Macromolecular Reaction Engineering最新文献

Back Cover: Polymer networks are synthesized to selectively target trans-resveratrol. By employing a statistical design of experiments, the polymerizations are conducted using ultraviolet light initiation, thus yielding materials with molecularly imprinted binding sites tailored for trans-resveratrol. These materials are successfully applied in purifying trans-resveratrol from winemaking residues, demonstrating their practical utility. This is reported by Amir Bzainia, Rolando C. S. Dias, and Mário Rui P. F. N. Costa in article number 2200076.

Herein, the poly(ɛ-caprolactone)-poly(ethylene glycol)-poly(ɛ-caprolactone) (PCL-PEG-PCL) macro xanthate reversible addition–fragmentation chain-transfer agent is obtained on the polyethylene glycol (PEG) (600, 1000, and 1500 g mol⁻¹) block, after the addition of ɛ-caprolactone via ring-opening polymerization. Then, poly (styrene-b-ɛ-caprolactone-b-PEG-b-ɛ-caprolactone-b-styrene) pentablock copolymer is synthesized reversible addition–fragmentation chain-transfer (RAFT) solution polymerization technique via mediated PCL-PEG-PCL xanthate macro-RAFT agents and 2,2′-azobisisobutyronitrile as initiator. The products are demonstrated using Fourier transform infrared spectrophotometer (FT-IR), proton nuclear magnetic resonance (¹H-NMR), carbon nuclear magnetic resonance (¹³C-NMR), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC) analyses. First-order linear kinetic graphs of the reaction mechanism are observed with an increase in molecular weights (M_W) between 16 000 and 36 000 g mol⁻¹. The narrow dispersity (Đ = 1.40–1.48) polymer formation of styrene (St) controlled by RAFT polymerization confirms the increase in molecular weight according to the polymerization time. The reaction kinetics are first order and the rate constants are found to be k₁ = 6.16 × 10⁻⁴s⁻¹, k₂ = 6.91 × 10⁻⁴ s⁻¹ and k₃ = 7.33 × 10⁻⁴ s⁻¹. Thermal and spectroscopic analyses prove that the reactions are carried out successfully.

The crystallinity of Linear Low-Density Polyethylene (LLDPE) is influenced significantly by short-chain branches (SCBs) present in the backbone of the polymer. Despite the importance of this aspect, with only a few linear comonomers being currently used in the commercial production of LLDPE. It is found that by introducing branched comonomers, the melting point and crystallinity of LLDPE can be influenced to a greater extent than with linear comonomers. Since only a few linear comonomers are currently used in the production of LLDPE, the characterization of LLDPEs with branched comonomer has been often overlooked. By combining High-Temperature-Size-Exclusion Chromatography (HT-SEC), Nuclear Magnetic Resonance (NMR) spectroscopy, and Infrared (IR) spectroscopy, it is shown that standard HT-SEC analysis using an IR detector is also applicable to polymers containing branched comonomers.

Front Cover: In article number 2300006, Nermin Orakdogen and co-workers deal with temperature-optimized synthesis of N-(alkyl)acrylamide-based semi-interpenetrating polymer network reinforced with silica nanoparticles and functionalized with methacrylic acid units by varying the polymerization temperature. The gelation is performed at different temperatures to evaluate the formation mechanism. The mechanical properties, swelling properties and susceptibility to stimuli show a wide dependence on the polymerization temperature.

Ethylene/1-hexene copolymerization with two MgCl₂-supported Ziegler-Natta catalysts containing no internal electron donor or diethylphthalate (DEP) is conducted for different polymerization time . Effects of DEP on active center distribution are studied by fractionating each copolymer sample into boiling n-heptane soluble (C7-sol) and insoluble (C7-ins) fractions, and counting the number of active centers in the copolymer fractions . The main effect of introducing DEP in the catalyst are reduction in the Ti content and significant increase in the proportion of active centers producing C7-ins fraction. The propagation rate constants of ethylene insertion (k_pE) and 1-hexene insertion (k_pH) are respectively estimated by linear fitting/extrapolating the change of apparent propagation rate constants (k_pi)_a with polymer yield according to a simplified multi-grain particle model. In both catalysts, k_pE in the C7-ins fraction is 9–12 times larger than that in the C7-sol fraction, and k_pH in the C7-ins fraction is 3–4 times larger than that in the C7-sol fraction. The two groups of active centers have distinctly different catalytic properties. Introducing DEP reduced the k_pE and k_pH values and the extent of diffusion limitation . In summary, addition of electron donor in MgCl₂-supported Z-N catalyst significantly changed the active center distribution and catalytic properties of its two groups of active centers.

The reactivity of different polyethylene modifiers based on acrylic acid (AA) and maleic anhydride (MA) with polyamide 6 (PA6) is investigated, using several degrees of functionalization. The polymer blends are processed in an internal mixer and injection molded. Mechanical, rheological, infrared spectroscopy, thermal, thermomechanical properties, and morphology are evaluated. The torque rheometry results show that higher functionalization degrees favored a high reactivity with PA6. As a consequence, there is an increase in the viscosity of the polymer blends, which is reflected in the reduction of the melt flow index (MFI), compared to PA6. High impact strength and elongation at break properties confirm the blends' compatibility. The elastic modulus and the tensile strength maintain high values, suggesting a balance of mechanical properties. In addition, the polymer blends' heat deflection temperature (HDT) and thermal stability properties are comparable to neat PA6. The morphology obtained by scanning electron microscopy show dispersed and refined particles in the PA6 matrix, indicating stabilization at the interface. Incorporating only 10% of high-density polyethylene grafted with acrylic-acid (HDPE-g-AA) is very efficient in optimizing the properties of PA6, contributing to broadening the range of applications for the processing industry.

Polymer and many other flows exhibit non-Newtonian rheological behavior. For some materials, the thermal dependence of viscosity is also essential to be established. It can be described by considering an activation energy, estimated by using the viscosity measurements at different temperatures. Nevertheless, the test temperatures must be reliable and accurate. An annular measuring device (TRAC: Thermo-Rheo Annular Cell) is previously proposed for highly robust temperature measurement and viscosity identification by inverse method, which exploits the viscous dissipation in the flow. This work explains how critical viscosity points, identified thanks to the TRAC, can be used to estimate the activation energy with different approaches involving the principle of time-temperature superposition. Thanks to the thermal characteristics of the annular flow, the thermal dependence of viscosity can also be estimated from direct temperature measurements to perform fast analysis, without using inverse method.

Soft sensors (SS) are of importance in monitoring polymerization processes because numerous production and quality variables cannot be measured online. Adaptive SSs are of interest to maintain accurate estimations under disturbances and changes in operating points. This study proposes an adaptive SS to online estimate the mass conversion in the emulsion copolymerization required for the production of Styrene-Butadiene rubber (SBR). The SS includes a bias term calculated from sporadic laboratory measurements. Typically, the bias is updated every time a new laboratory report becomes available, but this strategy leads to unnecessarily frequent bias updates. The SS includes a statistic-based tool to avoid unnecessary bias updates and reduce the variability of the bias with respect to classical approaches. A control chart (CC) for individual determinations combined with an algorithmic Cusum is used to monitor the statistical stability of the average prediction error. The adaptive SS enables a bias update only when a loss of said statistical stability is detected. Several bias update methods are tested on a simulated industrial train of reactors for the latex production in the SBR process. The best results are obtained by combining the proposed CC-based approach with a previously developed Bayesian bias update strategy.