The RPPFM is employed to describe the gas‐phase catalytic polymerization of ethylene in the presence of supported or self‐supported Z‐N catalysts. Numerical simulations are carried out to analyze the effect of the catalyst type on the polymerization rate, particle overheating and the average molecular polymer properties of the polyolefin. It is shown that non‐porous, self‐supported Ziegler‐Natta catalysts exhibit higher particle growth rates and lower particle overheating. The average molecular weight of polyethylene produced by both catalysts is almost identical. Depending on particle size and polymer crystallinity, the average monomer solubility and the effective monomer diffusivity can significantly vary.
The copolymerization behavior of the acidic monomer 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (APSA) and 1‐vinylimidazole in inverse miniemulsion was studied under various conditions. Initially, different surfactants and surfactant concentrations were investigated. After determining a suitable composition of the miniemulsion, changes in the reaction behavior under different pH values and monomer feed compositions were studied. The highest polymerization rates could be produced under neutral conditions over all monomer feed ratios. The addition of acid or base to change the pH value of the monomer mixture also has influence on the polymers obtained. The thermal stability, rheological stiffness and intrinsic viscosity increase when Na‐APSA is incorporated.
The influence of 1‐hexene is examined on the kinetics of ethylene copolymerization with a metallocene catalyst in gas phase. A model is derived, which is able to describe a large reaction rate increase due to a small amount of incorporated comonomer. This complexation model describes the measured reaction rates for ethylene and 1‐hexene, and the co‐monomer incorporation. Polymer properties were analyzed, such as comonomer weight fraction. The density, melting point, and molecular weight of the produced polymer decreased with increase in 1‐hexene gas concentration. The in situ 1‐hexene sorption is estimated and follows Henry's law, but seems much higher than reported in the literature.
A kinetic model is developed for the heterogeneous free‐radical copolymerization of vinylidene fluoride and hexafluoropropylene in supercritical CO2. The model accounts for polymerization in both the dispersed (polymer‐rich) phase and in the continuous (polymer‐free) supercritical phase, for radical interphase transport, diffusion limitations, and chain‐length‐dependent termination in the polymer‐rich phase. A parameter evaluation strategy is developed and detailed to estimate most of the kinetic parameters a priori while minimizing their evaluation by direct fitting. The resulting model predictions compare favorably with the experimental results of conversion and MWD at varying monomer feed composition, monomer concentration, interphase area, and pressure of the system.
The use of pressure‐drop and constant‐pressure dilatometry for obtaining rate data for liquid propylene polymerization in filled batch reactors was examined. The first method uses reaction temperature and pressure as well as the compressibility of the reactor contents to calculate the polymerization rate; in the second, the polymerization rate is calculated from the monomer feed rate to the reactor. Estimated polymerization rates compare well to those obtained using the well‐developed isoperibolic calorimetry technique, besides pressure‐drop dilatometry provides more kinetic information during the initial stages of the polymerization than the other methods.
Batch radical polymerization of non‐ionized methacrylic acid, 30 wt.‐% in aqueous solution, has been studied at 50 °C and ambient pressure with 2‐mercaptoethanol (ME) as the chain‐transfer agent (CTA). Initial polymerization rate decreases with CTA concentration, which has been varied up to 20 mol‐%. A kinetic model is presented which includes chain‐length‐dependent termination and uses an empirical function to account for the dependence of termination rate on both monomer conversion and molar mass of the polymeric product. In conjunction with PREDICI simulation, this model affords for an adequate representation of the measured monomer conversion vs. time profiles.
A continuous loop reactor was used for the production of 2‐ethylhexyl acrylate (2‐EHA), methyl methacrylate (MMA) and acrylic acid (AA) pressure sensitive adhesive by both emulsion and miniemulsion polymerization. Similar high monomer conversions were achieved in both processes, but striking differences in polymer architecture were found. A mathematical model was used to analyze these differences concluding that because the costabilizer suppressed monomer diffusion from miniemulsion droplets, the average polymer concentration in the polymerization loci was lower in the miniemulsion process. This resulted in less chain transfer to polymer, and hence in lower sol molecular weight and gel content.
The importance of radical transfer between the reactive phases in precipitation polymerization processes is investigated with the vinyl chloride suspension polymerization as an example. A two‐film model that accounts for a mass transfer resistance in both the monomer‐rich and the polymer‐rich phase is constructed and applied. Equilibrium is assumed at the interphase boundary. Based on model calculations using intrinsic rate coefficients obtained by regression to experimental data the effect of accounting for radical transfer between the reactive phases on the simulated monomer conversion and total moments of the molar mass distribution is demonstrated. It is found that the effect of radical transfer between the reactive phases is most pronounced at low polymerization temperatures.
