Stimuli-responsive self-immolative aliphatic polycarbonates (APCs) and polyesters (APEs) have attractive advantages for biomedical and pharmaceutical applications. In the present work, polycondensation of o-nitrobenzyl-protected serinol was explored as a simple route to obtain light-responsive polycarbonate (LrPC) and polyester (LrPE). By exposure to UV light, these polymers decomposed rapidly and completely into oligomers and small molecules, as detected by size exclusion chromatography (SEC), UV/vis, and 1H nuclear magnetic resonance (NMR) spectroscopies. The degradation mechanism of serinol-based APC and APE was investigated with the help of the Boc-protected model APC and APE, showing that the APC underwent intramolecular cyclization, accompanied by intermolecular transcarbamation, and degraded into oxazolidinone and 2-aminopropanol terminated oligourethanes. Different from APC, the degradation process of serinol-based APE has been proven by electrospray ionization time-of-flight mass spectrometry (ESI-ToF-MS) to follow intramolecular cyclization of the functional amine group with the remote ester group, forming a ten-membered cyclic degradation compound. Further processing of the serinol-based polymers was performed by preparation of nanoparticles (NP). With light-responsive characteristics, a drug delivery system could be potentially obtained enabling a controllable drug release. Based on this strategy, a variety of self-immolative polymers responsive to different triggers can be prepared by polycondensation without the limit of ring-opening polymerization and will expand the family of biodegradable polymers.
Keywords: biodegradable polymers; light-responsive polymers; nanoparticles; o-nitrobenzyl group; polycarbonates; polycondensation; polyesters.