Macromolecular Reaction Engineering最新文献

ω-Alkenyltrimethylsilanes of different alkenyl moieties, i.e., 3-butenyltrimethylsilane, 5-hexenyltrimethylsilane, and 7-octenyltrimethylsilane, are used as model compounds to study the alkenyl length effect in copolymerization of ethylene with steric-hindered tri-substituted silane-functionalized α-olefins over MgCl₂/TiCl₄ catalysts. The experimental results reveal that 3-butenyltrimethylsilane tops the three α-olefins in incorporation rate into PE while 7-octenyltrimethylsilane is slightly better than 5-hexenyltrimethylsilane. The coordination-insertion events for different ω-alkenyltrimethylsilanes are investigated by DFT simulation. The results suggest that the three ω-alkenyltrimethylsilanes encounter similar energy barriers during insertion, with similar repulsive interactions between the bulky trimethylsilane substituent and growing PE chain found in the energy decomposition of transition state configuration. However, complexation abilities at the Ti active site for the three ω-alkenyltrimethylsilanes follow the order of 3-butenyltrimethylsilane > 5-hexenyltrimethylsilane > 7-octenyltrimethylsilane, in line with their molecular compactness, which are deemed to be where the alkenyl length effect originates in the ω-alkenyltrimethylsilane/ethylene copolymerization.

This work addresses a comparative study focused on the synthesis of alkyd resins from different renewable resources such as chia, castor and palm vegetable oils through the alcoholysis–polycondensation process. The formed alkyd resins are analyzed by Fourier transform infrared (FTIR), ¹H NMR, and ¹³C NMR. Besides, intrinsic viscosity and gel permeation chromatography (GPC) assays are conducted to evaluate the differences between the obtained resins focusing on their molecular weight and physicochemical properties. FTIR shows a satisfactory conversion from vegetable oils to alkyd resins. Both ¹H NMR and ¹³C NMR indicate that alkyd resins are successfully synthesized. The values for molecular-weight dispersity (Ð_M) obtained for the resins are 2.3, 1.3, and 1.7 from chia, palm, and crude castor, along with the weight-average molecular weight (M_w) of 4516, 1025, and 2451 g mol⁻¹, respectively. The chia alkyd resin shows a 571.92 cP and is the highest viscosity obtained. It is also observed that an increase in phthalic anhydride can increase the molecular weight of the alkyd resin. This comparative study indicates that chia oil alkyd resin has enormous potential to be employed as a surface coating agent.

The oil well drilling process is a nonlinear system with transient nature. Conventional drilling is unable to assure safe and cost-effective operation for fractured, cavernous, and highly permeable carbonate reservoirs, which contain the largest oil reserves worldwide. Concerning drilling technologies, Pressurized Mud Cap Drilling (PMCD) is suitable for the challenging scenario previously mentioned. According to PMCD technique, a sacrificial fluid is injected through the drill string and a light annular mud is pumped in countercurrent through the annulus region (bullheading), without surface return, forcing gas and drilled cuttings back to formation. A two-phase flow distributed model (Drift Flux Model – DFM) is developed to properly describe the complex nature of the system. Also, an experimental facility, presenting field similarity, is employed to validate the open – closed loop schemes. The main objective of the controller (control reconfiguration with gain scheduling) is to regulate annulus pressure, handling gas kick, drilling fluid losses and inverse response dynamics. Besides, gas injection, migration and bullheading are studied. The simulations, validated through experimental data, highlight the methodology usefulness for field applications.

A mathematical model is proposed that couples the decomposition kinetics of persulfate (S₂O₈²⁻) and the free radical polymerization kinetics of itaconic acid (IA); the results are compared with experimental data reported in the literature. It is found that the former is highly affected by the acidification of the aqueous medium which is caused by the equilibrium dissociation of IA but mainly by HSO₄⁻ produced by side reactions of the S₂O₈²⁻ decomposition. This qualitatively explains the dependence of d[S₂O₈²⁻]/dt with [IA] and the initial concentration of persulfate ([S₂O₈²⁻]₀), reported in the literature. According to the model results, temperature overshoots are very likely to occur in the experiments so there is doubt whether the reaction order >1 with respect to [IA] that is sometimes reported in the literature for the rate of polymerization (Rp) is an artifact related to an imprecise temperature (T) control or is due to a more complex mechanism. Due to the higher activation energy of the persulfate decomposition compared to the propagation reaction, small variations of T can lead to significant variations of d[S₂O₈²⁻]/dt but to an almost imperceptible effect on Rp. Recommendations for future experimental work and refinement of the kinetic model are provided.

