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Wax characterisation by instrumental analysisWebber, Glenda Vanessa 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: Various companies produce waxes, which are used extensively in various applications, either as
produced or as chemically or physically modified value-added products. They are used in the
traditional candle industry and applications including hot melt adhesives, inks, plastics, polishes
and emulsions for rust prevention or fruit coating. Insight into the properties of these waxes is
required to assist the applications chemist in understanding the role of the wax component in a
specific formulation.
Analytical techniques such as differential scanning calorimetry (DSC), thermogravimetry (TG),
rheometry, gel permeation chromatography (GPC), high temperature gas chromatography
(HTGC) and infra-red spectroscopy (IR) were used to characterise Fischer Tropsch, polyethylene,
natural and petroleum waxes. Property profiles were formulated by integrating the results from
the various techniques. The results of traditional wax analyses (e.g. congealing point, melting
point, penetration, density and viscosity) were also correlated to relevant analytical results
obtained from the instrumental techniques. Structure-property relationships have been proposed. / AFRIKAANSE OPSOMMING: Verskeie maatskappye vervaardig wasse, wat in menige toepassings gebruik word - of direk, of
as chemies- of fisies- veranderde produkte van hoër waarde. Benewens die tradisionele
kersbedryf, word die wasse in toepassings soos warmsmeltkleefmiddels, ink, plastiek,
roeswerende- en vrugtebedekkings- emulsies en politoere gebruik. Wetenskaplikes betrokke by
die formuleering van wasse vir verskillende toepassings sal baat vind by beter inligting van
waseienskappe en die rol van waskomponente in formulasies.
Tegnieke, bv. differensialeskandeerkalorimetrie (DSC), termogravimetrie (TG), reologie,
gelpermeasiechromotografie (GPC), hoëtemperatuurgaschromatografie (HTGC) en infrarooispektroskopie
(IR), is gebruik om Fischer Tropsch-, polietileen-, petroleum- en natuurlike wasse
te karakteriseer. Profiele van waseienskappe is geformuleer deur die integrasie van die
data verkry van die verskillende analitiese tegnieke. Die resultate van tradisionële wasanalises
(bv. stolpunt, smeltpunt, penetrasie, digtheid, viskositieit en olie-inhoud) word ook in verband
gebring met die resultate van die instrumentele analises. Verbande tussen struktuur en
waseienskappe word ook voorgestel.
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Polymerisation of 1,5-hexadienesSmit, Madri 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: In this study, the feasibility of the non-conjugated 1,5-hexadiene as monomer in
metallocene catalised cyclopolymerizations was considered. Homopolymers and
copolymers with ethylene, propylene, 1-pentene, 1-hexene and 2-methyl-1,5-
hexadiene as comonomers were synthesised in the presence of Cp2ZrCh and
rac-Et(lnd)2Zrh. The microstructure (stereoregularity and cyclisation) and
number-average molecular weight were determined from NMR analysis.
Crystalline oligomers with functional (eg -OH) and vinylidene end groups were
obtained. / AFRIKAANSE OPSOMMING: Die studie behels die ondersoek rakende die gebruik van ongekonjugeerde 1,5-
heksadieen as monomeer in metalloseengekataliseerde polimerisasies.
Homopolimere, sowel as kopolimere van etlieen, propileen, 1-penteen, 1-
hekseen en 2-metiel-1,5-heksadieen, is in die teenwoordigheid van Cp2ZrChen
rac-Et(lnd)2ZrCI2 gepolimeriseer. Die mikrostruktuur (stereochemie en
siklisering) en die getal-gemiddelde molekulêre gewig van die gesintetiseerde
polimere is met behulp van KMR spektroskopie ondersoek. Die studie het
getoon dat kristallyne oligomere met funksionele (bv -OH) en vinilideen endgroepe
gesintetiseer is.
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The investigation and analysis of RAFT-mediated block copolymers in aqueous dispersed mediaPretorius, Nadine O. 12 1900 (has links)
Dissertation (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: Polymers prepared via radical techniques are very common in our every day environment. The
technique is however limited by a lack of control over the polymerization and an inability to
produce block copolymers. Block copolymers have a significant number of potential applications in
advanced materials and as a result are a field in which significant research is being conducted.
