Effect of crosslinker structure and crosslinker/monomer ratio on network parameters and thermodynamic properties of Poly (N-isopropylacrylamide) hydrogels


Gökçeören A. T. , Şenkal B. F. , ERBIL C.

JOURNAL OF POLYMER RESEARCH, vol.21, no.3, 2014 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 21 Issue: 3
  • Publication Date: 2014
  • Doi Number: 10.1007/s10965-014-0370-2
  • Title of Journal : JOURNAL OF POLYMER RESEARCH

Abstract

The effect of polymer composition and polymerization parameters such as the type of crosslinker and comonomer, crosslinker/monomer ratio and polymerization temperature on the polymer-solvent interactions and mechanical properties of tetraallylammonium bromide (TAB)-crosslinked N-isopropylacrylamide (NIPAAm), N,N'-methylenebisacrylamide (BIS)-crosslinked NIPAAm and TAB-crosslinked NIPAAm - itaconic acid (IA) hydrogels were studied. It was observed that the hydrogels prepared by 0.7 mole / L concentration of NIPAAm and crosslinked with BIS exhibited mechanical weakness and, they were broken even under a pressure, being less than 5.0 N at a swelling temperature of 25 A degrees C while the PNIPAAm hydrogels crosslinked with ionic-octafunctional crosslinker, TAB, had better compression properties. A decrease in the concentration of NIPAAm, increasing TAB content, addition of a hydrophilic/weakly acidic comonomer, IA and an increase in the functionality of crosslinker resulted in the decreasing values of the poymer-solvent interaction parameter, chi at 25 A degrees C. The values of chi , effective crosslinking density (nu(e)) and enthalpy changes during the shrinkage process in the ranges of 33(o) - 45 A degrees C and 37(o)- 45 A degrees C indicated the exothermal nature of phase transition and the importance of intermolecular interactions between PNIPAAm chains. The partial molar dilution-enthalpies (Delta H-1) and -entropies (Delta S-1) that were calculated from the values of enthalpic and entropic components of chi also indicated a similar trend, referring to a decrease in ordered-structuring of water molecules around hydrophobic isopropyl groups with an increase in the swelling temperature.