Spelling suggestions: "subject:"copolymers"" "subject:"kopolymers""
361 |
The effect of molecular composition on the properties of polyolefin-wood compositesBasson, Nicolaas Christiaan 03 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Polymer composites, and in particular wood-polymer composites have become commercially and
environmentally important materials. Studies in polyolefin-wood composites have mostly focused
on polypropylene (PP) and polyethylene (PE). To our knowledge, no study has been undertaken on
advancing impact polypropylene copolymer (IPPC)-wood composites as a suitable alternative to
using PP and PE. IPPC have proven to be a suitable alternative to PP at low temperatures to
improve impact resistance for manufactured polymer products, and could be a great addition to
improved properties for wood polymer composites.
This study shows that the physical properties of IPPC-wood composites can be markedly improved
when compatibilizer(s) are used to improve the distribution of the wood within the matrix, as well
as improving the interaction between the wood and the polymer matrix.. The use of different
compatibilizers, vi polypropylene-graft-maleic anhydride (PPgMA) and poly(ethylene-co-vinyl
alcohol) (EvOH) results in different physical properties. Using simple admixtures of the PPgMA
and EvOH in IPPC-wood composites result in a large spread of results, while pre-reacting the
PPgMA and EvOH to form a joint compatibilizer gives reproducible results w.r.t the physical
testing.
A study of the fundamental interactions of the compatibilizer(s) with the molecular components of
the IPPCs was undertaken. The IPPCs used were fractionated by preparative temperature rising
elution fractionation, and the fractions were mixed with the compatibilizers. To this end,
fluorescence microscopy was utilized to study the interaction. The results clearly indicate that the
interaction of the PPgMA with the fractions differ from that of the EvOH. These differences can be
explained in terms of the chemical composition distribution within the IPPC fractions.
Atomic force microscopy (AFM) was used to study adhesive forces between compatibilizer,
polymer and cellulose and lignin. Successful coating of AFM tips with PPgMA and EvOH was
achieved. Whilst interactions based on chemical force microscopy (CFM) could not be quantified,
the AFM results in conjunction with fluorescence spectroscopy provided meaningful insight in the
way that compatibilizers interact with both the wood and the impact copolymers used in this study. / AFRIKAANSE OPSOMMING: Polimeer saamgestelde material, en meer spesifiek hout-polimeer saamgestelde material het die
afgelope tyd belangrike produkte geword, beide kommersieel en in verband met
omgewingvriendelikheid. Navorsing op die gebied van poli(olefien)-hout komposiete het tot op
hede meestal gefokus op die grbruik van poli(propileen) (PP) en poli(etileen) (PE). Sover dit on
kennis strek is daar nog geen studie gedoen om die gebied van impak polipropileen kopolimere
(IPPK)-hout komposiete uit te bou nie. IPPKs is ‘n geskikte alternatief vir PP in veral laetemperatuur
aanwendings. Die gebruik van IPPKs as matriks vir die hout komposiete kan ‘n groot
staqp vorentoe beteken.
Hierdie studie wys dat die fisiese eienskappe van iPPK-hout komposiete merkwaardig verbeter kan
word waneer versoeningmateriale gebruik word om die verspreiding van die hout in die polimeermatriks
sowel as die interaksie tussen die hout en polimeer te verbeter. Die gebruik van
verskillende versoenings material, t.w poli(propileen-ent-maleinsuur anhidried) (PPeMA) en
pol(etlieen-ko-viniel alkohol) (EVOH). Deur gebruik te maak van eenvoudige mengsels van
PPeMA en EVOH in IPPK-hout composite het ‘n geweldige wye verpreiding van resultate tot
gevolg gehad, terwyl ‘n voorafgaande reaksie tussen die PPeMA en die EVOH om ‘n saamgestelde
versoeningmateriaal te maak tot gevolg gehad het dat reproduseerbare resultate verkry kon word.
‘n Studie van die fundamentele interaksies van die versoeningsmateriale met die molkulêre
komponente van die IPPKs is uitgevoer. Die IPPKs is gefraksioneer deur preparatiewe
temperatuur-stygende uitloog frakasionering en die fraksies is gemeng met die versoeningmateriale.
Fluoressensie mikroskopie is gebruik om hierdie interaksies te bestudeer. Die resultate dui duidelik
daarop dat die interaksie van die PPeMA met die fraksies verskil met die van die EVOH. Die
verskille kan verduidelik word aan die hand van die chemiese samestelling verspreiding van die
IPPK fraksies.
