Linear thermoplastic polyesters are commonly used in high volume applications such as food containers, films and textile fibers. The physical and mechanical properties of these materials are well documented and are a function of chemical structure and morphology (e.g. semi-crystalline, amorphous, etc.). Polyesters, as are many organic polymers, are quite flammable. Polydimethylsiloxane homopolymer exhibits low mechanical strength and, even at high molecular weight, exists as a viscous fluid rubbery gum due to its low glass transition temperature of approximately -123°C. However, one of the many attractive properties of this polymer is its relatively low flammability and if properly designed, organic "sand-like" silicates are produced in oxidizing atmospheres at elevated temperatures (e.g. 500-700°C). This thesis discusses the synthesis and characterization of novel, high molecular weight cycloaliphatic and aromatic polyester/ poly(dimethylsiloxane) segmented copolymers. The cycloaliphatic copolymers were synthesized via a melt process using a high trans content 1,4 dimethylcyclohexanedicarboxylate, and 1,4 butanediol or cyclohexanedimethanol, while the partially aromatic systems were synthesized using dimethyl terephthalate and butanediol. Primary and secondary aminopropyl terminated poly(dimethylsiloxane) oligomers of controlled molecular weight were endcapped with excess diester to form an amide linked diester terminated oligomer. The latter was then incorporated into the copolymer via melt transesterification to afford a multiphase segmented copolymer. Selected compositions showed enhanced ductility and hydrophobic surface modification. The polysiloxane segment was effeciently incorporated into the copolymers and was unaffected by the transesterification catalyst under typical reaction conditions. The homopolymers and copolymers were characterized by solution, thermal, and mechanical, and surface techniques. The segmented copolymers were demonstrated to be microphase separated as determined by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and transmission electron microscopy. The surface of the copolymers was enriched with the polysiloxane segment as evidenced by contact angle analysis. Thermal gravimetric analysis of the segmented copolymers containing identical amounts of PDMS, but varying in the primary or secondary nature of their amide linkages, exhibited quantitatively identical char yields and weight loss behavior. The segmented copolymers exhibited char yields in air superior to those of their respective homopolymers. Additionally, aromatic poly(tetramethyleneoxide) (PTMO) based polyether/polyester segmented copolymers were modified with poly(dimethylsiloxane). DMA revealed an apparent shift (higher Tg) of the PTMO segment reflecting an increase in phase mixing with the "hard" polyester segment, possibly induced by the hydrophobic PDMS phase. / Master of Science

Poly(ethylene terephthalate) (PETE) packaging is becoming an increasingly popular choice of packaging material for milk, but has the disadvantage of releasing odorous acetaldehyde into food matrices. Sensory detection group thresholds for acetaldehyde in whole, low fat and nonfat unflavored milks were 3939, 4020, and 4040 ppb respectively with no significant difference due to fat level. Chocolate flavored milk and spring water showed detection thresholds levels for acetaldehyde of 10048 and 167 ppb respectively. This information assisted in determining if acetaldehyde migration from the package to the product would influence the flavor of the product. Whole milk was packaged in glass, high density polyethylene (HDPE), amber PETE, clear PETE, and clear PETE with UV light block and was exposed to fluorescent light of 1100-1300 lux (100-120 FC) at 4oC for 18 days. Sensory and chemical analysis and was done on milk from all containers over a period