Graft copolymers synthesis by dynamic covalent reorganization of polycaprolactone and poly(ethylene-co-vinyl alcohol)

Dynamic covalent reorganization of polycaprolactone (PCL) and poly(ethylene-co-vinyl alcohol) (EVOH) were realized by solvent free transesterification reactions. Organometallic and organic catalysts effect on these reactions was first evaluated from kinetic studies on small molar mass model reactants. Kinetic constants and activation energies of these second order reverse reactions were calculated. At the higher temperatures, side reactions were observed; they were identified as being principally dehydration reactions. Reactions conducted onto polymers were slower than those on model reactions. This was due to the immiscibility of the used polymers resulting in diffusion controlled reactions. Two competitive types of reactions were detected, since at the catalyst addition, fast induced reorganization of PCL leading to low PCL molar mass decreases the mixing torque, followed by grafting reactions of PCL onto EVOH, resulted in an important increase of the mixing torque. Substitution rate of the EVOH hydroxyl groups were measured up to 14% by 1H-NMR spectroscopy. Increasing substitution rate leaded to a decrease of the copolymer crystallinity and the more substituted copolymers were amorphous. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012