| Phenol-formaldehyde (PF) resins have been the subject of this work. {dollar}sp{lcub}13{rcub}{dollar}C liquid-state and solid-state NMR has been used to investigate the molecular structure of mainly novolak and partially of resole resins. {dollar}sp1{dollar}H wideline in combination with {dollar}sp{lcub}13{rcub}{dollar}C solid-state NMR relaxometry has been applied to study the curing and the molecular dynamics of phenolic resins. It was the intention to provide an insight in the relationship between resin composition, resin structure and subsequent resin properties (by means of the molecular dynamics).; An improved {dollar}sp{lcub}13{rcub}{dollar}C liquid-state NMR quantification technique of novolaks in THF-CDCl{dollar}sb3{dollar} solutions is demonstrated. Full quantitative {dollar}sp{lcub}13{rcub}{dollar}C liquid-state spectra of phenol-formaldehyde resins with high signal-to-noise ratio were obtained by using chromium acetylacetonate under optimized spectral conditions within a few hours spectrometer time. Attached proton test (APT) spectra enabled proper peak assignments in the region with significant overlap. For several novolaks, prepared under different catalytic conditions, the degree of polymerization, degree of branching, number average molecular weight, isomeric distribution, and the number of unreacted ortho and para phenol ring positions was determined with a reduced margin of error, by analyzing and integrating the {dollar}sp{lcub}13{rcub}{dollar}C spectra.; The power of {dollar}sp{lcub}13{rcub}{dollar}C solid-state NMR in the analysis of cured PF resins is shown. Particular importance was ascribed to the question of the quantifiability of the experiments when it was desired to measure the degree of conversion by means of a {dollar}sp{lcub}13{rcub}{dollar}C CP/MAS contact time study. The network structure present, and thus also the mechanical properties, is critically dependent upon the final degree of conversion obtained after curing. The degree of conversion, which depended on the cure conditions (cure temperature, cure pressure and cure time), was limited by vitrification as was demonstrated by DSC experiments. Changes in the spin-lattice relaxation time {dollar}Tsb{lcub}rm 1H{rcub}{dollar} were observed, providing criteria to follow the curing evolution.; FT-Raman spectroscopy showed to be complementary to {dollar}sp{lcub}13{rcub}{dollar}C NMR for the determination of the degree of polymerization and of conversion in PF prepolymers or in cured PF resins.; In the last part of this work it was shown that {dollar}sp1{dollar}H wideline and {dollar}sp{lcub}13{rcub}{dollar}C CP/MAS solid-state NMR relaxometry provides interesting information concerning the molecular dynamics of cured novolak resins and resole/novolak copolymers. The relaxation times investigated were the spin-lattice relaxation time {dollar}(Tsb{lcub}rm 1H{rcub}){dollar}, the spin-lattice relaxation time in the rotating frame {dollar}(Tsb{lcub}rm 1pH{rcub}){dollar}, and the spin-spin relaxation time {dollar}(Tsb{lcub}rm 2H{rcub}).{dollar} It was noticed that these relaxation times of the PF resins, at temperatures below the glass transition temperature, were ascertained not only by dynamic phenomena, but also a contribution from the spin diffusion mechanism should be implemented. Measurements as a function of the temperature indicated for a reversible hydrogen bond deformation, confirmed by FT-IR measurements.; {dollar}sp{lcub}13{rcub}{dollar}C CP/MAS and {dollar}sp1{dollar}H wideline NMR can be applied as complementary techniques in order to investigate phenol-formaldehyde resins in the solid state. The chemical structure and the molecular dynamics of these resins can be studied in an adequate manner. Correlations can be made between their relaxation times, their chemical structure and their macroscopic properties. |
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