Temperature-Responsive Properties of Poly(acrylic acid-co-acrylamide) Hydrophobic Association Hydrogels with High Mechanical Strength

Abstract

A novel type of hydrophobic association hydrogels (HA-gels) was prepared through micellar copolymerization of acrylic acid (AA), acrylamide (AAm) as basic monomers and a small amount of octylphenol polyoxyethylene ether acrylate with seven ethoxyl units (OP7-AC) as hydrophobic association monomer. The HA-gels exhibited desirable mechanical property and stably reversible phase transition between opaque and transparency. The influences of adding urea and varying AA:AAm molar ratio on the phase transition behavior were discussed, which indicated that the phase transition was introduced by forming or dissociating of hydrogen bonding between amide and carboxyl groups. The introduction of hydrophobic units (OP7-AC) to poly(acrylic acid-co-acrylamide) (P(AA-AAm)) copolymer would result in the adulterating and cross-linking effects on the transition temperature. The former sharply reduced the transition temperature while the later gradually raised it. The transition temperature became linearly dropping with the increasing sodium dodecyl sulfate (SDS) content in the HA-gels. Therefore, the phase transition temperature can be finely adjusted by means of changing AA:AAm ratio, concentration, OP7-AC and/or SDS dosages in the synthesis of HA-gels.

Thermo-Responsive Hydrogels for Stimuli-Responsive Membranes

“…Along with this, structure formation is kinetically slower than dissolution and hysteresis is often observed between heating and cooling cycles ( Figure 5) [14,36,67,68]. Both these effects have similar root causes.…”

“…The swelling and collapse of a covalently crosslinked Am-AA based hydrogel is reversible and appears complete under light transmittance observation [68], however when viewed by mass or volume, reversibility is not complete with the absolute swelling volume becoming larger after each temperature cycle. Along with this, structure formation is kinetically slower than dissolution and hysteresis is often observed between heating and cooling cycles ( Figure 5) [14,36,67,68].…”

“…Confirmation of hydrogen bonding in Am-AA based hydrogels is often provided using urea [35,66], a known hydrogen bond and hydrophobic interaction disrupting analyte [67].One worker reported complete dissolution of Am-AA complexation at 10 wt% urea in water as confirmed by light transmittance [68]. The effectiveness of urea does not clearly identify hydrogen bonding as the sole force causing dissolution.…”

“…Both PAm and PAA homopolymers show negligible volume change with temperature change in pure water [14,15,41]. It has been shown that in a gel network, the monomer ratio (Am:AA) must be between 1:9 and 8:2 for any volume phase transition to occur [68].…”

Light-Sensitive Polymeric Nanoparticles Based on Photo-Cleavable Chromophores

“…As a result, the polymer exhibits a random-coil morphology. [132][133] While the preparation of macroscopic hydrogels from these materials was achieved by hydrophobic association crosslinking by Yang et al, 134 the transfer of this concept to the nanoscale was recently demonstrated by Echeverria et al by radical crosslinking copolymerization of acrylamide with acrylic acid in the presence of N,N'-methylenebis(acrylamide) in inverse emulsion. 135 Microgels prepared by this synthetic pathway represent an interesting alternative to the widely examined systems exhibiting a negative volume phase transition.…”