Atoomkrag mikroskopie (AKM) is gebruik om die adhesive-kragte tussen die versoeningmateriale,
polimere, sellulose en lignien. AKM tippe is suksesvol bedek met PPeMA en EVOH,
onderskeidelik. Alhoewel interaksies gebaseer op chemiese krag mikroskopie (CKM) nie
gekwantifiseer kon word nie, lewer hierdie resultate tesame met die fluoressensie spektroskopie
unieke insig in die manier wat versoeningmateriale met beide die hout en die polimeer reageer.
|
362 |
The effect of in-process ethylene incorporation on the evolution of particle morphology and molecular characteristics of commercial heterophasic ethylene propylene copolymers (HEPCs)Botha, Linda 04 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Impact copolymers or heterophasic polypropylene-ethylene-co-propylene copolymers (HEPCs) commonly produced in industry are valued for their good mechanical properties, combining the rigidity of the polypropylene matrix with the toughness of the dispersed ethylene-propylene copolymer. The potential for further optimisation and tailoring of product properties can be realised through an improved understanding of how the copolymer phase produced in the second reactor develops with increasing ethylene incorporation, providing an intermediate link between predicted physical behaviour and the process parameters required to achieve this. To this end, the morphological development of heterophasic or impact copolymers, has been a topic of interest of many studies to date, yet due to the complexity of these polymers, there is still some uncertainty with regards to the mechanism of copolymer growth as well as the structure-function relationships that exist. These studies were limited either due to the use of autoclave products or final impact copolymer products obtained from industry. The work presented in this study was aimed at understanding how the nascent copolymer phase develops during a transition from homopolymer to the final copolymer. This was done by selecting samples at certain intervals from two different commercial gas-phase processes, yielding two sets of four samples, each with a range of increasing ethylene contents. These samples provided the unique opportunity to study the early development of copolymer in a sequential manner (as each sample builds on the morphology of the previous one). The morphological development of copolymer in these samples was investigated by high resolution FE-SEM and it was observed that the copolymers showed different degrees of internal and external distribution as well as porosity for the different sets, determined by the initial porosity of the homopolymer. It was also found that the copolymer was radially distributed throughout the particle in all instances, suggesting that ethylene monomer diffusion limitations did not play a significant role in the copolymerization process.
A further aim of the study was to determine the effect of ethylene incorporation on bulk sample crystallinity, microstructure and chemical composition. It was observed by SCALLS and TREF that increasing ethylene incorporation attenuated the crystallinity of the homopolymer, resulting in a distribution of components with different crystallinities within the samples, suggesting some interaction between the developing copolymer and existing homopolymer. During the microstructural development of these samples, longer or more blocky ethylene sequences seemed to be favoured above isolated ethylene sequences with increasing ethylene incorporation and it was shown by solid-state NMR that ethylene partitioning between both amorphous and rigid environments occurred. Detailed characterization (solution and solid-state 13C NMR, HT-SEC and HT-HPLC) of the semi-crystalline copolymer fractions provided some information on the development of microstructure and chemical composition in these fractions that are responsible for compatibilization between the homopolymer matrix and dispersed rubber phase. Based on the different observations from the investigations outlined above, a model for copolymer development in each set was proposed and related to the physical property development observed for these samples. / AFRIKAANSE OPSOMMING: Die impak-kopolimere – ook bekend as heterofase polipropileen-etileen-kopropileen kopolimere (HEPC’s) – wat tans in die bedryf vervaardig word, is bekend vir hul goeie meganiese eienskappe, naamlik om die styfheid van ’n polipropileenmatriks met die sterkte van ’n etileen-propileen kopolimeer, wat in die matriks versprei is, te kombineer. Die potensiaal vir die optimisering en pasmaak van produkeienskappe kan bewerkstellig word deur