Phase equilibria effect on catalytic olefin polymerization

There are many reasons why phase equilibria during the catalytic polymerization are important and why many researches are interested in exploring them. In any type of catalytic polymerization (solution, slurry, gas-dispersion) the proportional relation of the monomer concentration at the active catalyst site to the polymerization rate is essential. Phase equilibria between a solvent, polymer, monomer(s) and co-monomer(s) and related transport processes are important not only for the polymerization kinetics itself, but also the polymer structure formation or subsequent product degassing are closely related to them. Nowadays many experimental techniques are available (e.g. DSC with pressure cell, low-field NMR, (co-)sorption balances), thus the thermodynamics of polyolefins is persistently studied and a lot of new quantitative knowledge about polyolefin thermodynamics was accumulated. But still there is a need for new data required by new or existing production processes and new grades of polyolefins. In this contribution we present data relevant for gas-phase and slurry polymerization, i.e. sorption equilibria of polymer/solvent(g) and polymer/diluent(l) systems respectively. Sorption of gaseous penetrants in polymer particles was measured by gravimetric method and the results go hand in hand with swelling data measured in video-microscopic apparatus. Thus we gradually developed a huge database of experimental results including sorption of commonly used hydrocarbon penetrants (C2-C7) in various polyethylene and polypropylene samples (covering the full spectrum of commercially produced grades) at different temperatures (relevant to polymerization conditions). Moreover, by using a pressure-decay apparatus we are able to determine also kinetic parameter – diffusion coefficient of gases in polyolefin particles. Sorption of liquid penetrants in polyolefins was measured using new methodology developed in our laboratory and we present results for the system polymer (PE or PP) and liquid hydrocarbon (C6-C8). Solubilities are measured at different temperatures. Next we present swelling equilibria of polyolefin particles in various liquid diluents and preliminary results of co-swelling experiments for the system PE-hexane-ethylene are discussed. Podivinská M., Jindrová K., Chmelař J., Kosek J.: Swelling of polyethylene particles and its relation to sorption equilibria under gas-phase polymerization conditions, Journal of Applied Polymer Science, 2017, 45035: 1-7. Chmelař, J., R. Pokorný, P. Schneider, K. Smolná, P. Bělský and J. Kosek (2015). Free and constrained amorphous phases in polyethylene: Interpretation of 1H NMR and SAXS data over a broad range of crystallinity. Polymer 58: 189-198. Chmelař J., Smolná K., Haškovcová K., Podivinská M., Maršálek J., Kosek J.: Equilibrium sorption of ethylene in polyethylene: Experimental study and PC-SAFT simulations, Polymer, 2015, 59: 270-277. Chmelař J., Haškovcová K., Podivinská M., Kosek J.: Equilibrium Sorption of Propane and 1‑Hexene in Polyethylene: Experiments and Perturbed-Chain Statistical Associating Fluid Theory Simulations, Industrial and Engineering Chemistry Research, 2017, 56, 6820−6826

Evolution of high impact polypropylene morphology upon thermal treatment

Morphology and especially the rubber content and distribution in high impact polypropylene (hiPP) are the crucial factors determining the material mechanical properties such as toughness and impact resistance. The final properties are influenced by the size of rubbery domains and their compatibility with the iPP matrix. The hiPP morphology is affected during each stage of its evolution. During the polymerization, the polymer powder with the semi‑continuous rubbery network is predetermined by the replication phenomenon, where the forming polymer particle copies the catalyst architecture and the rubber phase grows on the catalyst fragments distributed in the homopolymer particle. Thus the principally controlling parameters affecting the particle morphology are the catalyst itself, reaction conditions and the rubber content [1]. On the other hand, during the particle melting in the extruder, the phase separation takes place and the final morphology is governed by the rubber composition and molar weight (i.e., by the viscosity ratio between the polymer matrix and the rubber). The suitable set of accurate characterization methods has to be employed to comprehensively map the heterophase polymer morphology and the appropriate statistical descriptors then allow to objectively describe the polymer overall morphology [2]. For the hiPP morphology mapping, the combination of X‑Ray microCT, AFM and confocal Raman microscopy was employed in our work. This contribution explains the influence of various rubber content and composition (i.e., ethylene/propylene ratio) and various viscosity ratios between rubber and polypropylene matrix on the hiPP morphology. The morphology evolution upon thermal treatment including the phase separation was studied in the wide range of melting times and melting temperatures. Finally, the influence of hiPP morphology on its mechanical properties is demonstrated with respect to various rubber characteristics. ____ [1] Smolná, K., Gregor T., Buráň Z., Kosek J.: Formation and Distribution of Rubbery Phase in High Impact Polypropylene Particles. Macromolecular Materials and Engineering, 2016. 301(4): p. 390-400. [2] Smolná, K., Gregor T., Kosek J.: Morphological analysis of high-impact polypropylene using X-ray microCT and AFM. European Polymer Journal, 2013. 49(12): p. 3966-3976

Structure–stability correlation of copolyimide membranes derived from aliphatic/alicyclic/aromatic diamine and aromatic dianhydrides

Byly syntetizovány nové polyamové kyseliny s periodickou sekvencí monomerních jednotek typu -A-B-A-C- (A je odvozeno od diaminu, B od dianhydridu benzofenon-3,4:3’,4’-tetrakarboxylové kyseliny a C od dianhydridu benzen-1,2,4,5-tetrakarboxylové kyseliny), které byly použity pro přípravu polyimidových membrán. Tyto membrány byly analyzovány různými metodami pro vyšetření vlivu diaminové jednotky (alifatické/alicycklické/aromatické) na morfologii, teplotní stabilitu a mechanické vlastnosti membrán. Maloúhlový a širokoúhlový rentgenový rozptyl a mikroskopie atomárních sil odhalily amorfní charakter všech membrán kromě těch, které obsahují 1,6-diaminohexanovou jednotku. Termogravimetrická analýza ukázala pokles počáteční teploty rozkladu z 551/501 °C na 437/395 °C (v atmosféře N2 resp. O2), když se od aromatických diaminů přejde k diaminům alifatickým. Z dynamické mechanické analýzy vychází poměrně vysoký počáteční elastický modul pružnosti u všech membrán při frekvencích 1, 10 a 20 Hz. Vlastnosti připravených kopolymerních polyimidových membrán jsou perspektivní pro celou řadu potenciálních technologických aplikací.New polyamic acids with -A-B-A-C- type periodic sequence of monomeric units (A derived from a diamine, B from benzophenone-3,30,4,40-tetracarboxylic dianhydride, and C from benzene-1,2,4,5-tetracarboxylic dianhydride) are prepared and transformed into polyimide membranes that are examined by various methods in order to investigate the influence of diamine units (aliphatic,alicyclic, or aromatic) on the morphology, thermal stability, and mechanical properties of membranes. Small- and wide-angle X-ray scattering and Atomic force microscopy show amorphous character of all membranes except for those containing hexane-1,6-diamine units. Thermogravimetric analysis reveals a decrease in the initial decomposition emperature from 551/501 °C to 437/395 °C (for N2/O2 atmosphere) when going from membranes with aromatic to those with aliphatic diamine units. Dynamic mechanical analysis shows quite high initial storage modulus (2100–3300 MPa) for all membranes at frequencies of 1, 10, and 20 Hz. The properties of prepared copolymeric polyimide are promising for a wide range of their potential technological applications