Abstract
Polyfurfuryl alcohol (PFA) is one of the most intriguing polymers because, despite its easy polymerization in acid environment, its molecular structure is definitely not obvious. Many studies have been performed in recent decades, and every time, surprising aspects came out. With the present study, we aim to take advantage of all of the findings of previous investigations and exploit them for the interpretation of the completely cured PFA spectra registered with three of the most powerful techniques for the characterization of solid, insoluble polymers: Solid-State 13C-NMR, Attenuated Total Reflectance (ATR), Fourier Transform Infrared (FTIR) spectroscopy, and UV-resonant Raman spectroscopy at different excitation wavelengths, using both an UV laser source and UV synchrotron radiation. In addition, the foreseen structures were modeled and the corresponding 13C-NMR and FTIR spectra were simulated with first-principles and semi-empiric methods to evaluate their matching with experimental ones. Thanks to this multi-technique approach, based on complementary analytical tools and computational support, it was possible to conclude that, in addition to the major linear unconjugated polymerization, the PFA structure consists of Diels-Alder rearrangements occurring after the opening of some furanic units, while the terminal moieties of the chain involves γ-lactone arrangements. The occurrence of head-head methylene ether bridges and free hydroxyl groups (from unreacted furfuryl alcohol, FA, or terminal chains) could be excluded, while the conjugated systems could be considered rather limited.
Highlights
The polymerization of furfuryl alcohol (FA) in acid environment to polyfurfuryl alcohol (PFA)is a subject that has attracted the interest of many scientists between the 1950s and today
The approach we consider in the present paper consists of evaluating the proposed arrangements summarized in Table 1, discriminating between those structures that are possible and those that are not on the basis of the results obtained by 13 C-NMR, Fourier Transform Infrared (FTIR) and Raman spectroscopies on our thermoset Polyfurfuryl alcohol (PFA) sample, and comparing the registered spectra with the computational data to strengthen the spectral interpretation
To strengthen the conclusions drawn out complementing the spectroscopic results, a computational effort was made in order to simulate both 13 C-NMR and FTIR spectra of a mixture of the most probable
Summary
The polymerization of furfuryl alcohol (FA) in acid environment to polyfurfuryl alcohol (PFA). Is a subject that has attracted the interest of many scientists between the 1950s and today. This dark thermosetting polymer has been investigated in consideration of various synthetic and analytic. Polymers 2019, 11, 2126 perspectives, and new information about its structure has always jumped out. Dunlop & Peters—1953 [1] Ring opening
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