Reactive processing methods for functionalisation of polymers and in-situ compatibilisation of poly(ethylene terephthalate)-based blends

One of the main objectives of this study was to functionalise various rubbers (i.e. ethylene propylene copolymer (EP), ethylene propylene diene terpolymer (EPDM), and natural rubber (NR)) using functional monomers, maleic anhydride (MA) and glycidyl methacrylate (GMA), via reactive processing routes. The functionalisation of the rubber was carried out via different reactive processing methods in an internal mixer. GMA was free-radically grafted onto EP and EPDM in the melt state in the absence and presence of a comonomer, trimethylolpropane triacrylate (TRlS). To optinuse the grafting conditions and the compositions, the effects of various paranleters on the grafting yields and the extent of side reactions were investigated. Precipitation method and Soxhlet extraction method was established to purifY the GMA modified rubbers and the grafting degree was determined by FTIR and titration. It was found that without TRlS the grafting degree of GMA increased with increasing peroxide concentration. However, grafting was low and the homopolymerisation of GMA and crosslinking of the polymers were identified as the main side reactions competing with the desired grafting reaction for EP and EPDM, respectively. The use of the tri-functional comonomer, TRlS, was shown to greatly enhance the GMA grafting and reduce the side reactions in terms of the higher GMA grafting degree, less alteration of the rheological properties of the polymer substrates and very little formation of polyGMA. The grafting mechanisms were investigated. MA was grafted onto NR using both thermal initiation and peroxide initiation. The results showed clearly that the reaction of MA with NR could be thermally initiated above 140°C in the absence of peroxide. At a preferable temperature of 200°C, the grafting degree was increased with increasing MA concentration. The grafting reaction could also be initiated with peroxide. It was found that 2,5-dimethyl-2,5-bis(ter-butylproxy) hexane (TIOI) was a suitable peroxide to initiate the reaction efficiently above I50°C. The second objective of the work was to utilize the functionalised rubbers in a second step to achieve an in-situ compatibilisation of blends based on poly(ethylene terephthalate) (PET), in particular, with GMA-grafted-EP and -EPDM and the reactive blending was carried out in an internal mixer. The effects of GMA grafting degree, viscosities of GMAgrafted- EP and -EPDM and the presence of polyGMA in the rubber samples on the compatibilisation of PET blends in terms of morphology, dynamical mechanical properties and tensile properties were investigated. It was found that the GMA modified rubbers were very efficient in compatibilising the PET blends and this was supported by the much finer morphology and the better tensile properties. The evidence obtained from the analysis of the PET blends strongly supports the existence of the copolymers through the interfacial reactions between the grafted epoxy group in the GMA modified rubber and the terminal groups of PET in the blends.

Synthesis and evaluation of novel ligands for quantum dot stabilisation and polymerisation studies

This thesis describes the design and synthesis of a variety of functionalised phosphine oxides and sulfides, based on the structure of trioctylphosphine oxide, synthesised for the purpose of surface modification of quantum dots. The ability of the ligands to modify the surface chemistry via displacement of the original hexadecylamine capping layer of quantum dots was evaluated. Finally the surface modified quantum dots were investigated for enhancement in their inherent properties and improved compatibility with the various applications for which they were initially designed. Upon the commencement of research involving quantum dots it became apparent that more information on their behaviour and interaction with the environment was required. The limits of the inherent stability of hexadecylamine capped quantum dots were investigated by exposure to a number of different environments. The effect upon the stability of the quantum dots was monitored by changes in the photoluminescence ability of their cores. Subtle differences between different batches of quantum dots were observed and the necessity to account for these in future applications noted. Lastly the displacement of the original hexadecylamine coating with the "designer" functionalised ligands was evaluated to produce a set of conditions that would result in the best possible surface modification. A general procedure was elucidated however it was discovered that each displacement still required slight adjustment by consideration of the other factors such as the difference in ligand structure and the individuality of the various batches of quantum dots. This thesis also describes a procedure for the addition of a protective layer to the surface of quantum dots by cross-linking the functionalised ligands bound to the surface via an acyclic diene metathesis polymerisation. A detailed description of the problems encountered in the analysis of these materials combined with the use of novel techniques such as diffusion ordered spectroscopy is provided as a means to overcome the limitations encountered. Finally a demonstration of the superior stability, upon exposure to a range of aggressive environments of these protected materials compared with those before cross-linking provided physical proof of the cross-linking process and the advantages of the cross-linking modification. Finally this thesis includes the presentation of initial work into the production of luminescent nanocrystal encoded resin beads for the specific use in solid phase combinatorial chemistry. Demonstration of the successful covalent incorporation of quantum dots into the polymeric matrices of non-functionalised and functionalised resin beads is described. Finally by preliminary work to address and overcome the possible limitations that may be encountered in the production and general employment of these materials in combinatorial techniques is given.