of 18 days. Emphasis was on oxidation, acetaldehyde and lacks freshness off-flavors and byproducts. All volatile flavor compounds studied (acetaldehyde, pentanal, dimethyl disulfide, and hexanal) were increased in light-exposed milk samples. Amber PETE showed the least amount of oxidation off-flavor, while clear PETE with UV block showed significantly less oxidation off-flavor than glass, clear PETE or HDPE on day 7 and 18. Acetaldehyde was not detected by sensory analysis in either light-exposed or light-protected samples. Chemical analysis showed relative acetaldehyde levels in glass (2220 ppb), HDPE (1265 ppb), amber PETE (3397 ppb), clear PETE (2930 ppb), and clear PETE with UV light block (1754 ppb) were all below concentrations found for human flavor threshold. / Master of Science

Poly(dimethylsiloxane-b-methylvinylsiloxane) (PDMS-b-PMVS) diblock copolymers were synthesized via anionic living polymerization with controlled molecular weights and narrow molecular weight distributions. Targeted molecular weights agreed well with experimental values determined by 1H NMR, 29Si NMR, and GPC. Morphologies were investigated by DSC to analyze glass transition temperatures. Only one Tg was observed for each PDMS-b-PMVS block copolymer suggesting that the blocks were miscible in bulk. Tg's ranged from approximately -126 to -128 °C and were between the Tg's of the PDMS (-123 °C) and PMVS (-137 °C) homopolymers. The PMVS blocks were functionalized with trimethoxysilethyl or triethoxysilethyl pendent groups via hydrosilations to yield poly(dimethylsiloxane-b-[poly(methylvinyl)-co-(methyl-(2-trimethoxysilethyl)siloxane)] (PDMS-b-[PMVS-co-PMTMS]) or poly(dimethylsiloxane-b-[poly(methylvinyl)-co-(methyl-(2-triethoxysilethyl)siloxane)] (PDMS-b-[PMVS-co-PMTES]) copolymers, respectively. The PMVS blocks were either derivatized with the functional groups or half of the repeat units were functionalized. The fully hydrosilated materials were diblock copolymers, and the materials that were 50% hydrosilated had a random sequence of methylvinylsiloxy units and methyl-(trialkoxysilethyl)siloxy units. The PDMS-b-[PMVS-co-PMTES] block copolymers had Tg's ranging from -124 to -126 °C and only one Tg was observed. Surface tension measurements suggested that PDMS-b-[PMVS-co-PMTES] copolymers formed aggregates in toluene. Stable suspensions of superparamagnetic cobalt nanoparticles were prepared in toluene in the presence of PDMS-b-[PMVS-co-PMTMS] or PDMS-b-[PMVS-co-PMTES] copolymers via thermolysis of Co2(CO)8. It is hypothesized that the block copolymers functioned as micellar templates for the cobalt nanoparticles. TEM micrographs showed non-aggregated cobalt nanoparticles coated with copolymers that had mean particle diameters ranging from ≥10-15 nm. Specific saturation magnetizations of these cobalt-copolymer complexes ranged from 90-110 emu g-1 Co, comparable to literature values for this particle size. / Master of Science

Yes / Interpolymer complex formation of poly(acrylic acid) with other macromolecules can occur via several mechanisms that vary depending on the pH. At low pH the protonated acid functional group can form bonds with both donor and acceptor moieties, resulting in desolvated structures consisting of two polymers. Complexes were formed in dilute solutions of PAA, functionalised with acenaphthylene, with a range of other polymers including: poly(NIPAM); poly(ethylene oxide) (PEO); poly(dimethylacrylamide) (PDMA); poly(diethyl acrylamide) (PDEAM) poly(vinyl alcohol) (PVA) and poly(vinyl pyrolidinone) (PVP). Fluorescence anisotropy was used to demonstrate complex formation in each case by monitoring the reductions in segmental motion of the chain as the complexes formed. Considerations of the molecular structures of the complexing moieties suggest that solvation energies and pKas play an important role in complex formation.

