Characterization of acrylic dental polymers

The chemical structure and the molecular parameters of four dental acrylic polymer materials (samples P-1 to P-4) and two polyacrylic acids of different molecular weight (relative molecular mass) used as model compounds (samples Paa-1 and Paa-2) were studied and correlated with polymer structure and molecular weight All polymer samples show low molecular weights, MW, and broad poly-dispersity as obtained by GPC. Samples P-3 and P-4 show the lower MW and bi-modal distribution. one peak corresponding to the polymer and the other to a low molecular weight compound at a lower concentration The other polymer samples show unimodal distribution Initially, all samples were soluble in water and dioxane above 99.8% However, after lyophilization at -50 °C they showed different degrees of solubility because of partial gelation The FTIR and, 1 H and 13 C-NMR spectra of Paa-1, Paa-2 in D 2 O show the pattern characteristic of poly(acrylic acid) The polymers of P- 1 and P-2 are mainly poly(acrylic acid) The P-3 spectra show the peak pattern for an (acrylic acid/methyl acrylate) copolymer of about 2:1 composition as calculated from the NMR spectra. The P-4 is an oligomer derived from 2-hydroxyethyl methacrylate Solid 13 C-NMR spectra confirm the above structures and evidence anhydride formation after lyophilization. The MW and the linear expansion coefficient, α, were derived from intrinsic viscosity in theta and perturbed conditions. From this, the steric hindrance parameter, A, the molecular stiffness. σ, and the second virial coefficient, A 2 , were calculated using different thermodynamic models. The Flory-Fox-Shafgagen and the Stockmayer-Fixman models fit better the experimental data and can be used to describe the molecular parameters of the acrylic polymers. Light scattering was used to compare results.