Papers by George Karanikolopoulos
Macromolecular Chemistry and Physics, 2003
Three non‐bridged dimethylzirconocene complexes; i.e., bis(η5‐cyclopentadienyl)dimethylzirconium ... more Three non‐bridged dimethylzirconocene complexes; i.e., bis(η5‐cyclopentadienyl)dimethylzirconium (1), bis(η5‐tert‐butyl‐cyclopentadienyl)dimethylzirconium (2), bis(η5‐indenyl)dimethylzirconium (3), and the chiral zirconocene rac‐ethylenebis(η5‐indenyl)dimethylzirconium (4) were synthesized and used as catalysts for the polymerization of methyl methacrylate, MMA, combined with tris(pentafluorophenyl)borate (A) or tetrakis(pentafluorophenyl)borate dimethylanilinum salt (B) in the presence of ZnEt2. The evolution of the polymerization characteristics; i.e., molecular weight, molecular‐weight distribution, and yield were examined for the above systems. The influence of the nature of the solvent was also investigated. The aggregation behavior, the steric hindrance, and the lipophilicity of the active catalytic systems are the most important parameters determining the polymerization characteristics. The tacticity of the products is reported and the influence of the catalyst structure is d...
Όταν αναφέρεται κάποιος σε πολυμερικά υλικά συνήθως κάνει λόγο για εύκαμπτα, εύκολα επεξεργάσιμα ... more Όταν αναφέρεται κάποιος σε πολυμερικά υλικά συνήθως κάνει λόγο για εύκαμπτα, εύκολα επεξεργάσιμα υλικά τα οποία επιπρόσθετα λειτουργούν ως μονωτές απέναντι στον ηλεκτρισμό. Η διατύπωση αυτή χαρακτηρίζεται ως αληθής για την μεγάλη πλειοψηφία των παραπάνω υλικών. Είναι σημαντική παρόλα αυτά η ύπαρξη μιας ειδικής κατηγορίας τέτοιων υλικών, τα οποία χαρακτηρίζονται ως «Συζυγή Πολυμερή» (Conjugated Polymers) τα οποία εμφανίζουν τις ηλεκτρικές και θερμικές εκείνες ιδιότητες που παραδοσιακά αποδίδονται σε μέταλλα και ημιαγωγούς, ενώ διατηρούν παράλληλα τις καλές μηχανικές ιδιότητες και την ευκολία στην επεξεργασία που χαρακτηρίζουν τα «κλασσικά» πολυμερικά υλικά. Όπως βέβαια γίνεται κατανοητό οι παραπάνω ιδιότητες καθιστούν τα υλικά αυτά ιδιαίτερα ελκυστικά για μια ευρεία σειρά εφαρμογών που αφορούν τομείς όπως: ηλεκτρομαγνητική Θωράκιση συσκευών, μπαταρίες (1) , κατασκευή Τρανζίστορ Επίδρασης Πεδίου (FETs: Field Effect Transistors, all Polymer FET (2),(3)), Διόδων Εκπομπής Φωτός (LEDs). 2) ΛΙΓΑ ΛΟΓΙΑ ΓΙΑ ΤΗΝ ΧΗΜΕΙΑ ΤΩΝ « ΣΥΖΥΓΩΝ ΠΟΛΥΜΕΡΩΝ » Ο Όρος «Συζυγή Πολυμερή» φανερώνει μια κύρια ανθρακική αλυσίδα, για το πολυμερικό υλικό, η οποία ενέχει ακόρεστο σύστημα και πιο συγκεκριμένα ένα αυστηρά εναλλασσόμενο σύστημα απλών και διπλών δεσμών κατά μήκος της ανθρακικής αλυσίδας (δεν αποκλείεται η παρεμβολή ετεροατόμων στην παραπάνω κύρια ανθρακική αλυσίδα του πολυμερούς πχ πολυπυρρόλια, πολυθειοφαίνια κ.α, ωστόσο, και για λόγους απλότητας, γίνεται αναφορά σε ανθρακικής αλυσίδας
Single site Metallocene catalysts as useful tools for the synthesis of well defined complex Macro... more Single site Metallocene catalysts as useful tools for the synthesis of well defined complex Macromolecular structures for polar monomers.
