Role of Functional Groups in the Monomer Molecule on the Radical Polymerization in the Presence of Graphene Oxide. Polymerization of Hydroxyethyl Acrylate under Isothermal and Non-Isothermal Conditions

Functional groups in a monomer molecule usually play an important role during polymerization by enhancing or decreasing the reaction rate due to the possible formation of side bonds. The situation becomes more complicated when polymerization takes place in the presence of graphene oxide since it also includes functional groups in its surface. Aiming to explore the role of functional groups on polymerization rate, the in situ bulk radical polymerization of hydroxyethyl acrylate (HEA) in the presence or not of graphene oxide was investigated. Differential scanning calorimetry was used to continuously record the reaction rate under both isothermal and non-isothermal conditions. Simple kinetic models and isoconversional analysis were used to estimate the variation of the overall activation energy with the monomer conversion. It was found that during isothermal experiments, the formation of both inter- and intra-chain hydrogen bonds between the monomer and polymer molecules results in slower polymerization of neat HEA with higher overall activation energy compared to that estimated in the presence of GO. The presence of GO results in a dissociation of hydrogen bonds between monomer and polymer molecules and, thus, to higher reaction rates. Isoconversional methods employed during non-isothermal experiments revealed that the presence of GO results in higher overall activation energy due to the reaction of more functional groups on the surface of GO with the hydroxyl and carbonyl groups of the monomer and polymer molecules, together with the reaction of primary initiator radicals with the surface hydroxyl groups in GO

Synthesis, reaction kinetics and characterization of graphene-based nanocomposite polymeric materials

