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Synthesis of novel siloxane-containing block and graft copolymers by anionic polymerization and the macromonomer techniqueSmith, Steven D. January 1987 (has links)
The synthesis of novel well defined graft copolymers is now possible with the recent advent of the macromonomer technique. Copolymers with narrow molecular weight distributions of the backbone as well as the grafts are possible.
The anionic alkyl- lithium initiated ring opening polymerization of the hexamethylcyclotrisiloxane has been investigated to prepare polymers of controlled molecular weights and narrow molecular weight distributions. This technique was extended to the preparation of macromonomers and from these macromonomers the synthesis of graft copolymers.
These siloxane macromonomers were then incorporated into acrylic and styrenic copolymers via free radical and anionic techniques. A series of graft copolymers were characterized by a variety of methods. The resulting copolymers exhibit interesting thermal properties dependent on graft molecular weight and composition. Well-defined morphologies were observed by TEM analysis, indicative of the unique structures prepared.
Graft copolymers offer unique possibilities of structure property relationships, often forming two phase morphologies that give rise to properties of both constituents. This allows the preparation of polymers designed to give optimal characteristics. / Ph. D.
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Study of the dilute solution properties of various homo- and block co-polymers by variable temperature size exclusion chromatographyDas, Pradip Kumar January 1984 (has links)
The Variable Temperature Size Exclusion Chromatography (VTSEC) was used to study the dilute solution properties of various homo- and block copolymers as well as polymer blends, focus being primarily on the configuration-dependent properties such as average chain dimensions and hydrodynamic behavior of polymers.
The study constituted of three parts. In the first part, the dilute solution properties of a series of poly(alkyl methacrylates) with varying side alkyl(ester) group were investigated as to the effect of the size of the side group on the average chain dimensions at various temperatures. The VTSEC results were found to reveal that the effect of the side group depends on the extent of chain flexibility imparted by the side group.
In the second part, VTSEC was employed to investigate the applicability and validity of the various models for block copolymers in solution. For this purpose, several series of samples (all anionically synthesized) with various composition and molecular weight were used: i) poly(alkyl methacrylates), their diblock copolymers and blends and ii) diblock and triblock copolymers of poly(styrene/substituted styrene) and poly(butadiene/isoprene). VTSEC results showed that the applicability of each model to a block copolymer in solution depends on the compatibility among the components, the composition of the samples, the solvating power of the solvent used and the operating temperature. Micellization in the hydrocarbon diblock copolymer solutions was found to occur in selective solvent, its extent depending on the solubility parameter difference between the components, molecular weight, composition and solvent power.
In the third part, poly(methyl methacrylate) samples with varying tacticities were studied as to the effect of stereochemical configuration on their dilute solution behavior and found to indicate that both syndiotactic and isotactic stereosequences are required for stereoassociation.
Two new VTSEC data reduction procedures were devised in order to correct for the temperature drifts due to instrumentation in the first and to neutralize the effect of molecular weight in the second. In the second, termed as the Molecular Weight-Elution Volume Superposition Procedure, the effect of molecular weight alone was enutralized leaving only the effect of the intrinsic character (such as the size of the side group) of the sample in the elution behavior.
Numerical computations, using the Matxrix Generation method based on the Rotational Isomeric State approximation, were carried out for stereoregular chains in order to evaluate their chain dimensions at various temperatures. / Ph. D.
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Characterization of block copolymers and polymer blends by inverse gas chromatographySheehy, Daniel P. January 1984 (has links)
The accuracy and utility of using Inverse Gas Chromatography (IGC) to characterize the microphase structure of block copolymers, and the strength of the thermodynamic interactions between the components of polymer blends and the unlike segments of block copolymers was examined. There were three parts to the study. First, the Scott ternary solution model, which is used for the study of thermodynamic interactions in polymer blends, was extended to low molecular weight mixtures. From vapor-liquid equilibrium data in the literature, the Gibbs free energy of mixing of binary mixtures (G<sub>M</sub> ) calculated with the model were compared to experimental values. Mixtures containing ketones, aromatics hydrocarbons, chlorinated hydrocarbons, alcohols and water were studied. With the exception of mixtures containing water and low molecular weight alcohols, a fair to good correlation between theoretical and experimental values was observed. Second, the Gibbs free energy of mixing of nitrocellulose, polyvinyl chloride and poly(vinylidene fluoride) containing blends were measured with the Scott model from IGC data. For the nitrocellulose containing blend, the calculated Gibbs free energy of mixing values were large in magnitude (-2.0 to -5.0 calories/gram) and in fair agreement with the experimental heats of mixing determined from microcalorimetry measurements. For the remaining blends, the IGC data could not be distinguished from the results normally obtained for immiscible blends. The calculated G<sub>M</sub> values were small in magnitude relative to the experimental error of the quantities. Concerning the block copolymers, the relative incompatibility of the constituent blocks of perfectly alternating block copolymers of polydimethylsiloxane and bis-A-polycarbonate and styrene-isoprene-styrene triblock copolymers was reflected in the measured G<sub>M</sub> values. Overall, it was concluded that IGC is a good method for characterizing thermodynamic interaction between blend and copolymer constituents, but a severe limitation of the method is that the interactions are often too weak to measure accurately.