Reversible Addition-Fragmentation chain transfer (RAFT) is a living free radical process that
overcomes the disadvantages inherent in the traditional process.
In this study the mediation behaviour of two inherently different RAFT agents was investigated by
the “living” free radical polymerization of model monomers via the RAFT process in homogeneous
and aqueous dispersed media with the focus on differentiating between the two types of agents. To
ensure that the agents were comparable a new RAFT agent had to be prepared which has not
previously been documented. The efficiency of the RAFT agents was compared in terms of rate
effects, the predictability of the molecular weights of the polymers, the polydispersities of the
polymers and their ability to allow block copolymer formation via sequential addition of monomers.
Block copolymerizations were conducted by the addition of new monomer to the already existing
RAFT end-capped chains. Monomer addition was done via three different approaches; namely shot
addition, feed addition and pre-swelling (in the case of emulsions). Chromatographic analysis was
conducted on the resulting block copolymers via liquid chromatography at critical conditions (LCCC),
and its online coupling with size-exclusion chromatography (SEC) to obtain two-dimensional
information on the differences in heterogeneity of their molecular distributions. Other analyses
included dynamic light scattering analysis (DLS) and transmission electron microscopy (TEM).
The detailed analysis enabled the understanding of the different products that are produced via the
two different classes of RAFT agent. Potential causes for the differences are discussed and possible
areas for future research are highlighted. The work presented here is the most detailed investigation
of this class of polymerization to date and will provide new insight for researchers working in this
vibrant and important research field. / AFRIKAANSE OPSOMMING: Polimere gesintetiseer deur die gebruik van radikaal tegnieke is algemeen in ons daaglikse
omgewing.
Die tegniek is egter beperk deur die gebrek aan beheer oor die polimerisasie en die onvermoë om
blokkopolimere te sintetiseer. Blokkopolimere beskik oor ‘n aansienlike hoeveelheid potensiele
aanwendinge in gevorderde materiale en is gevolglik ‘n belangrike navorsingsgebied. Omkeerbare
addisie fragmentasie ketting oordrag (OAFO) is ‘n lewende vrye radikaal proses wat die inherente
nadele van die tradisionele proses oorkom.
In die betrokke studie is die mediasie gedrag van twee verskillende OAFO agente bestudeer deur
die lewende vrye radikaal polimerisasie van model monomere deur die OAFO proses in homogene
en waterig dispersie media met die fokus op differensiering tussen die twee tipes agente. Om te
verseker dat die twee agente vergelykbaar is, is ‘n nuwe OAFO agent voorberei wat tot op hede nog
nie gedokumenteer is nie. Die effektiwiteit van die OAFO agente is vergelyk in terme van tempo
effekte, die voorspelbaarheid van die molekulêre massa van die polimere, die polidispersiteit van
die polimere en die moontlikheid om blokkopolimerisasie deur kronologiese byvoeging van
monomere te fasiliteer. Blokkopolimerisasie is uitgevoer deur die byvoeging van nuwe monomeer
tot die alreeds bestaande OAFO eind-groep kettings. Monomeer byvoegings is uitgevoer deur drie
verskillende metodes; naamlik vulskoot addisie, voer addisie en vooraf swelling (in die geval van
emulsies). Chromatografiese analise is uitgevoer op die resulterende blokkopolimere deur vloeistof
chromatografie by kritieke kondisie (LC-CC) en die aanlyn koppeling met grootte-uitsluiting
vloeistof chromatografie, om twee-dimensionele informasie omtrent die verskille in heterogeniteit
van hul molekulere verdeling te bepaal. Verdere analise sluit dinamiese verstrooing mikroskopie en
transmissie elektron mikroskopie in.
