L. Katsikas | University of Belgrade (original) (raw)

Papers by L. Katsikas

Research paper thumbnail of The polymerisation kinetics of lower dialkyl itaconates

Macromolecular Chemistry and Physics, 1999

ABSTRACT The free radical polymerisation kinetics of diethyl- (DEI), dipropyl- (DnPI), dibutyl- (... more ABSTRACT The free radical polymerisation kinetics of diethyl- (DEI), dipropyl- (DnPI), dibutyl- (DnBI), and dihexyl itaconate (DHI) in the bulk were studied in the temperature range from 50 to 70°C. The concentration of the initiator, 2,2′-azoisobutyronitrile (AIBN), was varied between 0.02 and 0.085 mol/dm3. The rate of polymerisation (Rp), degree of polymerisation (DP), overall polymerization rate constant (K), the ratio of the propagation and termination rate constants (kp/kt1/2), as well as the chain transfer constant to monomer (CM) were determined. The values of Rp, K, and kp/kt1/2 of the investigated monomers all increase with increasing size of the alkyl group in the ester substituent, whereas CM decreases when going from the dimethyl to the dihexyl ester. The values of CM are larger than the corresponding values for the alkyl esters of methacrylic acid.

Research paper thumbnail of The thermal degradation of poly(iso-butyl methacrylate) and poly(sec-butyl methacrylate)

Journal of the Serbian Chemical Society

The non-oxidative thermal degradation of poly(iso-butyl methacrylate) and poly(sec-butyl methacry... more The non-oxidative thermal degradation of poly(iso-butyl methacrylate) and poly(sec-butyl methacrylate) was investigated by studying changes in the polymer residue. Due to the different number of β-hydrogens in their ester substituents, these two polymeric isomers behave differently when subjected to elevated temperatures. Poly(iso-butyl methacrylate) degrades quantitatively by depolymerisation with zip lengths of the same order of magnitude as those of poly(methyl methacrylate). Poly(sec-butyl methacrylate) degrades by a combined degradation mechanism of depolymerisation and de-esterification. De-esterification becomes a significant thermolysis route at temperatures higher than 240 ºC.

Research paper thumbnail of Photochemistry of Semiconductor Colloids. 36. Fluorescence Investigations on the Nature of Electron and Hole Traps in Q-Sized Colloidal CdS Particles

Berichte der Bunsengesellschaft für physikalische Chemie

ABSTRACT

Research paper thumbnail of Thermal stability of starch benzoate

Polymer Degradation and Stability

Starch esterification with benzoyl chloride was performed in two steps, the first being the alkal... more Starch esterification with benzoyl chloride was performed in two steps, the first being the alkali treatment of the starch and the second, esterification. Samples of hydrophobic starch benzoate were synthesized with degrees of substitution: 0.73, 1.18 and 1.76 and their thermal stability was investigated by non-oxidative, non-isothermal thermogravimetry. It was shown that starch benzoate was thermally less stable than native

Research paper thumbnail of ChemInform Abstract: Synthesis and Characterization of Thiol-Stabilized CdTe Nanocrystals

Research paper thumbnail of CdS Nanoclusters: Synthesis, Characterization, Size Dependent Oscillator Strength, Temperature Shift of the Excitonic Transition Energy, and Reversible Absorbance Shift

The Journal of Physical Chemistry, 1994

Improved synthetic routes and sizeselective precipitation have enabled the preparation of almost ... more Improved synthetic routes and sizeselective precipitation have enabled the preparation of almost monodisperse CdS clusters. Six samples of 1-thioglycerol stabilized clusters with diameters of approximately 13, 14, 16, 19, 23, and 39 A have been prepared as fully redispersible ...

Research paper thumbnail of The synthesis and characterization of 2-mercaptoethyl methacrylate

Hemijska industrija, 2005

Research paper thumbnail of The thermal degradation of poly(diethyl fumarate)

Polymer Degradation and Stability, 2006

The kinetics and mechanism of the thermal degradation of poly(diethyl fumarate) (PDEF) were studi... more The kinetics and mechanism of the thermal degradation of poly(diethyl fumarate) (PDEF) were studied by thermogravimetry, as well as by analysis of the thermolysis volatiles and polymer residue. The characteristic mass loss temperatures were determined, as were the overall thermal degradation activation energies of three PDEF samples of varying molar mass. Ethylene and ethanol were present in the thermolysis volatiles at degradation temperatures below 300 C, while diethyl fumarate was also evidenced at higher degradation temperatures. The amount of monomer increased with increasing degradation temperature. The dependence of the molar mass of the residual polymer on the degradation time and temperature was established and the number of main-chain scissions per monomer unit, s/P 0 , calculated. A thermal degradation mechanism including de-esterification and random main-chain scission is proposed. The thermal degradation of PDEF was compared to the thermolysis of poly(ethyl methacrylate) (PEMA), poly(diethyl itaconate) (PDEI) and poly(ethyl acrylate) (PEA).