Finally, the microphase structure of the above copolymers were studied by IGC from the retention behavior of hydrocarbon probes below the upper glass transition temperature of the copolymers. The degree of microphase separation, the size of the hard phases and the continuity of the soft phases in the copolymers characterized, and the results obtained were consistent with small angle x-ray, electron microscopy and differential scanning calorimetry data on the same materials. / Doctor of Philosophy
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1D vs. 2D shape selectivity in the crystallization-driven self-assembly of polylactide block copolymersInam, M., Cambridge, G., Pitto-Barry, Anaïs, Laker, Z.P.L., Wilson, N.R., Mathers, R.T., Dove, A.P., O'Reilly, R.K. 13 April 2017 (has links)
Yes / 2D materials such as graphene, LAPONITE® clays or molybdenum disulfide nanosheets are of extremely high interest to the materials community as a result of their high surface area and controllable surface properties. While several methods to access 2D inorganic materials are known, the investigation of 2D organic nanomaterials is less well developed on account of the lack of ready synthetic accessibility. Crystallization-driven self-assembly (CDSA) has become a powerful method to access a wide range of complex but precisely-defined nanostructures. The preparation of 2D structures, however, particularly those aimed towards biomedical applications, is limited, with few offering biocompatible and biodegradable characteristics as well as control over self-assembly in two dimensions. Herein, in contrast to conventional self-assembly rules, we show that the solubility of polylactide (PLLA)-based amphiphiles in alcohols results in unprecedented shape selectivity based on unimer solubility. We use log Poct analysis to drive solvent selection for the formation of large uniform 2D diamond-shaped platelets, up to several microns in size, using long, soluble coronal blocks. By contrast, less soluble PLLA-containing block copolymers yield cylindrical micelles and mixed morphologies. The methods developed in this work provide a simple and consistently reproducible protocol for the preparation of well-defined 2D organic nanomaterials, whose size and morphology are expected to facilitate potential applications in drug delivery, tissue engineering and in nanocomposites. / University of Warwick, Materials GRP, EPSRC, The Royal Society, ERC
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A self-healable fluorescence active hydrogel based on ionic block copolymers prepared via ring opening polymerization and xanthate mediated RAFT polymerizationBanerjee, S.L., Hoskins, Richard, Swift, Thomas, Rimmer, Stephen, Singha, N.K. 12 February 2018 (has links)
Yes / In this work we report a facile method to prepare a fluorescence active self-healable hydrogel via incorporation of fluorescence responsive ionic block copolymers (BCPs). Ionic block copolymers were prepared via a combined effect of ring opening polymerization (ROP) of ε-caprolactone and xanthate mediated reversible addition–fragmentation chain transfer (RAFT) polymerization. Here polycaprolactone (PCL) was modified with xanthate to prepare a PCL based macro-RAFT agent and then it was utilized to prepare block copolymers with cationic poly(2-(methacryloyloxy)ethyltrimethyl ammonium chloride) (PCL-b-PMTAC) and anionic poly(sodium 4-vinylbenzenesulfonate) (PCL-b-PSS). During the block formation, the cationic segments were randomly copolymerized with a trace amount of fluorescein O-acrylate (FA) (acceptor) whereas the anionic segments were randomly copolymerized with a trace amount of 9-anthryl methylmethacrylate (AMMA) (donor) to make both the segments fluorescent. The block copolymers form micelles in a DMF : water mixture (1 : 4 volume ratio). The ionic interaction of two BCPs was monitored via Förster resonance energy transfer (FRET) and zeta potential measurements. The oppositely charged BCPs were incorporated into a polyacrylamide (PAAm) based hydrogel that demonstrated self-healing behavior and is also highly fluorescent. / IIT Kharagpur and MRC (MR/N501888/2)
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Two-dimensional chromatographic characterisation of PS-b-PEO copolymers at the critical conditions of their corresponding homopolymersGrabowsky, Monika Elvira 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Block copolymers are very interesting materials but they are quite complex. During polymer
synthesis only a certain amount of control can be enforced. As copolymers are made up of two
or more different homopolymer segments, and therefore have different end group possibilities,
varying block lengths and block sequences, they have complex structures and are therefore
difficult to analyse.