Die detaileerde analise onthul die samestelling van die verskillende produkte wat geproduseer is
deur die verskillende klasse van OAFO agent. Potensiele oorsake vir die verskille is bespreek en
moontlike areas vir toekomstige navorsing is benadruk. Die werk hier voorgestel is die mees
gedetaileerde navorsing van hierdie tipe klas van polymerisasie tot op hede en beloof nuwe insig vir
navorsers betrokke in hierdie dinamiese en belangrike navorsingsveld.
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AB diblock copolymers via RAFT-mediated miniemulsion polymerizationBailly, Nathalie 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--Stellenbosch University, 2008. / The Reversible addition fragmentation chain transfer (RAFT) technique is a robust and
versatile technique that enables the synthesis of polymers of controlled molecular
weight and polydispersity. The application of the RAFT technique in heterogeneous
aqueous media has attracted great interest in academics and industry due to it being
more environmentally friendly, besides its other advantages. To date, the synthesis of
well-defined high molecular weight polymers via the RAFT process under industrially
relevant conditions still remains a challenge for polymer chemists.
The study addresses the application of the RAFT process in heterogeneous media,
namely in miniemulsion polymerization, for the synthesis of AB diblock copolymers of
n-butyl methacrylate and styrene.
AB diblock copolymers of high molecular weight were successfully prepared via a twostep
method. In the first step, a dithiobenzoate monofunctional RAFT agent was used in
bulk polymerization with the first monomer, n-butyl methacrylate. After the
polymerization, the majority of the polymer chains contained the thiocarbonyl-thio
RAFT agent functionality, which makes the chains potentially active for chain
extension. The polymeric RAFT agent (also referred to as the starting block) obtained in
the first step was chain extended in the second step, in miniemulsion, upon further
addition of fresh initiator and the second monomer, styrene.
The effects of the initiator/RAFT agent concentration ratio on the miniemulsion systems
were investigated. The miniemulsion systems used for the high molecular weight AB
diblock copolymers exhibited living features despite the high polydispersity indices.
Kinetic results showed an increase in the rate of polymerization throughout the
polymerization. Size exclusion chromatography (SEC) results indicated significant
broadening in the molecular weight distributions and a steep increase in the
polydispersity during the polymerization. It was concluded that the broad molecular
weight distributions and steep increase in the polydispersity was not only related to the
initiator concentration but possibly due to other factors such as inhomogeneity in the miniemulsion system and a transition in the kinetic behavior during the polymerization.
Secondary particle formation emerged from kinetic data and transmission electron
microscopy (TEM) results, but this were not supported by the SEC results.
The effect of the use of a water-soluble initiator on the miniemulsion system was also
investigated. Results indicated a similar behavioral pattern as observed in the AIBNinitiated
systems, and not much improvement in terms of the molecular weight
distributions and polydispersity was seen.
The effect of the molecular weight of the diblock copolymers on the miniemulsion
system was investigated. Poly(n-butyl methacrylate)-b-poly(styrene) diblock
copolymers of lower molecular weight were synthesized via the two-step process.
Kinetic results indicated a similar behavioral trend as to that of the high molecular
weight diblock copolymers synthesized, however SEC chromatograms showed
narrower molecular weight distributions and low polydispersity indices.
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An investigation of the effect of chain length on stereo-regulation with C2 symmetric metallocene catalystsAmer, Ismael 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / This study concerns the polymerization of propylene both in the presence and absence of
molecular hydrogen. The percentage of hydrogen used as a terminating agent in the
polymerization reactions was varied from 0.1 wt% to 15.0 wt% in order to compare a
variety of polymers with different percentages of hydrogen incorporated. Two ansa
metallocene catalysts were used: (A) rac-[ethylene bis(indenyl)] zirconium dichloride
(rac-Et(Ind)2ZrCl2) and (B) dimethylsilyl-bis(2-methyl benzoindenyl) zirconium
dichloride (rac-Me2Si(2-MeBenz[e]Ind)2ZrCl2). Methylaluminoxane (MAO) was used as
cocatalyst for both of the two catalysts.
Characterization of the polymers included using nuclear magnetic resonance
spectroscopy (NMR) for information concerning the microstructure of the polymers, high
temperature gel permeation chromatography (HT-GPC) for molecular weight and
molecular weight distributions and differential scanning calorimetry (DSC) to investigate
the melting point and crystallization behaviour of the polymers.