Research paper thumbnail of Radical polymerization of monoethyl itaconate

Hemijska industrija, 2003

Research paper thumbnail of The thermal degradation of poly (dimethyl itaconate-co-4-vinylpyridine)

Journal of thermal …, 2000

Copolymers of dimethyl itaconate (DMI) and 4-vinylpyridine (4VP) were synthetized in toluene at 6... more Copolymers of dimethyl itaconate (DMI) and 4-vinylpyridine (4VP) were synthetized in toluene at 60°C with 0.26 mol% of AIBN as initiator. Their compositions were determined by differential refractometry and by differential scanning calorimetry. The 4VP contents of the copolymer samples ranged between 7 and 75 mol%. The reactivity ratios calculated via the Fineman-Ross method were r 1 =0.24 (DMI) and r 2 =0.57 (4VP).

Research paper thumbnail of Improvement to the Flynn−Wall Method of Determining Apparent Activation Energies of the Thermal Degradation of Polymers †

The Journal of Physical Chemistry B, 2003

An improvement to the Flynn-Wall method of determining apparent activation energies of the therma... more An improvement to the Flynn-Wall method of determining apparent activation energies of the thermal degradation of polymers is presented. The method involves the deconvolution of differential thermogravimetric (TG) curves and the reconstruction of the corresponding TG curves of the individual thermal degradation processes, to which the Flynn-Wall method is then applied separately. The method is illustrated using poly-(diisobutyl itaconate) as an example. † Part of the special issue "Arnim Henglein Festschrift".

Research paper thumbnail of A "Double-Diamond Superlattice" Built Up of Cd17S4(SCH2CH2OH)26 Clusters

Science, 1995

A simple preparation of Cd(17)S(4)(SCH(2)CH(2)OH)(26) clusters in aqueous solution leads to the f... more A simple preparation of Cd(17)S(4)(SCH(2)CH(2)OH)(26) clusters in aqueous solution leads to the formation of colorless blocky crystals. X-ray structure determinations revealed a superlattice framework built up of covalently linked clusters. This superlattice is best described as two enlarged and interlaced diamond or zinc blende lattices. Because both the superlattice and the clusters display the same structural features, the crystal structure resembles the self-similarities known from fractal geometry. The optical spectrum of the cluster solution displays a sharp transition around 290 nanometers with a large absorption coefficient ( approximately 84,000 per molar per centimeter).

Research paper thumbnail of The thermal degradation of poly(di-n-hexyl itaconate) prepared in the presence of n-dodecyl mercaptan

Polymer Degradation and Stability, 1993

ABSTRACT

Research paper thumbnail of On the thermolysis of poly(chloroalkyl methacrylates) and poly(chloroalkyl acrylates). Part 4: Poly(2,2-dichloroethyl acrylate) and poly(2,2,2-trichloroethyl acrylate)

Polymer Degradation and Stability, 1994

ABSTRACT

Research paper thumbnail of Colloidal Zn_1−xCd_xS: optical saturation of the exciton band and primary photochemistry studied by subpicosecond laser flash photolysis

Journal of the Optical Society of America B, 1990

Quantum-size crystallites of Zno 95 Cdo 05 S in an aqueous colloidal solution were optically exci... more Quantum-size crystallites of Zno 95 Cdo 05 S in an aqueous colloidal solution were optically excited using intense subpicosecond laser pump pulses tuned to the exciton band. Optical probing in the UV registered saturation and the kinetics of ground-state recovery due to carrier recombination, with lifetimes in the 0.8-30-psec range. Optical probing at 616 nm monitored the yield of Auger electron emission. The saturation and yield curves, as a function of pump fluence, are described by a simple kinetic model that involves the exciton lifetime before trapping (-30 fsec) and the maximum number of electrons (-16) that can be emitted per particle.

