ABSTRACT
Responsive hydrogel networks comprising of poly(methacrylic acid) (PMAA) backbone and oligomeric ethylene glycol (PEG) grafts were synthesized by free-radical solution polymerization and their equilibrium swelling properties were characterized in aqueous solutions of a homologous series of alcohols. These hydrogels are known to exhibit swelling transitions in response to external stimuli which lead to formation or disruption of hydrogen-bonded complexes between the backbone and the grafts. Swelling studies performed in aqueous mixtures of methanol, ethanol and propanol revealed that the effectiveness of an alcohol in breaking the PMAA/PEG complexes increased as the aliphatic segment length of the alcohol was increased. These results confirm the importance of hydrophobic interactions for stabilizing the complexes. Studies performed to determine the effect of the synthesis conditions on the equilibrium swelling properties revealed that the equilibrium degree of swelling increased as the solvent fraction during synthesis was increased. Finally, molecular stimulations revealed that it is sterically possible to form complexes with a 1:1 stoichiometry between chains of poly(methacrylic acid) and poly(ethylene glycol) with essentially no additional bond strain.
Subject(s)
Biocompatible Materials/chemistry , Hydrogels/chemistry , Polyethylene Glycols/chemistry , Polymethacrylic Acids/chemistry , Alcohols/chemistry , Computer Simulation , Models, Molecular , Polyethylene Glycols/chemical synthesis , Polymethacrylic Acids/chemical synthesis , Solvents/chemistryABSTRACT
In this contribution the literature relevant to characterization of polyelectrolytes, polyelectrolyte complexes and hydrogels using luminescence spectroscopy is reviewed. A brief introduction to the fundamentals of luminescence is followed by a description of the various types of spectroscopic studies which may be used to characterize hydrogels. In addition to experiments based upon the addition of a viscosity, temperature- or polarity-sensitive fluorescent probe to characterize the local environment, experiments and techniques based upon luminescence quenching, fluorescence polarization, phosphorescence depolarization and excimer fluorescence are discussed. This review succinctly describes the utility of luminescence spectroscopy in the characterization of hydrogel systems, with a focus on recent developments in the characterization of hydrogels and polyelectrolyte complexes.
Subject(s)
Electrolytes/chemistry , Gels/chemistry , Dansyl Compounds/chemistry , Fluorescence Polarization , Fluorescent Dyes , Luminescent Measurements , Methylmethacrylates/chemistry , Molecular Weight , Polyethylene Glycols/chemistry , Pyrenes/chemistryABSTRACT
Literature relevant to characterization of hydrogels and cross-linked polymer networks using nuclear magnetic resonance (NMR) spectroscopy has been extensively reviewed. After a brief introduction to the fundamentals of NMR spectroscopy, a variety of NMR techniques are considered, including 13C NMR of swollen polymer networks, end-group studies by 13C NMR with labelled initiators, spin-spin and spin-lattice relaxational studies to distinguish species based upon mobility, and characterization of specific interactions using the nuclear Overhauser effect. Finally, a brief treatment of the characterization of polymer structural quantities such as composition, tacticity and sequence distribution by NMR spectroscopic studies is presented. Although our discussion is representative rather than exhaustive, we are confident that this review will demonstrate the utility of NMR spectroscopy for characterization of hydrogel networks which have applications as biomaterials.
