Bożena Król

Two‐step polymerization of propylene over MgCl2‐supported titanium catalyst

The prepolymerization effect on propylene polymerization in the presence of a MgCl 2 -supported titanium catalyst was studied. The catalyst was pre-activated by polymerizing a small amount of propylene in the presence of Et 3 Al and cyclohexylmethyldimethoxysilane under mild conditions, and then it was used in a second step of propylene polymerization. Comparative studies of the polymerization process involving the investigated catalyst and its unmodified counterpart showed the rate-enhancement effect of prepolymerization and the same molecular weights, MWDs and isotacticities of the polymers obtained. Concentrations of active sites and propagation rate as well as transfer rate constants were found from detailed kinetic studies. The findings revealed that the activating effect of catalyst prepolymerization resulted from the increased concentration of active sites. This in turn is the result of the slow and uniform fragmentation of initial catalyst agglomerates with the prepolymer created under mild conditions. The prepolymerization process causes no change in the reactivity of active sites since the chain propagation and chain transfer rates are the same for single-step and two-step polymerization reactions; similarly, the properties of the polymers produced are unchanged.

Modelling the surface free energy parameters of polyurethane coats—part 1. Solvent-based coats obtained from linear polyurethane elastomers

Polyurethane elastomers coating were synthesised by using typical diisocyanates, polyether and polyester polyols and HO-tertiary amines or diols as a chain extenders. Mole fractions of structural fragments (κexp) responsible for the polar interactions within polyurethane chains were calculated by 1H NMR method. Obtained results were confronted with the analogous parameter values (κtheor) calculated on the basis of process stoichiometry, considering the stage of the production of isocyanate prepolymers and reaction of their extension for polyurethanes. Trials of linear correlation between the κexp parameters and surface free energy (SFE) values of investigated coatings were presented. SFE values were determined by Owens–Wendt method, using contact angles measured with the goniometric method. Based on achieved results, another empirical models, allowing for prediction the influence of the kind of polyurethane raw materials on SFE values of received coatings were determined. It was found that it is possible to regulate the SFE in the range millijoules per cubic metre by the selection of appropriate substrates. It has been found that use of 2,2,3,3-tetrafluoro-1,4-butanediol as a fluorinated extender of prepolymer chains is essential to obtain coatings with increased hydrophobicity, applied among others as biomaterials—next to diphenylmethane diisocyanate and polyoxyethylene glycol.

Nature of activating effect of two‐step polymerization of propylene

The prepolymerization effect on propylene polymerization in the presence of a TiCl 3 -based catalyst, modified by di-n-buthyl ether, was studied. The influence of prepolymerization on the electron spin resonance spectra and morphology of the catalyst, as well as the properties and the morphology of both prepolymer and regular polymerization products, was investigated. The polymer morphology was evaluated through scanning electron microscopy, polymer bulk density, and particle size distribution. Some evidence of the enhancement effect of prepolymerization on the catalyst activity and stereospecificity was obtained. No influence from prepolymerization was observed on molecular weight and its distribution, melting point, and crystallinity of polypropylene. These findings, when discussed in connection with the morphology results of the catalyst and prepolymer, showed that the prepolymerization performed at mild reaction conditions prevents fast and extensive fragmentation of the original catalyst agglomerates. The more controlled breakup of the catalyst particles in the course of slowed growth of prepolymer exposes the occluded catalyst fragments with uniform size and prevents their reagglomeration. Resulting from the above, catalyst homogeneity, catalyst activity, and polymer morphology are improved.

Comparison of Hydrolytic Resistance of Polyurethanes and Poly(Urethanemethacrylate) Copolymers in Terms of their Use as Polymer Coatings in Contact with the Physiological Liquid

Abstract PU elastomers were synthesized using MDI, PTMO, butane-1,4-diol or 2,2,3,3-tetrafiuorobutane-1,4-diol. Using the same diisocyanate and polyether reagents urethane segments were prepared, to be inserted in the poly(urethane-methacrylate) copolymers. Bromourethane or tetraphenylethane-urethane macroinitiators were used as transitional products reacting with MMA according to the ARGET ATRP. 1H and 13C NMR spectral methods, as well as DSC and TGA thermal methods, were employed to confirm chemical structures of synthesised elastomers and copolymers. To investigate the possibility of using synthesized polymers as biomaterials a research on keeping them in physiological liquid at 37°C was performed. A loss in weight and ability to sorption of water was determined and by using GPC the molecular weight changes were compared. Additionally, changes in the thermal properties of the samples after exposure in physiological liquid were documented using both the TGA and DSC methods. The studies of surface properties (confocal microscopy and SFE) of the obtained polymers were performed. The structure of the polymer chains was defined by NMR. Possible reasons of hydrolysis were discussed, stating that new copolymers are more resistant and polar biomaterials can be less interesting than elastomers.

Methods of increasing hydrophobicity of polyurethane materials: important applications of coatings with low surface free energy

The synthesis of polyurethane coatings by polyaddition in bulk using polyesterols and polyetherols with variable polarity was successfully carried out. IR and NMR spectra confirmed the structure of obtained polyurethanes and the incorporation of a polydimethylsiloxane(PDMS) modifier into the polyurethane structure. The differential scanning calorimetry and IR spectroscopy were employed for the microstructural assessment of the obtained materials. It was noted that crucial effect on free surface energy of the coatings has polyol structure as well as ratio of hard to soft segments. The contact angle measurements indicated that with increasing content of the polysiloxane in the flexible PTMO segments, the hydrophobicity significantly increased. It was demonstrated that hydrophobicity and mechanical strength, which are important for applications as biomaterials, are adversative in significant extent. The resulting coatings were characterized in terms of the heat resistance and changes during incubation in a Baxter saline solution.