Different techniques exist by which polymers can be analysed to determine the
aforementioned distributions. In order to achieve a complete characterisation of a polymer
structure, it is best to first use a separation technique to fractionate the polymer into more
homogeneous fractions, and then use identification techniques to analyse these fractions.
Polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymers were investigated using
liquid chromatography at the critical conditions (LCCC) of the copolymers' corresponding
homopolymers, two-dimensional liquid chromatography (2D-LC) and FTIR. The block
copolymers were analysed using the established LCCC of PS but it was found that even
though separation of PS homopolymer and copolymer was obtained, PS blocks of the
copolymers contributed to some extent to the retention of the PEO blocks.
Some of the block copolymer samples were fractionated at the established critical
conditions of PS. These fractions were qualitatively and quantitatively analysed using FTIR
spectroscopy. The settings for the 2D-LC analysis were established, using LCCC of PS as the
first dimension and as the second dimension SEC, using DMF as eluent. DMF was a suitable
solvent to be used for the second dimension because PS, PEO and PS-b-PEO exhibited good
solubility in this solvent. THF did not dissolve the block copolymers completely.
The same solvent system as used for LCCC of PS was used for LCCC of PEO, but the
critical conditions correspond to a different solvent composition. The block copolymers were
analysed using the established LCCC of PEO but it was found that even though separation of
PEO homopolymer and copolymer was obtained, the PEO blocks of the copolymers
contributed to some extent to the retention of the PS blocks. Some of the block copolymer
samples were fractionated at the established critical conditions of PEO. These fractions were
qualitatively and quantitatively analysed using FTIR spectroscopy. The settings for the 2D-LC
analysis were established, using LCCC of PEO as the first dimension and as the second
dimension SEC using DMF as eluent was used. Lastly, qualitative and quantitative analyses of
the block copolymers were carried out using FTIR spectroscopy. / AFRIKAANSE OPSOMMING: Alhoewel blokkopolimere baie interessante verbindings is, is hulle redelik ingewikkeld.
Gedurende die kopolimerisasiereaksie kan daar net 'n sekere mate van kontrole behaal word.
Aangesien kopolimere uit twee of meer homopolimeersegmente, met verskillende end-groep
moontlikhede, bloklengtes en blokvolgordes bestaan, is dit baie moeilik om hierdie verbindings
te analiseer.
Verskillende tegnieke kan gebruik word vir die analise van polimere en die bepaling van
bogenoemde verspreidings. Ten einde 'n polimeerstruktuur volledig te karakteriseer is die beste
manier om eers 'n skeidingstegniek te gebruik om die polimeer in meer homogene fraksies te
fraksioneer en dan daarna hierdie fraksies te analiseer.
Polistireen-blok-poli(etileenoksied) (PS-b-PEO) kopolimere is ondersoek deur gebruik te
maak van vloeistofchromatografie by kritiese kondisies (LCCC) van die kopolimeer se
ooreenkomstige homopolimere; twee-dimensionele vloeistofchromatografie (2D-LC) en FTIR.
Die blokkopolimere is gekarakteriseer deur gebuik te maak van bevestigde LCCC van PS. Daar
is egter gevind dat alhoewel skeiding van die PS homopolimeer en die kopolimeer behaal is, PS
blokke van die kopolimere in 'n mate bygedra het tot die retensie van die PEO blokke.
Sommige van die blok-kopolimeermonsters is gefraksioneer by die bepaalde kritiese
kondisies van PS. Hierdie fraksies is kwalitatief en kwantitatief geanaliseer deur gebruik te maak
van FTIR spektroskopie. Die stellings vir die 2D-LC analise is bepaal deur gebruik te maak van
LCCC van PS as die eerste dimensie en SEC as die tweede dimensie, met DMF as elueermiddel.
DMF was 'n geskikte oplosmiddel vir die tweede dimensie aangesien PS, PEO en PS-b-PEO
goed oplosbaar is daarin. Die blokkopolimere was nie volledig oplosbaar in THF nie.
