Polymerization Behavior and ¹³C NMR Representation of Green Copal Resins under Heat-Pressurized Process

The artificial heat-pressurized treatment is contributed to the polymerization of the natural copal resin samples, and the bond breaking of the conjugated double bond on the side chain of the terpenes.Thus it turns into green, yellow-green, dark-orange and black copal resins (heat-pressurized treatment), which have the great commercial value.The microstructure, IR spectra and ¹³C NMR resonance spectra of the copal resin samples before and after heat-pressurized treatment are investigated in depth by using SEM, FTIR, ¹³C NMR and so on.The results show that the heat-pressurized treatment leads to the mutual polymerization of the primary particles in copal resin samples, forming the secondary irregular micro-spherical particles with a size of 180~210 nm.The micro-spherical particles are randomly distributed with the good interface bonding.The corresponding infrared absorption spectra at 3 077 (ν_C-H), 1 643 (ν_C=C), 889 cm^-1 (ν_C-H) and the ¹³C NMR peak (chemical shift: δ=15.8×10^-6, 82.0×10^-6, 108.0×10^-6, 215.1×10^-6) gradually disappear.The derived ¹³C NMR peak (chemical shift: δ=135×10^-6~137×10^-6and δ=33.9×10^-6) is of great significance in the identification.