Food Chemistry, 2015
Reliable methods for quantification of synthetic water-soluble colors in complex food matrices ar... more Reliable methods for quantification of synthetic water-soluble colors in complex food matrices are currently not available. The present work describes the development and validation of an improved protocol for the analysis of synthetic food colorants in complex food matrices presenting high protein and/or fat content. The method developed employs an extraction stage, followed by a subsequent sonification, centrifugation and concentration step. A final clean up via SPE on polyamide cartridges was also employed. The isolated colorants were separated and analyzed by an RP-HPLC/DAD system. High and consistent recoveries (min. 81%) and low RSDs (max. 6%) were achieved for all studied colorants. The issue of high fat content matrices was also addressed showing the need for an additional defatting step in the procedure. Overall, the protocol presented shows high precision and accuracy of detection and can provide the basis for future development of similar methods in other complex food matrices.
Macromolecules, 2001
Polymerization of methyl methacrylate (MMA) by the three component catalytic system Cp2ZrMe2/B(C6... more Polymerization of methyl methacrylate (MMA) by the three component catalytic system Cp2ZrMe2/B(C6F5)3/ZnEt2 (1), in toluene, under thoroughly purified conditions, was found to produce polymers of high molecular weights (Mw > 60 × 103), low polydispersities (Mw/Mn = 1.12−1.22) and almost quantitative yields. The polymerization process is characterized by a pronounced induction period followed by a rapid and constant rate of polymerization. The molecular weight of PMMA increases by increasing the conversion and is proportional to the ratio of [MMA]0/[Zr]0, while Mw/Mn remains intact, meaning that the present polymerization proceeds in a well-controlled fashion. Evidence for effects of [ZnEt2] and temperature in the molecular characteristics of the final products are also presented in this study. Moreover, the catalytic system 1 was found to catalyze the polymerization of other alkyl methacrylates (alkyl = n-butyl, n-hexyl) to high molecular weight syndiotactic materials, with narrow molecular weight distrib...
Journal of Polymer Science Part A: Polymer Chemistry, 2004
Statistical copolymers of methyl methacrylate (MMA) with n-butyl-, sbutyl, t-butyl-, n-hexyl-, de... more Statistical copolymers of methyl methacrylate (MMA) with n-butyl-, sbutyl, t-butyl-, n-hexyl-, decyl-, stearyl-, allyl-, trimethylsilyl-and trimethylsilyloxyethyl methacrylate were prepared by zirconocene-catalyzed copolymerization. The reactivity ratios of MMA copolymers with butyl-, hexyl-, and stearyl methacrylate were estimated using the Finemann-Ross, the inverted Finemann-Ross, and the Kelen-Tü dos graphical methods. Structural parameters of the copolymers were obtained from the calculated dyad sequences, derived by using the reactivity ratios. The effect of the nature of the methacrylate ester group and the catalytic system used on the copolymer structure is discussed. The glass-transition temperature (T g) values of MMA copolymers with butyl-and hexyl methacrylate were measured and examined in the frame of several theoretical equations, allowing the prediction of these T g values. The best fit was obtained using Barton and Johnston equations, taking the monomer sequence distribution of the copolymers into account.
Macromolecules, 2003
ABSTRACT Graft copolymers having poly(methyl methacrylate), PMMA, backbone and polystyrene, PS, p... more ABSTRACT Graft copolymers having poly(methyl methacrylate), PMMA, backbone and polystyrene, PS, polyisoprene, PI, poly(ethylene oxide), PEO, poly(2-methyl-1,3-pentadiene), P2MP, and PS-b-PI branches were prepared using the macromonomer methodology and high-vacuum techniques. The methacrylic macromonomers, mMM, were synthesized by anionic polymerization, whereas their homopolymerization and copolymerization with MMA were performed by metallocene catalysts. Relatively high macromonomer conversions were obtained in all cases. The parameters affecting the polymerization characteristics were examined. Well-defined poly(butyl methacrylate)-b-poly(methyl methacrylate) block copolymers were prepared for the first time by sequential addition of monomers starting from n-butyl methacrylate. The samples were characterized by size exclusion chromatography, SEC, 1H and 13C NMR spectroscopy, low-angle laser light scattering, LALLS, and differential scanning calorimetry, DSC.