Dieselfde oplosmiddelsisteem soos gebruik vir die LCCC van PS is gebruik vir die
LCCC van PEO, maar die kritiese kondisies stem ooreen met 'n ander oplosmiddelsamestelling.
Die blokkopolimere is geanaliseer deur gebruik te maak van die bevestigde LCCC van PEO,
maar daar is bevind dat alhoewel skeiding van die PEO homopolimeer en kopolimeer behaal is,
die PEO blokke van die kopolimere in 'n mate bygedra het tot die retensie van die PS blokke.
Sommige van die blokkopolimeermonsters is gefraksioneer by die bevestigde kritiese kondisies
van PEO. Hierdie fraksies is kwalitatief en kwantitatief geanaliseer deur gebruik te maak van
FTIR spektroskopie. Die stellings vir die 2D-LC analise is bepaal deur gebruik te maak van LCCC van PEO as die eerste dimensie en SEC as die tweede dimensie, met DMF as
elueermiddel. Laastens is kwalitatiewe en kwanitatiewe analises van die blokkopolimere m.b.v.
FTIR spektroskopie uitgevoer.
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Novel synthesis of block copolymers via the RAFT processBowes, Angela 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / The synthesis of complex architectures, namely block copolymers with tailored enduse
properties, is currently an important research area in academia and industry. The
challenge is finding a versatile polymerization technique capable of controlling the
molecular properties of the formed copolymers, which in turn determines their
macroscopic properties. Reversible addition-fragmentation chain transfer (RAFT)-
mediated living polymerization is a robust technique capable of producing controlled
polymer products. With the great advances in living polymerization techniques and
the environmental awareness of society there is an increasing demand to produce
these polymer products via the RAFT living technique in heterogeneous media.
Conventional emulsion and miniemulsion polymerization present various problems
when used to produce polymers mediated by the RAFT process. There is an inherent
need to find cost effective and flexible operating conditions to conduct RAFT
polymerization in heterogeneous media with the ability to produce well-defined block
copolymers.
In this study the use of three novel trithiocarbonate RAFT agents to produce welldefined
AB-type, ABA-type and star block copolymers via the RAFT process was
investigated. Optimal operating conditions for the production of living block
copolymers in homogenous and heterogeneous media were determined. The main
focus was on the development of the RAFT process in heterogeneous media to
efficiently produce block copolymer latex products. The RAFT-mediated
miniemulsion polymerization system stabilized with non-ionic surfactants was
thoroughly investigated. The ability of the ab initio and in situ RAFT-mediated
emulsion polymerization systems to produce controlled latexes was demonstrated.
Controlled block copolymer products were successfully synthesized in homogenous
and heterogeneous media via the RAFT process when the optimum reaction
conditions were chosen.
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Synthesis and characterisation of organic-inorganic hybrid block copolymers of polydimethylsiloxane and polystyreneBayley, Gareth Michael 03 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Hybrid A-B type block copolymers of polydimethylsiloxane (PDMS) and polystyrene (PS)
were synthesised. Three different synthetic routes, which allowed control over polymer
structure, were chosen to synthesise these block copolymers. The first technique, coupling of
functional prepolymers, involved using anionic polymerisation to produce PDMS and PS
functional prepolymers of controlled structure. These prepolymers were functionalised with
either silane or allyl functionality and then coupled using a hydrosilylation reaction with
Karstetds platinum catalyst. This technique was the least efficient in block synthesis due to
the incompatibility of the disparate prepolymers. The second technique under study,
sequential anionic polymerisation, gave excellent block copolymer formation with good
control over the chain architecture. The final technique employed atom transfer radical
polymerisation (ATRP) of styrene using a bromoisobutyrate functionalised PDMS
macroinitiator. Silane functional PDMS molecules underwent a hydrosilylation reaction with
allyl-2-bromo-2-methyl-propionate to produce the bromoisobutyrate functionalised polymer in
excellent yields. Subsequent ATRP with styrene allowed the successful synthesis of block
copolymers of controlled structure. Chromatographic systems that allowed liquid
chromatography at the critical conditions (LC-CC) of PS and gradient elution chromatography
(GEC) of the products were developed. GEC was used successfully in the monitoring of the
presence and removal of PDMS homopolymer present in the block copolymer products. LCCC
at the critical point of PS allowed successful chromatographic separation of PS
homopolymer from the block material, as well as, the molecular weight distribution of the
block material according to the segmental length of the PDMS component. LC-CC coupled to
FT-IR using a LC-transform device allowed successful characterisation of the block
copolymer chemical composition. Corona treatment was used to modify the surface structure
of the block copolymer films. Optical microscopy and slow positron beam studies highlighted
the formation of a thin silica like layer on the surface of the films after corona. The positron
studies enabled determination of the silica like layer’s thickness. Contact angle studies
provided the first evidence of hydrophobic loss and recovery for these PDMS containing
hybrid polymer materials after corona treatment. A novel offline coupling technique was
developed between LC-CC separation and transmission electron microscopy (TEM) analysis.
