Water-Soluble “Poly(propylene oxide)” by Random Copolymerization of Propylene Oxide with a Protected Glycidol Monomer

Acrylamide-induced enhanced solubilization of poly(propylene glycol) in aqueous solution

Acrylamide (AM)-induced enhanced solubilization of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) has been phenomenologically reported in a previous study. However, little is known about its mechanism. In this study, poly(propylene glycol) (PPG) serves as a model system to clarify this enhanced solubilization phenomenon, driven by two specific reasons. First, it helps eliminate any interference from PEO segments. Second, the liquid state of low molecular weight PPG proves advantageous for characterizing molecular interactions. The phenomenon of AM-induced enhanced solubilization has been conclusively demonstrated in the PPG system for the first time. Addition of AM consistently raises the cloud point of PPG aqueous solution. Subsequently, the structure and molecular interactions within the PPG/AM aqueous solution were investigated. Notably, there is no robust association or hydrogen bond between PPG and AM molecules; instead, only van der Waals forces are found to be at play. A model has been constructed, grounded in the contacts between PPG and the solvent during the coil-to-globule transition, to better understand the observed impact of AM on the clouding behavior of PPG aqueous solutions. The mechanism behind the enhanced solubilization has been ascribed to AM's ability to contact with PPG during the temperature-induced dehydration process, thereby assisting in sustaining the PPG's dissolved state.

Investigation of the oxygen coverage effect on the direct epoxidation of propylene over copper through DFT calculations

The direct epoxidation of propylene is one of the most important selective oxidation reactions in industry. The development of high-performance copper-based catalysts is the key to the selective oxidation technology and scientific research of propylene. The mechanism of propylene's partial oxidation catalyzed by Cu(111) under different oxygen coverage conditions was studied using density functional theory calculations and microkinetic modeling. We report here in detail two parallel reaction pathways: dehydrogenation and epoxidation. The transition states and energy distributions of the intermediates and products were calculated. The present results showed that propylene oxide (PO) selectivity was high under low oxygen coverage, and increasing the oxygen coverage would decrease the PO selectivity but increase the PO activity, and there was an inverse relationship between PO selectivity and activity. Increasing oxygen coverage would reduce the energy barrier for the C-O bond formation of C3H5O due to the weaker adsorption strength of C3H5, thus decreasing the PO formation selectivity. On the other hand, increasing oxygen coverage would reduce the energy barrier for the possible reaction steps of propylene epoxidation in general, and thus increasing the catalytic activity. It might be proposed that the active site for propylene epoxidation is the metallic copper or partially oxidized copper in terms of the change of PO formation selectivity with oxygen coverage.

Cu(triNHC)-catalyzed polymerization of glycidol to produce ultralow-branched polyglycerol

We have successfully synthesized a novel form of polyglycerol with an unprecedentedly low degree of branching (DB = 0.08-0.18), eliminating the need for glycidol protection. Leveraging the remarkable efficiency and selectivity of our Cu(triNHC) catalyst, comprising copper(i) ions and NHC ligands, we achieved a highly selective polymerization process. The proposed Cu-coordination mechanisms presented the formation of linear L1,3 units while effectively suppressing dendritic units. Consequently, our pioneering approach yielded polyglycerol with an ultralow DB and exceptional yields. To comprehensively assess the physical properties and topology of the synthesized polyglycerol, we employed 1H diffusion-ordered spectroscopy, size-exclusion chromatography, and matrix-assisted laser desorption/ionization-time of flight spectrometry. Remarkably, the ultralow-branched cyclic polyglycerol (DB = 0.08) synthesized at 0 °C showcased extraordinary characteristics, exhibiting the lowest diffusion coefficient and the highest molecular weight. This achievement establishes the significant potential of our polyglycerol with a low degree of branching, revolutionizing the field of biocompatible polymers.

Selective ring-opening polymerization of glycidyl ester: a versatile synthetic platform for glycerol-based (co)polyethers

Linear polyglycerol is highly valued for its excellent hydrophilicity and biocompatibility as well as its multihydroxy nature. We report here a convenient route for controlled synthesis of polyglycerol through ring-opening...

Crystal-plane-controlled selectivity and activity of copper catalysts in propylene oxidation with O2

The selectivity of PO is inversely proportional to its activity on copper catalysts.

A DFT and microkinetic study of propylene oxide selectivity over copper-based catalysts: effects of copper valence states

The development of high-performance copper-based catalysts is critical for the selective oxidation of propylene in both technology and scientific fields.

A general concept for the introduction of hydroxamic acids into polymers

Polyethers (PEG) with hydroxamic acid groups enable chelation of a variety of metal ions, coating of metal oxide surfaces and stabilization of nanoparticles. In contrast to catechol, hydroxamic acids are oxidation stable and biocompatible.

