MoO-20
ELECTROSPRAY MASS SPECTROMETRY OF PHENOL-RESORCINOL-FORMALDEHYDE
WOOD ADHESIVE NOVOLAK RESINS
Robert Franich, Jeremy Warnes and Kirk Torr
Wood Products Division
New Zealand Forest Research Institute Limited
Private Bag 3020, Rotorua, New Zealand
Novolak resins of phenol, resorcinol and formaldehyde form the basis of high-performance adhesives for bonding wood for exterior and marine service. The adhesive resins can be prepared under a variety of conditions, but all using a stoichiometric deficiency of formaldehyde. For bonding wood, the adhesive resin is mixed with additional formaldehyde as a "hardener" and the resin then undergoes further condensation reactions to form a high molecular weight polymer with excellent physical and biological durability.
Novolaks prepared under different synthesis conditions have widely-differing polymerisation rates which can be accentuated by addition of polymerisation catalysts. In order to rationalise the kinetics data for a variety of adhesive resins, structural and compositional information was obtained using positive and negative ion electrospray mass spectrometry.
Negative ion spectra acquired in methylcyanide-water gave definitive information on the linear chain length of the various resins, and showed singly-charged ions up to 12-13 resorcinol-methylene units long, thereafter, up to 23 resorcinol-methylene units long (Figure 1), showed doubly-charged ions. Positive ion spectra showed some fragmentation with rearrangement to resorcinol- and hydroxyl-substituted tropylium cations.
Figure 1: Doubly-charged ion formed from high molecular weight resorcinol novolak.
The paper will present the electrospray spectra acquired for selected phenol-resorcinol-formaldehyde novolak resins, discuss the ions formed, and attempt to correlate the novolak structures deduced from the mass spectra with polymerisation kinetics.