The polypropylenes prepared with the dimethylsilyl-bis(2-methyl benzoindenyl)
zirconium dichloride catalyst system were compared to the polypropylenes synthesized
with ethylene-bis(indenyl) zirconium dichloride. In particular, the effects of hydrogen on
the microstructure, molecular weight, molecular weight distribution, melting point and
crystallization behaviour were investigated.
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Synthesis and application of surfactants containing polymerizable groupsPienaar, Adele 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: The surfmers sodium l l-rnethacryloyloxy undecanyl-I sulfate (MET) and sodium 11-
crotonoyloxy undecanyl-I sulfate (CRO) were synthesized and purified. Both contain a
sulfonate and polymerizable double bond connected by a hydrocarbon chain. Sodium 4-[ 11-
(3-carboxypropionoyloxy)-undecyloxy] benzenesulfonate (PSA-MA) could not be
synthesized successfully. MET and CRO were characterized by means of nuclear magnetic
resonance spectroscopy (NMR), elemental analysis (EA), thermal gravimetric analysis
(TGA), determination of the critical micelle concentration (CMC), differential scanning
calorimetry (DSC), and microscopy. MET and CRO displayed a liquid crystalline behavior.
MET and CRO were used in combination with poly(diallyl dimethyl ammonium chloride) to
form polyelectrolyte-surfactant complexes by common precipitation in water. These
complexes were redissolved in methanol and cast in films. The cast films were investigated
by wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS) with regard
to ordered mesomorphous phases. Due to the destabilization of the lyotropic phase, little
order were observed in the complexes.
MET was co-polymerized with styrene and methyl methacrylate, in different proportions, by
means of free radical polymerization. The co-polymers were characterized by NMR and
infrared spectroscopy (Ik) and analyzed by DSC, TGA and gel permeation chromatography
(GPC). All analytical techniques showed that the co-polymers were synthesized successfully.
TEM indicated a fine, lamellar micro-structure. / AFRIKAANSE OPSOMMING: Die polimeriseerbare sepe, natrium-ll-metakrieloloksi-undekaniel-l sulfaat (MET) en
natrium-ll-krotonieloksi-undekaniel-l-sulfaat (CRO) is berei en gesuiwer. Beide bevat 'n
sulfonaat en 'n polimeriseerbare dubbelbinding wat deur 'n koolwaterstofketting verbind
word. Natrium-4-[11-(3-karboksipropionieloksi)-undekieloksi]-benseensulfaat (PSA-MA)
kon nie suksesvol berei word me. MET en CRO is deur middel van
kernmagnetieseresonansspektroskopie (KMR), elementele-analise (EA), termiesegravimetriese
analise (TOA), kritiese miselkonsentrasie (CMC),
differensieelskandeerkalorornetrie (DSC) en mikroskopie gekarakteriseer. Beide MET en
CRO het 'n vloei-kristalgedrag getoon.
MET en CRO is met poli(diallieldimetielammoniumchloried) gereageer om polyelektrolietseepkompleks
te vorm deur presipitasie uit water. Die komplekse is in metanol opgelos en
films daarvan gemaak. Die films is deur wyehoek X-straal diffraksie (WAXS) en kleinhoek
X-straaldiffraksie (SAXS) ondersoek om geordende mesomorfiese fases te ondersoek. As
gevolg van destabilisasie van die liotropiese fase is min orde in die komplekse gevind.
MET is met stireen en metielmetakrilaat deur middel van vryeradikaalpolymerisasie
gekopolimeriseer. Die kopolimere is deur middel van KMR- en infrarooispektroskopie (IR),
DSC, TOA en gelpermeasiechromotagrafie (OPC) ondersoek. Al hierdie analitiese metodes
het die suksesvolle sintese van die kopolimere bewys. Transmissie-elektronmikroskopie het
die teenwoordigheid van 'n fyn, laminere mikro-struktuur bewys.