Hydroxamic acids (HA) form stable complexes with a large variety of metal-ions, affording hydroxamates with high complexation constants. Hydroxamic acid moieties play a crucial role in the natural iron metabolism. In this work, 1,4,2-dioxazoles linked to a hydroxyl group are introduced as key compounds for the installation of hydroxamic acids at synthetic polymers in well-defined positions. A general synthetic scheme is developed that gives access to a series of novel functional key building blocks that can be universally used to obtain hydroxamic acid-based monomers and polymers, for instance as protected HA-functional initiators or for the synthesis of a variety of novel HA-based monomers, such as epoxides or methacrylates. To demonstrate the excellent stability of the dioxazole-protected hydroxamic acids, direct incorporation of the dioxazole-protected hydroxamic acids into polyethers is demonstrated via oxyanionic polymerization. Convenient subsequent deprotection is feasible under mild acidic conditions. α-Functional HA-polyethers, i.e. poly ethylene glycol, polypropylene glycol and polyglycerol based on ethylene oxide, propylene oxide and ethoxy ethyl glycidyl ether, respectively are prepared with low dispersities (<1.2) in the molecular weight range of 1000 to 8500 g mol^–1. Water-soluble hydroxamic acid functional poly(ethylene glycol) (HA-PEG) is explored for a variety of biomedical applications and surface coating. Complexation of Fe(iii) ions, coating of various metal surfaces, enabling e.g., solubilization of FeO_x nanoparticles by HA-PEGs, are presented. No impact of the polyether chain on the chelation properties was observed, while significantly lower anti-proliferative effects were observed than for deferoxamine. HA-PEGs show the same complexation behavior as their low molecular weight counterparts. Hydroxamic acid functional polymers are proposed as an oxidatively stable alternative to the highly established catechol-based systems.

Oxidation-responsive polyether block copolymers lead to non-ionic polymer surfactants with multiple amine N-oxides

Oxidation of tertiary amines leads to multiple amine N-oxide moieties and a highly polar polyether structure. Combination with the apolar poly(propylene oxide) affords unusual surfactants.

Computational study on epoxidation of propylene by dioxygen using the silanol-functionalized polyoxometalate-supported osmium oxide catalyst

The silanol-functionalized POM-supported single-site Os oxide catalyst has been theoretically considered for epoxidation of propylene in the presence of dioxygen based on density functional theory calculations.

Conventional Oxyanionic versus Monomer-Activated Anionic Copolymerization of Ethylene Oxide with Glycidyl Ethers: Striking Differences in Reactivity Ratios

Detailed understanding of the monomer distribution in copolymers is essential to tailor their properties. For the first time, we have been able to utilize in situ ¹H NMR spectroscopy to monitor the monomer-activated anionic ring opening copolymerization (AROP) of ethylene oxide (EO) with a glycidyl ether comonomer, namely, ethoxy ethyl glycidyl ether (EEGE). We determine reactivity ratios and draw a direct comparison to conventional oxyanionic ROP. Surprisingly, the respective monomer reactivities differ strongly between the different types of AROP. Under conventional oxyanionic conditions similar monomer reactivities of EO and EEGE are observed, leading to random structures (r_EO = 1.05 ± 0.02, r_EEGE = 0.94 ± 0.02). Addition of a cation complexing agent (18-crown-6) showed no influence on the relative reactivity of EO and EEGE (r_EO = r_EEGE = 1.00 ± 0.02). In striking contrast, monomer-activated AROP produces very different monomer reactivities, affording strongly tapered copolymer structures (r_EO = 8.00 ± 0.16, r_EEGE = 0.125 ± 0.003). These results highlight the importance of understanding reactivity ratios of comonomer pairs under certain polymerization conditions, at the same time demonstrating the ability to generate both random and strongly tapered P(EO-co-EEGE) polyethers by simple one-pot statistical anionic copolymerization. These observations may be generally valid for the copolymerization of EO and glycidyl ethers.

Polymerization of Ethylene Oxide, Propylene Oxide, and Other Alkylene Oxides: Synthesis, Novel Polymer Architectures, and Bioconjugation

The review summarizes current trends and developments in the polymerization of alkylene oxides in the last two decades since 1995, with a particular focus on the most important epoxide monomers ethylene oxide (EO), propylene oxide (PO), and butylene oxide (BO). Classical synthetic pathways, i.e., anionic polymerization, coordination polymerization, and cationic polymerization of epoxides (oxiranes), are briefly reviewed. The main focus of the review lies on more recent and in some cases metal-free methods for epoxide polymerization, i.e., the activated monomer strategy, the use of organocatalysts, such as N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs) as well as phosphazene bases. In addition, the commercially relevant double-metal cyanide (DMC) catalyst systems are discussed. Besides the synthetic progress, new types of multifunctional linear PEG (mf-PEG) and PPO structures accessible by copolymerization of EO or PO with functional epoxide comonomers are presented as well as complex branched, hyperbranched, and dendrimer like polyethers. Amphiphilic block copolymers based on PEO and PPO (Poloxamers and Pluronics) and advances in the area of PEGylation as the most important bioconjugation strategy are also summarized. With the ever growing toolbox for epoxide polymerization, a "polyether universe" may be envisaged that in its structural diversity parallels the immense variety of structural options available for polymers based on vinyl monomers with a purely carbon-based backbone.

Hyperbranched Poly(propylene oxide): A Multifunctional Backbone-Thermoresponsive Polyether Polyol Copolymer

Backbone-thermoresponsive hyperbranched poly(propylene oxide)-based polyether polyols have been synthesized by anionic ring-opening copolymerization of glycidol and propylene oxide. The number of functional hydroxyl end groups and the lower critical solution temperature (LCST) can be readily adjusted by varying the comonomer ratio. Molecular weights in the range of 1200-2000 g/mol were achieved. Hyperbranched polyether polyols with LCST values between 24 and 83 °C can be obtained in a convenient one-step reaction.