beter begrip ten opsigte van hoe die kopolimeerfase wat in die tweede reaktor vervaardig word, ontwikkel as gevolg van toenemende inkorporasie van etileen, en hoe dit ’n skakel skep tussen voorspelbare fisiese gedrag en die prosesparameters wat nodig is hiervoor. Tot datum het heelparty studies gefokus op die morfologiese ontwikkeling van heterofase of impak-kopolimere, maar as gevolg van die komplekse aard van hierdie polimere is daar nog steeds onsekerheid oor die meganisme van kopolimeerontwikkeling, asook die verwantskappe tussen die polimeerstruktuur en -funksie. Sodanige studies was beperk omdat óf outoklaafprodukte óf finale produkte van industriële prosesse gebruik is. Die doel van hierdie studie was om begrip te kry vir hoe die kopolimeerfase ontwikkel tydens ’n oorgang van homopolimeer tot die finale produk. Hiervoor is twee stelle van vier monsters met toenemende etileeninhoude tydens die oorgang in twee verskillende gasfaseprosesse verkry. Hierdie monsters het die unieke geleentheid gebied vir die opvolgende bestudering van die vroeë ontwikkeling van die kopolimeer, deurdat elke monster voortgebou het op die morfologie van die vorige monster. Die morfologiese ontwikkeling van die kopolimeer is ondersoek deur van hoëresolusie FE-SEM gebruik te maak. Verskillende wyses van interne en eksterne verspreiding, sowel as porositeit van die onderskeie stelle (soos bepaal deur die aanvanklike porositeit van die homopolimeer), is vir die verskillende prosesse waargeneem. Daar is ook waargeneem dat die kopolimeer in alle gevalle op verskeie straalposisies binne die partikel versprei is, waarvan afgelei kan word dat monomeerdiffusiebeperking nie ’n beduidende rol in die kopolimerisasieproses speel nie.
’n Verdere doel van hierdie studie was om die uitwerking van etileen-inkorporasie op die kristalliniteit, mikrostruktuur en chemiese samestelling van die polimeer te bepaal. Deur middel van SCALLS en TREF is bevind dat toenemende etileen-inkorporasie die kristalliniteit van die homopolimeer verswak het. Die gevolg was die vorming van ’n verskeidenheid komponente met verskillende kristalliniteite, wat dui op ’n interaksie tussen die groeiende kopolimeer en die bestaande homopolimeer. Tydens die ontwikkeling van die mikrostruktuur van die monsters het dit geblyk dat lang, opeenvolgende etileeneenhede tydens toenemende etileen-inkorporasie vinniger ontwikkel as afgesonderde etileen- en propileeneenhede. Deur middel van soliedefase-KMR is daar bewys dat die etileen in beide amorfe en kristalagtige areas versprei is. Die semi-kristallyne kopolimere wat deur TREF verkry is, is verder gekarakteriseer met behulp van KMR in oplossing sowel as die soliede fase, HT-SEC en HT-HPLC, wat meer inligting verskaf oor die ontwikkeling van die mikrostruktuur en chemiese samestelling van hierdie fraksies wat normaalweg verantwoordelik is vir die interaksies tussen die homopolimeermatriks en die verspreide rubberfase. Op grond van die waarnemings soos hierbo vermeld, word ’n model vir die kopolimeerfase-ontwikkeling van elke stel monsters in hierdie studie voorgestel en verbind met die ontwikkeling van die waargenome fisiese eienskappe.
|
363 |
The effect of iodo alkyl chain transfer agents on the seeded emulsion homo- and co-polimerisation of styrene and butyl acrylateBeyers, Cornelis Petrus January 1999 (has links)
Thesis (MSc) -- Stellenbosch University, 1999. / ENGLISH ABSTRACT: A free-radical polymerisation process, which has characteristics of a living polymerisation
system, as it is capable of producing polymers of pre-determined molecular masses with a
narrow molecular mass distribution, is discussed. It is also possible to make blockcopolymers
by adding adding different monomers. The basic objective was to describe,
discuss and explain the results of the effects of alkyl iodides as chain transfer agents on
the seeded emulsion homo- and co-polymerisation of styrene and butyl acrylate.
lodoacetonitrile and 1-phenylethyliodide were used as alkyliodides, acting as degenerative
chain transfer agents.
First, the effects of these alkyl iodides as chain transfer agents on the molecular mass,
molecular mass distribution, glass transition temperature, conversion and particle size for
the seeded emulsion polymerisation of styrene were studied. Second, the effects of alkyl
iodides as chain transfer agents on the kinetics of radical emulsion polymerisation,
especially the average amount of radicals per latex particle, were investigated. Third, the
possibility of producing block-copolymers by emulsion polymerisation, using alkyl iodides
as chain transfer agents, was investigated.