La poly(ADP-ribosyl)ation est une modification post-traductionnelle qui est stimulée en réponse à des dommages à l'ADN. Les poly(ADP-ribose) polymerases (PARPs) synthétisent des polymères branchés de poly(ADP-ribose) (PAR) qui peuvent se lier de manière covalente et non-covalente à des protéines jouant ainsi un rôle dans des processus tels que la progression du cycle cellulaire, la réparation de l'ADN, la stabilité de l'intégrité génomique et l'apoptose. Le cycle de dégradation du PAR induit aussi une variation des réserves en nucleotides comme le NAD+, l'ATP et l'AMP, influençant les voies énergétiques des cellules. Les techniques de « Matrix Assisted Laser Desorption Ionisation » (MALDI) et de quantification de nucleotides par colorimétrie, fluorométrie et HPLC ont été utilisées pour déterminer de nouveaux partenaires protéiques interagissant avec le polymère d'ADPr, par l'entremise d'interaction directe, covalente et non-covalente, ou par l'entremise d'interaction indirecte, via le cycle de synthèse/dégradation du PAR qui induit d'importants changements métaboliques cellulaires.

Les dommages directs induits à l'ADN par les radiations ultraviolettes (UV) sont éliminés grâce à la réparation par excision de nucleotides (NER). La poly(ADP-ribose) polymerase-1 (PARP-1) est une enzyme impliquée dans différentes voies de réparation de l'ADN. Notre laboratoire a montré que la PARP-1 était activée par les dommages directs dus aux UV et que son absence retarde significativement la réparation de ces dommages dans un gène rapporteur viral. Le but de ce projet était de déterminer si la PARP-1 affectait le NER de l'ADN génomique des cellules eucaryotes. Nous avons observé un délai dans la réparation des dommages directs à l'ADN causés par les UV dans les cellules eucaryotes n'exprimant pas la PARP-1. De plus, la PARP-1 immunoprécipite in vivo avec des protéines impliquées dans la phase de reconnaissance de ces dommages. Nos résultats montrent donc que la PARP-1 joue aussi un rôle dans le NER.

L'intégrité de l'ADN génomique humain est maintenue par des systèmes de réparation de l'ADN qui protègent les cellules des dommages causés par des agents environnementaux ou des lésions spontanées de l'ADN. Chaque cellule peut subir jusqu'à 10⁵ lésions par jour, y compris les cassures double-brin de l'ADN (CDB). La poly(ADPribosyl)ation (PARylation) est l'un des premiers événements de signalisation moléculaire survenant aux CDBs. Il est catalysé par les poly(ADP-ribose)polymérases (PARP) qui sont directement activées par ces lésions d'ADN. Le fait de ne pas générer de poly(ADP)ribosyl (pADPr) en réponse à des dommages à l'ADN par une inhibition chimique ou par l'absence de PARP-1 augmente la sensibilité cellulaire au stress génotoxique, indiquant que la pADPr elle-même est une molécule clé de signalisation des dommages à l'ADN. L'inhibition de l'enzyme de signalisation des dommages à l'ADN, la poly(ADP-ribose) polymérase-1 (PARP-1) est l'une des nouvelles thérapies les plus prometteuses contre le cancer. Les inhibiteurs de PARP sensibilisent les cellules cancéreuses aux agents endommageant l'ADN et tuent efficacement les cellules cancéreuses du sein, des ovaires et du pancréas déficientes en BRCA1 (Breast Cancer gene 1) et BRCA2 (Breast Cancer gene 2), ce qui suggère que les cellules déficientes en réparation des CDBs sont extrêmement sensibles à l'inhibition de PARP. Pourtant, les mécanismes sous-jacents à cette létalité synthétique entre le déficit de réparation du CDB et l'inhibition de PARP restent mal définis. Il y a un débat considérable sur le mécanisme par lequel l'inhibition de PARP tue les cellules déficientes en réparation de l'ADN, et le plein potentiel des inhibiteurs de PARP dans le traitement du cancer ne peut être obtenu que par une compréhension claire des voies de réponse aux dommages de l'ADN (DDR) aux CDB et comment ils sont affectés par les inhibiteurs de PARP. L'objectif général de ma thèse est d'étudier le rôle de PARP-1 dans la réparation DSB et d'identifier les interacteurs de PARP-1 qui jouent également un rôle dans