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Abstract  

In the present work Lyocell fibers were subjected to graft copolymerization of poly-N-isopropylacrylamide (pNIPAAm) thermosensitive polymer. The thermal degradation and stability of lyocell/pNIPAAm copolymers gels were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). pNIPAAm/lyocell copolymers are thermally stable and more resistant to temperature than lyocell fibres. Thermal characterization was analyzed as a function of percentage by mass of the pNIPAAm grafted. It has been shown that for pNIPAAm/lyocell copolymers, degradation occurs at higher temperature when increasing the degree of grafting.

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Magyar Sebészet
Authors: János Varga, László Janovák, Erika Varga, Gábor Erős, Imre Dékány, and Lajos Kemény

(N,N-dimethylacrylamide-co-acrylamide) and poly(N-isopropylacrylamide-co-acrylamide)/kappa-Carrageenan hydrogels for immobilization of lipase Int J Biol Macromol 40 3 281 5

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Abstract  

We studied the effect of variations in the composition of the 3D polymer matrix on the water adsorption properties of poly(N-isopropylacrylamide-co-acrylamide) [abbreviated as poly(NIPAAm-co-AAm)]-based gels containing fillers of diverse hydrophilicities (Na-montmorillonite and hydrophobized montmorillonite). The hydrophilicity of the polymer matrix was modified by varying the ratio of the initial monomers, since acrylamide (AAm) is hydrophilic, whereas N-isopropylacrylamide (NIPAAm) is relatively hydrophobic. Filler content was varied in the range of 1–25 wt%. The water content of polymers, fillers and composites, a parameter determined by their different hydrophilicities was characterized by gravimetry and/or thermoanalytical methods (TG, DSC). The water content of the samples was found to be controllable by varying the hydrophilicity of the polymer matrix and/or the amount and hydrophilicity of the fillers added. Swelling of the relatively hydrophobic poly(NIPAAm) can be increased by the addition of hydrophobic fillers, whereas that of the hydrophilic poly(AAm) can be enhanced by the addition of hydrophilic fillers. The effect of changes in composition on the desorption enthalpies of the samples was determined. The water content of the copolymer increases with increasing the ratio of the hydrophilic monomer, which is due to an increase in the so-called free water content. In the case of the hydrophobic poly(NIPAAm) it is primarily hydrophobic association interactions that dominate the interaction between the polymer matrix and the lamellae of the filler, whereas in the case of the hydrophilic poly(AAm) hydrophilic interactions are dominant.

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Abstract  

Aqueous solution of polyacrylic acid (PAA), poly-N-isopropylacrylamide (PNIPAAm), bovine serum albumin (BSA), superoxide dismutase (SOD) and their mixtures (PAA-BSA, PAA-Cu-BSA, PNIPAAm-BSA, PAA-SOD) were irradiated in the presence of oxygen in neutral media (pH 7.0) with 60Co γ-rays. In addition, aliquots of aqueous solutions of PAA, PAA-Cu2+, BSA and PAA-Cu2+-BSA saturated with N2 and N2O were also irradiated. The decomposition rate of irradiated solutions were measured by UV-visible spectrophotometry, fluorescence spectroscopy, and high performance liquid chromatography (HPLC). Protective effect of copper ions on radiolysis of aqueous solution of PAA-Cu-BSA and conversion of Cu(II) to Cu(I) was observed. The possible mechanism of this phenomenon is discussed.

