Degradable polyacetals and polyacetal/polycyclooctene Co-polymers from a novel dioxepin

Abstract

Self-amplified degradable polyacetals and degradable polyacetal/polycyclooctene co-polymers were prepared via ring-opening metathesis polymerization (ROMP) of a newly-reported 3-bromopropyl-functionalized dioxepin monomer. Despite the relatively low ring-strain energy (RSE) of the monomer (calculated to be 4.34 kcal mol⁻¹) compared to other small cyclic olefins, homopolymerization produced 3-bromopropyl-functionalized polyacetals up to M_n = 9.15 kg mol⁻¹. Acid catalyzed degradation experiments monitored by nuclear magnetic resonance (NMR) spectroscopy revealed the degradation to be self-amplifying in nature, since each instance of acetal hydrolysis released an equivalent of HBr. Co-polymerization of cis-cyclooctene and the 3-bromopropyl-functionalized dioxepin resulted in successful co-polymerization. The co-polymers degraded into small polycyclooctene fragments in acidic media, which was evidence the co-polymerization was successful, and the degradable acetal linkages were incorporated in multiple places along the co-polymer backbone.