Effect of concentration of the crosslinking agent and diluent during polymerization on the viscoelastic spectra of poly(2‐hydroxyethyl methacrylate) networks

Abstract

The effect of concentration of the crosslinking agent (ethylene dimethacrylate) and diluent (water) during the crosslinking copolymerization on the shape and position of retardation spectra in the dry state has been investigated for poly(2‐hydroxyethyl methacrylate) networks. With increasing water content during network formation, the maxima of the retardation spectra, Lm, increase and the position of the spectra is shifted toward shorter retardation times, τ. The results are in quantitative agreement with the modified Rouse–Mooney (R–M) molecular theory and suggest the influence of deformation due to the diluent during network formation on the viscoelastic behavior. With increasing content of the crosslinking agent, the retardation spectra are shifted toward longer times. At a constant reference temperature T0 = 115°C the retardation time, τm, at the maxima of the spectra increases with increasing content of effective chains in the network, νe. However, after a correction for the effect of the monomeric frictional coefficient, ξ M0, τm/ξ M0 decreases with increasing ve at a rate which agrees quantitatively with the R–M theory. The slope of the retardation spectra in the main transition region and the value of their maxima decrease with increasing ve; a comparison of these dependences with theory leads to the most probable distribution of submolecules in the chains. The contribution of long retardation times to the equilibrium compliance, Je, of the systems under investigation was estimated; it was shown that the application of the Thirion–Chasset extrapolation method for the determination of Je of loose networks requires a certain type of dependence of the retardation or relaxation spectra on τ.

Viscoelastic Behavior of Poly(methyl methacrylate) Networks with Different Cross-Linking Degrees

“…Intermolecular constraints play an important role in the segmental dynamics of all polymeric systems in the bulk state. , A particular case in this context is that of cross-linked polymers. Several works have studied the influence of the cross-linking degree on the α-relaxation by distinct techniques, such as dielectric spectroscopy, dynamic mechanical analysis, or creep and stress−strain measurements. − Those studies revealed that the most striking effects caused by the increase of cross-linker concentration is the broadening of the relaxation and the slowing down of the segmental dynamics, which implies a shift of the transition zone to longer times or lower frequencies. In addition, the KWW asymmetry can be removed as seen, for example, by dielectric spectroscopy …”

Hydrophilic polyurethane networks based on poly(ethylene oxide): synthesis, characterization, and properties. Potential applications as biomaterials

“…The numerous methods which have been developed to synthesize hydrophilic polymer networks can be classified into three groups: (1) methods involving free radical copolymerization of two monomers, one of them being bif Dedicated to Professor W. H. Stockmayer on the occasion of his 70th birthday in grateful recognition and with best regards. unsaturated and present in small proportions (e.g., 2hydroxyethyl methacrylate (HEMA) and ethylene dimethacrylate (DME)1'4); (2) methods involving graft copolymerization (e.g., graft copolymers of poly(HEMA) onto poly(vinylpyrrolidone)5 or poly(vinylpyrrolidone) onto silicone rubber6); and (3) methods involving step growth polymerization between preexisting linear polymer chains and an appropriate functional reagent (e.g., reaction between an , -dihydroxy polymer and a pluriisocyanate7 0024-9297/84/2217-0945$01.50/0 © 1984 American Chemical Society (compounds containing three or more isocyanate functions are referred to as "pluriisocyanates")). The use of hydrophilic polymer networks as biomaterials has been extensively developed since the pioneering work of Wichterle and Lim.1,8 Around 1960, these authors established that hydrogels synthesized from methacrylic esters containing at least one alcohol group per monomer unit are potentially efficient as biomaterials9 in orthopedic surgery, as plastic implants, and chiefly as soft contact lenses, owing to their good biocompatibility.…”