Macromolecular Reaction Engineering最新文献

The radical polymerization kinetics of 2-(dimethylamino)ethyl methacrylate (DMAEMA) is explored in dimethyl sulfoxide, ethanol (EtOH), ethanol-water (EtOH/H₂O), and water. In situ nuclear magnetic resonance (NMR) spectroscopy is used to study both solvolysis and polymerization kinetics. Hydrolysis of nonionized DMAEMA occurs in H₂O and ethanolysis in EtOH/H₂O mixtures to form both methacrylic acid (MAA) and ethyl methacrylate (EMA), with the presence of water increasing the rate of ethanolysis in the mixed solvent. Although some solvolysis occurred in EtOH and EtOH/H₂O containing 25 wt.% H₂O, the rates are sufficiently low that essentially poly(DMAEMA) homopolymer is synthesized, unlike the DMAEMA/MAA copolymer formed in water and the DMAEMA/MAA/EMA terpolymer formed in water-rich EtOH/H₂O. A model is constructed to represent the polymerization of nonionized DMAEMA in solution, with the experimental results used to estimate key rate coefficients. The model predictions show good agreement with the experimental data on monomer conversion, average molar masses, and molar mass distributions. Similarly, the rate coefficients for polymerization of ionized DMAEMA are estimated based on experiments conducted in water at pH 1 and 4. The understanding gained from these studies is combined into a comprehensive mechanistic model to describe the polymerization of partially-ionized DMAEMA in the presence of hydrolysis.

Single hollow particles are used in various fields, particularly in thermal insulation materials, owing to their low thermal conductivity attributed to encapsulated air properties. “The self-assembling phase separated polymer (SaPSeP) method” is an original hollowing method that is proposed by this laboratory 25 years ago. Most hollow particles prepared by the SaPSeP method have carbon, oxygen, and hydrogen polymer shells, which lack sufficient heat resistance. In this study, hollow particles with a silicone shell, which is highly heat-resistant, are prepared using the SaPSeP method using a trimer of 3-methacryloxypropylmethyldimethoxysilane (MPDS). The MPDS trimer (3MPDS) is synthesized through the sol–gel reaction of MPDS with a basic aqueous solution. Additionally, hollow particles are prepared using a new silicone oligomer composed of MPDS and dimethoxymethylvinylsilane (DMVS). Both hollow particles prepared from 3MPDS and from a new silicone oligomer composed of MPDS and DMVS showed high heat resistance. They maintained their hollow structure even when exposed to temperatures up to 900 °C.

Micrometer-sized monodisperse silicone droplets are prepared through a sol–gel process involving 3-methacryloxypropylmethyldimethoxysilane (MPDS) at room temperature for 1.5 h in the presence of NH₃ as a catalyst. The size of the obtained droplets is controlled by changing the stabilizer concentration and solvent polarity. However, the obtained droplets have not maintained their particulate shape in the dry state due to the absence of a cross-linking structure. Thus, radical polymerization is performed on the obtained silicone droplets at 70 °C for 2 h; consequently, spherical particles with high monodispersity are observed in the dry state, indicating the presence of a cross-linked structure. Microcompression tests are conducted to evaluate the mechanical properties of the silicone particles. Initially, the recovery ratio (elasticity) is not high because the molecular weight of the silicone particles is low, ≈600, due to MPDS cyclization (MPDS trimer). Anionic ring-opening polymerization is therefore performed to extend the molecular weight of the MPDS trimer. Benzyldodecyldimethylammonium bromide and tetrakis[tris(dimethylamino)phosphoranylidenamino]phosphonium chloride are used as catalysts for anionic ring-opening polymerization. These catalysts increased the molecular weight to ≈2000 and 7600, respectively. Furthermore, the silicone particles obtained through anion ring-opening polymerization and radical polymerization have high recovery ratios (elasticity).

A novel linear low-density polyethylene containing H-shape long-chain-branching structures (LCB-LLDPE) is industrially synthesized with Ziegler-Natta catalysts and gas-phase polymerization process at the assistance of ω-alkenylmethyldichlorosilane copolymerization-hydrolysis chemistry. The incorporated LCB structures are characterized by NMR, SEC, and SAOS (small amplitude oscillatory shear) measurements. With a same-sourced plain LLDPE as a comparison benchmark, the new LCB-LLDPE is studied for its properties on various aspects, revealing, among others, significantly reinforced rheological properties, including enhanced shear-thinning behavior, a significant strain-hardening phenomenon in extensional flow, and substantially increased melt strength, as well as significantly improved optical properties, which all benefit its application in extrusion blow molding for thin-film production.