A kinetic model for the graft polymerization of VAc from PEG was developed using the method of moments. Experiments were carried out to verify the model. The effect of various parameters, such as initiator concentration, temperature, and PEG molecular weight on the polymerization kinetics was examined. Polymerization rate, grafting efficiency, graft copolymer molecular weight, and PEG grafted ratio were measured. The model was in good agreement with the experimental data. No gel effect was observed at the studied PEG/VAc weight ratio of 1:1. The chain transfer constant to PEG was correlated to be . The model was also applied in a semi‐batch reaction and compared with the experimental results.
Bioactive coatings constitute an interesting approach to enhance healing around implants, such as stent‐grafts used in endovascular aneurysm repair. Three different plasma techniques, namely NH3 plasma functionalization and atmospheric‐ or low‐pressure plasma polymerization, are compared to create amino groups and covalently bind CS and EGF bioactive molecules on PET. The latter presents the greatest potential. CS + EGF coating is shown to strongly decrease cell apoptosis and cell depletion in serum‐free medium, while increasing cell growth compared to unmodified PET. This versatile biomimetic coating holds promise in promoting vascular repair around stent‐grafts, where resistance to apoptosis is a key issue.
This paper reports a novel amphoteric aliphatic polycarbonate bearing both amine and carboxyl groups. In the absence of protection‐deprotection chemistry, the multi‐functionalized copolymer is synthesized by one‐step enzymatic copolymerization. The influences of the reaction conditions including monomer feed ratio and polymerization time are explored. The simultaneous incorporation of amine and carboxyl functionalities provides the copolymer with a pH‐tunable self‐aggregation feature, leading to various aggregation states including precipitated agglomerate, well‐dispersed positively or negatively charged nanoparticles in a controlled manner. The copolymer displays minimal cytotoxicity to 293T and HeLa cells.
Methylene blue‐conjugated polyacrylamide nanoparticles are prepared through a microemulsion polymerization, after conjugation of the dye with a monomer. The nanoparticles have a 50–60 nm diameter in solution. This conjugation method enables a large increase in loading of methylene blue per nanoparticle and also minimizes dye leaching out of the nanoparticle. Furthermore, the dye content can be controlled by variation of the dye amount, enabling a more refined control of the singlet oxygen production ability. The nanoparticles are coated with F3 peptides, which give specific targeting to selected tumor cells, 9L, MDA‐MB‐435, and F98, in vitro. In addition, MTT assays reveal that the nanoparticles have no dark toxicity but excellent PDT efficacy increasing with the nanoparticle dose and irradiation time.
A study on the effect of process conditions and composition of the reacting mixture on the kinetics and particle properties in the copolymerization of styrene and divinylbenzene in supercritical carbon dioxide is presented. Polystyrene‐block‐polydimethylsiloxane and Krytox 257 FSL (Dupont) were used as stabilizers, and their performance compared. A 38 mL, high‐pressure view cell, equipped with one frontal and two lateral sapphire windows, was used as the reacting vessel. The polymer product was characterized for total monomer conversion, gel content, molecular weight averages of the sol fraction and particle size distribution. Acceptable polymerization rates and partially‐agglomerated spherical particles were produced under the conditions tested.
Single pulse–pulsed laser polymerization–electron paramagnetic resonance (SP‐PLP‐EPR) has been introduced as a powerful method for the very detailed analysis of termination kinetics. During polymerization an intense laser pulse is applied in order to almost instantaneously produce a burst of radicals. The decay of radical concentration is measured by highly time‐resolved EPR and is analyzed with respect to the rate coefficients for the termination of two radicals of identical size. SP‐PLP‐EPR experiments have been carried out for an itaconate monomer, for several methacrylates in bulk and in a solution of ionic liquids, for methacrylic acid in aqueous solution, and for the solution polymerization of butyl acrylate in toluene at low temperature. The data fully support the composite model, which assumes a stronger chain‐length dependence of termination for radicals of smaller size and a weaker one for large radicals. The SP‐PLP‐EPR technique is also applicable in systems with more than one type of growing radicals, as is the case with butyl acrylate polymerization at higher temperature and with RAFT polymerizations, where the novel method may be used for a comprehensive kinetic analysis.
Acrylate–alkyd hybrid latex via miniemulsion polymerizations show promise as water‐borne coating systems. However, poor homogeneity of the particles caused by the immiscibility of the alkyd in polyacrylate limits monomer conversion and film formation. To resolve this problem, the hybrid miniemulsion polymerization of acrylate in the presence of linoleic acid and sunflower seed oil was carried out. Products were characterized by solvent extraction, dynamic light scattering, gel permeation chromatography (GPC), differential scanning calorimeter (DSC), and transmission electron microscopy (TEM). The results provide clear evidence that substituting a fatty acid or natural oil with smaller molecular size (weight) for a conventional alkyd improves the grafting efficiency, and enhances the homogeneity of the hybrid polymer particles in water‐borne latex systems.
