Macromolecular Reaction Engineering最新文献

Front Cover: The deposition process during emulsion polymerization is classified as particulate and reaction fouling. The deposited material is composed of latex particles and emulsifier with particle size and number depending on the respective equilibrium composition of the fluid phase. The figure shows the deposition of latex particles after a reaction time of 240 minutes. Further details can be found in article 2300057 by Wolfgang Augustin and co-workers.

In vinyl/divinyl copolymerization, a crosslink is formed by the reaction between an active center and a pendant double bond. When both the active center and the pendant double bond are located within the same polymer molecule, the cyclization occurs, which is ineffective for growth in molecular weight. In the present model, the network dimension theory is applied to estimate the mean-square radius of gyration for the growing polymer molecule, which is used to account for the enrichment effect of pendant double bonds around the active center for the cyclization reaction. The model is applied to the miniemulsion copolymerization, and both conventional free-radical polymerization and ideal living polymerization are considered. Some of important characteristics of network architecture formed in these two types of polymerization mechanisms that cannot be predicted based on the classical chemical kinetics can be reproduced by the model, such unique characteristics as the pendant double bonds are consumed from the beginning of polymerization in the conventional free-radical polymerization but not so in the living polymerization. The present model provides useful insights into the size and structural dependent network formation kinetics without relying on the lattice model.

Polymeric particles less than 100 nm in size (polymer nanoparticles), which are useful in the fields of medicine and so on, are synthesized through emulsion polymerization, wherein surfactants are essential for maintaining their dispersion stability, contaminating particle surfaces and causing high environmental pollution. The soap-free emulsion polymerization (SFEP) of styrene in a packed reactor using microglass beads enables the synthesis of polymer nanoparticles without surfactants. Ultraviolet irradiation is used for radical polymerization using an initiator during the SFEP of styrene. The reaction space in the packed reactor is controlled by the size of glass beads to be filled in the reactor. A decrease in the size of the glass beads narrows the reaction space, causing the average polystyrene particle size to reach 27.3 nm and suppress convection flow by the wall of the glass beads, thereby limiting particle motion and preventing particle growth through particle collisions.

Front Cover: Polymer reaction engineering (PRE) is a key competence for process scale-up, but the information collected in daily plant operation is not fully exploited. What do catalytic olefin polymerization plants tell us? In article 2300046, by Vasileios Touloupidis and João B. P. Soares, a method to increase catalyst and process know-how, based on experimentally acquired results from a continuous tandem reactor polymerization process is proposed and validated using small-scale experiments.

Mineral–rubber composites based on phosphorylated butadiene rubber (PhBR), including pure expanded perlite (EP) and modified phosphorylated expanded perlite (PhEP) as fillers, are developed. The process involves forming PhBR and its composites—EP/PhBR and PhEP/PhBR—through the oxidative chlorophosphorylation (OxCh) reaction. An in-depth comparative analysis is conducted on the thermal destruction of the PhBR matrix and the EP/PhBR, and PhEP/PhBR composites. The thermogravimetric (TG)/differential thermogravimetry (DTG) analyses reveal three stages of thermal degradation for the PhBR matrix and both composites, highlighting the notable effects of EP and PhEP in the second and third stages of the degradation process. In comparison, the PhEP/PhBR composite exhibits reduced weight loss, the highest integral procedural decomposition temperature (IPDT) value, and a lower T_max on the DTG curve, compared with the EP/PhBR composite and the PhBR matrix. The mechanism of the thermal destruction reaction and the kinetic parameters E_a and A are calculated using the model-fitting Coats–Redfern method.

Transparent and light films with high electrical conductivity are preferred for flexible electronic applications. Here, a film exhibiting high transparency, electrical conductivity, and flexibility is produced using a polyimide (PI) substrate and multiwalled carbon nanotubes (MWCNTs) through spray coating. Cost-effective MWCNTs are used instead of other electrically conductive materials, including silver nanowire ink, single-walled carbon nanotubes (SWCNTs), and other carbon materials. The average sheet resistance of the prepared MWCNT–PI film is 520.2 Ω □⁻¹ (infinite for the bare PI film), which is lower than the sheet resistances of the SWCNT–PI film reported by another group. This can be attributed to the increase in electrical conductivity of the highly transparent PI film due to the use of MWCNTs. The transparency of the MWCNT–PI film is 71.834% at 550 nm. When MWCNTs and PI are combined, MWCNTs protrude from the surface of the PI film, creating networks and increasing electrical conductivity. Atomic force microscopy analysis reveals that MWCNT networks form on the surface of the MWCNT–PI film. This study suggests the possibility that MWCNTs can also be used as carbon materials for flexible and highly transparent films.

In the present work, the catalyst performances of USY and REY zeolites and MgO, ZnO, and Mg_xAlO_y oxides are investigated in the pyrolysis of virgin high-density polyethylene (HDPE) and of post-consumer polyolefin waste. The influence of operation parameters and catalyst deactivation resistance over four reaction cycles are evaluated. The results indicate that basic oxides do not show relevant cracking activity, so that the only identified effect for these catalysts is the production of liquid products with higher contents of paraffins when compared to thermal pyrolysis. Among the evaluated oxides, Mg_xAlO_y is the most active and resistant to deactivation. The zeolites promote cracking and secondary reactions of isomerization, cyclization, and aromatization. Particularly, USY promotes the production of higher-quality oils and shows higher deactivation resistance, when compared to REY. Additionally, a significant loss of catalyst activity is identified in reactions conducted with post-consumer polyolefin wastes. However, increase in rates of coke formation and the presence of contaminants (such as halogens and metals) are not detected in the catalysts after the reactions.

Liquid carbon dioxide (LCO₂) or supercritical carbon dioxide (ScCO₂) can be used as an important solvent medium for preparing polymer particles through dispersion polymerization. However, based on the weak solvent characteristics of CO₂, the development of stabilizers used in dispersion polymerization has always been an important challenge. These stabilizers are progressing toward the low-cost, pollution-free, and simple synthesis routes, et al. In this research, pentaerythritol tetra (3-mercaptopropionate) (PTMP) is used to control the homopolymerization or copolymerization of vinyl acetate (VAc)/vinyl propionate (VPr), the homopolymers or copolymers with thiol group are synthesized by the one-pot method. These homopolymers or copolymers are used as the stabilizers to stabilize the dispersion polymerization of N-vinyl-2-pyrrolidone (NVP) in ScCO₂. The results show that the structural unit proportion of the stabilizers, the concentration of stabilizers or 2, 2´-azobis(isobutyronitrile) (AIBN), and the time interval for dispersion polymerization have significant impacts on the conversion percentage of NVP and the molecular weight of polymers. The maximum conversion percentage of NVP can get to 95%, and the molecular weight of poly(N-vinyl-2-pyrrolidone)(PNVP) can reach 22.3 kPa. SEM analysis indicates that the PNVP obtained has regular spherical characteristics.