Research paper thumbnail of Synthesis, morphology and optical properties of multi-pods Au/FeO(OH) and Au/Fe2O3 nanostructures

Materials Science and Engineering: B, 2012

Research paper thumbnail of Preparation and Thermal Stability of Elastomers Based on Irregular Poly(urethane-isocyanurate) Networks

Materials and Manufacturing Processes, 2009

Research paper thumbnail of The homogeneous photopolymerization of methyl methacrylate by colloidal cadmium sulfide

Macromolecular Chemistry and Physics, 1994

A completely new method of initiating the homogeneous radical polymerization of methyl methacryla... more A completely new method of initiating the homogeneous radical polymerization of methyl methacrylate in bulk or in solution via the photogeneration of an electron hole pair in colloidal cadmium sulfide is presented. A polymerization mechanism involving an excited cadmium sulfide particle in both the initiation and termination steps is proposed. In the initiation a methyl methacrylate molecule is oxidized by a positive hole photogenerated in a CdS particle, which results in a novel chain-end structure of the poly(methy1 methacrylate) (PMMA). Degradative chain transfer to reduced excited cadmium sulfide particles is responsible for chain termination. Thus, for the first time, a detailed polymerization mechanism in which all states of the polymerization, i. e., initiation, propagation, chain transfer and termination, is presented for the polymerization of vinyl monomers initiated by semiconductors. Thermogravimetry (TG) showed that the newly synthesized PMMA has greatly enhanced thermal stability when compared to normal radically prepared PMMA. In fact, the thermal stability approaches that of anionically prepared PMMA but is experimentally much easier to prepare. This technique enables the homogeneous embedding of CdS particles in a polymer matrix. 0 1994, Huthig & Wepf Verlag, Basel CCC 1022-1352/94/$08.00 *) In an earlier paper '@, we reported on the use of sodium 1-(4'-dodecyl)benzenesulfonate plus HClO, as stabilizer. As the sodium salt of the sulfonic acid contains varying amounts of Na,SO,, which might disturb the formation of a clear colloidal solution, we have changed the recipe in the way here described.

Research paper thumbnail of Photochemistry of colloidal semiconductors. 30. HPLC investigation of small CdS particles

Research paper thumbnail of Photochemistry of semiconductor colloids. 35. Size separation of colloidal cadmium sulfide by gel electrophoresis

Langmuir, 1990

Preparative gel electrophoresis was applied to separate Q-size cadmium sulfide colloids into frac... more Preparative gel electrophoresis was applied to separate Q-size cadmium sulfide colloids into fractions containing highly monodisperse particles. The fractions were characterized by transmission electron microscopy as well as absorption and emission spectroscopy. The results show that gel electrophoresis is superior to all known techniques for the preparation of homogeneously sized nanocrystallites.

Research paper thumbnail of The polymerisation kinetics of lower dialkyl itaconates

Macromolecular Chemistry and Physics, 1999

ABSTRACT The free radical polymerisation kinetics of diethyl- (DEI), dipropyl- (DnPI), dibutyl- (... more ABSTRACT The free radical polymerisation kinetics of diethyl- (DEI), dipropyl- (DnPI), dibutyl- (DnBI), and dihexyl itaconate (DHI) in the bulk were studied in the temperature range from 50 to 70°C. The concentration of the initiator, 2,2′-azoisobutyronitrile (AIBN), was varied between 0.02 and 0.085 mol/dm3. The rate of polymerisation (Rp), degree of polymerisation (DP), overall polymerization rate constant (K), the ratio of the propagation and termination rate constants (kp/kt1/2), as well as the chain transfer constant to monomer (CM) were determined. The values of Rp, K, and kp/kt1/2 of the investigated monomers all increase with increasing size of the alkyl group in the ester substituent, whereas CM decreases when going from the dimethyl to the dihexyl ester. The values of CM are larger than the corresponding values for the alkyl esters of methacrylic acid.

Research paper thumbnail of The thermal degradation of poly(iso-butyl methacrylate) and poly(sec-butyl methacrylate)

Journal of the Serbian Chemical Society

The non-oxidative thermal degradation of poly(iso-butyl methacrylate) and poly(sec-butyl methacry... more The non-oxidative thermal degradation of poly(iso-butyl methacrylate) and poly(sec-butyl methacrylate) was investigated by studying changes in the polymer residue. Due to the different number of β-hydrogens in their ester substituents, these two polymeric isomers behave differently when subjected to elevated temperatures. Poly(iso-butyl methacrylate) degrades quantitatively by depolymerisation with zip lengths of the same order of magnitude as those of poly(methyl methacrylate). Poly(sec-butyl methacrylate) degrades by a combined degradation mechanism of depolymerisation and de-esterification. De-esterification becomes a significant thermolysis route at temperatures higher than 240 ºC.