To the best of the author's knowledge, results of work carried out in this study offer the first
proof that the "living"/controlled radical polymerisation of styrene, with alkyl iodides as
chain transfer agents, can be successfully carried out in emulsion. Addition of different
alkyl iodides as chain transfer agents, in different concentrations, led to marked changes in
the molecular mass, molecular mass distribution, glass transition temperature, conversion
and particle size for the seeded emulsion polymerisation of styrene. The molecular
masses of the polystyrene that was produced ranged from 156 to 663 577 while the
average molecular mass distribution was below 2. Addition of these alkyl iodides to a
seeded styrene polymerisation under zero-one conditions led to an average number of
free radicals per latex particle that was greater than 1. A styrene seed latex with functional
iodine end-groups was created and was successfully co-polymerised with butyl acrylate
to produce a perfect styrene-butyl acrylate block-copolymer.
This work has industrial importance as it allows the molecular mass, molecular mass
distribution and particle size of polymers to be controlled. These factors are directly
related to their micro- and macrostructure of polymers. / AFRIKAANSE OPSOMMING: Die vrye-radikaal polimerisasie proses wat die eienskappe van In lewendige polimerisasie
sisteem toon, omdat dit moontlik is om 'n polimeer met voorafbepaalde molekulêre
massas en 'n baie klein molekulêre massa verspreiding te berei, is bespreek. Dit is ook
moontlik om, deur die byvoeging van 'n tweede monomeer, 'n blok ko-polimere te maak.
Die doel was om die effekte wat alkieljodiede as ketlingoordragagente op die "seed"
homo- en ko-polimerisasie van stireen en butiel akrielaat gehad het te beskryf en te
verklaar. Jodoasetonitriel en 1-fenieletieljodied is gebruik as degeneratiewe
kettingoordragagente.
Eerstens is die uitwerking van hierdie alkieljodiede as kettingoordragagente op die
molekulere massa, molekulere massa verspreiding, glas oorgang temperatuur, opbrengs
en partikelgrote van die "seed" emulsie polimerisasie van stireen bestudeer. Tweedens is
na die uitwerking van alkiekjodiede op die kinetika van In emulsie radikaal polimerisasie
gekyk met spesifieke 1<lem op die gemiddelde aantal radikale per emulsie partikel.
Derdens is die moontlikheid om blok ko-polimere te berei ondersoek.
Na die beste van die outeur se wete is die resultate van hierdie studie die eerste bewys
dat die "Iewendige"/gekontroleerde radikaal polimerisasie van stireen met alkieljodiede as
ketlingoordragagente suksesvol in emulsie polimerisasie uitgevoer kan word. Die
byvoeging van verskillende alkieljodiede, in verskillende konsentrasies, het aanleiding
gegee tot opmerklike veranderinge in die molekulere massa, molekulere massa
verspreiding, glas oorgang temperatuur, opbrengs en partikelgrote van die "seed" emulsie
polimerisasie van stireen. Die molekulere massas van die bereide polistiereen het
gewissel tussen 156 en 663 577 en die gemiddelde molekulere massa verspreiding was
onder 2. Byvoeging van die alkieljodiede by die "seed" polimerisasie van stireen onder
zero-een toestande het In gemiddelde aantal radikale per emulsie partikel van bo 1
gelewer. In Funksionele "seed" emulsie met jodium eindgroepe was geproduseer na 'n
suksesvolle ko-polimerisasie met butiel akrielaat en 'n perfekte stireen-butiel akrilaat kopolimeer
is verkry.
Hierdie werk het industriele belang aangesien dit die beheer van molekulere massa,
molekulere massa verspreiding en partikelgrote moontlik maak wat 'n direkte effek het op
die mikro- en makro strukture van die polimeer.
|
364 |
Free volume of electrospun organic-inorganic copolymersBasson, Neil 04 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Two series of amphiphilic, organic-inorganic graft copolymers of poly(methyl
methacrylate) and poly(dimethylsiloxane) (PMMA-graft-PDMS), as well as
poly(acrylonitrile) and poly(dimethylsiloxane) (PAN-graft-PDMS), were synthesized
via conventional free radical copolymerization using the ―grafting through‖ technique.
