Hyperbranched polymers represent a significant advancement in macromolecular architecture due to their unique combination of globular three-dimensional structures, high functionality at the chain ends, low intrinsic viscosity, and enhanced solubility compared to linear counterparts. Among these, hyperbranched polyesters (HBPs) have garnered particular interest for their potential in biomedical applications, including drug delivery and nanomedicine. This work presents a novel thermal strategy to generate highly branched, biodegradable poly(ε-caprolactone)-based (PCL) materials through the controlled insertion of in situ-generated carbenes derived from thermolytic activation of diazirine end groups. The approach leverages the reactivity of carbene species formed upon heating of a hydroxyl-functional aromatic diazirine initiator, which enables random yet invasive C–H and C–O bond insertions into the growing polyester backbone. This process results in the formation of a hyperbranched core with multiple pendant bromine functionalities.
The synthesis begins with the organocatalytic ring-opening polymerization (ROP) of ε-caprolactone (CL) and brominated ε-caprolactone (BrCL), initiated by 4-[3-(trifluoromethyl)-3H-diazirin-3-yl] benzyl alcohol (TFDBA). The resulting linear copolymers bear terminal diazirine moieties that remain intact during initial polymerization. Subsequent heating at 100 °C induces thermolysis of the diazirine group, releasing molecular nitrogen and generating a highly reactive carbene species at the chain end. This carbene undergoes spontaneous insertion into non-activated C–H and C–O bonds within the polymer chains—both intra- and intermolecularly—leading to the formation of new branching points. The extent of hyperbranching is confirmed by 19F NMR spectroscopy, showing progressive disappearance of the CF3 signal and appearance of new fluorine environments consistent with carbene incorporation. SEC-td analysis reveals substantial increases in molar mass (Mw up to ~10-fold) and dispersity (ÐM > 1.5), indicative of branching. Notably, despite the increase in molecular weight, intrinsic viscosity remains comparable to linear analogs, as evidenced by Mark–Houwink plots yielding α values between 0.38 and 0.48—well below the typical 0.7–0.8 for linear polymers—confirming a highly branched structure.
Further characterization using 1H and 13C NMR confirms retention of the C–Br resonance at δ = 45.9 ppm, proving the bromine functionality survives the branching process. The average number of arms (Narms) was calculated based on absolute molar masses from SEC-td, dispersity, and NMR-derived Mn, revealing a decrease from 12 to 7 as BrCL content diminishes—a phenomenon attributed to steric hindrance imposed by the bromine substituent, which limits carbene access to potential insertion sites.MDR1 Antibody site These hyperbranched PCL-based polymers are then utilized as macroinitiators for copper(0)-mediated radical dispersion polymerization (Cu(0)-RDRP), enabling grafting-from functionalization.58-27-5 supplier By selectively initiating polymerization from the bromine end groups, amphiphilic copolymers were synthesized with hydrophobic PCL cores and hydrophilic polyethylene glycol methyl ether acrylate (PEGMEA) side chains.PMID:35217681 Successful grafting was verified by SEC-td, showing a marked shift in molecular weight distribution and reduced dispersity.
Self-assembly of the HBP2-g-PEGMEA50 copolymer via solvent switch method yielded spherical core-shell micelles with an average diameter of ~50 nm, as determined by dynamic light scattering (DLS). Transmission electron microscopy (TEM) confirmed the spherical morphology and uniform size distribution. These findings demonstrate a powerful, one-pot, thermally driven route to hyperbranched, multifunctional polymers with tailored architectures suitable for advanced nanostructured delivery systems. The method combines simplicity, high efficiency, and structural versatility, making it a promising platform for next-generation biomaterials.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com