Characterization of acrylic dental polymers

The chemical structure and the molecular parameters of Four dental acrylic polymer materials (samples P-l to P-4) and two polyacrylic acids of differe nt molecular weight (relative molecular mass) used as model compounds (samp les Paa-l 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 lowe r MW and bi-modal distribution, one peak corresponding to the polymer and t he other to a low molecular weight compound at a lower concentration. The o ther polymer samples show unimodal distribution. Initially, all samples wer e soluble in water and dioxane above 99.8%. However, after lyophilization a t -50 degrees C they showed different degrees of solubility because of part ial gelation. The FTIR and, H-1 and C-13-NMR spectra of Paa-l, Paa-2 in D2O show the pattern characteristic of poly(acrylic acid). The polymers of P-l and P-2 are mainly poly(acrylic acid). The P-3 spectra show the peak patte rn 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 a- hydroxyethyl methacrylate. Solid C-13-NMR spectra confirm the above structu res and evidence anhydride formation after lyophilization. The MW and the l inear expansion coefficient, alpha, were derived from intrinsic viscosity i n theta and perturbed conditions. From this, the steric hindrance parameter , A, the molecular stiffness, sigma, and the second virial coefficient, A(2 ), were calculated using different thermodynamic models. The Flory-Fox-Shaf gagen 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.