This allowed easy sample preparation without the difficult bulk extraction procedures needed
to remove homo-PS contaminants from the block copolymer. This technique also provided
morphological information as a function of PDMS segmental length.
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Synthesis and characterization of graft and block copolymers using hydroborationBaleg, Abd-Almonam 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Graft and block copolymers were synthesized using multifunctional and
monofunctional macroinitiators to produce the copolymers. The process involved
hydroboration of commercially available unsaturated rubbers and chain-end
unsaturated macromonomers with 9-borabicyclo [3.3.1] nonane (9-BBN). The
resulting secondary alkyl 9-BBN moieties in the starting materials were subsequently
exposed to oxygen in the presence of free radical polymerizable monomers to
facilitate the formation of graft and block copolymers.
This research was initiated by first studying the hydroboration of a model compound,
2-hexene, in order to determine the optimal conditions for the graft reactions. The
model compound was subsequently used as a macroinitiator to initiate the
polymerization of methylmethacrylate (MMA). The same borane chemistry was
extended to the synthesis of polystyrene (PS) block copolymers. Chain-end
unsaturated PS macromonomers, synthesized by anionic polymerization, were
effectively hydroborated and then polymerized to produce PS-b-PMMA block
copolymers.
The synthesis of polyolefin graft copolymers was subsequently achieved by
hydroboration. Several commercial rubbers with different levels of unsaturated
segments were efficiently grafted with vinyl monomers MMA and styrene (St)
following the “graft from” approach. The grafted reactions were carried out under
various reaction conditions to determine the effect of the following factors:
concentration of oxygen, amount of borane and monomer concentration. By
controlling these factors, different graft densities were achieved with high graft
efficiencies. All reactions produced mixed products including unreacted
(non-functional) macroinitiator, homopolymer, graft copolymer and in case of the
highly unsaturated polymer a crosslinked gel.
Finally, the chemical compositions as well as the molar mass distribution of the graft
copolymers were fully characterized by different chromatographic techniques.
1H-NMR and FTIR were also used to confirm the structure of these copolymers.
Gradient HPLC was developed and extensively used to characterize the graft
copolymers.
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Novel siloxane block copolymersStaisch, Ingrid 12 1900 (has links)
Thesis (PhD (Chemistry and Polymer Science))--Stellenbosch University, 2008. / The research presented in this dissertation was concerned with the living radical
polymerization (LRP) of an amphiphilic, water-soluble, bi-substituted and
biologically compatible acrylamide derivative, namely n-acryloylmorpholine (NAM).
The primary objective of this research was the synthesis of novel block
copolymers containing poly(dimethylsiloxane) (PDMS) and various chain lengths
of poly(acryloylmorpholine) (polyNAM) using a LRP technique, namely reversibleaddition
fragmentation chain transfer (RAFT) polymerization. This is the first report
on the synthesis of these block copolymers using RAFT polymerization. These
novel siloxane block copolymers were synthesized using a monohydroxyterminated
PDMS material which had to first be modified into a thiocarbonylthiocontaining
moiety in order for it to be used as macromolecular chain transfer agent
(macroCTA) in the RAFT copolymerization with NAM.
Suitable reaction conditions for the synthesis of these novel block copolymers had
to, firstly, be determined, and secondly, optimized. In order to determine suitable
reaction conditions, a series of homopolymerizations with NAM were first
performed in order to compare which chain transfer agent (CTA), solvent,
temperature etc. could possibly be best suited for the block copolymerizations of
PDMS-b-polyNAM. Reported in this work is the first account of the
homopolymerization of NAM and 2-(dodecylsulfanyl)thiocarbonylsulfanyl-2-methyl
propionic acid (DMP) as CTA using RAFT polymerization.
The resulting novel siloxane block copolymers are amphiphilic in nature and the
existence of these structures was confirmed by size exclusion
chromatography/multiangle light scattering (SEC/MALS), proton nuclear magnetic
resonance (1H-NMR) spectroscopy, gel elution chromatography (GEC) and
transmission electron microscopy (TEM). Interesting phase behaviour was
observed in the latter technique.
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