Detection, Quantification, and “Click-Scavenging” of Impurities in Cyclic Poly(glycidyl phenyl ether) Obtained by Zwitterionic Ring-Expansion Polymerization with B(C6F5)3

Computational Analysis of the Lewis Acid-Catalyzed Zwitterionic Ring-Expansion Polymerization (ZREP) of Monosubstituted Ethylene Oxide

This study investigates the reaction mechanism of the zwitterionic ring expansion polymerization (ZREP) of monosubstituted ethylene oxide using boron-based Lewis acids as catalysts to produce cyclic polyethers. The research analyzes various parameters, such as the nature of the substituents (electron-withdrawing, EWG or electron-donating, EDG), the type of catalyst, and the solvent, to understand their influence on the reaction's kinetics, thermodynamics, and regioselectivity. Key findings include that EDGs lower the kinetic barrier of the rate-determining step and favor the reaction at the substituted carbon, while EWGs increase this barrier, making the reaction less favorable. The study also shows that all catalysts tested efficiently activate the epoxide monomer with similar barriers for the rate-determining step, and the regioselectivity trends align with the substituent's electronic effects. Steric effects of substituents were found to dominate the competition between monomer addition and cyclization termination, with most catalysts promoting cyclization. Additionally, the solvent had minimal impact on the polymerization mechanism. This computational study provides valuable insights into the synthesis of cyclic polymers and advances the development of catalysts for ZREP of monosubstituted ethylene oxide.

Varying the Core Topology in All-Glycidol Hyperbranched Polyglycerols: Synthesis and Physical Characterization

In the present study, low molecular weight cyclic polyglycidol is used as a macroinitiator for hypergrafting glycidol and producing cyclic graft hyperbranched polyglycerol (cPG-g-hbPG) in the molecular weight range of 103-106 g mol-1. Linear graft hyperbranched polyglycerol (linPG-g-hbPG) and hyperbranched polyglycerol (hbPG) are prepared as reference samples. This creates a family of hbPG structures with cyclic, linear, and star cores, allowing to evaluate their properties in solution and in bulk. The morphology study of the high molecular weight structures using atomic force microscopy revealed a spherical shape for cPG-g-hbPG and hbPG, and a cylindrical shape for linPG-g-hbPG in the nanometric range. Small angle X-ray scattering confirmed the compact particle-like structure of this family of hbPG architectures. Interestingly, the glass transition temperature showed a structure dependence, with cPG-g-hbPG having the highest values and hbPG having the lowest values for the same molecular weight. This study is a step forward in the generation of water-soluble polymers with tailored structure and functionality for advanced applications.

In Vitro Biocompatibility and Endothelial Permeability of Branched Polyglycidols Generated by Ring-Opening Polymerization of Glycidol with B(C6F5)3 under Dry and Wet Conditions

Polyglycidol or polyglycerol (PG), a polyether widely used in biomedical applications, has not been extensively studied in its branched cyclic form (bcPG), despite extensive research on hyperbranched PG (HPG). This study explores the biomedical promise of bcPG, particularly its ability to cross the blood-brain barrier (BBB). We evaluate in vitro biocompatibility, endothelial permeability, and formation of branched linear PG (blPG) as topological impurities in the presence of water. Small angle X-ray scattering in solution revealed a fractal dimension of approximately two for bcPG and the mixture bc+blPG, suggesting random branching. Comparisons of cytotoxicity and endothelial permeability between bcPG, bc+blPG, and HPG in a BBB model using hCMEC/D3 cells showed different biocompatibility profiles and higher endothelial permeability for HPG. bcPG showed a tendency to accumulate around cell nuclei, in contrast to the behavior of HPG. This study contributes to the understanding of the influence of polymer topology on biological behavior.

Understanding zwitterionic ring-expansion polymerization through mass spectrometry

Zwitterionic ring-expansion polymerization (ZREP) is a polymerization method in which a cyclic monomer is converted into a cyclic polymer through a zwitterionic intermediate. In this review, we explored the ZREP of various cyclic polymers and how mass spectrometry assists in identifying the product architectures and understanding their intricate reaction mechanism. For the majority of polymers (from a few thousand to a few million Da) matrix-assisted laser desorption/ionization time-of-flight mass spectrometry is the most effective mass spectrometry technique to determine the true molecular weight (MW) of the resultant product, but only when the dispersity is low (approximately below 1.2). The key topics covered in this study were the ZREP of cyclic polyesters, cyclic polyamides, and cyclic ethers. In addition, this study also addresses a number of other preliminary topics, including the ZREP of cyclic polycarbonates, cyclic polysiloxanes, and cyclic poly(alkylene phosphates). The purity and efficiency of those syntheses largely depend on the catalyst. Among several catalysts, N-heterocyclic carbenes have exhibited high efficiency in the synthesis of cyclic polyesters and polyamides, whereas tris(pentafluorophenyl)borane [B(C6F5)3] is the most optimal catalyst for cyclic polyether synthesis.

