ABSTRACT Although Ziegler‐Natta (ZN) catalysts are used since the 1950s, they remain employed in industry because of their robustness and low‐cost relative to many newer catalyst systems. In this study, we investigated the effect of tetrahydrofuran (THF) as an internal donor on the performance of a ZN catalyst for polyethylene (PE) production. Catalysts with varied THF contents were prepared and evaluated under identical polymerization conditions. Catalyst productivity was quantified as (kg poly Ti − 1 h − 1 ), while the resulting polymers were characterized by high‐temperature size‐exclusion chromatography (HT‐SEC), molecular‐weight‐distribution (MWD) deconvolution, and thermal analysis (DSC). Adjusting the amount of internal donor affected catalytic activity. The lowest THF loading increased activity by 27%. Variation of the THF concentration produced changes in productivity, with a maximum at a Ti/THF ratio of 0.5, while higher Ti/THF ratios up to 5, decreased the catalytic activity. The polymer microstructure and properties were insensitive to THF content. HT‐SEC analysis showed miniscule changes in the MWD and the deconvoluted molecular‐weight fractions. Similarly, melting behavior varied only within 1.4°C across the catalyst series. Within experimental uncertainty, THF primarily affects activity rather than polymer characteristics. Thus, tuning the amount of donor provides a practical lever to enhance productivity while preserving the polymer's properties.
This work presents a dynamic, model-based kinetic measurement method that couples vapor-liquid-equilibrium with reaction kinetics for the bulk-phase polymerization of propylene in a bench-scale reactor. This model couples Peng-Robinson-based flash calculations with a simplified kinetic scheme (activation, propagation, deactivation). Reactor pressure-time trajectories from polymerizations (at 20 degrees C-30 degrees C) are used as model input. The novelty of this approach lies in explicitly embedding vapor-liquid equilibrium into the dynamic pressure-based calibration of polymerization kinetics under bulk pre-polymerization conditions. Through the process of parameter tuning, the simulated and measured reactor pressure drop caused by conversion of liquid propylene to polypropylene in a multi-component mixture are aligned, yielding the simulated polymerization rate and the elementary reaction rate constants. The model reproduces the characteristic pressure decrease and end-point yields within acceptable deviations and demonstrates instantaneous catalyst activity profiles, the activity decay over reaction time, and the temperature response of the catalyst. This approach enables access to detailed catalytic polymerization kinetics of propylene at mild temperatures which are typically used under industrial pre-polymerization reactors.
Atom transfer radical polymerization (ATRP) has historically required an oxygen-free environment to prevent oxidation of both the polymeric radical and the active copper catalyst, limiting its deployment in industrial-scale processes. In this study, ATRP of styrene was successfully carried out in the presence of oxygen by using triethylborane (TEB) complexed with an aryl amine to form air-stable complexes, which served as an essential component of the reaction mixture. Polymerizations conducted in DMSO at 80 degrees C reached high yields within 10 h while maintaining relatively low dispersity (& ETH; approximate to 1.11), although the molecular weights exceeded theoretical values. When the reaction was allowed to proceed for 24 h, dispersity increased and a low-molecular-weight shoulder became apparent on GPC. When the complexed triethylborane was omitted, no polymerization was observed to occur when carried out in the presence of oxygen. The brominated polystyrene precursor formed with oxygen present was successfully chain extended, indicating chain end fidelity and consistent with the ATRP mechanism.
ABSTRACT Polyvinylidene fluoride (PVDF) is a semicrystalline fluoropolymer mostly produced by free‐radical suspension or emulsion polymerization. It has the second largest production capacity among all fluoropolymers, following only polytetrafluoroethylene. This great industrial attention is due to its excellent chemical and physical properties, among which its inertness and resistance to chemicals and heat, its high melting point and high tensile strength. As a result, it is one of the first materials of choice in the field of membrane separations, especially for micro and ultrafiltration. In addition, due to its piezoelectric, pyroelectric, and optical properties, PVDF is finding more and more extensive application in batteries and sensors. Given the important role played by PVDF in the polymer market, this review is aimed at reporting the latest advancements in its manufacturing, with particular reference to the innovations introduced following the new legislation on environmental protection from perfluoroalkyl substances. The main focus is on the emulsion polymerization process, where experimental conditions and models from the literature are presented and discussed. After having clarified the polymer reaction engineering aspects for this material, the latest advancements in the application of PVDF are reviewed, with the aim of highlighting its strengths as well as points for improvement.
ABSTRACT The free‐radical polymerization behavior of methyl methacrylate (MMA) is investigated in the presence and absence of trisilanol isobutyl polyhedral oligomeric silsesquioxane (TSI‐POSS) at 70°C and 80°C using a calorimetric approach based on continuous temperature monitoring. The reaction temperature is experimentally recorded, and the corresponding heat flow is estimated from an energy balance, enabling the calculation of monomer conversion and polymerization rate ( R p ) as functions of time. The experimental data are further analyzed to estimate the k t /k p 2 ratio (ratio of the termination to the squared propagation rate coefficients), which serves as a comparative indicator of changes in the balance between termination and propagation. The results reveal a non‐monotonic evolution of the k t /k p 2 ratio, characterized by an initial decrease followed by an increase and a subsequent decline, suggesting behavior consistent with diffusion‐controlled polymerization regimes. The presence of TSI‐POSS is associated with a decrease in the polymerization rate and an increase in the k t /k p 2 ratio, suggesting the influence of diffusion‐related limitations on the polymerization process. These observations are qualitatively consistent with diffusion‐related effects, although independent characterization would be required to confirm the underlying mechanisms.