Water-soluble monomers are extensively used in the production of polymeric materials in aqueous media for various applications. Acrylic acid–polyethylene glycol 2-methyl-2-propenyl ether (AA-HPEG) copolymers belong to the class of comb-like polycarboxylate ether (PCE) polymers, employed as superplasticizers for cementitious materials. Due to different reactivity ratios of AA and HPEG, semibatch operations with optimized monomer addition profiles are required to enhance the incorporation of HPEG into the copolymer. The kinetics of this system is complex and, like other water-soluble monomers, depends on monomer concentration, pH, and ionic strength. Despite its high-volume industrial usage, the kinetics of this system have received little attention in the literature. Furthermore, the presence of the HPEG, with 55 ethylene oxide (EO) units in the side chain, complicates the precise determination of individual monomer conversions. To address this, various characterization methods are evaluated, including proton nuclear magnetic resonance (¹H-NMR) and size-exclusion chromatography (SEC). Results show that HPEG conversion is determined more accurately using ¹H-NMR signals from the polymer than unreacted monomer signals or SEC traces. Aqueous semibatch AA-HPEG copolymerization experiments are conducted in acidic media to investigate the effects of comonomer feeding time, initiator and chain-transfer agent concentrations on the copolymerization kinetics, HPEG incorporation, and molar mass.

This work reports the hollow latex (HL) particles developed from natural rubber latex particles (NRPs), known for their broad size distribution and non-spherical shape. HL-NRPs, prepared via the seeded emulsion polymerization in one pot, are studied as potential bio-based nanocapsules for the first time. Effects of types of crosslinking agents and swelling agents, the addition of sodium dodecyl sulfate (SDS), and monomer compositions on the void formation and expansion are systematically investigated. The combined effects of phase separation between NR core swelled with divinyl benzene (DVB) and hydrophilic poly(methyl methacrylate/acrylic acid) P(MMA/AA) shell, the entanglement of rubber chains copolymerized with MMA/DVB/AA monomers, and the osmosis from external aqueous medium promoted the void formation. While crosslinking agents affected the void formation and shell strength, SDS and type of monomers governed colloidal stability and polymerization loci as well as morphology, respectively. The ability of HL-NRPs as nanocapsules is explored by encapsulating fluorescent dyes, i.e., hydrophilic fluorescein isothiocyanate (FITC) and lipophilic Nile red (NiR), as model cargo. From the dye release test after 24 h, the cumulative concentrations of FITC in methanol and of NiR in tetrahydrofuran are 0.17 and 0.11 µg mL⁻¹, respectively. The results suggested that FITC is released from HL-NRPs easier than NiR possibly due to the different encapsulation location.

There is significant interest in developing paints based on structural colors, which do not fade like dyes and pigments. To use these paints as coatings, it is necessary to have a technology that can easily impart structural color to the material's surface without changing color based on the viewing angle. In addition, water-repellent properties that lead to stain resistance are required for practical application. This study applies a structural color coating by synthesizing hydrophobic melanin particles using the Michael addition reaction and arranging these particles on a substrate at high speed. The resulting coating film shows angle-independent structural color due to the amorphous structure of the particle arrangement, and the color tone could be controlled by adjusting the particle size. The combination of the particle's hydrophobic surface and the microscopic unevenness from the arrangement structure produced a superhydrophobic coating with a contact angle of over 160°. Since the Lotus effect, resulting from superhydrophobic surfaces, can maintain the cleanliness of structural color coatings, the findings of this research will contribute to the development of next-generation coating technology.

This work aimed analyzing the chemical and thermal aspects of Polylactic Acid (PLA) composites with Coconut Fiber (CF) and irradiated Coconut Fiber (CFI), upon castor oil (CO) addition. Influence of treated and untreated CF, at 10 and 20 wt.%, on the crystallization kinetics of PLA/CO composites is also investigated. At first, CF is chemically treated through mercerization under NaOH solution with subsequent gamma irradiation. Chemical changes include absence of bands ≈3300 cm⁻¹ and the presence of vibrations at 3000–2851 cm⁻¹ in composites with treated fibers, as evidenced by fourier transform infrared spectroscopy (FTIR). Thermal behavior, as well as crystallization kinetics, are investigated by differential scanning calorimetry (DSC) at different heating rates (5, 10, 15, and 20 °C min⁻¹), using Pseudo-Avrami (PA), Kissinger-Akahira-Sunose (KAS), and Ozawa-Flynn-Wall (OFW) models. Activation energy (E_a) is calculated using OFW, KAS, Friedman (FR), and Vyazovkin (VZ) methods. Results showed changes in the FTIR spectra for PLA/5%CO/10%CF and PLA/5%CO/20%CFI, indicating absence of the carbonyl group (1594 cm⁻¹) present in the ester group of PLA. Insertion of CFs increased the crystallization temperature. Presence of CFI provided an inversion in E_a, when compared to PLA/CO, suggesting that irradiation induces PLA stronger interactions. Gathered results highlight the potential of modified coconut fibers for the development of sustainable composite materials.