Dynamic covalent exchange induced cyclization in poly(methacrylic anhydride)

Abstract

Dynamic covalent exchange of anhydride moieties in highly crosslinked poly(methacrylic anhydride) (PMAA) was studied via recycling through repetitive grinding and compression molding at elevated temperatures and pressures (130 °C and 152 MPa for 2 hours). The formation of cyclic anhydrides from the exchange between adjacent moieties was observed through IR spectroscopy after each recycling process. In particular, the carbonyl region in the IR spectrum of PMAA exhibits changes that are attributed to increased 6-membered cyclic structures during the recycling process. Computationally-generated vibrational spectra of acyclic and cyclic methacrylic anhydride showed that the spectral changes were due to the fact that cyclic anhydrides exhibit more strain than in acyclic anhydrides. The computational method was validated through the accurate prediction of small molecule acyclic and cyclic anhydrides IR spectra. The observed cyclization was then used to explain the changes in the material properties of PMAA as a function of recycling processes.