ce processus. Les cellules eucaryotes réparent les CDBs par deux voies principales, la jonction d'extrémité non homologue (NHEJ) et la recombinaison homologue (HR). La HR est initiée par la liaison des CDBs par BRCA1 et le complexe MRE11-RAD50-NBS1 et des nucléases EXO1/DNA2 pour générer de l'ADN simple-brin, qui est ensuite utilisé par la recombinase RAD51 et le complexe BRCA1-PALB2-BRCA2. Une question clé dans notre domaine concerne les facteurs critiques pour réguler le choix de la voie CDB. HR est initiée à partir d'extrémités DSB hautement résectées, tandis que dans le NHEJ, la résection est empêchée par des facteurs de réparation clés incluant RIF1 et 53BP1. En utilisant des cellules déficientes en PARP-1, nous avons observé que deux inhibiteurs de la résection de l'ADN et des régulateurs de choix de voie, RIF1 et 53BP1, la formation de foyers induits par des dommages à l'ADN sont fortement altérés. Cela confirme notre hypothèse selon laquelle PARP-1 participe à la réparation du DSB en influençant la résection de l'ADN. Afin de mieux comprendre le mécanisme de résection et le rôle que PARP-1 y joue, nous avons identifié d'autres protéines qui interagissent avec PARP-1 et modulent ce processus. Pour ce faire, nous avons utilisé des données sur les protéines de liaison au pADPr générées à la fois dans notre laboratoire et celui de notre collaborateur Ted Dawson de Johns Hopkins. Les candidats sélectionnés à partir de ces listes ont été criblés pour identifier une seule cible qui démontrerait un phénotype similaire à la perte de PARP-1. Deux cibles initiales ont été explorées et finalement une seule protéine à doigt de zinc a été choisie comme cible principale. Nous devons relever la fonction de ce doigt de zinc en HR, dans l'espoir qu'il permettra de découvrir davantage les mécanismes de PARP-1 en résection. En résumé, cette thèse élucide le rôle de PARP-1 dans la résection de l'ADN et identifie une protéine à doigt de zinc non étudiée auparavant qui interagit avec PARP-1 et partage une fonction similaire à PARP-1 dans la résection de l'ADN. / The integrity of human genomic DNA is maintained by DNA repair systems that will protect cells from damage by environmental agents or spontaneous DNA lesions. Each cell can experience up to 10⁵ lesions daily, including DNA double-strand breaks (DSB)s. Poly(ADP-ribosyl)ation (PARylation) is one of the earliest molecular signalling events occurring at DNA DSBs. It is catalysed by poly(ADP-ribose) polymerases (PARPs) that are directly activated by those DNA lesions. Failure to generate pADPr in response to DNA damage by either chemical inhibition or absence of PARP-1 increases the cellular sensitivity to genotoxic stress, indicating that pADPr itself is a key DNA damage signalling molecule. Inhibition of the DNA damage signalling enzyme poly(ADP-ribose) polymerase-1 (PARP-1) is among the most promising new therapies in cancer. PARP inhibitors sensitize cancer cells to DNA damaging agents and efficiently kill BRCA1- and BRCA2-deficient breast, ovarian and pancreatic cancer cells, suggesting that cells deficient in DSB repair are exquisitely sensitive to PARP inhibition. Yet, the mechanisms underlying this synthetic lethality between DSB repair deficiency and PARP inhibition remain poorly defined. There is considerable debate about the mechanism through which PARP inhibition kills DNA repair-deficient cells, and the full benefit of PARP inhibitors in cancer therapy can only be achieved by a clear understanding of the DNA damage response (DDR) pathways to DSBs and how these are affected by PARP inhibitors. The overall aim of my PhD is to investigate the role of PARP-1 in DSB repair and identify interactors of PARP-1 which also play a role in this process. Eukaryotic cells repair DSBs by two major pathways, non-homologous end-joining (NHEJ) and homologous recombination (HR). HR is initiated by the binding of DSB by BRCA1 and the end resection of the DSB by MRE11 (and the associated NBS1, RAD50, CtIP, and EXO1) to generate single-stranded DNA, which is further processed by RAD51 and