Reliable methods for quantification of synthetic water-soluble colors in complex food matrices ar... more Reliable methods for quantification of synthetic water-soluble colors in complex food matrices are currently not available. The present work describes the development and validation of an improved protocol for the analysis of synthetic food colorants in complex food matrices presenting high protein and/or fat content. The method developed employs an extraction stage, followed by a subsequent sonification, centrifugation and concentration step. A final clean up via SPE on polyamide cartridges was also employed. The isolated colorants were separated and analyzed by an RP-HPLC/DAD system. High and consistent recoveries (min. 81%) and low RSDs (max. 6%) were achieved for all studied colorants. The issue of high fat content matrices was also addressed showing the need for an additional defatting step in the procedure. Overall, the protocol presented shows high precision and accuracy of detection and can provide the basis for future development of similar methods in other complex food matrices.
Όταν αναφέρεται κάποιος σε πολυμερικά υλικά συνήθως κάνει λόγο για εύκαμπτα, εύκολα επεξεργάσιμα ... more Όταν αναφέρεται κάποιος σε πολυμερικά υλικά συνήθως κάνει λόγο για εύκαμπτα, εύκολα επεξεργάσιμα υλικά τα οποία επιπρόσθετα λειτουργούν ως μονωτές απέναντι στον ηλεκτρισμό. Η διατύπωση αυτή χαρακτηρίζεται ως αληθής για την μεγάλη πλειοψηφία των παραπάνω υλικών. Είναι σημαντική παρόλα αυτά η ύπαρξη μιας ειδικής κατηγορίας τέτοιων υλικών, τα οποία χαρακτηρίζονται ως «Συζυγή Πολυμερή» (Conjugated Polymers) τα οποία εμφανίζουν τις ηλεκτρικές και θερμικές εκείνες ιδιότητες που παραδοσιακά αποδίδονται σε μέταλλα και ημιαγωγούς, ενώ διατηρούν παράλληλα τις καλές μηχανικές ιδιότητες και την ευκολία στην επεξεργασία που χαρακτηρίζουν τα «κλασσικά» πολυμερικά υλικά.
The ring-opening polymerization of e-caprolactone (e-CL) and d-valerolactone (d-VL) using nine ca... more The ring-opening polymerization of e-caprolactone (e-CL) and d-valerolactone (d-VL) using nine catalytic systems consisting of a combination of three C 2v zirconocene complexes and three borate cocatalysts is discussed. The polymerizations proceed in a well-controlled manner, producing polymers with relatively high molecular weights and narrow molecular weight distributions. Kinetic experiments of the polymerization of e-CL with the catalytic system Cp 2 ZrMe 2 /B(C 6 F 5 ) 3 (1) showed a linear dependence between polymerization yield and molecular weight with time, as well as between the molecular weight with the molar ratio of the monomer over the catalyst [e-CL]/[Zr], indicating sufficient control of the polymerization reaction. The catalytic system (1) was utilized for the synthesis of well-defined block copolymers of MMA with e-CL and d-VL. All samples were characterized by size exclusion chromatography, nuclear magnetic resonance, and differential scanning calorimetry. V V C 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3524-3537, 2007
Polymerization of methyl methacrylate (MMA) by the three component catalytic system Cp2ZrMe2/B(C6... more Polymerization of methyl methacrylate (MMA) by the three component catalytic system Cp2ZrMe2/B(C6F5)3/ZnEt2 (1), in toluene, under thoroughly purified conditions, was found to produce polymers of high molecular weights (Mw > 60 × 10 3 ), low polydispersities (Mw/Mn ) 1.12-1.22) and almost quantitative yields. The polymerization process is characterized by a pronounced induction period followed by a rapid and constant rate of polymerization. The molecular weight of PMMA increases by increasing the conversion and is proportional to the ratio of [MMA]0/[Zr]0, while Mw/Mn remains intact, meaning that the present polymerization proceeds in a well-controlled fashion. Evidence for effects of [ZnEt2] and temperature in the molecular characteristics of the final products are also presented in this study. Moreover, the catalytic system 1 was found to catalyze the polymerization of other alkyl methacrylates (alkyl ) n-butyl, n-hexyl) to high molecular weight syndiotactic materials, with narrow molecular weight distribution, in very high conversion. Well-controlled copolymerization of MMA with n-hexyl methacrylate was successful by the effective catalytic action of 1, leading to multiblock polymeric structures. Copolymerization of MMA with stearyl methacrylate was also achieved, with the above-mentioned catalytic system. Evidence for the aggregation of the polymeric products in THF and toluene solutions was found by static and dynamic light scattering. The comparison of the polymerization results of this work with other studies clearly shows that in order to obtain improved molecular characteristics, thorough purification protocols should be applied.
