Graft Copolymers Synthesis by Dynamic Covalent Reorganization of Polycaprolactone and Poly(ethylene-co-vinyl alcohol) S. Touhtouh, 1,2,3 F. Becquart, 1,2,3 M. Taha 1,2,3 1 Universite ´ de Lyon, F-42023, Saint Etienne, France 2 CNRS, UMR 5223, Inge ´nierie des Mate ´riaux Polyme `res, 42023, Saint-Etienne, France 3 imp@ujm, Faculte ´ des Sciences et Techniques, Rue Dr Michelon, F-420023, Cedex, Saint-Etienne, France Received 20 September 2010; accepted 24 May 2011 DOI 10.1002/app.34962 Published online 2 September 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: Dynamic covalent reorganization of poly- caprolactone (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 1 H-NMR spectroscopy. Increasing substitution rate leaded to a decrease of the copolymer crystallinity and the more substituted copolymers were amorphous. V C 2011 Wiley Peri- odicals, Inc. J Appl Polym Sci 123: 3145–3153, 2012 Key words: biopolymers; compatibility; graft copolymers; kinetics; immiscibility INTRODUCTION A particular interest in Dynamic Covalent Chemis- try, where covalent bonds are formed and broken under conditions of equilibrium thermodynamic control, have been related in interesting studies dur- ing the last decades. 1 Dynamic covalent reactions allow readjustment of the product distribution of a reaction, even once the initial products have been formed, by changing the reactions environment (concentration, temperature). 2–6 Unifying concepts concerning these dynamic covalent reactions were proposed in the last decades. 1,2,4 The concept of the dynamic covalent chemistry was clearly defined by Rowan et al in a review with numerous examples. 4 Covalent bonds may be reversibly formed and bro- ken under thermodynamic control to form the most stable products. Poly(ethylene-co-vinyl alcohol)-g-polycaprolactone properties depends on the structure of these copoly- mers. 3 Crystallinity, biodegradability, biocompati- bility, and adhesion properties are function of poly(ethylene-co-vinyl alcohol) (EVOH) to polycap- rolactone (PCL) ratios and also of the molar mass of each constituent. The graft copolymers prepared in this study are candidates for developing therapeutic devices such as temporary prostheses, and also as scaffolds for tissue engineering. Alcoholysis reaction, often used in dynamic cova- lent chemistry and used here for poly(ethylene-co- vinyl alcohol)-g-polycaprolactone preparation, is a well-known reaction between ester functions and alcohol functions leading to new ester and alcohol by an exchange reaction. This reaction is more commonly called transesterification considering the interchange where at least one ester function is involved in the reaction. Two main applications of these reactions are found in the literature: the first one concerns fatty acids chemistry, whereas the sec- ond one is used for depolymerization by methanoly- sis or glycolysis generally for recycling purpose of polycondensation polymers. Primary alcohols are known as the most reactive, with some exceptions, where secondary alcohol are more reactive when specific catalysts, such as organocadmium com- pounds are used. 7 Two categories of catalyst were found in literature: alkoxydes like Mg(CH 3 O) 2 , Ca(CH 3 O) 2 , and Correspondence to: M. Taha (mtaha@univ-st-etienne.fr). Journal of Applied Polymer Science, Vol. 123, 3145–3153 (2012) V C 2011 Wiley Periodicals, Inc.