Mechanistic studies on the advanced oxidation and photochemical transformation of cyanotoxins (microcystins)

The increased occurrence of cyanobacteria (blue-green algae) blooms and the production of associated cyanotoxins have presented a threat to drinking water sources. Among the most common types of cyanotoxins found in potable water are microcystins (MCs), a family of cyclic heptapeptides containing substrates. MCs are strongly hepatotoxic and known to initiate tumor promoting activity. The presence of sub-lethal doses of MCs in drinking water is implicated as one of the key risk factors for an unusually high occurrence of primary liver cancer. ^ A variety of traditional water treatment methods have been attempted for the removal of cyanotoxins, but with limited success. Advanced Oxidation Technologies (AOTs) are attractive alternatives to traditional water treatments. We have demonstrated ultrasonic irradiation and UV/H2O2 lead to the degradation of cyanotoxins in drinking water. These studies demonstrate AOTs can effectively degrade MCs and their associated toxicity is dramatically reduced. We have conducted detailed studies of different degradation pathways of MCs and conclude that the hydroxyl radical is responsible for a significant fraction of the observed degradation. Results indicate preliminary products of the sonolysis of MCs are due to the hydroxyl radical attack on the benzene ring and substitution and cleavage of the diene of the Adda peptide residue. AOTs are attractive methods for treatment of cyanotoxins in potable water supplies. ^ The photochemical transformation of MCs is important in the environmental degradation of MCs. Previous studies implicated singlet oxygen as a primary oxidant in the photochemical transformation of MCs. Our results indicate that singlet oxygen predominantly leads to degradation of the phycocyanin, pigments of blue green algae, hence reducing the degradation of MCs. The predominant process involves isomerization of the diene (6E to 6Z) in the Adda side chain via photosensitized isomerization involving the photoexcited phycocyanin. Our results indicate that photosensitized processes play a key role in the environmental fate and elimination of MCs in the natural waters. ^

Planktonic foraminiferal faunas from surface-sediment samples from the South China Sea and the western Pacific

We present 30 new planktonic foraminiferal census data of surface sediment samples from the South China Sea, recovered between 630 and 2883 m water depth. These new data, together with the 131 earlier published data sets from the western Pacific, are used for calibrating the SIMMAX-28 transfer function to estimate past sea-surface temperatures. This regional SIMMAX method offers a slightly better understanding of the marginal sea conditions of the South China Sea than the linear transfer function FP-12E, which is based only on open-ocean data. However, both methods are biased toward the tropical temperature regime because of the very limited data from temperate to subpolar regions. The SIMMAX formula was applied to sediment core 17940 from the northeastern South China Sea, with sedimentation rates of 20-80 cm/ka. Results revealed nearly unchanged summer temperatures around 28°C for the last 30 ky, while winter temperatures varied between 19.5°C in the last glacial maximum and 26°C during the Holocene. During Termination 1A, the winter estimates show a Younger Dryas cooling by 3°C subsequent to a temperature optimum of 24°C during the Bölling=Alleröd. Estimates of winter temperature differences between 0 and 100 m water depth document the seasonal variations in the thickness of the mixed layer and provide a new proxy for estimating past changes in the strength of the winter monsoon.

Concentrations of IPSO25 in surface sediments from coastal and near-coastal Antarctic locations

The presence of a di-unsaturated highly branched isoprenoid (HBI) lipid biomarker (diene II) in Southern Ocean sediments has previously been proposed as a proxy measure of palaeo Antarctic sea ice. Here we show that a source of diene II is the sympagic diatom Berkeleya adeliensis Medlin. Furthermore, the propensity for B. adeliensis to flourish in platelet ice is reflected by an offshore downward gradient in diene II concentration in >100 surface sediments from Antarctic coastal and near-coastal environments. Since platelet ice formation is strongly associated with super-cooled freshwater inflow, we further hypothesize that sedimentary diene II provides a potentially sensitive proxy indicator of landfast sea ice influenced by meltwater discharge from nearby glaciers and ice shelves, and re-examination of some previous diene II downcore records supports this hypothesis. The term IPSO25-Ice Proxy for the Southern Ocean with 25 carbon atoms-is proposed as a proxy name for diene II.