BRCA1-PALB2-BRCA2. A key question in our field regards which factors are critical for regulating the DSB pathway choice. HR is initiated from highly resected DSB ends, whereas in NHEJ, resection is prevented by key repair factors that include RIF1 and 53BP1. Using PARP-1-deficient cells, we have observed that two inhibitors of DNA resection and regulators of pathway choice, RIF1 and 53BP1, are strongly impaired in forming DNA damage-induced foci. This supports our hypothesis that PARP-1 participates in DSB repair by influencing DNA resection. In order to further understand the mechanism of resection and the role that PARP-1 plays in it we also aim to identify other proteins which interact with PARP-1 and modulate this process. To accomplish this, we made use of data on PAR binding proteins generated both in our lab and that of our collaborator Ted Dawson. The candidates selected from these lists were screened to identify a single target that would demonstrate a similar phenotype to PARP-1 loss. Two initial targets were further explored and finally a single zinc finger protein was selected as our primary target. We aim to characterize the function of this zinc finger in HR, in the hopes that it will further uncover the mechanisms of PARP-1 in resection. In summary this thesis elucidates the role of PARP-1 in DNA resection and identifies a previously unstudied zinc finger protein which interacts with PARP-1 and shares a similar function to PARP-1 in DNA resection.

L'ADN, support de l'information génétique, subit chaque jour de nombreuses attaques pouvant induire différents types de lésions. Que ce soit d'origine environnementale (agents chimiques), rayonnements ionisants) ou d'origine endogène (métabolisme de L'ADN, radicaux libres), chacun de ces agents peut provoquer des cassures simple ou double-brin dans la molécule d'ADN. Ces lésions doivent être détectées rapidement et réparées fidèlement, afin d'éviter d'engendrer une mutation pouvant déclencher une maladie telle le cancer, ou encore éviter de se transmettre à la descendance. Au cours de l'évolution, la cellule eucaryote a développé différentes voies spécifiques pour répondre à un stress génotoxique. Ainsi il existe un véritable réseau de surveillance et d'évaluation des dommages permettant à la cellule lésée de réparer l'ADN ou d'entrer en apoptose si les dommages sont trop importants. La poly(ADP-ribosyl)ation des protéines est une modification post-traductionnelle qui intervient rapidement dès qu'une cassure dans la molécule d'ADN est détectée. Le polymère est synthétisé à partir du NAD+ par une famille d'enzymes appelées PARP (poly(ADP-ribose)polymérase), dont le rôle principal est la maintien de l'intégrité du génome. Cette modification affecte les propriétés physico-chimiques ainsi que la fonction des protéines cibles. Celle-ci permet, entre autre, le recrutement des enzymes de réparation de l'ADN. Ce signal demeure toutefois transitoire, le polymère formé étant rapidement dégradé par la PARG (poly(ADP-ribose)glycohydrolase. Ce travail présente une analyse structurale de la PARP-3, un membre peu caractérisé de la famille PARP, ainsi qu'une analyse fonctionnelle de mutants de phosphorylation de la PARP-1 (premier article) qui montre que la phosphorylation du premier doigt de zinc de cette protéine altère son recrutement et sa persistance aux sites de cassure de l'ADN. Par ailleurs, de nombreuses évidences montrent que que la poly(ADP-ribosyl)ation des protéines peut survenir dans un contexte autre que les dommages à l'ADN, le second article présente les métabolismes qui peuvent être associés aux PARP-1 et 2 ainsi qu'à la PARG et monte un possible nouveau rôle biologique pour la PARP-1.