Pickering Emulsion Formation of Paraffin Wax in an Ethanol–Water Mixture Stabilized by Primary Polymer Particles and Wax Microspheres Thereof

Stable dispersions of paraffin wax droplets and their nano- and microspheres have broad applications. Despite intensive efforts, the production of uniform wax spheres remains a challenge. For their preparation, abundant surfactants and other additives are commonly used to stabilize the dispersions. These additives are hardly removable and entrain often adverse consequence in many applications, particularly in biological and medical applications, where microspheres with absolutely clean surface are preferred. We report here a novel process to prepare stable dispersion of wax droplets in a water–ethanol mixture with a narrow size distribution by simply shaking without any surfactants. The process is featured by using primary polymer particles (PPs) of poly­(do­decene-­tri­hydroxy­methyl­propane­ tri­acrylate) as a Pickering stabilizer. PPs were prepared by precipitation polymerization without any surfactant and stabilizer. By rapidly cooling the wax emulsion, solid wax spheres with good uniformity were obtained. Their size, between 50 and 480 μm, was easily adjustable by changing the shaking rate, number of PPs, and particularly the size of PPs. The morphology of the wax spheres was examined by SEM, which showed that they were covered by a layer of PPs. The formation mechanism of the microspheres was also discussed on the basis of the adsorption energy of PPs on wax spheres, estimated from the corresponding contact angle of the solvent toward the PPs and the wax. This paper presents a novel pathway for the preparation of wax microspheres with only polymer particles without the need for any other additives

Preparation of Highly Uniform Polyurea Microspheres through Precipitation Polymerization and Their Characterization

Uniform polyurea (PU) microspheres were prepared through precipitation polymerization of isophorone diisocyanate (IPDI) in water–acetone mixed solvent, under mechanical oscillation and quiescent conditions. Higher yield with better uniformity for the microspheres was achieved under the quiescent process. The preparation was therefore optimized for the quiescent process. The maximal IPDI loading reached 11.0 wt % with the yield of the microspheres of 88.5%. With acetone replaced by acetonitrile, this yield was increased further to 93.5% combined with also a higher IPDI loading of 15.0 wt % at the same time. The chemical structure of PU was studied using nuclear magnetic resonance. PU microspheres, insoluble in most of organic solvents tested, were dissolved in <i>m</i>-cresol at 30 °C and in acetic acid at 66 °C. These results showed that the PU microspheres consisted of only linear polymers. This work provides therefore a simple and promising protocol for large-scale production of highly uniform polymer microspheres through precipitation polymerization without any additives

Phase Transition and Fluorescence Emission of Multiresponsive Poly(ethylene glycol-<i>co</i>-siloxane) and Its Application for Uric Acid Detection

In recent years, multiresponsive polymers with nonconjugated chromophores featuring cluster-triggered emission (CTE) have attracted significant attention due to their wide applications and interests in fundamental studies. There is a lack of studies correlating the fluorescent properties to their distinct stimuli-responsiveness although CTE materials have been well studied. Herein, we introduced a poly(ethylene glycol)-polysiloxane copolymer, PEG-Si, which exhibits responsiveness to temperature, pH, CO2, and salinity, with adjustable phase transition and reversible fluorescence. PEG-Si was synthesized by a catalyst-free aza-Michael addition of PEG diacrylate with bis(3-aminopropyl)-tetramethyldisiloxane in dichloromethane. The structure of PEG-Si was characterized using various spectroscopic methods such as NMR and Fourier transform infrared spectroscopy (FTIR). The light transmittance and fluorescence performance of PEG-Si were measured at different temperatures under varying conditions, including polymer composition, concentration, pH, and bubbled CO2, to observe their evolution. The relationship between fluorescence properties and the phase transition process was described. The results demonstrate that PEG-Si can be used as a temperature and pH fluorescence thermometer and biosensor for detection of uric acid with a detection limit of 1.02 μmol/L. This study proposes a practical strategy for designing multiresponsive polymers with CTE features and provides significant insights into the correlation between stimuli-responsiveness and fluorescent properties, which contributes to the development of advanced materials with diverse applications

Immobilization of Lipase from <i>Pseudomonas fluorescens</i> on Porous Polyurea and Its Application in Kinetic Resolution of Racemic 1‑Phenylethanol

A porous polyurea (PPU) was prepared through a simple protocol by reacting toluene diisocyanate with water in binary solvent of water–acetone. Its amine group was determined through spectrophotometric absorbance based on its iminization with <i>p</i>-nitrobenzaldehyde amines. PPU was then used as a novel polymer support for enzyme immobilization, through activation by glutaraldehyde followed by immobilization of an enzyme, lipase from <i>Pseudomonas fluorescens</i> (PFL), via covalent bonding with the amine groups of lipase molecules. Influences of glutaraldehyde and enzyme concentration and pH in the process were studied. The results revealed that the activity of the immobilized PFL reached a maximum at GA concentration of 0.17 mol/L and at pH 8. Immobilization rate of 60% or higher for PFL was obtained under optimized condition with an enzyme activity of 283 U/mg. The porous structure of PPU, prior to and after GA activation and PFL immobilization, was characterized. The activity of the immobilized PFL at different temperature and pH and its stability at 40 °C as well as its reusability were tested. The immobilized enzyme was finally used as enantioselective catalyst in kinetic resolution of racemic 1-phenylethanol (1-PEOH), and its performance compared with the free PFL. The results demonstrate that the enzyme activity and stability were greatly improved for the immobilized PFL, and highly pure enantiomers from racemic 1-PEOH were effectively achieved using the immobilized PFL. Noticeable deactivation of PFL in the resolution was observed by acetaldehyde in situ formed. In addition, the immobilized PFL was readily recovered from the reaction system for reuse. A total of 73% of the initial activity was retained after 5 repeated reuse cycles. This work provides a novel route to preparation of a polyurea porous material and its enzyme immobilization, leading to a novel type of immobilized enzyme for efficient kinetic resolution of racemic molecules

Polyurea Structure Characterization by HR-MAS NMR Spectroscopy

Owing to the presence of abundant interchain interactions such as hydrogen bonds, polyureas (PU) are only swellable or soluble in a limited number of highly protonic solvents, and the viscosity of the solutions obtained is very high, making their chemical structure characterization hard or even impossible by standard NMR. Accurate structure analysis is also hard by solid-state NMR due to low spectral resolution. The presence of a side reaction in their synthesis generating biuret cross-links is often invoked to explain their insolubility. Here we demonstrate that High Resolution Magic Angle Spinning (HR-MAS) NMR is an efficient tool for the chemical structure analysis even for cross-linked PU. With ¹H, ¹³C, and ¹H–¹⁵N HSQC combined, a variety of linear and cross-linked PU is analyzed by HR-MAS NMR, and conclusive information on their chemical structure is obtained, which reveals for the first time that the biuret group is absent in all PU