This doctoral dissertation was held in the Department of Chemistry at Aristotle University of Thessaloniki in the Laboratory of Chemistry, Technology of Polymers and Colours for the acquisition of Doctoral Degree in Chemistry. The purpose of the thesis was the study of the polymeric kinetics and the properties of the nanocomposite materials that result from the addition of Graphite Oxide (GO) when it is prepared in two ways (Hummers and Staudenmaier) as well as graphite oxide which has been subjected to Functionalized Graphite Oxide (FGO) in the polymeric PBMA matrix. Furthermore, a kinetic study of the nanocomposites resulting from the addition of GO and FGO prepared by the Hummers method in PSt polymer matrix and two copolymers Poly(styrene-co-methacrylate butyl) in proportion 20/80 and 60/40 respectively was performed. For this purpose, the technique of in situ polymerization of mass was used. The polymerization kinetic was studied in regular intervals. The structural and morphological characteristics of the nanocomposite materials were studied by (HATR-IR) Spectroscopy. The formula of the nanocomposites formed was tested by X-ray diffraction (XRD). Molecular weight distributions were calculated by GPC. The proportion of copolymers was studied by NMR. The glass transition temperature (Tg) was determined by DSC and DMTA. The thermal stability and the characteristics of nanocomposites degradation were investigated through TGA. In conclusion, both the graphite oxide and the surface-modified were used as inclusions in the synthesis of the nanocomposites, with regard to their final products, having been converted to graphene oxide and modified graphene oxide respectively, as their exfoliation takes place during the polymerization (intercalation polymerization). In the context of the kinetic study it was observed that the addition of graphite oxide reduced the polymerization rate and the degree of conversion of the nanocomposites comparatively to the pure polymer while the addition of modified graphite oxide did not affect the rate of polymerization compared to the pure polymers. Furthermore, the conversion rates corresponding to the nanocomposite materials that have in their structure FGO are equivalent to those of the pure polymer. The thermal stability of the two types of nanocomposite materials increases compare to the pure polymer. This increase is also analogous to the percentage as the increasing content of the sample in graphene oxide with or without surface modification revealed a shift of the thermostatic analysis curves to higher temperatures. The Mn increased upon the addition of GO inclusions, and it was observed that as the proportion of the additive increases, the Mn increases. Conversely proportional were the Mn as the FGO content increases, while the polydispersity coefficient which is attributed to the cross-linked is reduced. The latter is due to modifying factor. Finally, the addition of the inclusions resulted in an increase of (Tg) from both DSC and DMA compared to the pure polymer in both types of nanocomposites.Η παρούσα διδακτορική διατριβή εκπονήθηκε στο τμήμα Χημείας του Αριστοτελείου Πανεπιστημίου Θεσσαλονίκης στο εργαστήριο Χημείας και Τεχνολογίας Πολυμερών και Χρωμάτων για την απόκτηση Διδακτορικού Διπλώματος Ειδίκευσης στη Χημεία. Σκοπός της παρούσας εργασίας υπήρξε η μελέτη της κινητικής του πολυμερισμού και των ιδιοτήτων των νανοσύνθετων υλικών που προκύπτουν κατά την προσθήκη οξειδίου του γραφίτη (Graphite Oxide - GO), όταν αυτό παρασκευάζεται με δύο τρόπους (Hummers και Staudenmaier), καθώς επίσης και οξειδίου του γραφίτη που έχει υποστεί επιφανειακή τροποποίηση-λειτουργικοποίηση (Functionalized Graphite Oxide - FGO), στην πολυμερική μήτρα PBMA. Επιπλέον πραγματοποιήθηκε κινητική μελέτη των αντίστοιχων νανοσύνθετων που προκύπτουν κατά την προσθήκη των GO και FGO παρασκευασμένων με τη μέθοδο Hummers στην πολυμερική μήτρα του PSt και σε δύο συμπολυμερή Πολύ(στυρενίου-co-μεθακρυλικού βουτυλεστέρα) με αναλογίες 20/80 και 60/40 αντίστοιχα. Για τον σκοπό αυτό χρησιμοποιήθηκε η τεχνική του in situ πολυμερισμού μάζας. Η κινητική του πολυμερισμού μελετήθηκε σταθμικά. Τα δομικά και μορφολογικά χαρακτηριστικά των νανοσύνθετων υλικών μελετήθηκαν με Φασματοσκοπία Υπέρυθρου με κεφαλή αποσβένουσας ακτινοβολίας (HATR-IR). Ο τύπος των νανοσύνθετων που σχηματίστηκαν ελέγχτηκε με περίθλαση ακτινών Χ (XRD). Οι κατανομές των μοριακών βαρών υπολογίστηκαν με χρωματογραφία διέλευσης μέσω πηκτής (GPC). Η αναλογία των συμπολυμερών μελετήθηκε με τον πυρηνικό μαγνητικό συντονισμό (NMR). Η θερμοκρασία υαλώδους μετάβασης (Τg) προσδιορίστηκε με την χρήση της Διαφορικής Θερμιδομετρίας Σάρωσης (DSC) και της Δυναμικής Θερμομηχανικής Ανάλυσης (DMTA). Η θερμική σταθερότητα και τα χαρακτηριστικά της αποικοδόμησης των νανοσύνθετων ερευνήθηκαν μέσω της Θερμοσταθμικής Ανάλυσης (TGA). Συμπερασματικά, τόσο το οξείδιο του γραφίτη όσο και το επιφανειακά τροποποιημένο που χρησιμοποιήθηκαν ως εγκλείσματα κατά την σύνθεση των νανοσύνθετων, ως προς τα τελικά τους προϊόντα έχουν μετατραπεί σε οξείδιο του γραφενίου και τροποποιημένο οξείδιο του γραφενίου αντίστοιχα, καθώς λαμβάνει χώρα η αποφύλλωσή τους κατά τον πολυμερισμό (πολυμερισμός ενδοπαρεμβολής). Στο πλαίσιο της κινητικής μελέτης παρατηρήθηκε, πως η προσθήκη του οξειδίου του γραφίτη ελάττωσε την ταχύτητα πολυμερισμού και τον βαθμό μετατροπής των νανοσύνθετων υλικών σε σχέση με το καθαρό πολυμερές, ενώ η προσθήκη τροποποιημένου οξειδίου του γραφίτη δεν επηρέασε την ταχύτητα του πολυμερισμού σε σύγκριση με τα καθαρά πολυμερή. Επιπλέον, οι βαθμοί μετατροπής που αντιστοιχούν στα νανοσύνθετα υλικά που έχουν στην δομή τους FGO παρουσιάζουν αντίστοιχους με αυτούς του καθαρού πολυμερούς. Η θερμική σταθερότητα των δύο ειδών νανοσύνθετων υλικών αυξάνεται συγκριτικά με το καθαρό πολυμερές. Η αύξηση αυτή είναι ανάλογη και της επιφόρτισης, καθώς όσο αυξανόταν η περιεκτικότητα του δείγματος σε οξείδιο του γραφενίου με ή χωρίς επιφανειακή τροποποίηση διαπιστώθηκε μετατόπιση των καμπυλών της θερμοσταθμικής ανάλυσης σε μεγαλύτερες θερμοκρασίες. Τα μέσα μοριακά βάρη κατά αριθμό αυξήθηκαν κατά την προσθήκη των εγκλεισμάτων GO, ενώ παρατηρήθηκε ότι όσο αυξάνεται η περιεκτικότητα του προσθέτου αυξάνεται και το μέσο μοριακό βάρος κατ’ αριθμό. Αντιστρόφως ανάλογα ήταν τα μέσα μοριακά βάρη κατ’ αριθμό όσο αυξάνεται η περιεκτικότητα των FGO, ενώ παράλληλα μειώνεται ο συντελεστής πολυδιασποράς, που αποδίδεται στη δικτύωση. Η τελευταία δημιουργείται εξαιτίας του τροποποιητικού παράγοντα. Τέλος, η προσθήκη των εγκλεισμάτων είχε ως αποτέλεσμα και αύξηση της θερμοκρασίας υαλώδους μετάβασης (Tg) και από το DSC αλλά και από το DMA συγκριτικά με το καθαρό πολυμερές και στα δυο είδη νανοσυνθέτω

