Macromolecular Reaction Engineering最新文献

Poly[(n-butyl methacrylate)-co-(n-butyl acrylate)]-based core-shell latexes are prepared by emulsion polymerization with a shell copolymer glass transition temperature (T_g) of 5 °C, but differences in core copolymer wt.% (4–90) and T_g (5–25 °C), and in wt.% of diacetone acrylamide (DAAM) in the shell copolymer, which facilitates crosslinking in the percolating phase of films through addition of adipic acid dihydrazide. Analysis of samples removed from reactions, together with analysis of film cross-sections by atomic force microscopy (AFM), confirms the core-shell particle structures and honeycomb morphologies in films, with simultaneous AFM and infrared spectroscopy showing the distribution of hydrazone crosslinks. Increasing wt.% DAAM (i.e., degree of crosslinking) in the percolating phase shifts film tensile stress–strain curves towards higher stresses and lower extensions at break. For core and shell copolymer T_gs of 5 °C there is a small effect of core wt.%. At 70 and 80 wt.% core, increasing core copolymer T_g also shifts the curves towards higher stresses and lower extensions at break. Thus by combining effects of core copolymer wt.% and T_g with effects of wt.% DAAM in the shell through the soft–soft nanocomposite approach, it is possible to achieve a wide range of tensile deformation behavior in films that have quite similar overall copolymer compositions.

Fabrics consisting of cotton-core/polypyrrole (PPy)-sheath fibers (cotton/PPy fabrics) are synthesized by aqueous chemical oxidative seeded polymerization of pyrrole and are utilized as a solar evaporation device. Scanning electron microscopy studies and elemental microanalyses reveal the thickness of the PPy sheath increases from a few tens nm to ≈200 nm with an increase of pyrrole monomer concentration in the polymerization system. The temperature of cotton/PPy fabrics increases upon irradiation with artificial sunlight to ≈33–45 °C in the dry state, due to light-to-heat photothermal conversion by the PPy component. Thanks to the photothermal property of the fabrics, water impregnated within the cotton/PPy fabrics can evaporate efficiently under the irradiation of artificial sunlight. Light-induced water evaporation experiment using an artificial seawater confirms that ionic concentrations drastically decreases, indicating successful desalination.

Low-Density Polyethylene (LDPE) reactors have the potential for rupture because of thermal runaway from auto-accelerating chemistry. Pockets of unmixed, highly reactive, LDPE constituents, called hot spots, are often generated by conditions within the reactor and are the main source of thermal runaway. Because of this, there is a need to define thresholds of hot spot conditions that produce runaway. Computational Fluid Dynamics is used to study an isolated LDPE sphere with varying initial temperature, initial catalyst concentration, and volume to determine which combinations promote thermal runaway. It is found that increasing both initial temperature and initial catalyst concentration increased thermal runaway likelihood, while, counter-intuitively, hot spot volume has no effect. An LDPE runaway map is provided to quantify the combinations that result in safe reactor operation. This allows manufacturers to make more informed control actions and to determine safe reactor conditions based on local mixture composition and temperature alone.

A new design policy to synthesize nanogel molecules having desired dimensions under unperturbed state is proposed. Miniemulsion copolymerization of vinyl and divinyl monomers, both conventional free-radical polymerization and ideal living polymerization, is used to illustrate the method. For the network formation dynamics, the newly proposed model that takes into account the size and structure dependence of cross-linking/cyclization reactions is employed. The master curve relationship that indicates the maximum average dimensions for randomly cross-linked networks is used as a guideline and the network dimension is controlled by the magnitude of network maturity index NMI, which is the average number of cycle rank per primary chain. By appropriately sizing the NMI, it is possible to synthesize network polymers with dimensions equal to or greater than the maximum dimensions achievable with a homogeneous, randomly cross-linked network polymer of the same cycle rank and molecular weight. The current strategy of designing and controlling 3D size is applicable regardless of the reaction mechanism of network formation and will also be applied to the synthesis of macro-gels.

While precipitation polymerization allows the synthesis of microgels with controlled functional-group distributions, the structural development of these microgels during the polymerization process still remains unclear. In this study, microgels with different reactivity ratios between the monomer and charged co-monomer are prepared by precipitation polymerization, and the evolution of their size, thermoresponsive behavior, and surface properties during polymerization are evaluated. In particular, the surface properties of the microgels are analyzed quantitatively using the softness parameter and the surface charge density is calculated using Ohshima's equation. The results allowed describing the structural changes of microgels during precipitation polymerization well and provided design guidelines for functional microgels with controlled functional group distributions.

Poly(vinylidene fluoride) (PVDF) is among the most produced fluoropolymers, second only to polytetrafluoroethylene. Despite its popularity, the complex microstructural properties achieved during the polymerization are not well documented in the literature. In particular, available models only track the chain length distribution of the polymer, while neglecting the distribution of other important properties, affecting the final behavior of the product. In this work, a 2D kinetic model, evaluating not only the chain length but also the number of terminal double bonds (TDBs) per chain, is developed. The numerical solution of the model is achieved by fractionating the population of polymer chains into classes with a specific number of TDBs and using the method of moments for each class. The model results are compared with experimental evidences for the amount of produced polymer, moles of main chain-ends, number, and weight average molecular weight as well as full molecular weight distribution. Based on this comparison, kinetic parameters are estimated by optimization using genetic algorithm. The model reliability is finally verified using additional experimental data at different temperatures and amounts of initiator.

The demand for sustainable polymer particles production is growing, driven by the need for efficient, biocompatible, and biodegradable materials. In this context, the present study explores the production of poly(butylene succinate) (PBS) particles in a single step using a green heterogeneous suspension process, using vegetable oil as the suspending medium. Particularly, the effects of oil type (soybean, corn, sunflower), dispersed phase holdup (10–30 wt.%), stabilizers (Span 20, Span 80, Tween 80, Brij 52, Brij 93, Igepal-co-520,  Polyglycerol polyricinoleate (PGPR)), reaction time (1–5 h), and temperature (100–160 °C) on the suspension polymerization are investigated. Results indicate that particle size and shape are influenced by the vegetable oil and stabilizer. Additionally, it is shown that the particle size distribution is affected by the use of a sonicator, allowing the manufacture of even smaller microsized particles. Based on the results, a 30 wt.% holdup in corn oil with a blend of surfactants can be recommended, producing spherical particles with an average diameter of 100 µm. Moreover, higher reaction temperatures (160 °C) and longer reaction times (5 h) positively impacted the molar mass of the obtained particles. Finally, cytotoxicity tests using Bone Marrow-Derived Macrophages cells confirmed the safe use of PBS microparticles at concentrations up to 1000 µg mL⁻¹

One of the questions still remaining regarding emulsion polymerization is the issue of mass transfer versus reaction limitation since, by its nature, emulsion polymerization requires monomer transport across an aqueous phase. This question is brought into focus lately by the growing use of miniemulsion polymerization in which the monomer transport step is much less important. This paper will explore the possible rate of monomer transport via collision and ratio this to the maximum rate of polymerization using the Damkohler analysis formality. Results indicate that systems relying on monomer transport by collision will be almost universally monomer-transport-limited, thus exhibiting lower-than-expected rates of polymerizations.