Effect of ionomer/multiplet formation on mechanical properties and ascorbic acid release behavior of PNIPAAm hydrogels copolymerized by DMAEMA, DMAPMAAm and MAPTAC

Şimşek C., Eroglu Z. E., Erbil C.

IRANIAN POLYMER JOURNAL, vol.28, pp.977-990, 2019 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 28
  • Publication Date: 2019
  • Doi Number: 10.1007/s13726-019-00762-y
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.977-990
  • Keywords: Cationic PNIPAAm hydrogel, Compression modulus, Ionomer, multiplet formation, Hydrophilic-hydrophobic transition, L-Ascorbic acid, Conductometric titration, SWELLING BEHAVIOR, N-ISOPROPYLACRYLAMIDE, INITIATION MECHANISM, TEMPERATURE, POLYMERIZATION, WATER, POLYMERS, CHLORIDE, STIMULI, SOLUTE
  • Istanbul Technical University Affiliated: Yes


Poly(N-isopropylacrylamide) (PNIPAAm) hydrogels containing N-[3-(N,N-dimethylamino)propyl]methacrylamide (DMAPMAAm), 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) and [3-(methacryloylamino)propyl]trimethylammonium chloride (MAPTAC) as cationic monomers were cross-linked with N,N'-methylenebisacrylamide (BIS) and tetraallylammonium bromide (TAB). The swelling degrees, uniaxial compression moduli and L-ascorbic acid (L-AA) releases of these cationic PNIPAAm hydrogels synthesized in 1,4-dioxane were compared with the one prepared in distilled-deionized water (DDW) and in aqueous sodium hydroxide solution (0.1 N NaOH). P(NIPAAm-co-MAPTAC)/BIS and P(NIPAAm-co-DMAEMA)/BIS hydrogels at 37 degrees C in DDW and at 37 degrees C/pH 4 exhibited higher gel strengths and compressive moduli than all the others cross-linked and copolymerized with TAB and DMAPMAAm, respectively. All the observations indicated that the physical cross-linking points created by ionomer pairs of MAPTA(+)Cl(-) units and the hydrophobic contributions of ester groups in the DMAEMA units might be a reason of their improved mechanical properties in DDW at 37 degrees C. Further, the charge screening effect of chloride ions in the swelling medium at pH 4 also resulted in the improved compressive moduli compared to the ones in DDW. The water diffusion into/from all the copolymeric PNIPAAm hydrogels during the swelling/deswelling processes at 25 degrees C/37 degrees C in DDW and their L-AA releases at 37 degrees C in DDW also revealed the importance of these ionic and hydrophobic effects. Water transport through the ones cross-linked with TAB was controlled by non-Fickian process due to the repulsive forces between the quaternized ammonium groups on the chemical cross-links while in the case of P(NIPAAm-co-MAPTAC)/BIS, water transport followed Fickian diffusion because the multiplet formations behaved as additional cross-links. Furthermore, P(NIPAAm-co-MAPTAC)/BIS hydrogel due to the ionomer-multiplet transitions at 37 degrees C in DDW has exhibited less-Fick diffusion that resulted in a lower diffusion coefficient during the release of L-AA as compared to the others.