Boron-Based Poly(Asymmetric Substituted Glycolide) Nanospheres

Abstract

Optically active boron-based asymmetrically structured poly(substituted glycolide) homopolymers (BF2I-PASG) were prepared from a library of asymmetric substituted glycolide (ASG, I-VI) monomers (linear alkyl (propyl methyl-I and propyl ethyl-II) or branched (isoisobutyl methyl-III, isobutyl ethyl-IV, isoleucine methyl-V, isoleucine ethyl-VI) glycolide), which have an analogous structure to lactide (LA) and glycolide (GA), using BF2dbmOEtOH (BF2I) as the initiator in the presence of Sn(Oct)2 catalyst in a solvent-free environment. The presence of amorphous BF2I-PASG (Tg: 4.1-31.9 °C), as indicated by the DSC analysis, which is suitable for short-term drug release, is attributed to the asymmetric structure of monomers I-VI, including various substituted side groups on the GA rings. The thermal stability (i.e., Td) of BF2I-PASG was examined by TGA analysis, revealing a single-step degradation that shifted towards higher Td values, from 346 °C to 377 °C, as the length of the alkyl side group on the polymer backbone increased. BF2I-PASGs exhibit high extinction coefficients of up to 53,750 M⁻¹·cm⁻¹, demonstrating strong π-π* transitions and intense blue fluorescence, with fluorescence lifetimes following a single-exponential decay as high as 1.96 ns and good quantum yields ranging from up to 75%. Additionally, the nanoparticles (NPs) of these polymers possess a smooth surface and regular spherical shape, with average diameters as small as 236 nm, low and narrow polydispersity indices (PDI) ranging from 0.062 to 0.136, and a drug loading value of approximately ≥ 5%, showing a controlled release profile for the paclitaxel anticancer drug.