Dynamic covalent exchange in methacrylic anhydride copolymers

Methacrylic anhydride (MAA)-based copolymers were synthesized to probe how the molecular environment around the anhydride moieties impacts the ability of dynamic covalent exchange between anhydrides impacts the ability to recyclable the crosslinked (co)polymers. The comonomers methyl methacrylate (MMA) and n -butyl acrylate (BA) were copolymerized with MAA to yield crosslinked copolymers with varying compositions and their thermal and physical properties were studied as a function of the number of recycling events and copolymer composition. Dynamic covalent exchange was studied via recycling through repetitive grinding and compression molding at elevated temperatures and pressures (130 degrees C and 152 MPa for 2 h). It is concluded that adjacent anhydride moieties can undergo exchange to produce cyclic anhydrides, as observed through IR spectroscopy after heat treatments. Peak deconvolution was utilized to determine the degree of cyclization. Significant increases in monomer conversion occurred and anhydride cyclization was apparent during the first recycling process. Additional recycling processes continued to change the degree of cyclization, but the extent was dependent on the comonomer type. The degree of cyclization was found to be lower in the co-polymers compared to the homopolymer, probably because the interruption of MAA units by the comonomer units along the backbone reduces the ability to cyclize. Thermal properties (glass transition temperature, Tg) of the polymers were also impacted, however the static material properties (modulus and hardness) did not exhibit any dependence on cyclization due to the immobile nature of the highly crosslinked network at room temperature.