Role of Functional Groups in the Monomer Molecule on the Radical Polymerization in the Presence of Graphene Oxide. Polymerization of Hydroxyethyl Acrylate under Isothermal and Non-Isothermal Conditions

Functional groups in a monomer molecule usually play an important role during polymerization by enhancing or decreasing the reaction rate due to the possible formation of side bonds. The situation becomes more complicated when polymerization takes place in the presence of graphene oxide since it also includes functional groups in its surface. Aiming to explore the role of functional groups on polymerization rate, the in situ bulk radical polymerization of hydroxyethyl acrylate (HEA) in the presence or not of graphene oxide was investigated. Differential scanning calorimetry was used to continuously record the reaction rate under both isothermal and non-isothermal conditions. Simple kinetic models and isoconversional analysis were used to estimate the variation of the overall activation energy with the monomer conversion. It was found that during isothermal experiments, the formation of both inter- and intra-chain hydrogen bonds between the monomer and polymer molecules results in slower polymerization of neat HEA with higher overall activation energy compared to that estimated in the presence of GO. The presence of GO results in a dissociation of hydrogen bonds between monomer and polymer molecules and, thus, to higher reaction rates. Isoconversional methods employed during non-isothermal experiments revealed that the presence of GO results in higher overall activation energy due to the reaction of more functional groups on the surface of GO with the hydroxyl and carbonyl groups of the monomer and polymer molecules, together with the reaction of primary initiator radicals with the surface hydroxyl groups in GO

Effect of Graphene Oxide on the Reaction Kinetics of Methyl Methacrylate In Situ Radical Polymerization via the Bulk or Solution Technique

The synthesis of nanocomposite materials based on poly(methyl methacrylate) and graphene oxide (GO) is presented using the in situ polymerization technique, starting from methyl methacrylate, graphite oxide, and an initiator, and carried out either with (solution) or without (bulk) in the presence of a suitable solvent. Reaction kinetics was followed gravimetrically and the appropriate characterization of the products took place using several experimental techniques. X-ray diffraction (XRD) data showed that graphite oxide had been transformed to graphene oxide during polymerization, whereas FTIR spectra revealed no significant interactions between the polymer matrix and GO. It appears that during polymerization, the initiator efficiency was reduced by the presence of GO, resulting in a reduction of the reaction rate and a slight increase in the average molecular weight of the polymer formed, measured by gel permeation chromatography (GPC), along with an increase in the glass transition temperature obtained from differential scanning calorimetry (DSC). The presence of the solvent results in the suppression of the gel-effect in the reaction rate curves, the synthesis of polymers with lower average molecular weights and polydispersities of the Molecular Weight Distribution, and lower glass transition temperatures. Finally, from thermogravimetric analysis (TG), it was verified that the presence of GO slightly enhances the thermal stability of the nano-hybrids formed

