Raman monitoring of the polymerization reaction of a hybrid protective for wood and paper

The cellulosic materials (wood and paper) but also stone materials, exposed outdoors or in high humidity conditions, are subject to various forms of degradation, including the biological deterioration caused by various microorganisms such as bacteria, fungi and algae. Here we present a monitoring by micro-Raman spectroscopy of the polymerization reaction of a new polymer for the protection of materials of interest for cultural heritage, in particular for lignocellulose. The polymer is a hybrid organic-inorganic polyamidoamine (PAA) functionalized with hydrophilic and siloxanic groups. The polyamidoamines are polymers characterized by the presence of amide and tertiary amino groups, obtained by polyaddition of bis-acrylamides with primary and secondary mono/ di- amines in protic polar solvents. The mechanism of addition of the amine to the acrylamide double bond is a nucleophilic addition 1-4 to the α, β unsaturated carbonyl compound. To monitor the progress of the reaction of polymerization with Raman spectroscopy, we have followed the decrease of the intensity of the C=C bond stretching vibration peak at 1629 cm-1 of bisacrylamide, which should disappear when the polymerization reaction is complete, with respect to the peak intensity of the carbonyl group stretching mode at ≈ 1650 cm-1. To optimize the reaction conditions between the bisacrylamide and the primary amine, with and without siloxanic functionality, molar ratio of the reactants, type of solvent (water, methanol, ethanol), order of mixing of the reactants (amine, amide), reaction temperature (25 °C, 55 °C, 93 °C) have been varied. Raman spectra indicate that the most favorable conditions are obtained when the solutions are concentrated, when methanol is used as solvent and when bisacrylamide is added dropwise to the solution containing the primary amine. The proposed polymer is being tested as a useful tool for the protection of wood or paper artifacts of interest for Cultural Heritage conservation.