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: In papermaking, fillers and additives are used to enhance paper properties. In this study spherical modified poly(vinyl alcohol) (PVA) particles were prepared for use as fillers. In order to determine the mechanism of adhesion of additives to cellulose (paper) fibres, these particles were modified to have surface functionality, with cationic and anionic surface charges, similar to charged polyelectrolyte additives. Typically, retention aids used to improve the fibre–fibre and fibre–filler bonding are able to conform to the surface of the fibres and fillers. Oppositely charged components show strong affinity for each other, e.g. cationic polyelectrolyte groups adhere to anionic surface charges on the fibres. The spherical PVA particles were prepared by the saponification of spherical poly(vinyl pivalate) (PVPi) precursor particles. These PVPi particles, prepared via suspension polymerisation, were cross-linked with a divinyl ether comonomer. The vinyl pivalate (VPi) suspension polymerisation was successfully carried out and afforded relatively uniformly distributed PVPi particles, with diameters of 0.5–10 mm. The cross-linked PVPi particles were then saponified in tetrahydrofuran (THF) as swelling solvent, to afford PVA with various degrees of saponification (DS). The spherical shape was lost and fibrous material was obtained when uncross-linked PVPi particles were saponified. Cross-linking the spherical PVPi particles (PVA precursor) proved innovative, and essential in maintaining the spherical form during saponification to PVA/PVPi. By varying the saponification time periods, various DS were obtained, as characterised by solid state NMR spectroscopy. Surface modification of the PVA/PVPi particles was carried out with cationic and anionic groups via the Williamson ether synthesis. Ionic modification of these rigid spherical PVA/PVPi particles was carried out in order to study their adherence to cellulose fibres, compared to the adherence of similarly modified starches with cellulose fibres. Fluorescent labelling of the different modified particles was carried out using two complimentary coloured fluorescent markers. Fluorescence imaging and scanning electron microscopy (SEM) enabled the observation of particle– fibre and particle–particle interaction. Results indicated that the negative groups are sparse on the cellulose fibres, and therefore particles with low functionality but which are able change shape and conform and adhere to the surface of the cellulose fibres are required for effective adhesion. These modified spherical PVA/PVPi particles are unique as they mirror the chemistry of functionalised starch and cellulose particles, yet maintain their shape and have a fixed size, measurable by SEM and transmission electron microscopy (TEM). Field-flow fractionation was also used to characterise and measure these relatively large cross-linked and fixed diameter particles. / AFRIKAANSE OPSOMMING: In papierproduksie word vulstowwe en bymiddels gebruik om die eienskappe van papier te verbeter. In hierdie studie is sferiese poli(vinielalkohol) (PVA) partikels berei vir gebruik as vulstowwe. Om ten einde die meganisme van die bymiddelklewing aan die sellulose vesels (papier) te bepaal, is die oppervlakke van hierdie partikels gewysig met kationiese of anioniese groepe, om 'n oppervlak soortgelyk aan dié van funksionele poliëlektrolietbymiddels te verskaf. Die retensiemiddels wat gebruik word om die vesel–vesel en vesel–vulstof binding te verbeter is tipies in staat om te konformeer aan die oppervlak van die vesels en vulstowwe. Teenoorgesteldgelaaide komponente toon 'n sterk affiniteit vir mekaar, bv. kationiese poliëlektrolietgroepe is vasklewend aan die anioniesgelaaide oppervlakke van die vesel. Die sferiese PVA partikels is berei deur die verseping van sferiese poli(vinielpivalaat) (PVPi) partikels. Hierdie voorloper PVPi partikels, berei deur suspensiepolimerisasie, is gekruisbind met 'n divinieleter ko-monomeer. Die vinielpivalaat (VPi) suspensiepolimerisasie is suksesvol uitgevoer en relatief eenvormig verspreide sferiese PVPi partikels is berei, met deursnitte tussen 0.5–10 mm. Die gekruisbinde PVPi partikels is daarna gesaponifiseer in tetrahidrofuraan (THF) as oplosmiddel, om PVA met verskillende grade van verseping (DS) te berei. Die sferiese vorm raak verlore en veselagtige materiaal is verkry wanneer PVPi partikels met geen kruisbinding