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Atom transfer radical polymerisation of unusual monomersStaisch, Ingrid 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Controlled free radical polymerisation techniques offer several practical and
theoretical advantages compared to many other polymerisation techniques. Living
polymerisation techniques such as anionic polymerisations require the total exclusion
of impurities such as oxygen and moisture. Controlled free radical polymerisations,
however, do not require such stringent methods of practice. This is very advantageous
for industrial purposes.
Atom Transfer Radical Polymerisation (ATRP) is a form of a controlled/living free
radical polymerisation technique by which one is able to synthesize controlled
architectural structures and predetermine the molecular weights of macromolecules.
The monomers that were investigated for this research project include methyl
methacrylate (MMA), 4-vinylpyridine (4VP) and lauryl methacrylate (LMA). The
latter two monomers (4VP and LMA) are not commonly used in ATRP-mediated
reactions. The synthesis of block copolymers ofMMA and LMA were attempted. The
homopolymerisation of 4VP did not give the control expected when polymerising by
means of ATRP. This prompted an investigation into possible side reactions that
could take place with 4VP in this specific ATRP system. This included possible
quatemization of 4VP with the alkyl halide initiator species. / AFRIKAANSE OPSOMMING: Beheerde vrye-radikaalpolimerisasietegnieke bied verskeie praktiese en teoretiese
voordele bo verskeie ander vrye-radikaalpolimerisasietegnieke. Lewende
polimerisasietegnieke soos anioniese polimerisasie, vereis die totale uitsluiting van
onsuiwerhede soos suurstof en water. Beheerde vrye-radikaalpolimerisasies vereis
egter nie sulke streng reaksiekondisies nie. Hierdie is baie voordelig vir industriële
doeleindes.
Atoomoordragradikaalpolimerisasie (ATRP) is 'n tipe beheerde/lewende vryeradikaalpolimerisasietegniek
wat dit moontlik maak om die samestelling en struktuur
van makromolekules asook die molekulêre massa presies te beheer.
In hierdie studie is die monomere metielmetakrilaat (MMA), 4-vinielpiridien (4VP)
en laurielmetakrilaat (LMA) bestudeer. Laasgenoemde twee monomere (4VP en
LMA) word beskou as ongewone monomere om in ATRP-sisteme te gebruik. Daar is
gepoog om blok kopolimere van MMA en LMA te sintetiseer. Die homopolimerisasie
van 4VP het minder beheer gelewer as wat by beheerde vrye-radikaal sisteme soos
hierdie verwag word. Na aanleiding van hierdie resultate is 'n ondersoek geloods om
die moontlike newereaksies van 4VP in hierdie spesifieke ATRP-sisteem te
ondersoek. Daar is gepoog om te bewys dat die alkielchloriedinisieerder verdwyn
deur kwatemisasie met 4VP.
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Blends with low-density polyethylene (LDPE) and plastomersRabie, Allan John 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: This study describes the design, building and optimization of a fully functional
preparative TREF (Prep-TREF) apparatus. This apparatus allows for the fractionation of semicrystalline
polyolefins according to the crystallizability of the molecules. Various factors, such as
the sample cooling rate and the effect of on-support and off-support crystallization, are
investigated.
The preparative TREF is used to fractionate a commercial low-density polyethylene
(LOPE), two commercially available plastomers (polyethylene-l-octene copolymers), as well as
blends of the LOPE and the respective plastomers. It is shown that in each case the samples
fractionated by crystallizability. The fractions recovered from the Prep-TREF were characterized
by CRYSTAF, OSC and NMR analysis. It is shown how the results of this preparative
fractionation allow for a better understanding of the molecular heterogeneity in the LOPE and
plastomers.
New ways of presenting the data from the preparative fractionation, in terms of 3-
dimensional plots, are also investigated. These plots offer a novel way of presenting the
molecular heterogeneity in the samples in terms of the molecular crystallizability. These plots
highlight features that are difficult to detect in the conventional two-dimensional plots.
