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Molecular modelling - Structure and Properties of carbene-based catalyst
Kulovaná, Eva ; Zmrzlý, Martin (oponent) ; Richtera, Lukáš (vedoucí práce)
Molecular modelling enables to predict behaviour of the new compounds and helps to interpret experimental data. The objective of our study was the prediction of selected properties of polymerization catalysts based on carbenes, the prediction of their structures and spectral characteristics. To confirm the behaviour of carbenes and their precursors based on chlorides selected characteristics of a molecule were studied. The visualization of selected molecular orbitals and electrostatic potential-mapped electron density surface was made. Subsequently, bond distances and bond angles of selected imidazole and imidazoline compounds and from them prepared “free” carbenes were obtained by using computer programs. Data of structural similar compounds, which have been already characterized, were obtained from CCDC (Cambridge Crystallographic Data Centre) and were compared with our calculated data. Infrared (IR) and Raman spectra of the imidazole salt and the infrared spectrum of the appropriate carbene were measured. The spectra measured were compared with predicted spectra.
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Molecular modelling - Structure and Properties of carbene-based catalyst
Kulovaná, Eva ; Hermanová, Soňa (oponent) ; Richtera, Lukáš (vedoucí práce)
By using molecular modelling it is possible to predict the behaviour of new compounds and to help interpreting of the experimental data. The objective of the thesis was the prediction of selected properties of polymerization catalysts based on carbenes, the prediction of their structures and spectral characteristics and the study of the mechanism of the ring-opening polymerization of lactide. To confirm the behaviour of carbenes and their precursors based on chlorides selected characteristics of a molecule were studied. The calculation of selected molecular orbitals and electrostatic potential maps was made. Subsequently, bond distances and bond angles of selected imidazole and imidazoline compounds, “free” carbenes and their possible hydrolysis products were obtained by using computer programs. Data of structural similar compounds, which have already been characterized, were obtained from CCDC (Cambridge Crystallographic Data Centre) and were compared with the calculated data. Infrared and Raman spectra of the imidazole salt and the infrared spectrum of the appropriate carbene were measured. The measured spectra were compared with the predicted ones. For the better spectra interpretation the spectra of possible hydrolysis products were calculated. Subsequently, the mechanism of the ring-opening polymerization of lactide was investigated. Based on calculated energies of stationary points the novel mechanism of polymerization was suggested.
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Ring-opening Polymerization of Lactones and Lactides
Boháčová, Zdeňka ; Cihlář, Jaroslav (oponent) ; Lehocký,, Marián (oponent) ; Vojtová, Lucy (vedoucí práce)
Biodegradable aliphatic polyesters based on polylactones, polylactides and their copolymers are particularly interesting for their applications in the medical field. The major polymerization method used to synthesize these polymers has been the ring-opening polymerization (ROP) of lactones or lactides. Many organometallic compounds are effective initiators for the controlled ROP synthesis of polyesters but heavy metals derivatives are harmful for the human organisms. There has been an increasing interest in the development of efficient "green" catalytic systems for the synthesis of biodegradable aliphatic polyesters. This thesis is dedicated to the synthesis of aliphatic polyesters based on polycaprolactone, polylactide and polyglycolide and especially their copolymers using organic catalyst from the group of free N-heterocyclic carbenes (NHC) without the central heavy metal atom. A literature review is focused on the recent advances in the ROP of lactones and lactides using organic metal-free catalysts. However, there is no evidence of using carbenes for ROP synthesis of polyglycolide or its copolymers. An experimental part of this work briefly describes the preparation and properties of 1,3-di-tert-butylimidazol-2-ylidene (NHC-tBu) free carbene from its stable chloride salt. The next section is focused on the preparation of polyesters from cyclic ester monomers, namely L lactide, D,L-lactide, glycolide and -caprolactone using NHC-tBu catalyst. In particular, novel synthesis of thermosensitive amphiphilic triblock copolymers based on hydrophobic biodegradable polylactide, polyglycolide and biocompatible hydrophilic polyethylene glycol (PLGA–PEG–PLGA) using prepared NHC-tBu has been investigated. Consequently, influences of reaction conditions (i.e. monomers purification, reaction temperature, type of solvent, solvent to monomer ratio and initiator to catalyst ratio) have been evaluated. Finally, the comparison of PLGA–PEG–PLGA copolymers prepared using NHC-tBu and Sn(II)2-ethylhexanoate catalysts has been performed. It was demonstrated that combination of NHC-tBu with PEG creates the effective catalytic system for ring opening polymerization of lactone or lactides. Polymers were prepared with the high conversion of monomer (70 – 85%) and low polydispersity index (Mw/Mn at around 1.2). PLGA–PEG–PLGA copolymer with two phase transitions (sol-gel and gel-suspension) and gelation temperature between 35 – 43 °C was obtained. In most cases, changes in the reaction conditions did not have significant influence on chemical properties such as molecular weight or polydispersity index, however essentially affected the physical properties such as visco-elastic behaviors.
