Macromolecular Reaction Engineering最新文献

In this work, the synthesis of magnetic microspheres of poly(glycidyl methacrylate-co-divinylbenzene) via suspension polymerization is reported. The concentrations of divinylbenzeneand benzoyl peroxide in the microspheres synthesis are studied. The microspheres, characterized by thermal analysis , scanning electron microscopy, vibrating sample magnetometry , and light scattering detection , show good morphological control and thermal stability. This material presents a narrow size range and an appreciable fraction of superparamagnetic particles. The increase in divinylbenzene concentration can cause a decrease in the mean diameter of the microspheres. On the other hand, the increase in benzoyl peroxide concentration causes an increase in the mean diameter of the microspheres.

Models are developed for gas-phase ethylene/1-hexene copolymerization using a 3-site hafnocene catalyst. The models accurately predict joint molecular weight distribution and copolymer composition data for 15 semibatch lab-scale copolymerization runs and 6 steady-state pilot-plant copolymerization runs, respectively. Kinetic rate constants and activation energies, which are common to both models, are estimated for the three types of active sites for each reaction in the kinetic scheme. Using parameter subset selection and estimation techniques, it is found that 34 of the 61 parameters should be estimated from the data. Incorporating the pilot-plant data allow for estimation of two parameters, a deactivation rate constant and a β-hydride elimination activation energy, that are not estimable using the lab-scale data alone. At the 95% confidence level, 25 of the 34 parameters are significantly different than zero, which is more than the 19 significant parameter estimates obtained from the lab-scale data alone. Good fits to the data are obtained, as are reliable predictions for a validation run not used in parameter estimation.

The present work aims to produce  functionalized polymer networks to target the bioactive molecule trans-resveratrol found in winemaking residues, specifically at grape stems. The synergistic choice of photoinitiation, polymerization composition, and molecular imprinting approach allows the functionalization of these materials. Experimental design is applied to methodically perform the syntheses. The amount of crosslinker, the total monomer's concentration, and the ratio of trans-resveratrol to the functional monomer 4-vinylpyridine (4VP) are the factors selected for this experimental design. The binding capacities and the selectivity of the synthesized materials are assessed through sorption experiments in acetonitrile and hydroalcoholic media. Consequently, a multivariate linear regression analysis leads to describe the uptake of trans-resveratrol by the materials in both media. The crosslinker content and the ratio of trans-resveratrol to 4VP are found to be impactful parameters while designing such materials. These studies allow the identification of working conditions for sorption/desorption processes combining a high retention capability of the adsorbents with selectivity. Furthermore, four materials are selected to enrich trans-resveratrol from grape stems extracts in a continuous process of solid-phase extraction. The results show that the functionalized materials are able to enrich 12-fold the content of trans-resveratrol in some fractions demonstrating the interest of such polymers.

Polybutylene succinate (PBS) and other succinic (co)polyesters are biodegradable polymers with favorable mechanical and thermal properties that find use in many applications. Due to environmental concerns, polymers based on succinic acid (SA) have been gaining attention, as SA can be produced through biotechnological processes. Thus, this review aims to highlight the synthesis and characteristics of PBS and other succinic copolyesters, with emphasis in the works employing metallic catalysts and enzymes. In addition, the modification of the macromolecular structure by copolymerization or postpolymerization is also discussed. Currently, metallic catalysts are normally used in the synthesis of these materials, under conditions of high temperatures, which can favor the occurrence of thermal degradation, increasing the dispersion of chain length distributions. Moreover, the incrustation of metallic catalysts in polymeric materials makes their application in biomedical products difficult, due to toxicity requirements. In this context, enzymatic catalysis is gaining ground, offering milder synthesis temperatures, high selectivity, and uniformity of synthesized products. This biotechnological route can substitute oligomerization processes with metallic catalysis in future industrial processes, producing materials free from metallic contamination. In addition to production by catalytic routes, trends for future applications of succinic (co)polyesters are presented, with emphasis on the value-added materials sectors.

This work presents the development and validation of two virtual analyzers (density and Melt Index (MI)) for quality monitoring and control of the final product in an industrial unit of Linear Polyethylene (LPE). Both models are based on Feedforward Neural Networks which are improved through a strategy involving the initial estimation of weights and a constructive algorithm to define the number of hidden units. The initialization strategy is based on linearization of the neural model with only one hidden unit (nonlinear model) and subsequent optimization of this model by maximizing its similarity to the standard linear regression model whose solution is obtained analytically. The Initial Neural Model (INM) is then used as a starting point for a gradual increase in the number of hidden units. In a validation test involving MI and density values collected over 2 years of operation, the neural model is able to predict these properties with mean percentage errors equal to 0.81% (MI) and 0.04% (density) and determination coefficients equal to 0.970 (MI) and 0.983 (density). The population coefficient estimated in all tests involving grade transitions (0.96) shows a strong linear correlation between the proposed model and laboratory measurements.

Front Cover: Kinetic study of multi-step bulk-/gas-phase polymerization for synthesis of heterophasic polypropylene copolymers. Power compensation calorimetry is used for studying kinetics of bulkphase polymerization, while for gas-phase polymerization, kinetic data is obtained from semi-batch operation at constant conditions. The combination of both methods allows to precisely control the heterophasic copolymers formed. This is reported by Sina Valaei and Michael Bartke in article number 2200018.

Controlled polymerization techniques like the reversible-addition fragmentation chain transfer polymerization (RAFT) are sensitive to impurities such as oxygen. This work explores the application of re-initiation as a tool to enhance monomer conversion. A kinetic model for the oxygen inhibited RAFT dispersion polymerization for the synthesis of poly(4-vinylpyridine)-b-polystyrene (P4VP-b-PS) is developed. Thus, using the kinetic model, the re-initiation of the inhibited RAFT polymerization is partially (monomer conversion ≤10%) predicted. By implementing the re-initiation as a solution, the synthesis of P4VP-b-PS copolymers with the high conversion (>96%) and a good dispersity (≤1.2) is enabled.

Hybrid non-isocyanate poly(urethanes) (HNIPUs) are designed from a precursor whose carbonate functionality is derived from epoxy-functional statistical copolymers. Specifically, a bio-based diene (β-myrcene) is copolymerized via conventional free radical polymerization with glycidyl methacrylate (GMA) at different molar ratios, producing flexible copolymers with epoxy pendant groups, which are then reacted with carbon dioxide to yield the precursors with cyclic carbonate functionality. Subsequent addition of an amine-terminated telechelic poly(propylene glycol) (PPG) forms urethane linkages in the side chains, whose concentration is tuned by varying the GMA initial molar fraction. The NIPUs are end-capped with silanes to enable moisture curing, resulting in HNIPUs with elongations at break up to 150%, and relatively low elastic moduli varying from 32 kPa to 50 kPa as the number of urethane side linkages increases from 6 to 22. The swelling ratio of the NIPUs is also measured in tetrahydrofuran (THF). As the number of urethane side chains increases, the swelling ratio of the NIPUs decreases (710% to 620%), indicating a higher crosslinking density. All samples have gel contents higher than 50% in THF, indicating non-crosslinked species in the hybrid samples which confirms the relatively low reported tensile moduli.