Synthesis and Mechanism of Metal-Mediated Polymerization of Phenolic Resins

Abstract

Phenol-formaldehyde (PF) resin is a high performance adhesive, but has not been widely developed due to its slow curing rate and high curing temperature. To accelerate the curing rate and to lower the curing temperature of PF resin, four types of metal-mediated catalysts were employed in the synthesis of PF resin; namely, barium hydroxide (Ba(OH) 2 ), sodium carbonate (Na 2 CO 3 ), lithium hydroxide (LiOH), and zinc acetate ((CH 3 COO) 2 Zn). The cure-acceleration effects of these catalysts on the properties of PF resins were measured, and the chemical structures of the PF resins accelerated with the catalysts were investigated by using Fourier transform infrared (FT-IR) spectroscopy and quantitative liquid carbon-13 nuclear magnetic resonance ( 13 C NMR). The results showed that the accelerated efficiency of these catalysts to PF resin could be ordered in the following sequence: Na 2 CO 3 > (CH 3 COO) 2 Zn > Ba(OH) 2 > LiOH. The catalysts (CH 3 COO) 2 Zn and Na 2 CO 3 increased the reaction activity of the phenol ortho position and the condensation reaction of ortho methylol. The accelerating mechanism of (CH 3 COO) 2 Zn on PF resin is probably different from that of Na 2 CO 3 , which can be confirmed by the differences in the differential thermogravimetric (DTG) curve and thermogravimetric (TG) data. Compared to the Na 2 CO 3 -accelerated PF resin, the (CH 3 COO) 2 Zn-accelerated PF resin showed different peaks in the DTG curve and higher weight residues. In the synthesis process, the catalyst (CH 3 COO) 2 Zn may form chelating compounds (containing a metal-ligand bond), which can promote the linkage of formaldehyde to the phenolic hydroxyl ortho position.

Curing properties of high‐Ortho phenol‐formaldehyde resins with co‐catalysis

“…Table shows the thermal properties of the pure PF, HOPF, and cure‐accelerated HOPF resins. Compared with the pure PF resin, the HOPF resin exhibited similar thermal stability, which was consistent with previous work . While HOPF resin exhibited a higher weight residue at 600 °C than the pure PF resin, indicating that the HOPF resin possessed a tighter network.…”

“…As seen, the weak intensity of chemical shift at 155.0–163.0 ppm in the spectrum of HOPF may be caused by the low concentration of phenolic resin in DMSO‐ D6 during the 13 C‐NMR testing, which could also be observed in other report. The unsubstituted para and ortho carbons, which were the main reactive sites for methylolation reactions, could be observed at 119.5–121.4 and 116.0–117.1 ppm, respectively . While the absence of chemical shifts at 119.5–121.4 ppm indicated that all the reactive sites at the para positions were substituted.…”

“…The HOPF resins were synthesized according to the molar ratio phenol to formaldehyde was 1:2.2 . The additive amount of Na 2 CO 3 was 2.5% based on the total mass of phenol.…”

“…It has also been reported that the proportion of ortho – ortho linkages of novolac resins could be adjusted by using different bivalent metal salts during the synthesis process . Four types of catalysts [(CH 3 COO) 2 Zn, Na 2 CO 3 , Ba(OH) 2 , and LiOH] were used to prepare HOPF resins under alkaline conditions in our previous work . It was found that (CH 3 COO) 2 Zn and Na 2 CO 3 could facilitate the substitution of phenol ortho reactive sites, and increase the ratio of ortho / para ‐substituted positions.…”

Carbon Nanotube‐phenolic Resin Composite Electrode Fabricated by Far Infrared‐assisted Crosslinking for Enhanced Amperometric Detection

“…Phenolic resin (PR), i. e., phenol formaldehyde resin, is a synthetic polymer prepared by the polycondensation between phenol and formaldehyde . Because PR possesses the capabilities of heat resistance, flame retardancy and electrical insulation, it has been widely applied in electronic industry, aerospace engineering, building materials and electrical engineering .…”