In conclusion, the influences of various blending ratios of LOPE and plastomer on the
morphological and physical properties of the blends, such as haze, clarity, and tear-and impact
strength are determined. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie was die ontwikkeling en optimisering van 'n ten volle
funksionerende TREF. Hierdie tegniek word gebruik om polimeermengsels te fraksioneer deur
gebruik te maak van die kristaliseerbaarheid van polimere. Verskeie faktore soos die afkoel
spoed en die effect van met en sonder 'n ondersteuning(seesand) vir kristaliseering was
ondersoek.
Hierna is navorsing gedoen om 'n beter begrip ten opsigte van die meganiese, fisiese en
optiese eienskappe van lae-digtheid poliëtileen (LDPE) te ontwikkel. Hierdie LDPE is met die
affiniteitsreeks plastomere van die maatskappy, Dow Chemicals, gemeng om tendense in die
gefraksioneerde polimere te indentifiseer.
Een van Sasol se kommersiële LDPE produkte en twee van Dow Chemicals se
plastomere is individueel gefraksioneer. Die mengsel van die twee ongefraksioneerde LDPE en
plastomere is nog nooit voorheen op 'n molekulêre basis ondersoek nie. Dit is in hierdie studie
gedoen deur van TREF gebruik te maak.
Nuwe maniere is ontwikkel om data op 'n nuwe manier voor te stel deur middel van 3
Dimensionele grafieke te skep om resultate voor te stel wat andersins baie moelilik was om
voor te stel in een dimensie agv die hoeveelheid data wat geinterpreteer word.
Ten slotte is die invloed van die verskillende mengverhoudings van LDPE en plastomere
op die morfologiese en fisiese eienskappe soos deursigtigheid, helderheid, skeur- en
impaksterkte, ook ondersoek.
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New monomer for hydrophobic acrylic copolymers and their novel propertiesDe Vries, Andrew Robert 12 1900 (has links)
Thesis (DSc (Chemistry and Polymer Science))--University of Stellenbsoch, 2006. / The synthesis and characterization of a new tertiary alcohol (2-octyl-2-dodecanol) and “bushy-tailed”, hydrophobic acrylic monomer (2-octyl-dodecyl acrylate) from a 1-decene dimer (2-octyl-1-dodecene) precursor that was synthesized with metallocene technology is reported. Some preliminary applications of the newly synthesized 2-octyl-dodecyl acrylate were investigated. These applications included the use of 2-octyl-dodecyl acrylate as a reactive hydrophobe in mini-emulsion polymerizations, and as a reactive (internal) plasticizer.
In an attempt to selectively dimerize 1-decene, the effect of various factors on the oligomerization of 1-decene was investigated. These factors include the following:
i. Different temperatures: 5, 35, 70 and 90°C
ii. Different co-catalyst [methylaluminoxane (MAO)] concentrations
iii. Different catalysts: bis(cyclopentadienyl)zirconium dichloride (Cp2ZrCl2) and bis(cyclopentadienyl)hafnium dichloride (Cp2HfCl2)
iv. Different reaction times.
In all instances the final product obtained, under the abovementioned conditions, was a mixture of residual monomer, the dimer and trimer of 1-decene. These findings were corroborated with GC-MS and 1H-NMR spectroscopy.
The isolation and further processing of the dimer of 1-decene (2-octyl-1-dodecene) was investigated. The efficiency, in terms of the final product-composition for the amount of catalyst used and reaction time, of Cp2ZrCl2 compared to bis(cyclopentadienyl)hafnium dichloride (Cp2HfCl2; hafnocene) as catalyst for the oligomerization of 1-decene is also reported on. The results obtained indicated that Cp2ZrCl2 is the more efficient catalyst for the oligomerization of 1-decene. The effect of different reaction times (1, 3, 6, 24 hours) on the final product-composition for the oligomerization of 1-decene was also investigated. Longer reaction times (24 hours) seemed to be excessive. A reaction time of 6 hours was optimal. The purified 1-decene dimer (2-octyl-1-dodecene) was converted to the new tertiary alcohol (2-octyl-2-dodecanol) using the oxymercuration-demercuration procedure. The 2-octyl-dodecyl acrylate was synthesized by the esterification of the tertiary alcohol with acryloyl chloride in the presence of triethylamine. The new tertiary alcohol and acrylate were characterized by FT-IR and 1H-NMR spectroscopy.