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Ring-opening Polymerization of Lactones and Lactides
Boháčová, Zdeňka ; Cihlář, Jaroslav (oponent) ; Lehocký,, Marián (oponent) ; Vojtová, Lucy (vedoucí práce)
Biodegradable aliphatic polyesters based on polylactones, polylactides and their copolymers are particularly interesting for their applications in the medical field. The major polymerization method used to synthesize these polymers has been the ring-opening polymerization (ROP) of lactones or lactides. Many organometallic compounds are effective initiators for the controlled ROP synthesis of polyesters but heavy metals derivatives are harmful for the human organisms. There has been an increasing interest in the development of efficient "green" catalytic systems for the synthesis of biodegradable aliphatic polyesters. This thesis is dedicated to the synthesis of aliphatic polyesters based on polycaprolactone, polylactide and polyglycolide and especially their copolymers using organic catalyst from the group of free N-heterocyclic carbenes (NHC) without the central heavy metal atom. A literature review is focused on the recent advances in the ROP of lactones and lactides using organic metal-free catalysts. However, there is no evidence of using carbenes for ROP synthesis of polyglycolide or its copolymers. An experimental part of this work briefly describes the preparation and properties of 1,3-di-tert-butylimidazol-2-ylidene (NHC-tBu) free carbene from its stable chloride salt. The next section is focused on the preparation of polyesters from cyclic ester monomers, namely L lactide, D,L-lactide, glycolide and -caprolactone using NHC-tBu catalyst. In particular, novel synthesis of thermosensitive amphiphilic triblock copolymers based on hydrophobic biodegradable polylactide, polyglycolide and biocompatible hydrophilic polyethylene glycol (PLGA–PEG–PLGA) using prepared NHC-tBu has been investigated. Consequently, influences of reaction conditions (i.e. monomers purification, reaction temperature, type of solvent, solvent to monomer ratio and initiator to catalyst ratio) have been evaluated. Finally, the comparison of PLGA–PEG–PLGA copolymers prepared using NHC-tBu and Sn(II)2-ethylhexanoate catalysts has been performed. It was demonstrated that combination of NHC-tBu with PEG creates the effective catalytic system for ring opening polymerization of lactone or lactides. Polymers were prepared with the high conversion of monomer (70 – 85%) and low polydispersity index (Mw/Mn at around 1.2). PLGA–PEG–PLGA copolymer with two phase transitions (sol-gel and gel-suspension) and gelation temperature between 35 – 43 °C was obtained. In most cases, changes in the reaction conditions did not have significant influence on chemical properties such as molecular weight or polydispersity index, however essentially affected the physical properties such as visco-elastic behaviors.
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Molecular modelling - Structure and Properties of carbene-based catalyst
Kulovaná, Eva ; Hermanová, Soňa (oponent) ; Richtera, Lukáš (vedoucí práce)
By using molecular modelling it is possible to predict the behaviour of new compounds and to help interpreting of the experimental data. The objective of the thesis was the prediction of selected properties of polymerization catalysts based on carbenes, the prediction of their structures and spectral characteristics and the study of the mechanism of the ring-opening polymerization of lactide. To confirm the behaviour of carbenes and their precursors based on chlorides selected characteristics of a molecule were studied. The calculation of selected molecular orbitals and electrostatic potential maps was made. Subsequently, bond distances and bond angles of selected imidazole and imidazoline compounds, “free” carbenes and their possible hydrolysis products were obtained by using computer programs. Data of structural similar compounds, which have already been characterized, were obtained from CCDC (Cambridge Crystallographic Data Centre) and were compared with the calculated data. Infrared and Raman spectra of the imidazole salt and the infrared spectrum of the appropriate carbene were measured. The measured spectra were compared with the predicted ones. For the better spectra interpretation the spectra of possible hydrolysis products were calculated. Subsequently, the mechanism of the ring-opening polymerization of lactide was investigated. Based on calculated energies of stationary points the novel mechanism of polymerization was suggested.
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Molecular modelling - Structure and Properties of carbene-based catalyst
Kulovaná, Eva ; Zmrzlý, Martin (oponent) ; Richtera, Lukáš (vedoucí práce)
Molecular modelling enables to predict behaviour of the new compounds and helps to interpret experimental data. The objective of our study was the prediction of selected properties of polymerization catalysts based on carbenes, the prediction of their structures and spectral characteristics. To confirm the behaviour of carbenes and their precursors based on chlorides selected characteristics of a molecule were studied. The visualization of selected molecular orbitals and electrostatic potential-mapped electron density surface was made. Subsequently, bond distances and bond angles of selected imidazole and imidazoline compounds and from them prepared “free” carbenes were obtained by using computer programs. Data of structural similar compounds, which have been already characterized, were obtained from CCDC (Cambridge Crystallographic Data Centre) and were compared with our calculated data. Infrared (IR) and Raman spectra of the imidazole salt and the infrared spectrum of the appropriate carbene were measured. The spectra measured were compared with predicted spectra.
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