In both series the PDMS macromonomer content varied from 5 wt.% - 25 wt.% and
different graft lengths of 1000 g/mol and 5000 g/mol were used. A gradient elution
profile was developed to monitor the removal of the unreacted PDMS
macromonomer using hexane extraction. In the case of the PAN copolymer series,
the gradient profile showed that as the PDMS content in the feed increased, more
PAN-graft-PDMS molecules formed relative to homopolymer PAN. In the case of the
PMMA copolymer series, mostly PMMA-graft-PDMS molecules were formed as the
PDMS content in the feed increased. In the case of the PAN-graft-PDMS series, the
PDMS content affected the crystallization behaviour of the PAN segments and lead
to a decrease in crystallinity across the composition range as the PDMS content
increased. It is shown that the synthesized graft copolymers can be electrospun to
produce continuous nanofibers. The effects of polymer solution concentration,
copolymer composition and tip-to-collector distance on the fiber morphology are
discussed. The rapid stretching of the polymer jet, as well as the rapid solvent
evaporation during the electrospinning process, resulted in highly complex nonequilibrium
morphologies in the case of the electrospun PAN-graft-PDMS
copolymers. The crystallization behaviour of the electrospun fibers of PAN-graft-
PDMS was shown to be different from the unprocessed precursor material. Surface
oxidised MWCNTs were successfully incorporated and well dispersed into the graft
copolymers via the electrospinning process to produce nanocomposite nanofibers. In
the case of the PAN-graft-PDMS copolymer series, the presence of MWCNTs in the
nanocomposite nanofibers enhanced the overall degree of crystallinity when
compared to the unfilled nanofibers. For the first time positron annihilation lifetime
spectroscopy (PALS) analysis was performed on the various complex graft
copolymer compositions and their electrospun fiber analogues, as well as
nanocomposites, to investigate the free volume properties of the various materials. The results revealed that there are two distinct ortho-positronium (o-Ps) lifetime
parameters for these complex multiphased materials. The shorter lived lifetime -3
was attributed to the o-Ps annihilation in the amorphous regions of the crystalline
PAN phase in the PAN-graft-PDMS copolymer series, as well as to the o-Ps
annihilation in the amorphous PMMA phase in the case of the PMMA-graft-PDMS
copolymer series. The longer lived lifetime -4 was attributed to the o-Ps annihilation
in the more amorphous PDMS phase. In the case of the PMMA series the relative
fractional free volume was influenced by the graft lengths, where the 5000 g/mol
series showed a larger increase in fractional free volume relative to the shorter 1000
g/mol series. The effects of the tip-to-collector distance during electrospinning, as
well as the inclusion of MWCNTs, on the free volume properties are also discussed.
It is demonstrated how positron annihilation lifetime spectroscopy can provide
valuable and unique information on the internal structure and morphology of the
electrospun nanofibers. / AFRIKAANSE OPSOMMING: Twee reekse amfifiliese, organies-anorganiese entkopolimere van
poli(metielmetakrilaat) en poli(dimetielsiloksaan) (PMMA-ent-PDMS), asook
poli(akrilonitriel) en poli(dimetielsiloksaan) (PAN-ent-PDMS), is gesintetiseer deur
konvensionele vrye-radikaalkopolimerisasie. Die PDMS makromonomeerinhoud het
gewissel tussen 5 wt.% - 25 wt.% in albei reekse en sykettinglengtes van 1000 g/mol
en 5000 g/mol is gebruik. `n Gradient-eluasieprofiel is opgestel om die verwydering
van ongereageerde PDMS makromonomeer d.m.v. heksaanekstraksie te monitor. In
die PAN kopolimeer reeks het die gradient-eluasieprofiel gewys dat meer PAN-ent-
PDMS molekules vorm relatief tot die PAN homopolimeer sodra meer PDMS
bygevoeg word. In die PMMA kopolimeer reeks het meer PMMA-ent-PDMS
molekules gevorm sodra meer PDMS toegevoeg is. In die geval van die PAN-ent-
PDMS reeks, het die PDMS die kristallisasiegedrag van die PAN segmente
geaffekteer en `n afname in die totale kristalliniteit veroorsaak soos die PDMS
inhoud vermeerder het. Daar word bewys dat die gesintetiseerde entkopolimere geelektrospin