Stable polymer latex particles were successfully synthesized with the novel reactive hydrophobe 2-octyl-dodecyl acrylate in the mini-emulsion polymerization of butyl acrylate, methyl methacrylate and styrene. Phase-separation experiments showed that the presence of 2-octyl-dodecyl acrylate in the dispersed phase retards Ostwald ripening.
The novel acrylic monomer, 2-octyl-dodecyl acrylate, was copolymerized with styrene via conventional free radical polymerization. Both low and high molecular weight copolymers were prepared. Thermal analysis of the copolymers showed that 2-octyl-dodecyl acrylate does act as a reactive (internal) plasticizer. Blends of commercial virgin polystyrene and the synthesized low and high molecular weight copolymers were prepared. Partially miscible blends were obtained. Decreases in the glass transition temperatures of the blends compared to the virgin polystyrene were observed. The higher molecular mass styrene/2-octyl-dodecyl acrylate copolymers produced larger decreases in glass-transition temperatures.
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Synthesis and characterization of tailored polyurethane coatingsSeboa, Sharrief 12 1900 (has links)
Thesis (DSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / Aqueous polyurethane (PU) dispersions were synthesized for use in paper coatings. These
PUs contained a polyester polyol soft segment (content of between 65 to 75%) and a
urethane hard segment (content of between 30 to 35%). Triethylamine (TEA) was used as
the neutralizing agent. The polyester polyol segment consisted of neopentyl glycol (NPG),
adipic acid, 1,4-cyclohexane dicarboxylic acid (1,4-CHDCA) and 2-phosphonobutane-
1,2,4-tricarboxylic acid (PBTCA), while the urethane hard segment consisted of toluene
diisocyanate (TDI), dimethylolproponic acid (DMPA) and ethylene glycol (EG) as a chain
extender for increasing the hard segment content.
Waxes and fillers were incorporated into the PU coating mixtures to investigate their effect on
the barrier properties of the PU. Two types of fillers were used: nano-fillers and micro-fillers.
The nano-fillers used included the Cloisite nano-clays NC15A, NC93A and NC30B, and the
micro-fillers used included talc, kaolin clay and barium sulfate.
Two different polyester polyols were synthesized: one containing a phosphate and the other
containing no phosphate. The polyols were characterized in terms of their acid value,
hydroxyl value and molecular mass. The PUs synthesized from the polyol containing no
phosphate showed unfavourable barrier properties compared to results achieved with the
phosphate-containing PU.
The PU dispersions were applied to paperboard, and then dried at a maximum temperature
of 130oC for 15 to 60 seconds, depending on the coating volume. The PU-coated paperboard
was characterized primarily by determining the moisture vapour transmission rate (MVTR),
and by scanning electron microscopy (SEM).
PU films (stand alone, not supported by paper) were prepared by heating the concurrent PU
dispersion in Teflon holders over three different temperature stages (60, 90 and 120oC) for
about 2 days. The dried films were then characterized by thermogravimetric analysis (TGA),
differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Fourier
transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy.
The PU coatings showed self-assembly properties, which were affected primarily by the ionic
content (comprising of DMPA, PBTCA and excess TEA) and emulsion viscosity. These
self-assembly properties were analyzed by static contact angle (SCA) and MVTR measurements. It was found that the final coating properties were affected by the
self-assembly mechanism of the PU.
Generally, the phosphated PU coatings had lower MVTR values than the non-phosphated
PU coatings. SEM analysis showed that the phosphated PU coatings had no pinholes, while
the non-phosphated PU coatings had pinholes. DMA analysis showed that the phosphated
PUs had higher Tg values than the non-phosphated PUs. Further, the inclusion of the
phosphate monomer increased the emulsion stability and the compatibility between the hard
and soft segments of the PU.
Also, the exfoliated PU nanocomposites at 1% filler loading gave much better MVTR results
compared to the PU microcomposites. It also rendered the coating to be non-blocking, with
minimal change in MVTR.
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