Intrinsic viscosity and dielectric relaxation of ring polymers in dilute solutions

The absence of chain ends makes ring polymers distinctly different from their linear analogues. The intrinsic viscosity, complex viscosity and the dielectric relaxation of ring polymers are investigated within the tenets of the optimized Rouse-Zimm theory. The distance dependent excluded volume interactions (EVIs) are obtained from Flory's mean field theory. The hydrodynamic interactions (HIs) between the pairs of monomers are estimated using the preaveraged Oseen tensor. The intrinsic viscosity of linear and ring polymers both with and without EVI are compared as a function of ring size. A monotonically increasing trend of the intrinsic viscosity is observed in both cases. The intrinsic viscosity of both linear and ring polymers both with and without EVI show a very good agreement with the experimental results of polystyrene over a wide range of molecular weights in both good and theta solvents, respectively. The fractal dimensions of the ring polymers with EVI lie between that of a random walk and a self-avoiding walk model of linear polymers in three dimensions. The ring size increases with EVI and the effect of EVI is stronger on larger rings than that on smaller rings. The dielectric relaxation follow a connectivity independent universal scaling behavior at low and high frequency regions. The imaginary part of the complex dielectric susceptibility displays a local maxima in the intermediate frequency region, which reveals a structure dependent behavior of the rings. The theoretically calculated dielectric loss of ring polymers with HI matches well with those obtained from experiments.

Cyclic polymers: synthesis, characteristics, and emerging applications

Cyclic polymers with a ring-like topology and no chain ends are a unique class of macromolecules. In the past several decades, significant advances have been made to prepare these fascinating polymers, which allow for the exploration of their topological effects and potential applications in various fields. In this Review, we first describe representative synthetic strategies for making cyclic polymers and their derivative topological polymers with more complex structures. Second, the unique physical properties and self-assembly behavior of cyclic polymers are discussed by comparing them with their linear analogues. Special attention is paid to highlight how polymeric rings can assemble into hierarchical macromolecular architectures. Subsequently, representative applications of cyclic polymers in different fields such as drug and gene delivery and surface functionalization are presented. Last, we envision the following key challenges and opportunities for cyclic polymers that may attract future attention: large-scale synthesis, efficient purification, programmable folding and assembly, and expansion of applications.

Separation, identification, and confirmation of cyclic and tadpole macromolecules via UPLC-MS/MS

LC-MS/MS enables the separation and relative quantitation of cyclic and tadpole architectures of poly(glycidyl phenyl ether)s synthesized via ring-opening zwitterionic polymerization (ZREP).

Macrocyclization efficiency for poly(2-oxazoline)s and poly(2-oxazine)s

Poly(2-oxazine)s show higher tendency to undergo macrocyclization compared to poly(2-alkyl-2-oxazoline)s, increasing scale-up potential and applicability of these cyclic polymers.

Advancing macromolecular hoop construction: recent developments in synthetic cyclic polymer chemistry

Synthetic methodology to access cyclic macromolecules continues to develop via two distinct mechanistic classes: ring-expansion of macrocyclic initiators and ring-closure of functionalized linear polymers.

Broadband dielectric spectroscopy to validate architectural features in Type-A polymers: Revisiting the poly(glycidyl phenyl ether) case

Broadband dielectric spectroscopy (BDS) is a powerful technique that allows studying the molecular dynamics of materials containing polar entities. Among a vast set of different applications, BDS can be used as a complementary tool in polymer synthesis. In this work, we will show how BDS can be used to validate architectural features in Type-A polymers, those having a net dipole moment component along the chain contour. Specifically, we will focus on the evaluation of the dielectric relaxation of poly(glycidyl phenyl ether) (PGPE) samples designed and synthesized with a variety of topologies and regio-orders: linear regio-regular chains synthesized from monofunctional and bifunctional initiators, macrocyclic regio-regular chains, and linear and macrocyclic regio-irregular chains. Our study highlights the impact of using BDS as a complementary characterization technique for providing topological details of polymers, which are otherwise not possible with many traditional techniques (e.g., NMR and mass spectrometry).

Kinetic differences in the intercalation of linear and cyclic penta(ethylene oxide)s into graphite oxide leading to separation by topology

Intercalation kinetics in graphite oxide is critically dependent on the molecular topology.