Sea ice and wind variability during the Holocene in East Antarctica

A high-resolution continuous record of diatom census counts and diatom specific biomarkers in sediment core NBP0101-JPC24 allows assessment of oceanographic and environmental conditions in eastern Prydz Bay during the deglaciation (11 100-9000 cal yr BP) at decadal timescale. Our study improves previous snapshots investigations based on resin-embedded thin sections and presents a new proxy that compliments the diatom census counts. Our results suggest that the ice sheet retreat over the core site is dated at ~11 100 cal yr BP, setting the onset of local deglaciation and subsequent open marine conditions. The glacial retreat in Prydz Bay is due to global warming initiated at 18 cal ka BP and the regional development of the Prydz Bay cyclonic gyre. Our results further demonstrate that the deglaciation in eastern Prydz Bay can be separated in four phases: the first between 11 100 and 10 900 cal yr BP when the ice shelf was proximal and sea ice was almost perennial; the second and the third phases between 10 900-10 400 cal yr BP and 10 400-9900 cal yr BP, respectively, when the ice shelf retreated and seasonal sea ice cycle consequently developed promoting warmer water to pump into the bay within the gyre, which in turn forced the ice shelf recession and the yearly sea ice cycle establishment; and the fourth between 9900 and 9000 cal yr BP when Holocene condition were set with a recurrent seasonal sea ice cycle and a well established Prydz Bay gyre.

Biomarker distributions in sediment core PS2767-4

Here, we present a first (low-resolution) biomarker sea-ice proxy record from the High Arctic (southern Lomonosov Ridge), going back in time to about 60 ka (MIS 3 to MIS 1). Variable concentrations of the sea-ice diatom specific highly branched isoprenoid (HBI) with 25 carbon atoms ("IP25"), in combination with the phytoplankton biomarker brassicasterol, suggest variable seasonal sea-ice coverage and open-water productivity during MIS 3. During most of MIS 2, the spring to summer sea-ice margin significantly extended towards the south, resulting in a drastic decrease in phytoplankton productivity. During the Early Holocene Climate Optimum, brassicasterol reached its maximum, interpreted as signal for elevated phytoplankton productivity due to a significantly reduced sea-ice cover. During the mid-late Holocene, IP25 increased and brassicasterol decreased, indicating extended sea-ice cover and reduced phytoplankton productivity, respectively. The HBI diene/IP25 ratios probably reached maximum values during the Bølling-Allerød warm period and decreased during the Holocene, suggesting a correlation with sea-surface temperature.

Organic geochemical parameters (biomarker) in sedimentary sequences and sediment traps

For the reconstruction of sea-ice variability, a biomarker approach which is based on (1) the determination of sea-ice diatom-specific highly-branched isoprenoid (IP25) and (2) the coupling of phytoplankton biomarkers and IP25 has been used. For the first time, such a data set was obtained from an array of two sediment traps deployed at the southern Lomonosov Ridge in the central Arctic Ocean at water depth of 150 m and 1550 m and recording the seasonal variability of sea ice cover in 1995/1996. These data indicate a predominantly permanent sea ice cover at the trap location between November 1995 and June 1996, an ice-edge situation with increased phytoplankton productivity and sea-ice algae input in July/August 1996, and the start of new-ice formation in late September. The record of modern sea-ice variability is then used to better interpret data from sediment core PS2458-4 recovered at the Laptev Sea continental slope close to the interception with Lomonosov Ridge and recording the post-glacial to Holocene change in sea-ice cover. Based on IP25 and phytoplankton biomarker data from Core PS2458-4, minimum sea-ice cover was reconstructed for the Bølling/Allerød warm interval between about 14.5 and 13 calendar kyr BP, followed by a rapid and distinct increase in sea-ice cover at about 12.8 calendar kyr BP. This sea-ice event was directly preceded by a dramatic freshwater event and a collapse of phytoplankton productivity, having started about 100 years earlier. These data are the first direct evidence that enhanced freshwater flux caused enhanced sea-ice formation in the Arctic at the beginning of the Younger Dryas. In combination with a contemporaneous, abrupt and very prominent freshwater/meltwater pulse in the Yermak Plateau/Fram Strait area these data may furthermore support the hypothesis that strongly enhanced freshwater (and ice) export from the Arctic into the North Atlantic could have played an important trigger role for the onset of the Younger Dryas cold reversal. During the Early Holocene, sea-ice cover steadily increased again (ice-edge situation), reaching modern sea-ice conditions (more or less permanent sea-ice cover) probably at about 7-8 calendar kyr BP.

