On the structure and physicochemical properties of acrylic compounds

The chemical structure of four acrylic polymers (P1-P4) used for producing dental cements was studied by FTIR, 1 H and 13 C NMR, using polyaclylic acid (PAA) as a reference compound. Both, P1 and P2 are PAA polymers containing low concentration (<5 wt.%) of a carboxylic precursor. Besides, sample P2 contains also traces of the monomer (acrylic acid). Sample P3 is a random co-polymer (acrylic acid/methyl acrylate) in ratio 2: 1, whereas sample P4 is an oligomer of 2-hydroxyethylacrylate. Three thermodynamic models were applied to the study of the perturbed and non-perturbed molecular parameters of the polymers using viscosimetric and chromatographic determination of their molecular weights. The best fitting of the experimental results was obtained by the Flory-Fox-Schaefgen model In perturbed conditions samples P1 and P2 show the presence of flexible chains, while samples P3 and P4 contain semi-rigid chains. The lyophilization of the polymers at 50°C resulted in the formation of hydrolysable cyclic anhydrides (soluble fraction) and in chemical cross-linking (insoluble fraction).

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