A Versatile Method for Adjusting Thermoresponsivity: Synthesis and ‘Click’ Reaction of an Azido End‐Functionalized Poly(N‐isopropylacrylamide)

Abstract

The 2‐chloropropionamide derivative featuring an azido group is used as the initiator for the ATRP of N‐isopropylacrylamide (NIPAM) with copper(I) chloride (CuCl) and tris[2‐(dimethylamino)ethyl]amine (Me6TREN) to produce the PNIPAM end‐functionalized with an azido group. Subsequently, the ‘click’ reaction between the azido end‐group and acetylene derivatives is demonstrated to produce PNIPAM in which the end‐groups are modified by the phenyl, 4‐phenoxyphenyl, butyl, octyl, carboxylic acid, and hydroxymethyl groups. The resulting PNIPAM derivatives show a LCST that ranges from 34.8 to 44.6 °C depending on the introduced end‐group.magnified image

Well-defined poly(N-isopropylacrylamide) with a bifunctional end-group: synthesis, characterization, and thermoresponsive properties

“…These results indicated that hydrophobic end-groups decreased T cp s while hydrophilic end-groups tended to increase them, and the magnitude of the effect was depended on the nature of the endgroup. Similar phenomena have been reported by Kakuchi and coworkers [22]. The end-group effect, however, is less remarkable for longer chains.…”

“…As shown in Figure 4, small, but clearly discernible, signals at 8.16, 7.76, 7.54, 7.46 ppm are present in the inset spectrum, corresponding to the proton of 1,2,3-triazole ring and the phenyl protons adjacent to triazole ring. Additionally, signals at 5.32, 4.54, and 4.39 ppm corresponding to the methylene protons adjacent to triazole ring as well as ester group, respectively, are also observed [22]. Further evidence for the formation of triazole can be found in the FTIR spectra ( Figure 5), by monitoring the disappearance of absorption band at 2120 cm À1 , which indicates the complete consumption of alkyne end-groups.…”

“…It is known that the incorporation of hydrophobic or hydrophilic end-groups into the PNIPAM chain would affect its LCST, and thus there are many studies on the design, synthesis, and characterization of PNIPAM containing different end-groups [15,[21][22][23][24]. Generally, hydrophobic groups act by increasing the degree of ordering of solvating water while hydrophilic ones tend to decrease the ordering of solvating water.…”

“…As a result, an ever-increasing interest has been focused on the phase transition behavior of PNIPAM in aqueous solutions during the past decades. Many efforts have been devoted to providing insights into the influence of the factors regarding concentration [6,10], cosolvents [11][12][13], molecular weight, polydispersity [14][15][16][17], and tacticity [18][19][20] as well as end-group [21][22][23][24][25][26] on the thermoresponsive properties of PNIPAM.…”

“…In order to better characterize the end-group effect on the thermoresponsive properties of PNIPAM, welldefined polymers with the same molecular weight are important and necessary. Recently, an efficient method reported by Kakuchi and coworkers [22] was used to synthesize well-defined PNIPAMs with identical molecular weight and different end-groups by the combination of ATRP and click reaction. The advantages of this method lie in the capability of the rationalization of the end-group effect and complete elimination of the effect of the molecular weight on the thermoresponsive properties.…”