Diatoms and biomarkers in sediments from the Antarctic Peninsula

The Antarctic Peninsula (AP) has been identified as one of the most rapidly warming region on Earth. Satellite monitoring currently allows for a detailed understanding of the relationship between sea ice extent and duration and atmospheric and oceanic circulations in this region. However, our knowledge on ocean-ice-atmosphere interactions is still relatively poor for the period extending beyond the last 30 years. Here, we describe environmental conditions in Northwestern and Northeastern Antarctic Peninsula areas over the last century using diatom census counts and diatom specific biomarkers (HBIs) in two marine sediment multicores (MTC-38C and -18A, respectively). Diatom census counts and HBIs show abrupt changes between 1935 and 1950, marked by ocean warming and sea ice retreat in both sides of the AP. Since 1950, inferred environmental conditions do not provide evidence for any trend related to the recent warming but demonstrate a pronounced variability on pluri-annual to decadal time scale. We propose that multi-decadal sea ice variations over the last century are forced by the recent warming, while the annual-to-decadal variability is mainly governed by synoptic and regional wind fields in relation with the position and intensity of the atmospheric low-pressure trough around the AP. However, the positive shift of the SAM since the last two decades cannot explain the regional trend observed in this study, probably due to the effect of local processes on the response of our biological proxies.

Modyfikacja aglikonu Josamycyny z wykorzystaniem regioselektywnej substytucji nukleofilowej typu SN1’ i dipolarnej cykloaddycji Huisgena

Wydział Chemii: Zakład Syntezy i Struktury Związków Organicznych

Avances y desafíos de la agenda de cambio climático en la Zona Costero-Marina de El Salvador

Central America is one of the most vulnerable regions to the adverse effects of climate change, due to the rise of frequency and intensity that hydrometeorological phenomena have occurred in recent years. In El Salvador 484 people died and 800,000 more were affected because these extreme events and economic losses reached up to 6.711 million dollars. According to the climate projections over the next 50 years in the territory, is expected that extreme events such as droughts and rainfall will intensify. Within the last 30 years, July of 2014 is considered the one with less rainfall. Meanwhile, Tropical Depression 12E in 2011 provoked an outstanding rainfall average of 1,137 mm, affecting more than 500,000 people; most of them live in the coastal zone. The death of 34 people and living economic losses of 840.4 million was recorded, equivalent to 4% of GDP. El Salvador has policies, national plans and strategies aimed to reducing vulnerability, promoting adaptation to these changes and more effective risk management. This paper compiles the impacts of climate variability in El Salvador and the efforts of the State on adaptation to improve environmental and social resilience.

Towards the total synthesis of amphidinolides C and F

The amphidinolides are marine macrolides extracted from dinoflagellates of the genus Amphidinium. To date, 37 amphidinolides have been isolated and identified, most of them possessing cytotoxicity against human cancer cell lines. Among these, amphidinolides C, F, C2 and C3 represent synthetic targets of interest owing to their scarcity, structural complexity and promising biological activities. This thesis describes the work realised towards the total synthesis of amphidinolides C and F, with a focus on the different strategies investigated and the key fragments synthesised. In the first approach, the C18−C29 fragment of amphidinolide F was prepared using an intramolecular etherification of an epoxide under acidic catalysis to produce the 2,5-trans-disubstituted tetrahydrofuran ring featured in the natural product. Unfortunately, dithiane alkylation with the C1−C17 iodide counterpart generated the desired coupling product in low yield. A second approach proposing to build the C17−C18 bond by a silicon-tethered RCM proved unsuccessful, because the requisite diene could not be obtained. It was then envisioned to form the C18−C19 bond by displacement of a triflate with an alkyne and install the ketone at C18 by a protoborylation/oxidation sequence. To this end, the C19−C29 triflate precursor was synthesised. Displeasingly, the C1−C18 alkyne counterpart (work by Dr Filippo Romiti) could not be prepared and coupling of the two fragments was not attempted. In the latest approach, the C10−C29 fragment of amphidinolide F was obtained employing a boron-mediated aldol condensation and a dithiane alkylation to form the C13−C14 and C18−C19 bonds. Several endgame strategies were examined including the successful Yamaguchi esterification of the C13-epi C10−C29 fragment and the C1−C9 acid. A challenging Stille crosscoupling was then effected to close the macrocycle but only yielded the desired macrolactone in trace amounts after global desilylation.

