title: Interfacial and fluorescence studies on stereoblock poly(N-isopropylacryl amide)s.
abstract: Aqueous solution and water-air interfacial properties of associative thermally responsive A-B-A stereoblock poly(N-isopropylacryl amide), PNIPAM, polymers were studied and compared to atactic PNIPAM. The A-B-A polymers consist of atactic PNIPAM as a hydrophilic block (either A or B) and a water-insoluble block of isotactic PNIPAM. The surface tensions of aqueous PNIPAM solutions were measured as a function of both temperature and concentration. The isotactic blocks did not have an effect on the surface activity of the solutions. Rheological measurements on the water-air interface showed that the aggregated PNIPAMs containing isotactic blocks increased the elasticity of the surface significantly as compared to the atactic reference upon heating. Two fluorescence probes, pyrene and (4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (4HP), added to the aqueous polymer solutions were concluded to reside in surroundings with lower polarity and increased microviscosity in cases when the polymers contained isotactic blocks, as compared to ordinary atactic polymers.
authors.affiliation: Laboratory of Polymer Chemistry, Department of Chemistry, University of Helsinki, P.O Box 55, FIN-00014 HU, Finland.
authors.forename: Jukka
authors.initials: J
authors.lastname: Niskanen
authors.forename: Cynthia
authors.initials: C
authors.lastname: Wu
authors.forename: Maggie
authors.initials: M
authors.lastname: Ostrowski
authors.forename: Gerald G
authors.initials: GG
authors.lastname: Fuller
authors.forename: Heikki
authors.initials: H
authors.lastname: Tenhu
authors.forename: Sami
authors.initials: S
authors.lastname: Hietala
mesh_terms: D000178:Acrylamides / Q000737:chemistry*; D000180:Acrylic Resins; D005453:Fluorescence; D008958:Models, Molecular; D015394:Molecular Structure; D011108:Polymers / Q000737:chemistry*; D012212:Rheology; D013500:Surface Tension
chemical_list: D000178:Acrylamides; D000180:Acrylic Resins; D011108:Polymers; C052970:poly-N-isopropylacrylamide