-38 , as estimated from Fig. 2. Relatively rapid collapse of this gel would be expected only above 40 , as seen in Fig. 4.

Anhydrous Copolymerization of NIPAAM and N-Acryloxysuccinimide (NASI). In a modification of the procedure of Poliak et al., (4), NIPAAM (5 g, 44 mmol), NASI (0.372 g, 2.2 mmol) and 2,2 azobisisobutyronitrile (AIBN, 0.021 g, 0.13 mmol) were dissolved in 50 ml of dry tetrahydrofuran. The magnetically stirred solution was degassed, heated to 50 C for 24 hours under positive nitrogen pressure, and allowed to cool. The reaction mixture was filtered (0.45 i teflon filter) and the filtrate volume reduced by half. Ether was added with mixing to precipitate the copolymer. 

Anhydrous NIPAAM Homopolymers and NIPAAM-NASI Copolymers using Benzene as solvent. The procedure was the same as described for... 

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