Synthesis and characterization of poly(N‐isopropylacrylamide)s initiated with siloxane oligomer–(NH₄)₂Ce(NO₃)₆ redox pair

Abstract

Poly(N-isopropylacrylamide)s (PNIPAAM)s were synthesized via free-radical polymerization using a ceric ammonium nitrate, Ce(IV)-␣--dihydroxy(polydimethylsiloxane) (Tegomer H-Si 2111, PDMS) redox pair in hexane at 30°C in a nitrogen atmosphere. The dependence of the initiation and termination steps on the [NIPAAM]/ [Ce(IV)] and [NIPAAM]/[PDMS] ratios were studied using gravimetry and FTIR, 1 H-NMR, UV-vis, and GFAA spectroscopy techniques. Gravimetric results indicated that, in the case of high concentrations of PDMS, the percentage of the solid portions of the products decreased while the amount of the oligomeric NIPAAM chains increased, that is, as the amount of PDMS in hexane was increased, the number of the short NIPAAM chains having PDMS segments at the two ends, also increased. UV-vis results showed that the LCST of PNIPAAM initiated with Ce(IV) alone was higher than those of the ones that were synthesized using common initiator systems such as an ammonium persulfate-N,N,NЈ,NЈ-tetramethylethylenediamine redox pair and azobis(isobutyronitrile). Further, it was observed that both siloxane blocks and -NH-groups forming coordination bonds with free Ce(IV) ions and/or metal-ligand complexes had an important effect on the aggregation process of the chains.

Synthesis and Characterization of Novel Poly(N-isopropylacrylamide-co-N,N′-dimethylaminoethyl methacrylate sulfate) Hydrogels

“…The intensity of that band increases with DMAEMASA or DMAEMA content, and in the spectra of NIPAM-DMAEMASA gels, it attains a higher intensity than that of the amide I band (ν CO) − of NIPAM (1639/1642 cm −1 ). While the intensity of the amide II band, − due to bending of N−H bond at 1550 cm −1 in the spectra of DMAEMASA copolymers, decreased with a decrease in NIPAM content as expected, the same decrease in the intensity of the same band (1549 cm −1 ) was not observed in the spectra of DMAEMA copolymers. In the spectrum of the NIPAM-DMAEMASA gel, a double band between 3000−3500 cm −1 is observed due to stretching of the N−H bond, and the intensity of the band at a higher wavenumber increases with the DMAEMASA content of the copolymer.…”

N‐isopropylacrylamide–acrylamide copolymers initiated by ceric ammonium nitrate in water

“…For the formation of the low molecular weight chains bearing double bonds at the ends, there is no strong experimental evidence other than yields, FTIR results and molecular weights analysed by viscometry for Samples 3, 22–25. In addition, the findings in our previous work show a similarity with the present results 29…”

Well-Architectured Poly(dimethylsiloxane)-Containing Copolymers Obtained by Radical Chemistry

“…50,51 The polymerization of N-isopropylacrylamide (NIPAM) initiated by the (NH 4 ) 2 Ce IV (NO 3 ) 6 -R,ω-dihydroxyalkyl(polydimethylsiloxane) redox pair was also studied to obtain a thermosensitive triblock copolymer PNIPAM-b-PDMS-b-PNIPAM. 57 This polymerization was performed at 30 °C in hexane containing a small amount of 1,2-dichloroethane to increase the solubility of NIPAM (heterogeneous solution polymerization). Low conversions (<30%) were obtained after 48 h of reaction.…”

“…Poly(N-isopropylacrylamide) (PNIPAM) is known to exhibit a well-defined and reversible lower critical solution temperature (LCST) in water, around 32-34 °C, which is close to the body temperature. In a recent study, Uyanik et al 57 analyzed the solution properties of PNIPAM-b-PDMS copolymers by measuring the LCST. The LCST was found to be lower in concentrated solutions (<35 °C at 0.5 wt %) than in dilute solutions (>35 °C at 0.01 and 0.1 wt %), presumably a consequence of the presence of the hydropho-bic terminal PDMS group.…”