Tautomeric acetoacetate monomers as building units of functional copolymers

Abstract

Although synthetic polymers from tautomeric functional monomers have emerged as a new kind of materials due to potential applications their interest needs still to be revealed. In this work we have synthesized two series of tautomeric acetoacetate copolymers, with different composition, microstructure and properties. We have selected allyl acetoacetate (AAA) and 2-(acetoacetoxy)ethyl methacrylate (AEMA) monomers to copolymerize with styrene (St). The bulk copolymerization initiated with azobisisobutyronitrile was carried out at 60°C for different monomer feed compositions and times. The products were characterized by 1H NMR, HSQC NMR and size exclusion chromatography. The calculated monomer reactivity ratio obtained for poly(St-co-AAA) and for poly(St-co-AEMA), show noteworthy differences in the copolymerization behavior; r1r2 take values near 1 and zero for poly(St-co-AAA) and poly(St-co-AEMA), respectively. The glass transition temperature (Tg) values for copolymers were determined by differential scanning calorimetry. Two Tg temperatures were found for poly(St-co-AAA) which were close to the Tg values of corresponding homopolymers. On the other hand, only one Tg values characterized the St-co-AEMA copolymers system. Thermal stability has been studied by thermo gravimetric analysis (TGA). The copolymers St-co-AAA and St-co-AEMA exhibited higher thermal stability than homopolymer AAA and AEMA, respectively. Due to the functional group present in both monomers, they exhibit tautomeric equilibrium; an interesting NMR study in solution allowed us to demonstrate that the displacement of equilibrium depends on composition, microstructure and solvents. In view of future applications as nanomatrices for tissue engineering, these tautomeric copolymers (St-co-AAA), were nanostructured in AAO nanocavities and its morphological and surface characteristics analyzed by SEM.