Research paper thumbnail of Photochemistry of Semiconductor Colloids. 36. Fluorescence Investigations on the Nature of Electron and Hole Traps in Q-Sized Colloidal CdS Particles

Berichte der Bunsengesellschaft für physikalische Chemie

ABSTRACT

Research paper thumbnail of Thermal stability of starch benzoate

Polymer Degradation and Stability

Starch esterification with benzoyl chloride was performed in two steps, the first being the alkal... more Starch esterification with benzoyl chloride was performed in two steps, the first being the alkali treatment of the starch and the second, esterification. Samples of hydrophobic starch benzoate were synthesized with degrees of substitution: 0.73, 1.18 and 1.76 and their thermal stability was investigated by non-oxidative, non-isothermal thermogravimetry. It was shown that starch benzoate was thermally less stable than native

Research paper thumbnail of ChemInform Abstract: Synthesis and Characterization of Thiol-Stabilized CdTe Nanocrystals

Research paper thumbnail of CdS Nanoclusters: Synthesis, Characterization, Size Dependent Oscillator Strength, Temperature Shift of the Excitonic Transition Energy, and Reversible Absorbance Shift

The Journal of Physical Chemistry, 1994

Improved synthetic routes and sizeselective precipitation have enabled the preparation of almost ... more Improved synthetic routes and sizeselective precipitation have enabled the preparation of almost monodisperse CdS clusters. Six samples of 1-thioglycerol stabilized clusters with diameters of approximately 13, 14, 16, 19, 23, and 39 A have been prepared as fully redispersible ...

Research paper thumbnail of The synthesis and characterization of 2-mercaptoethyl methacrylate

Hemijska industrija, 2005

Research paper thumbnail of The thermal degradation of poly(diethyl fumarate)

Polymer Degradation and Stability, 2006

The kinetics and mechanism of the thermal degradation of poly(diethyl fumarate) (PDEF) were studi... more The kinetics and mechanism of the thermal degradation of poly(diethyl fumarate) (PDEF) were studied by thermogravimetry, as well as by analysis of the thermolysis volatiles and polymer residue. The characteristic mass loss temperatures were determined, as were the overall thermal degradation activation energies of three PDEF samples of varying molar mass. Ethylene and ethanol were present in the thermolysis volatiles at degradation temperatures below 300 C, while diethyl fumarate was also evidenced at higher degradation temperatures. The amount of monomer increased with increasing degradation temperature. The dependence of the molar mass of the residual polymer on the degradation time and temperature was established and the number of main-chain scissions per monomer unit, s/P 0 , calculated. A thermal degradation mechanism including de-esterification and random main-chain scission is proposed. The thermal degradation of PDEF was compared to the thermolysis of poly(ethyl methacrylate) (PEMA), poly(diethyl itaconate) (PDEI) and poly(ethyl acrylate) (PEA).

Research paper thumbnail of Radical polymerization of monoethyl itaconate

Hemijska industrija, 2003

Research paper thumbnail of The thermal degradation of poly (dimethyl itaconate-co-4-vinylpyridine)

Journal of thermal …, 2000

Copolymers of dimethyl itaconate (DMI) and 4-vinylpyridine (4VP) were synthetized in toluene at 6... more Copolymers of dimethyl itaconate (DMI) and 4-vinylpyridine (4VP) were synthetized in toluene at 60°C with 0.26 mol% of AIBN as initiator. Their compositions were determined by differential refractometry and by differential scanning calorimetry. The 4VP contents of the copolymer samples ranged between 7 and 75 mol%. The reactivity ratios calculated via the Fineman-Ross method were r 1 =0.24 (DMI) and r 2 =0.57 (4VP).

Research paper thumbnail of Improvement to the Flynn−Wall Method of Determining Apparent Activation Energies of the Thermal Degradation of Polymers †

The Journal of Physical Chemistry B, 2003

An improvement to the Flynn-Wall method of determining apparent activation energies of the therma... more An improvement to the Flynn-Wall method of determining apparent activation energies of the thermal degradation of polymers is presented. The method involves the deconvolution of differential thermogravimetric (TG) curves and the reconstruction of the corresponding TG curves of the individual thermal degradation processes, to which the Flynn-Wall method is then applied separately. The method is illustrated using poly-(diisobutyl itaconate) as an example. † Part of the special issue "Arnim Henglein Festschrift".

Research paper thumbnail of A "Double-Diamond Superlattice" Built Up of Cd17S4(SCH2CH2OH)26 Clusters

Science, 1995

A simple preparation of Cd(17)S(4)(SCH(2)CH(2)OH)(26) clusters in aqueous solution leads to the f... more A simple preparation of Cd(17)S(4)(SCH(2)CH(2)OH)(26) clusters in aqueous solution leads to the formation of colorless blocky crystals. X-ray structure determinations revealed a superlattice framework built up of covalently linked clusters. This superlattice is best described as two enlarged and interlaced diamond or zinc blende lattices. Because both the superlattice and the clusters display the same structural features, the crystal structure resembles the self-similarities known from fractal geometry. The optical spectrum of the cluster solution displays a sharp transition around 290 nanometers with a large absorption coefficient ( approximately 84,000 per molar per centimeter).

