title: Influence of a crown ether comonomer on the temperature-induced phase transition of poly(N-isopropylacrylamide) hydrogels.
abstract: Copolymerization of thermosensitive hydrogels based on poly(N-isopropylacrylamide) (PNIPA) is a possible route to enhanced storage capacity of guest molecules. This article describes the synthesis of the amphiphilic crown ether N9-propenoyl-3,6,12,15-tetraoxa-9,21-diazabicyclo[15.3.1]heneicosa-1(21),17,19-triene (CE) and its incorporation into a PNIPA hydrogel (PNIPA/CE). Mechanical measurements on the gel show that the CE units contribute to the elasticity of the network, but the swelling ratio in water is reduced compared to the unmodified system. The comonomer reduces the temperature of the volume phase transition (VPT), TVPT, and broadens the transition. Both the enthalpy and the entropy associated with the VPT decrease. Scattering measurements indicate that the local structural features on the scale of 10 A are unchanged, but the CE units form large clusters, the size of which increases with rising temperature. In the phase-separated state above TVPT these clusters are distributed on the polymer-water interface.
authors.affiliation: Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics, Budapest 1521, Hungary.
authors.forename: Katalin
authors.initials: K
authors.lastname: Kosik
authors.forename: Erzsébet
authors.initials: E
authors.lastname: Wilk
authors.forename: Erik
authors.initials: E
authors.lastname: Geissler
authors.forename: Krisztina
authors.initials: K
authors.lastname: László
mesh_terms: D000178:Acrylamides / Q000737:chemistry*; D000180:Acrylic Resins; D002152:Calorimetry, Differential Scanning; D043844:Crown Ethers / Q000737:chemistry*; D020100:Hydrogels / Q000737:chemistry*; D015394:Molecular Structure; D044367:Phase Transition; D011108:Polymers / Q000737:chemistry*; D013696:Temperature
chemical_list: D000178:Acrylamides; D000180:Acrylic Resins; D043844:Crown Ethers; D020100:Hydrogels; D011108:Polymers; C052970:poly-N-isopropylacrylamide