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.