Graft copolymers having poly(methyl methacrylate), PMMA, backbone and polystyrene, PS, polyisopre... more Graft copolymers having poly(methyl methacrylate), PMMA, backbone and polystyrene, PS, polyisoprene, PI, poly(ethylene oxide), PEO, poly(2-methyl-1,3-pentadiene), P2MP, and PS-b-PI branches were prepared using the macromonomer methodology and high-vacuum techniques. The methacrylic macromonomers, mMM, were synthesized by anionic polymerization, whereas their homopolymerization and copolymerization with MMA were performed by metallocene catalysts. Relatively high macromonomer conversions were obtained in all cases. The parameters affecting the polymerization characteristics were examined. Well-defined poly(butyl methacrylate)-b-poly(methyl methacrylate) block copolymers were prepared for the first time by sequential addition of monomers starting from n-butyl methacrylate. The samples were characterized by size exclusion chromatography, SEC, 1 H and 13 C NMR spectroscopy, low-angle laser light scattering, LALLS, and differential scanning calorimetry, DSC.
Well-defined graft copolymers with poly(methyl methacrylate) backbone and poly(styrene) (PS), pol... more Well-defined graft copolymers with poly(methyl methacrylate) backbone and poly(styrene) (PS), poly(isoprene) (PI), or poly(dimethylsiloxane) (PDMS) branches were synthesized by combining anionic and metallocene catalyzed polymerization. The synthetic strategy involves the preparation of methacryloyl macromonomers of PS, PI, and PDMS by anionic polymerization, followed by copolymerization with methyl methacrylate using the highly reactive catalytic system Cp 2ZrMe2/B(C6F5)3/ZnEt2. The macromonomers and the fractionated graft copolymers were characterized by size exclusion chromatography, low-angle laser light scattering, and 1 H NMR spectroscopy.
Statistical copolymers of methyl methacrylate (MMA) with n- butyl-, sbutyl, t-butyl-, n-hexyl-, d... more Statistical copolymers of methyl methacrylate (MMA) with n- butyl-, sbutyl, t-butyl-, n-hexyl-, decyl-, stearyl-, allyl-, trimethylsilyl-and trimethylsilyloxyethyl methacrylate were prepared by zirconocene-catalyzed copolymerization. The reactivity ratios of MMA copolymers with butyl-, hexyl-, and stearyl methacrylate were estimated using the Finemann-Ross, the inverted Finemann-Ross, and the Kelen-Tü dos graphical methods. Structural parameters of the copolymers were obtained from the calculated dyad sequences, derived by using the reactivity ratios. The effect of the nature of the methacrylate ester group and the catalytic system used on the copolymer structure is discussed. The glass-transition temperature (T g ) values of MMA copolymers with butyl-and hexyl methacrylate were measured and examined in the frame of several theoretical equations, allowing the prediction of these T g values. The best fit was obtained using Barton and Johnston equations, taking the monomer sequence distribution of the copolymers into account.
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Papers by George Karanikolopoulos