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Abstract  

The newly manufactured N-isopropylacrylamide (NIPAM) polymer gel is composed of four components, i.e., gelatin, monomer (NIPAM), crosslinker (N,N’-methylenebisacrylamide, Bis), and antioxidant (tetrakis hydroxymethyl phosphonium chloride, THPC). In this study, we investigated the effects of gel composition on the dose response of NIPAM polymer gel. A statistical experiment to analyze the contribution of each composition to the linearity and sensitivity of NIPAM gel was performed. Results indicate that the amount of gelatin, NIPAM (15.17%), Bis, and THPC have dominant effects on the sensitivity of the gel, with contributions of 59.73, 15.17, 10.64, and 14.45%, respectively. The amount of gelatin and Bis mainly affected the linearity of the gel, with contributions of 44.70 and 50.99%, respectively. The linearity of most compositions of the gel was greater than 0.99 when (%C)/(%T) was lower than 8.0. Optimal (%C)/(%T) for higher sensitivity should be in the range of 4−9. The temporal stability experiment showed that the dose response curve attained stability at about 5 h after irradiation and persisted up to 3 months.

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Abstract  

The miscibility of poly(N-isopropylacrylamide) (PNIPA) with poly(vinyl pyrrolidone) (PVP) and a cross-linked poly(acrylic acid) (Carbopol 971P) was evaluated from the rheological data of aqueous dispersions and the temperature of glass transitions of films made of binary mixtures. PNIPA has a low critical solubility temperature (LCST) of about 33C, below which 1% dispersion behaves as a viscous system. At temperatures above LCST, the hydrophobic interactions among the isopropyl groups initially provide transient networks of greater elasticity. The LCST of PNIPA as well as its T g (144C, estimated by DSC and MTDSC of films) were not modified by the presence of PVP. The immiscibility of PNIPA and PVP was confirmed by the absence of interaction between both polymers as shown by FTIR analysis of the films. In contrast, PNIPA and carbopol were miscible and the behaviour of their mixtures differed significantly from that of the parent polymers; i.e. a strong synergistic effect on the viscoelasticity of the dispersions was observed below the LCST. As temperature increased, the blends showed a decrease in the loss and storage moduli, especially those with greater PNIPA proportions. The fall was smoother as the PNIPA proportion decreased. This behaviour may be explained as the result of the balance between PNIPA/carbopol hydrogen bonding interactions (as shown in the shift of C=O stretch in FTIR spectra) and PNIPA/PNIPA hydrophobic interactions. The T g values of the films of the blends showed a positive deviation from the additivity rule; the mixtures containing more than 1:1 amide:carboxylic acid groups have a notably high Tg (up to 181C). This increase is related to the stiffness induced in the films by the PNIPA/carbopol interactions.

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Journal of Thermal Analysis and Calorimetry
Authors: Taís Vanessa Gabbay Alves, Eraldo José Madureira Tavares, Fauze Ahmad Aouada, Charles Alberto Brito Negrão, Marcos Enê Chaves Oliveira, Anivaldo Pereira Duarte Júnior, Carlos Emmerson Ferreira da Costa, José Otávio Carréra Silva Júnior, and Roseane Maria Ribeiro Costa

and Peppas, 1995, hydrogels of poly( N -isopropylacrylamide- co -methacrylic acid) are analyzed by swelling experiments, differential scanning calorimetry (DSC) and thermal mechanical analysis (TMA) [ 13 , 14 ]. Thermogravimetry (TG) and DSC are

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Journal of Thermal Analysis and Calorimetry
Authors: Mohammad Fares, Adeeb El-faqeeh, Hasan Ghanem, Mohammad Osman, and Elfatih Hassan

matrix tablets [ 12 ], starch/acrylic acid as super-absorbents [ 13 ] and starch/ N -isopropylacrylamide as smart core–shell polymer in supercritical carbon dioxide [ 14 ]. The grafting process have been widely accepted using different initiators

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.-J. Li , Y. Uozumi ,* A. , Moores * Green Chemistry 2013 , 15 , 2141 – 2148 . “Atom-economical in situ synthesis of BaSO 4 as imaging contrast agents within poly(N-isopropylacrylamide) microgels using one-step droplet

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2006 Effects of the reaction parameters on the properties of thermosensitive poly(N-isopropylacrylamide) microspheres prepared by precipitation and dispersion polymerization . J Polym Sci A 44 : 968 – 982 10.1002/pola.21223

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