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. 2020 Apr 20;5(17):10011-10020.
doi: 10.1021/acsomega.0c00365. eCollection 2020 May 5.

Synthesis and Thermal Properties of Resorcinol-Furfural Thermosetting Resin

Jie Liu  1 , Dipan Xuan  1 , Jing Chai  1 , Diandian Guo  1 , Yuanbo Huang  2 , Shouqing Liu  3 , Yi Tong Chew  4 , Shuirong Li  1 , Zhifeng Zheng  1
Affiliations

Synthesis and Thermal Properties of Resorcinol-Furfural Thermosetting Resin

Jie Liu et al. ACS Omega. .

Abstract

A mild and effective synthesis of resorcinol-furfural (RF) thermosetting resin was proposed with ethanol as a distinctive solvent, which, as a usually neglected factor, was shown to not only help form a homogeneous reaction system but also observably reduce the energy barriers between the early intermediates and transition states in addition reactions by explicit solvent effects, drawn from theoretical calculation conclusions. Besides, the para-additions on aromatic rings were more dominant than ortho-additions with the same reactants, which affected the final link types of monomers verified by Fourier transform infrared spectroscopy and two-dimensional nuclear magnetic resonance tests. The prepared resin can be assigned to a relatively fast gel speed and a high residual mass (65.25%) after pyrolysis in a N2 atmosphere by adjusting the molar ratios of F to R, and the curing of that was a complex reaction, with a curing temperature around 149 °C and an activation energy of about 49.11 kJ mol-1 obtained by the Kissinger method.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. Possible Resonance Equilibriums of Resorcinol under Alkaline Conditions and the Relative Energies (ΔE) of Different Routes Calculated at the B3LYP/6-311+G (d, p) Level with the PCM (Ethanol) Solvation Model
Figure 1
Figure 1
Optimized geometries and potential energy profiles for the formation of single addition products at the B3LYP/6-311+G (d, p) level with the PCM (ethanol) solvation model. (a–c) Reaction paths of intramolecular proton transfers with R1 as one of the substrates at o-, p1-, and p2- positions, respectively; (d,e) reaction paths of intramolecular proton transfers with R2 as one of the substrates at o- and p- positions, respectively; (f): reaction path of intramolecular proton transfer with P as one of the substrates at the p- position; (g,h) reaction paths of proton transfers with R2 as one of the substrates at the p- position with the synergistic effect of water and ethanol, respectively.
Figure 2
Figure 2
Calculated NPA charge distributions, EPS distribution on molecular van der Waals surfaces, and electron density contours of R1, R2, P, and F at the level of B3LYP/6-311+G (d, p), with the PCM (ethanol) solvation model. The transition from blue to red indicates a gradual decrease of ESP.
Figure 3
Figure 3
FT-IR spectra of (a) RFB-1, RFB-2, and RFB-3; (b) RFA-3, RFB-3, RFC-3, and RFD-3.
Chart 1
Chart 1. Possible monomer structures in RF resin
Figure 4
Figure 4
2D NMR chromatograms of (a) RFB-3 and (b) RFD-3.
Scheme 2
Scheme 2. A Possible Reaction Mechanism of RF Resin under Basic Conditions
For convenience, R1 and R2 were both represented by R, and three monomers were chosen as examples.
Figure 5
Figure 5
(a) DSC curves of RFA-3, RFB-3, RFC-3, and RFD-3 with the heating rate of 10 K min–1; (b) DSC curves of RFB-3 with different heating rates; (c) Plot of ln(β Tp–2) versus Tp–1of RFB-3 with an R-squared value of 0.98; (d) Plot of ln β versus Tp–1 of RFB-3 with an R-squared value of 0.99; (e) Plots of T versus β of RFB-3; (f) FT-IR spectra of RFB-3 and cured resins.
Figure 6
Figure 6
(a,c) TG curves of RFA-3, RFB-3, RFC-3, and RFD-3, uncured and cured, respectively; (b,d) DTG curves of RFA-3, RFB-3, RFC-3, and RFD-3, uncured and cured, respectively.
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