Oxidation-Responsive Aliphatic Polycarbonates from N-Substituted Eight-Membered Cyclic Carbonate: Synthesis and Degradation Study.

Abstract

Oxidation-responsive aliphatic polycarbonates represent a promising branch of functional biodegradable polymers. This paper reports the synthesis and ring-opening polymerization (ROP) of an eight-membered cyclic carbonate possessing phenylboronic pinacol ester (C3) and the H2 O2 -triggered degradation of its polymer (PC3). C3 is prepared from the inexpensive and readily available diethanolamine with a moderate yield and undergoes the well-controlled anionic ROP with a living character under catalysis of 1,8-diazabicyclo[5.4.0]undec-7-ene. It can also be copolymerized with l-lactide, trimethylene carbonate, and 5-ter-butyloxycarbonylamino trimethylene carbonate, affording the copolymers with a varied distribution of the repeating units. To clearly demonstrate the oxidative degradation mechanism of PC3, this paper first investigates the H2 O2 -induced decomposition of small-molecule model compounds by proton nuclear magnetic resonance (1 H NMR). It is found that the adduct products formed by the in-situ-generated secondary amines and p-quinone methide (QM) are thermodynamically unstable and can decompose slowly back to QM and the amines. On this basis, this paper further studies the H2 O2 -accelerated degradation of PC3 nanoparticles that are prepared by the o/w emulsion method. A sequential process of oxidation of the phenylboronic ester, 1,6-elimination of the in-situ-generated phenol, releasing CO2 and intramolecular cyclization or isomerization is proposed as the degradation mechanism of PC3.