Research paper thumbnail of The thermal degradation of poly(di-n-hexyl itaconate) prepared in the presence of n-dodecyl mercaptan

Polymer Degradation and Stability, 1993

ABSTRACT

Research paper thumbnail of On the thermolysis of poly(chloroalkyl methacrylates) and poly(chloroalkyl acrylates). Part 4: Poly(2,2-dichloroethyl acrylate) and poly(2,2,2-trichloroethyl acrylate)

Polymer Degradation and Stability, 1994

ABSTRACT

Research paper thumbnail of Colloidal Zn_1−xCd_xS: optical saturation of the exciton band and primary photochemistry studied by subpicosecond laser flash photolysis

Journal of the Optical Society of America B, 1990

Quantum-size crystallites of Zno 95 Cdo 05 S in an aqueous colloidal solution were optically exci... more Quantum-size crystallites of Zno 95 Cdo 05 S in an aqueous colloidal solution were optically excited using intense subpicosecond laser pump pulses tuned to the exciton band. Optical probing in the UV registered saturation and the kinetics of ground-state recovery due to carrier recombination, with lifetimes in the 0.8-30-psec range. Optical probing at 616 nm monitored the yield of Auger electron emission. The saturation and yield curves, as a function of pump fluence, are described by a simple kinetic model that involves the exciton lifetime before trapping (-30 fsec) and the maximum number of electrons (-16) that can be emitted per particle.

Research paper thumbnail of Synthesis, morphology and optical properties of multi-pods Au/FeO(OH) and Au/Fe2O3 nanostructures

Materials Science and Engineering: B, 2012

Research paper thumbnail of Preparation and Thermal Stability of Elastomers Based on Irregular Poly(urethane-isocyanurate) Networks

Materials and Manufacturing Processes, 2009

Research paper thumbnail of The homogeneous photopolymerization of methyl methacrylate by colloidal cadmium sulfide

Macromolecular Chemistry and Physics, 1994

A completely new method of initiating the homogeneous radical polymerization of methyl methacryla... more A completely new method of initiating the homogeneous radical polymerization of methyl methacrylate in bulk or in solution via the photogeneration of an electron hole pair in colloidal cadmium sulfide is presented. A polymerization mechanism involving an excited cadmium sulfide particle in both the initiation and termination steps is proposed. In the initiation a methyl methacrylate molecule is oxidized by a positive hole photogenerated in a CdS particle, which results in a novel chain-end structure of the poly(methy1 methacrylate) (PMMA). Degradative chain transfer to reduced excited cadmium sulfide particles is responsible for chain termination. Thus, for the first time, a detailed polymerization mechanism in which all states of the polymerization, i. e., initiation, propagation, chain transfer and termination, is presented for the polymerization of vinyl monomers initiated by semiconductors. Thermogravimetry (TG) showed that the newly synthesized PMMA has greatly enhanced thermal stability when compared to normal radically prepared PMMA. In fact, the thermal stability approaches that of anionically prepared PMMA but is experimentally much easier to prepare. This technique enables the homogeneous embedding of CdS particles in a polymer matrix. 0 1994, Huthig & Wepf Verlag, Basel CCC 1022-1352/94/$08.00 *) In an earlier paper '@, we reported on the use of sodium 1-(4'-dodecyl)benzenesulfonate plus HClO, as stabilizer. As the sodium salt of the sulfonic acid contains varying amounts of Na,SO,, which might disturb the formation of a clear colloidal solution, we have changed the recipe in the way here described.

Research paper thumbnail of Photochemistry of colloidal semiconductors. 30. HPLC investigation of small CdS particles

Research paper thumbnail of Photochemistry of semiconductor colloids. 35. Size separation of colloidal cadmium sulfide by gel electrophoresis

Langmuir, 1990

Preparative gel electrophoresis was applied to separate Q-size cadmium sulfide colloids into frac... more Preparative gel electrophoresis was applied to separate Q-size cadmium sulfide colloids into fractions containing highly monodisperse particles. The fractions were characterized by transmission electron microscopy as well as absorption and emission spectroscopy. The results show that gel electrophoresis is superior to all known techniques for the preparation of homogeneously sized nanocrystallites.