New Catalysts for the Renewable Production of Monomers for Bioplastics

Terephthalic acid (PTA) is one of the monomers used for the synthesis of the polyester, polyethylene terephthalate (PET), that is used for the large-scale manufacture of synthetic fibers and plastic bottles. PTA is largely produced from the liquid-phase oxidation of petroleum-derived p-xylene (PX). However, there are now ongoing worldwide efforts exploring alternative routes for producing PTA from renewable, biomass resources.

In this thesis, I present a new route to PTA starting from the biomass-derived platform chemical, 5-hydroxymethylfurfural (HMF). This route utilizes new, selective Diels-Alder-dehydration reactions involving ethylene and is advantageous over the previously proposed Diels-Alder-dehydration route to PTA from HMF via 2,5-dimethylfuran (DMF) since the H₂ reduction of HMF to DMF is avoided. Specifically, oxidized derivatives of HMF are reacted as is, or after etherification-esterification with methanol, with ethylene over solid Lewis acid catalysts that do not contain strong Brønsted acids in order to synthesize intermediates of PTA and its equally important diester, dimethyl terephthalate (DMT). The partially oxidized HMF, 5-(hydroxymethyl)furoic acid (HMFA) is reacted with high pressure ethylene over a pure-silica molecular sieve catalyst containing framework tin (Sn-Beta) to produce the Diels-Alder-dehydration product, 4-(hydroxymethyl)benzoic acid (HMBA), with ~30% selectivity at ~20% yield. If HMFA is protected with methanol to form methyl 5-(methoxymethyl)furan-2-carboxylate (MMFC), MMFC can react with ethylene in the presence of a pure-silica molecular sieve containing framework zirconium (Zr-Beta) to produce methyl 4-(methoxymethyl)benzenecarboxylate (MMBC) with >70% selectivity at >20% yield. HMBA and MMBC can then be oxidized to produce PTA and DMT, respectively. When Lewis acid containing mesoporous silica (MCM-41) and amorphous silica, or Brønsted acid containing zeolites (Al-Beta), are used as catalysts, a significant decrease in selectivity/yield of the Diels-Alder-dehydration product is observed.

An investigation to elucidate the reaction network and side products in the conversion of MMFC to MMBC was performed, and the main side products are found to be methyl 4-formylcyclohexa-1,3-diene-1-carboxylate and the ethylene Diels-Alder adduct of this cyclohexadiene. These products presumably form by a different dehydration pathway of the MMFC/ethylene Diels-Alder adduct and should be included when determining the overall selectivity to PTA or DMT since, like MMBC, these compounds are precursors to PTA or DMT.

Fundamental physical and chemical information on the ethylene Diels-Alder-dehydration reactions catalyzed by the Lewis acid-containing molecular sieves was obtained. Madon-Boudart experiments using Zr-Beta as catalyst show that the reaction rates are limited by chemical kinetics only (physical transport limitations are not present), all the Zr⁴⁺ centers are incorporated into the framework of the molecular sieve, and the whole molecular sieve crystal is accessible for catalysis. Apparent activation energies using Zr-Beta are low, suggesting that the overall activation energy of the system may be determined by a collection of terms and is not the true activation energy of a single chemical step.

Utilização do ciclo luminoso como indutor do crescimento de camarões Penaeus japonicus

Dissertação de mest. em Aquacultura, Unidade de Ciências e Tecnologias dos Recursos Aquáticos, Univ. do Algarve, 1997

The Photooxidation of Domoic Acid

Domoic acid (DA) is a naturally occurring cyanotoxin, which upon ingestion, is responsible for amnesic shellfish poisoning (ASP) in both humans and animals. Produced by the marine diatom, Pseudonitzschia, DA is accumulated by a number of marine organisms including shellfish, clams and mussels which upon consumption can lead to headaches, nausea and seizures. Possessing a variety of functional groups the structure of DA contains three carboxyl groups, a pyrrole ring and a potent conjugated diene region allowing for binding to glutamate receptors in the dorsal hippocampus of the brain causing the described detrimental effects. Although limitations have been placed regarding the amount of DA that may be contained in seafood no limitations have been placed on the amount present in drinking water. Natural degradation of the toxin may occur through reactive oxygen species such as the hydroxyl radical and singlet oxygen at the conjugated diene region. In this work the photooxidation of DA via singlet oxygen has been studied using sorbic acid as a model compound. The three major reaction pathways observed during the photooxdiation process for both acids include 2 + 4 cycloaddition to produce endoperoxides , 2 + 2 reaction to afford aldehydes and ketones or an ene reaction to generate hydroperoxides. Under similar reaction conditions for SA and DA, the endoperoxide has been seen to be the major product for photoxidation of SA while the hydroperoxide has been seen to be the dominant product during photooxidation of DA.