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Thermoassociative graft copolymers based on poly( N ‐isopropylacrylamide): Relation between the chemical structure and the rheological properties
Author(s) -
Durand Alain,
Hourdet Dominique
Publication year - 2000
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/(sici)1521-3935(20000501)201:8<858::aid-macp858>3.0.co;2-6
Subject(s) - copolymer , side chain , polymer chemistry , polyelectrolyte , poly(n isopropylacrylamide) , aqueous solution , rheology , chemistry , acrylate , materials science , grafting , chemical engineering , polymer , organic chemistry , engineering , composite material
new family of thermoassociative graft copolymers has been recently synthesised using a two‐step procedure. Schematically, their structure combines a weak polyelectrolyte backbone (poly(sodium acrylate), PAA) and thermosensitive side chains containing mainly N ‐isopropylacrylamide (NIPA). Taking advantage of this well controlled synthesis we have selectively varied the primary structure of the copolymers concerning the grafting extent, the length of the backbone, and the hydrophilic‐lipophilic balance of the side chains by incorporating either hydrophilic or hydrophobic comonomers. The thermoassociative properties of the resulting copolymers were studied in semi‐dilute solutions by rheology. It was clearly evidenced that the association temperature of the copolymers is selectively controlled in pure water (in the 0–100°C range) by the chemical composition of the side chains. Moreover, the magnitude of the thermothickening effect is directly related to the modification extent while the absolute value of the viscosity is modulated by the length of the PAA backbone. Very sharp transitions were also evidenced by developing specific attractive interactions between the PNIPA grafts and the PAA backbone dependent on the pH of the solutions. In all the cases we demonstrate that the associative behaviour is well correlated to the thermodynamic properties of the precursors. A good knowledge of their phase diagrams in aqueous solution is therefore a very strong guideline for designing copolymers with responsive properties.