verseep is. Kruisbinding van die sferiese PVPi partikels (PVA voorloper) is voordelig en noodsaaklik om die sferiese vorm tydens die verseping tot PVA/PVPi te behou. Deur die tydsduur van verseping te verander, is verskeie grade van verseping verkry en bevestig deur vaste toestand KMR spektroskopie. Oppervlakwysiging van die PVA/PVPi partikels, om kationiese en anioniese groepe aan te heg, is uitgevoer via die Williamson etersintese. Ioniese wysiging van hierdie stram, sferiese PVA/PVPi partikels is uitgevoer om ten einde hul klewing met sellulose vesels te bestudeer en te vergelyk met die klewing van soortgelyk gewysigde stysels. Fluoressensie merking van die verskillende gewysigde partikels is uitgevoer met behulp van twee komplimentêre gekleurde fluoressensie merkers. Fluoressensie beeldvorming en SEM verskaf die waarneming van partikel–vesel en partikel–partikel interaksie. Die resultate dui daarop dat die negatiewe groepe van die sellulose vesels skaars is, en daarom is partikels met ‘n lae funksionaliteit, maar wat in staat is om van vorm te verander, aan te pas en te konformeer aan die oppervlak van die sellulose vesels, nodig vir effektiewe adhesie. Hierdie gewysigde sferiese PVA/PVPi partikels is uniek aangesien hulle die chemie van gewysigde stysel en sellulose partikels naboots, maar steeds hul vorm behou met 'n vaste grootte; meetbaar deur SEM en TEM. Veld-vloei-fraksionering is ook gebruik vir die karakterisering van hierdie relatief groot, stram, gekruisbinde partikels met bepaalde deursneë.

The relaxation characteristics of rubbery poly(ethylene oxide) [PEO] networks have been investigated as a function of network composition and architecture via dynamic mechanical analysis and broadband dielectric spectroscopy. A series of model networks were prepared via UV photopolymerization using poly(ethylene glycol) diacrylate [PEGDA] as crosslinker: variations in crosslink density were achieved either by the introduction of water in the prepolymerization reaction mixture, or by the inclusion of mono-functional acrylate such as poly(ethylene glycol) methyl ether acrylate [PEGMEA] or poly(ethylene glycol) acrylate [PEGA]. Copolymerization with mono-functional acrylate led to the insertion of flexible branches along the network backbone, and the corresponding glass-rubber relaxation properties of the copolymers (i.e., Tg, relaxation breadth, fragility) were a sensitive function of network architecture and corresponding fractional free volume. Relatively subtle variations in network structure led to significant differences in relaxation characteristics, and a systematic series of studies was undertaken to examine the influence of branch length, branch end-group, and crosslinker flexibility on viscoelastic response. Dielectric spectroscopy was especially useful for the elucidation of localized, sub-glass relaxations in the polymer networks: the imposition of local constraint in the vicinity of the crosslink junctions led to the detection of a distinctive fast relaxation process in the networks that was similar to a comparable sub-glass relaxation observed in crystalline PEO and in the confined regions of PEO nanocomposites. Gas permeation studies on the model PEGDA networks confirmed their utility as highly-permeable, reverse-selective membrane materials, and strategic control of the network architecture could be used to optimize gas separation performance. Dynamic mechanical and dielectric measurements have also been performed on a semicrystalline polyester, poly(trimethylene terephthalate) [PTT], in order to assess the influence of processing history on the resultant morphology and corresponding viscoelastic relaxation characteristics. Studies on both quenched and annealed PTT revealed the presence of a substantial fraction of rigid amorphous phase (RAP) material in the crystalline samples: dielectric measurements showed a strong increase in relaxation intensity above the glass transition indicating a progressive mobilization of the rigid amorphous phase with increasing temperature prior to crystalline melting.