Miroslav Marek

Crosslinked ultra-thin polyimide film as a gas separation layer for composite membranes

Abstract Composite membranes with an ultra-thin polyimide separation layer were prepared by two-dimensional UV crosslinking of Langmuir-Blodgett films of a salt of polyamic acid based on 4,4′-hexafluoroisopropylidenebis(phthalic anhydride) and 2-(methacryloyloxy)ethyl 3,5-diaminobenzoate on the argon/water interface and then its deposition onto the surface of a porous support and by subsequent thermal imidization. Separation factors for CO2/N2, α = 6.4, and for O2/N2, α = 2.4, at permeation rates of the order 10−6 cm3 (STP)/(cm2 s cm Hg) were reached.

Ultra-thin polyimide film as a gas-separation layer for composite membranes

Abstract Composite membranes with an ultra-thin polyimide separation layer have been prepared by the deposition of dimethylalkylammonium salt of polyamic acid on a poly(phenylene oxide) porous support layer by the Langmuir—Blodgett technique and subsequent thermal cyclization of the polyimide precursor. In spite of a relatively mild thermal treatment, complete cyclization was achieved as observed by Fourier transform infra-red spectroscopy. The composite membrane with polyimide ultra-thin separation layer exhibited a considerably high permeation rate, maintaining a good selectivity.

New soluble polyimides prepared from 4,4'-(alkylenediyldioxy) dianilines

Abstract New soluble aromatic polyimides have been prepared from 4,4′-(hexafluoroisopropylidene)bis(phthalic anhydride) (6FDA) and 4,4′-(alkylenediyldioxy)dianilines. Their structures were determined by i.r., 1 H n.m.r. and 13 C n.m.r. spectroscopic measurements, based on model compounds prepared by reacting 6FDA with p -anisidine. These polymers show low glass transition temperatures and good solubility in various solvents, and are stable up to 440°C in a nitrogen atmosphere.

Enzymic deacetylation of derivatives of 1,2-O-isoproylidene-α-d-hexofuranoses

Abstract Enzymically catalysed, partial deacetylation of the 5,6-diacetates of 3-deoxy-1,2- O -isopropylidene-α- d - ribo -hexofuranose and 1,2- O -isopropylidene-α- d -gluco- and -allo-furanose with different substituents at C-3(OAc, OMe, NHAc) gives the 5-acetate, which migrates rapidly to give the 6-acetate. The initial rate of deacetylation depends on the size of the 3-substituent and the configuration at C-3.

CHEMICAL AND ENZYMIC DEACETYLATION OF METHYL 2,3,4-TRI-O-ACETYL-β-D-XYLOPYRANOSIDE

The deacetyiation of methyl 2,3,4-tri-O-acetyl-β-D-ylopyranoside was studied under different conditions of alkaline and enzymic hydrolysis. During enzymic deacetylation using porcine liver esterase a considerably higher amount of partially acetylated derivatives was observed in contrast to chemical hydrolysis.

Study of Polyimides Prepared from 3,3′,4,4′-Benzophenonetetracarboxylic Dianhydride and 4,4′-(Alkane-1, n-Diyldioxy)Dianilines

Abstract Polyimides based on 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and 4,4′-(alkane-1,n-diyldioxy)dianilines were prepared via the corresponding polyamic acids and characterized by solid-state 13C-NMR and IR spectroscopy. As shown by x-ray diffraction measurements, the polyimides are semicrystalline whereas the polyamic acids are entirely amorphous. Glass transition temperatures of the polyimides are lower compared with polyimides without flexible linkages. The polyimides are stable up to 400°C in nitrogen atmosphere.

Enzymic Deacetylation of Methyl 2,3-Di-O-Acetyl-α- and β-D-Threofuranoside

Enzymic deacetylation of methyl 2,3-di-O-acaetyl-α- and β-D-threofuranoside using porcine liver esterase affords monoacetates only (in the case of the α-anomer, the 3-O-acetylderivative exclusively) without any further hydrolysis to the corresponding diols.

Synthesis and properties of polyimides containing polybutadiene blocks

Polyimides containing polybutadiene blocks were prepared by copolycondensation of benzophenone-3,3′,4,4′-tetracarboxylic dianhydride, diphenylmethane-4,4′-diisocyanate and isocyanate-endcapped polybutadiene LBD-3000. 13C NMR CP-MAS and FTIR spectroscopies were used to determine the chemical structure of the copolymers. TGA showed that the thermal stability of the copolymers in inert atmosphere is almost independent of the polybutadiene content in the copolymer (as follows from the temperature of 10% and 20% weight loss). Stress–strain experiments showed that copolymers containing amounts of polybutadiene higher than 59 wt% exhibited elastomeric behaviour. © 1999 Society of Chemical Industry

Synthesis and properties of copolymers consisting of aramide and poly(6-hexanelactam) blocks

Abstract Low molecular weight aromatic polyamides of the meta-type which bear N-acyl-6-hexanelactam end-groups were prepared, characterized by NMR and utilized as initiators of the anionic polymerization of 6-hexanelactam. The resulting block copolymers poly(6-hexanelactam)-block-poly(-isophthalic acid-alt-2-methyl-1,3-phenylenediamine)-block-poly-(6-hexanelactam) were characterized by NMR, DSC, TGA, X-ray diffraction and microscopy of solution-cast films and compared with an aramide-polyamide 6 blend also prepared by polymerization.

Enzymic Preparation of Benzyl β-D-Glucopyranoside

Benzyl β-D-glucopyranoside was prepared by an enzyme-catalysed direct reaction between D-glucose, or better cellobiose, and benzyl alcohol in the presence of a minimum amount of water. The enzyme β-glucosidase was used in the immobilized form (adsorbed onto macroporous polyethylene terephthalate or covalently bound on polyglycidyl methacrylate), enabling multiple application.