Oxidation Degradable Aliphatic Polycarbonates with Pendent Phenylboronic Ester

Abstract

Functional polyesters and poly(carbonate)s (PCs) with controlled and on-demand degradation properties have great advantages for biomedical and pharmaceutical applications. Herein, we report a new kind of aliphatic PC that possesses the feature of oxidation promoted degradation. Two six-membered cyclic carbonates ( C1 and C2 ) containing phenylboronic ester group have been synthesized from serinol ( 1 ) and 2-aminomethyl-2-methylpropane-1,3-diol ( 2 ), respectively. Both monomers could undergo well-controlled ring-opening polymerization (ROP) catalyzed by an organic base, but the 5,5-disubstituted C2 has the character of equilibrium ROP and a much slower rate than the monosubstituted C1 . The copolymerization of C1 or C2 with trimethylene carbonate and its derivative leads to a series of copolymers. Two series of amphiphilic block copolymers ( BPC1 s and BPC2 s) have been prepared from C1 and C2 using poly(ethylene glycol) as the macroinitiator. They are able to form nanoparticles with the diameters less than 150 nm. The H 2 O 2 -triggered decomposition of C1, C2, and their corresponding noncyclic model compounds was studied by 1 H NMR, showing the consecutive process of oxidation, 1,6-elimination, release of CO 2, and intramolecular isomerization or cyclization. The degradation of the block copolymer nanoparticles, investigated by 1 H NMR, GPC, laser light scattering (LLS), and Nile Red fluorescence, can also be accelerated drastically by H 2 O 2 following the similar mechanism but is affected by steric hindrance of the polymer chain and heterogeneous microenvironment inside the nanoparticles. The results of 1 H NMR and LLS reveal that the nanoparticles of BPC1 and BPC2 exhibited different degradation profiles, with a slightly faster degradation rate for BPC2 . Of particular interest, BPC2 nanoparticle is sensitive to as low as 0.02 mM H 2 O 2 .