kan word om nanovesels te vorm. Die effek van
polimeeroplossingskonsentrasie, kopolimeersamestelling en punt-tot-versamelaarafstand
op die nanoveselmorfologie word bespreek. Die vinnige strekking van die
polimeerjet sowel as die vinnige verdamping van die oplosmiddel gedurende die
elektrospinproses het gelei tot hoogs komplekse nie-ekwilibrium morfologieë in die
geval van die ge-elektrospinde PAN-ent-PDMS kopolimere. Die kristallisasiegedrag
van die nanovesels van PAN-ent-PDMS het verskil van die onverwerkte voorloper
materiaal. Oppervlakgeoksideerde MWCNTs is suksevol geïnkorporeer en versprei
in die entkopolimere d.m.v. die elektrospinproses om nanosaamgestelde nanovesels
te vorm. Die teenwoordigheid van MWCNTs in die nanosaamgestelde nanovesels in
die PAN-ent-PDMS kopolimeerreeks het gelei tot `n verbetering in die algehele
kristalliniteit in vergelyking met die nanovesels sonder MWCNTs. Positronvernietigingsleeftyd-
spektroskopie (PALS) is vir die eerste keer gebruik om die vrye
volume van verskillende kompleks entkopolimeersamestellings, hul ge-elektrospinde
nanovesels sowel as nanosaamgestelde nanovesels te bestudeer. Die resultate het
getoon dat daar twee verskillende orto-positronium (o-Ps) leeftydparameters vir hierdie komplekse multifase materiale bestaan. Die korter leeftydparameter -3 word
toegeskryf aan die o-Ps vernietiging in die amorfe areas van die kristallyne PAN fase
in die PAN-ent-PDMS kopolimeerreeks, sowel as die o-Ps vernietiging in die amorfe
PMMA fase in die PMMA-ent-PDMS kopolimeerreeks. Die langer leeftydparameter
-4 word toegeskryf aan die o-Ps vernietiging in die amorfe PDMS fase. Die relatief
fraksionele vrye volume van die PMMA reeks is deur die verskillende syketting
lengtes beïnvloed. Die 5000 g/mol syketting het `n groter toename in fraksionele vrye
volume veroorsaak relatief tot die korter 1000 g/mol syketting. Die effek van die punttot-
versamelaar-afstand tydens die elektrospinproses op die vrye volume
eienskappe, sowel as die insluiting van MWCNTs, word bespreek. Daar word
aangedui hoe positron-vernietigingsleeftyd-spektroskopie waardevolle en unieke
inligting kan verskaf oor die interne struktuur en morfologie van die nanovesels.
|
365 |
The preparation, properties and structure of poly-p-xylyene and its copolymersLightfoot, Philip Kenneth January 2000 (has links)
No description available.
|
366 |
The sequestration and detection of aqueous uranium using a novel network polymerSaunders, Gregory David January 1999 (has links)
No description available.
|
367 |
The Synthesis of Cellulose Graft Copolymers Using Cu(0)-Mediated PolymerizationDonaldson, Jason 29 May 2013 (has links)
Cellulose is the most abundant renewable polymer on the planet and there is great interest in expanding its use beyond its traditional applications. However, its hydrophilicity and insolubility in most common solvent systems are obstacles to its widespread use in advanced materials. One way to counteract this is to attach hydrophobic polymer chains to cellulose: this allows the properties of the copolymer to be tailored by the molecular weight, density, and physical properties of the grafts. Two methods were used here to synthesize the graft copolymers: a ‘grafting-from’ approach, where synthetic chains were grown outward from bromoester moieties on cellulose (Cell-BiB) via Cu(0)-mediated polymerization; and a ‘grafting-to’ approach, where fully formed synthetic chains with terminal sulfide functionality were added to cellulose acetate with methacrylate functionality (CA-MAA) via thiol-ene Michael addition.
The Cell-BiB was synthesized in the ionic liquid 1-butyl-3-methylimidazolium chloride and had a degree of substitution of 1.13. Polymerization from Cell-BiB proceeded at similar but slightly slower rate than an analogous non-polymeric initiator (EBiB). The average graft density of poly(methyl acrylate) chains was 0.71 chains/ring, with a maximum of 1.0 obtained. The graft density when grafting poly(methyl methacrylate) was only 0.15, and this appeared to be due to the slow initiation of BiB groups. Using EBiB to model the reaction and improve the design should allow this to be overcome. Chain extension experiments demonstrated the living behaviour of the polymer.