Front Cover: This study deals with the development of a reaction kinetic model describing the inhibition mechanism of RAFT dispersion polymerization by oxygen and its application to investigate the effect of re-initiation on the synthesized polymer quality. The experimental validation of the kinetic model creates a functional digital twin, establishing a valid method for diblock copolymer synthesis from a non-successful polymerization attempt. This is reported by Emil Pashayev, Felix Kandelhard, and Prokopios Georgopanos in article number 2200068.

The mechanical properties and blocking resistance of films cast from latex particles can be improved by addition of a reinforcing polymer of high modulus that acts as a “hard” phase. This work demonstrates that blocking resistance, a key performance parameter for use in coatings, of such films can be understood in terms of the relative contribution of the “hard” and “soft” components to the rheological properties of the material. In order to do so, representative latexes that contain a semicrystalline core of poly(stearyl acrylate) as a reinforcing phase and a shell of amorphous poly(styrene-co-butyl acrylate) are synthesized. By varying the composition of the amorphous phase (glass transition temperature, molar mass) and the relative amorphous/semicrystalline fraction, it is demonstrated that the improvement in blocking resistance is strongly correlated with the increase in the modulus of the material but is also affected by the dynamics of polymer diffusion of chains in the soft phase. This work allows to establish design rules for polymer and colloidal structures that can be targeted to maximize blocking resistance.

In the recent years, the growing amounts and incorrect disposal of solid wastes have created serious negative environmental impacts, including land and water pollution. Chicken litter (CL) is a type of solid waste which is generated during chicken production, the appropriate final destination of which is still subject to technical discussion. Because CL is composed mostly of fibers, proteins, carbohydrates, and different minerals, the use of this material as a filler for the manufacture of polymer materials has been suggested. The main objective of the present work is the manufacture of polymer composites in situ polymerization using CL as a filler and succinic acid and 1,4-butanediol as monomers, considering that the fiber content in CL is ≈20 wt%. The obtained poly(butylene succinate) (PBS) composites are characterized by Fourier transformed infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), degradability in distilled water, and compression analyses. The results show that the addition of CL to the mixture do not affect the course of the polycondensation reaction significantly. Furthermore, compression tests show that the compressive strength of test pieces increases with the CL content.

The solubility of different alkanes in polyethylene (PE) of different densities, as well as the solubility of the polymers in the alkanes, and the degree of swelling of the powders are studied as a function of temperature. It is found that the solubility of linear low-density polyethylene (LLDPE) is as much as 6 times greater than that of high-density polyethylene (HDPE) at the same temperature, and that LLDPE swells at least 50% more than HDPE the same diluent at the same temperature. The breakthrough curves also show that lighter alkanes swell the PE more at a given temperature than heavier ones. Also, the breakthrough points (the temperature at which the swelling versus temperature curves change slope) occur at lower temperatures for PE of lower density. Gel formation is observed for medium and low density polyethylenes in pentane and hexane. This quantitative information will be useful in developing process models for different industrial polymerization processes, as particle swelling can have a significant impact on slurry viscosity and the flow stability and solids loading of commercial reactors.

Polyurethanes are probably the most versatile among polymers of greater industrial use due to the possibility of being produced in a wide range of density, hardness, and mechanical properties and through different conversion processes. Its synthesis involves a great variety of raw materials and proportions between them. A mathematical model that describes the polyurethane foam formation can be very useful for the development of formulations and in the definition of the processing conditions, avoiding great consumption of time and errors in the development and experiments. The present work studies this process using industrial formulation. The kinetic parameters of the reaction between polyol with isocyanate are determined calorimetrically using the adiabatic temperature rise method, obtaining the values of activation energy 22.2 kJ mol⁻¹ and heat of reaction 91.8 kJ mol⁻¹. Data liquid–vapor equilibrium of the hydrofluorolefin blowing agent in a polyol mixture are obtained and treated with Flory–Huggins model with good agreement with experimental data (deviation of 1.6%). The mathematical model is satisfactory to describe the expanding process in a pilot scale, under different conditions.