title: Hydrogen-bonding-driven spontaneous gelation of water-soluble phospholipid polymers in aqueous medium.
abstract: It has been found that mixing of two kinds of water-soluble phospholipids polymers, such as poly(2-methacryloyloxyethyl phosphorylcholine-co-methacrylic acid) (PMA) and poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) (PMB), spontaneously forms a hydrogel in aqueous medium at room temperature without any chemical treatment. However, the mechanism of spontaneous gelation has not been clarified yet. The purpose of this study is to investigate the gelation mechanism of the hydrogel. Moreover, effects of ions on gelation and dissolution behavior were observed. We investigated the mechanism of the hydrogel formation by spectroscopic techniques and a rheological method with attention to the interactions between polymer chains. Both Raman spectroscopic analysis and FT-IR analysis revealed that carboxyl groups in methacrylic acid (MA) formed dimer when two polymer solutions were mixed, and the results of the rheological study showed dissociation of carboxyl groups caused dissolution of the hydrogel. Thus, the gelation occurred due to the formation of dimers by hydrogen bonding which acts as a physical cross-linking of polymer chains. The hydrogel dissolved in a large amount of aqueous medium. We also observed the addition of inorganic salts during the preparation of the hydrogel affected the gelation and dissolution behaviors by a rheological and a weight measuring method, respectively. The gelation period became longer in the presence of NaCl and CaCl2 compared with that in the absence of these salts. NaCl and CaCl2 disturbed the formation of hydrogen bonding between carboxyl groups by stabilization of carboxylate anion of the MA units. On the other hand, addition of FeCl3 made the gelation period shorter and stabilized the hydrogel in the aqueous medium. This is because FeCl3 can suppress dissociation of the carboxyl groups by acidic condition of FeCl3 aqueous solution and cross-link the carboxylate anions in the PMA effectively.
authors.affiliation: Department of Materials Engineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Mizuna
authors.initials: M
authors.lastname: Kimura
authors.forename: Kikuko
authors.initials: K
authors.lastname: Fukumoto
authors.forename: Junji
authors.initials: J
authors.lastname: Watanabe
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Ishihara
mesh_terms: D002122:Calcium Chloride / Q000737:chemistry; D002712:Chlorides; D005290:Ferric Compounds / Q000737:chemistry; D020100:Hydrogels / Q000138:chemical synthesis / Q000737:chemistry*; D006860:Hydrogen Bonding; D008689:Methacrylates / Q000737:chemistry*; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000737:chemistry*; D011109:Polymethacrylic Acids / Q000737:chemistry*; D012965:Sodium Chloride / Q000737:chemistry; D012995:Solubility; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D014783:Viscosity
chemical_list: D002712:Chlorides; D005290:Ferric Compounds; D020100:Hydrogels; D008689:Methacrylates; D011109:Polymethacrylic Acids; D010767:Phosphorylcholine; C079200:poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate); D012965:Sodium Chloride; D002122:Calcium Chloride; C024555:ferric chloride