Development of Bio-Composites with Enhanced Antioxidant Activity Based on Poly(lactic acid) with Thymol, Carvacrol, Limonene, or Cinnamaldehyde for Active Food Packaging

The new trend in food packaging films is to use biodegradable or bio-based polymers, such as poly(lactic acid), PLA with additives such as thymol, carvacrol, limonene or cinnamaldehyde coming from natural resources (i.e., thyme, oregano, citrus fruits and cinnamon) in order to extent foodstuff shelf-life and improve consumers’ safety. Single, triple and quadruple blends of these active compounds in PLA were prepared and studied using the solvent-casting technique. The successful incorporation of the active ingredients into the polymer matrix was verified by FTIR spectroscopy. XRD and DSC data revealed that the crystallinity of PLA was not significantly affected. However, the Tg of the polymer decreased, verifying the plasticization effect of all additives. Multicomponent mixtures resulted in more intense plasticization. Cinnamaldehyde was found to play a catalytic role in the thermal degradation of PLA shifting curves to slightly lower temperatures. Release of thymol or carvacrol from the composites takes place at low rates at temperatures below 100 °C. A combined diffusion-model was found to simulate the experimental release profiles very well. Higher antioxidant activity was noticed when carvacrol was added, followed by thymol and then cinnamaldehyde and limonene. From the triple-component composites, higher antioxidant activity measured in the materials with thymol, carvacrol and cinnamaldehyde

Effect of Na- and Organo-Modified Montmorillonite/Essential Oil Nanohybrids on the Kinetics of the In Situ Radical Polymerization of Styrene

The great concern about the use of hazardous additives in food packaging materials has shown the way to new bio-based materials, such as nanoclays incorporating bioactive essential oils (EO). One of the still unresolved issues is the proper incorporation of these materials into a polymeric matrix. The in situ polymerization seems to be a promising technique, not requiring high temperatures or toxic solvents. Therefore, in this study, the bulk radical polymerization of styrene was investigated in the presence of sodium montmorillonite (NaMMT) and organo-modified montmorillonite (orgMMT) including thyme (TO), oregano (OO), and basil (BO) essential oil. It was found that the hydroxyl groups present in the main ingredients of TO and OO may participate in side retardation reactions leading to lower polymerization rates (measured gravimetrically by the variation of monomer conversion with time) accompanied by higher polymer average molecular weight (measured via GPC). The use of BO did not seem to affect significantly the polymerization kinetics and polymer MWD. These results were verified from independent experiments using model compounds, thymol, carvacrol and estragol instead of the clays. Partially intercalated structures were revealed from XRD scans. The glass transition temperature (from DSC) and the thermal stability (from TGA) of the nanocomposites formed were slightly increased from 95 to 98 °C and from 435 to 445 °C, respectively. Finally, better dispersion was observed when orgMMT was added instead of NaMMT

Polymerization Kinetics of <i>n</i>‑Butyl Methacrylate in the Presence of Graphene Oxide Prepared by Two Different Oxidation Methods with or without Functionalization

Nanocomposite materials based on poly­(butyl methacrylate) and either graphene oxide (GO) or functionalized graphene oxide (F-GO) were produced using the in situ bulk radical polymerization technique. It was found that the Hummers method results in a higher degree of oxidation, compared to the Staudenmaier, whereas F-GO was produced using a silane-modifying agent. Polymerization kinetics were studied both experimentally and theoretically, and it was found that the presence of hydroxyl groups in the surface of GO results in scavenging the primary initiator radicals, thus reducing the initiator efficiency and the reaction rate, whereas the number-average molecular weight of the polymer formed was increased. The presence of F-GO affected the polymerization kinetics in a different way resulting in partially grafted structures. The theoretical study included the addition of a phenomenological transfer to the polymer side-reaction to account for the polymerization occurring at the F-GO surface