The CA-MAA was synthesized by esterification with methacrylic acid. Reactions of CA-MAA with thiophenol and dodecanethiol resulted in quantitative addition of the thiol to the alkene. The grafts were synthesized by Cu(0)-mediated polymerization from a bifunctional initiator containing a disulfide bond, followed by reduction to sulfides. The synthetic polymers were successfully grafted to CA-MAA but the grafting yield was limited by the low sulfide functionality. Better retention of sulfide functionality is necessary for more efficient grafting. / Thesis (Master, Chemical Engineering) -- Queen's University, 2013-05-27 16:21:03.874
|
368 |
Photo-crosslinked and pH sensitive polymersomes for triggering the loading and release of cargoGaitzsch, Jens, Appelhans, Dietmar, Gräfe, David, Schwille, Petra, Voit, Brigitte 31 March 2014 (has links) (PDF)
Crosslinkable and pH-sensitive amphiphilic block copolymers are promising candidates to establish pH-stable and permeable vesicles for synthetic biology. Here, we report the fabrication of crosslinked and pH-stable polymersomes as swellable vesicles for the pH-dependent loading and release of small dye molecules. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
|
369 |
Molecular weight effects of PBT-6 polymeric semiconductor on charge carrier mobilityRavi Sankar, Ashwin 13 January 2014 (has links)
Organic π-conjugated Donor-Acceptor copolymers are emerging as potential candidate materials for organic field effect transistor (OFET) and organic photovoltaic (OPV) applications. The electron-deficient benzothiadiazole group coupled with an electron-rich oligothiophene to form donor-acceptor copolymers has attracted significant attention. These low optical band gap materials absorb photons in the range of 400-800 nm and exhibit good thermal stability. In particular, poly(benzothiadiazole-sexithiophene) (PBT6) exhibits excellent performance in optoelectronic devices and high thermal stability. Here, we present the chemical synthesis and characterization of the polymer, PBT6. Three samples of PBT-6 with differing molecular weights in the range of Mn 18000-45000 Da were synthesized. Each polymer was characterized with respect to its photophysical, thermal properties and field-effected mobility was determined. Devices were prepared by drop-casting polymer solutions in 1,2-dichlorobenzene (DCB) onto an OFET (bottom gate/bottom contact) substrate and the devices were used to examine the charge transport properties of each polymer system. The optimal solvent to be used for processing technique was determined and surface techniques using OTS-8 and OTS-18 were compared through contact angle measurements. The measured charge carrier mobilities were in the range of 0.45-0.6 cm² / V.s. Polymer films prepared via drop-casting and which were thermal annealed exhibit mobilities as high as 0.825 cm² / V.s. This work examines the effect of molecular weight on the charge carrier transport properties and demonstrates the correlation of performance with molecular ordering. Drop-casted films of PBT-6 exhibit highly ordered crystalline lamellar structure with high degree of π- π stacking with edge-on orientation on the substrate. The longer conjugation lengths promote intrachain charge transfer. This high degree of molecular ordering in high MW samples of PBT6 improves the interchain and intrachain charge transfer leading to enhanced mobilities. The increased molecular weight (MW) facilitates in forming more uniform thin films which is vital in processing and application of polymer thin film technologies. These results and observations clearly demonstrate the potential of PBT-6 as a semiconducting material for Optoelectronic devices.
|
370 |
Thermally cleavable Imine Base / Isocyanate Adducts and Oligomers suitable as Initiators for Radical Homo- and CopolymerizationPolenz, Ingmar, Laue, Andreas, Uhrin, Tamas, Rueffer, Tobias, Lang, Heinrich, Schmidt, Friedrich, Spange, Stefan 18 September 2014 (has links) (PDF)
The addition of isocyanates to C=N double bonds of imines gives triazindione heterocycle structures; their thermal properties are reported. Mono-isocyanates were used to form 2:1 adducts with the imine bases 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) and 2-tert-butyl-1,1,3,3-tetramethylguanidine (tBuTMG). A 2:1 stoichiometry of the adducts was proven by NMR and IR spectroscopy, and single crystal X-Ray diffraction; certain cleavage temperatures (70 and 160 °C) were measured. Thermal analysis (TG-MS) of adducts indicates the release of free isocyanate during adduct cleavage. Furthermore, a new class of step-growth oligomers (MN = 750–7,000 g∙mol–1) composed of multi-functional isocyanates and these imine bases was introduced. Their systematic spectroscopic and thermal analysis is shown revealing the similarity in their chemical properties to the 2:1 adducts. Radical homo- and copolymerization of acrylates is initiated by the meta-stable adducts and oligomers of this work; the generation of novel telomeric block-copolymer architectures composed of polyacrylate and oligourea building blocks is demonstrated. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
|
Page generated in 0.3225 seconds