Dendrimers are a class of perfectly branched symmetric monodisperse macromolecules, which are synthesized using a stepwise procedure. Due to their highly symmetric structure, they possess a definite core, discrete generations and a large number of terminal units. The large number of terminal units and its compact globular conformation endow this class of macromolecules with several unique properties. Over the past two decades, a number of researchers have synthesized a variety of dendrimers and explored their potential applications in various fields ranging from drug delivery, energy harvesting to catalysis. However, dendrimers require tedious stepwise synthesis and purification which limits their scalability. Hyperbranched polymers (HBPs) are a related class of macromolecules having similar highly branched structure but with large number of linear defects and, therefore, they may be considered as unsymmetrical analogues of dendrimers. Despite of having a large number of defects, HBPs display majority of the properties which dendrimers possess such as, high solubility, low chain entanglement, low solution and melt viscosity, encapsulation of guest molecules, conformational adaptability etc. The origin of these defects lies in the single-step statistical random growth process. Although, hyperbranched polymers possess a randomly branched structure, they also carry a large number of peripheral units, like dendrimers. Since, hyperbranched polymers are prepared in a single step, they can be readily scaled up which make them commercially attractive. One of the most widely used methods to prepare hyperbranched polymers is by polycondensation of a AB2 monomer. In our laboratory, during past decade a novel melt trans-etherification methodology was developed to prepare hyperbranched polyethers. For this method, a AB2 monomer was designed having two methoxy benzyl units and one aliphatic hydroxyl group, which in presence of a mild organic acid at 150°C undergoes melt polymerization under continuous removal of methanol. Although, this method allows one to prepare a variety of high molecular weight hyperbranched polyethers structures, it suffers from one serious limitation associated with the monomer structure; the aromatic ring in the monomer should be either electronically deactivated or per-substituted to preclude a side reaction due to electrophilic aromatic substitution, which could result in the formation of insoluble cross-linked product. Polyacetals are a class of polymers which readily degrades under mildly acidic conditions. One of the primary objectives of this thesis was to develop a simple strategy to prepare hyperbranched polyacetal, which would be a new class of highly branched acid-labile scaffold. To achieve this, we used a relatively under-explored chemistry based on trans¬acetalization. Solvent-free melt polymerization via trans-acetalization exhibited some advantages over the trans-esterification or trans-etherification processes; for instance, it required substantially low temperatures, afforded faster reaction rates and absence of side reactions that could lead to crosslinked products. In the 2nd chapter, the first synthesis of hyperbranched polyacetals via this novel melt trans-acetalization polymerization process has been described. The process proceeds via the self-condensation of an AB2 type monomer carrying a hydroxyl group and a dimethylacetal unit (see Figure 1); the continuous removal of low boiling methanol drives the equilibrium towards polymer formation. Here, since the incipient carbocation is stabilized by a neighbouring oxygen atom, it has a substantially lower reactivity and hence does not take part in the electrophilic aromatic substitution; therefore, per-alkylation of the monomer was not required to prevent crosslinking, unlike in the case of the melt trans-etherification process developed earlier. Figure1. Synthesis of hyperbranched polyacetals via trans-acetalization polymerization; different types of units, namely dendtritic (D), linear (L) and terminal (T) units are shown. We studied the degradation behaviour of the solid polymer in an aqueous buffer solution having a pH of 4. Due to the susceptibility of the acetal linkages to hydrolysis, the polymer degrades readily under these mildly acidic conditions to yield 4-hydroxymethyl benzaldehyde as the primary product. After observing the fast degradation kinetics of the hyperbranched polyacetal, we developed approaches to control the rate of degradation. Interestingly, because of the unique topology of hyperbranched structures, the rate of polymer degradation was readily tuned by changing just the nature monomer; longer chain dialkylacetals, such as dibutyl- and dihexylacetals based monomers yielded hyperbranched polymers bearing longer alkyl groups at their molecular periphery. The highly branched topology and the relatively high volume-fraction of the terminal alkyl groups resulted in a significant lowering of the ingress rates of the aqueous reagents to the loci of degradation and, consequently, the degradation rates of the polymers were dramatically influenced by the hydrophobic nature of the terminal alkyl substituents. In an effort to understand this, we performed the degradation studies in solution state, where all three polymers showed almost same rate of degradation. The simple synthesis and easy tuneability of the degradation rates make these materials fairly attractive candidates for use as degradable scaffolds. As already mentioned, the main difference between dendrimers and hyperbranched polymers is that HBPs carry a large number of statistically distributed linear defects. The origin of these linear segments is single step statistically random growth process. There are three kinds of linkages present in the HB structure. For a HB polymer generated from condensation polymerization of an AB2 monomer, these three kinds of linkages are: (i) the linkages where both the B groups have reacted is called a dendritic (D) unit, (ii) linkages where one of the B group has reacted is called a linear (L) unit, and (iii) linkages where both the B groups remain unreacted is called a terminal (T) unit. The defect levels in hyperbranched polymers is quantified by a parameter called degree of branching (DB), which is mole-fraction of dendritic and terminal units with respect to all types of repeat units. In a typical single step AB2 polycondensation process the DB value usually is around 0.5. The strategy most commonly used to achieve high DB values, specifically while using AB2 type self-condensations, is to design an AB2 monomer wherein the reaction of the first B-group leads to an enhancement of the reactivity of the second one. In the 3rd chapter the challenge of synthesizing defect-free hyperbranched polythioacetal has been addressed. In this study, it was shown that an AB2 monomer carrying a dimethylacetal unit and a benzyl thiol group undergoes a rapid self-condensation in the melt under acid-catalysis to yield a hyperbranched polydithioacetal (Figure 2a). By analyzing 1H, 13C, hetero-correlation NMR spectra and by comparison of the NMR spectrum of the polymer with those of model compounds, it was established that the HB polydithioacetals do not contain any linear defects. Furthermore, to understand the origin of defect-free structure, model reactions between dimethylacetal of tolualdehyde and benzyl mercaptan (Figure 2b) were carried out. NMR studies using of these model reactions reveal that the intermediate monothioacetal is relatively unstable under the polymerization conditions and transforms rapidly to the dithioacetal (Figure 2c); since this second step occurs irreversibly towards polymer formation, it leads to a defect-free hyperbranched dithioacetal. Isothermal TGA analysis proved to be an effective tool for monitoring the kinetics of the melt polymerization; these studies revealed that the formation of the polydithioacetal is significantly faster than previously studied polyacetal polymerization, and in the former case two distinct kinetic steps are clearly evident. Figure 2. (a) Synthesis of defect-free hyperbranched polythioacetal; chemical structure of monomer and hyperbranched polydithioacetal; (b) model reaction to probe the unstable intermediate, and (c) variation of the concentration of different species during the model reaction as a function of time showing the appearance and disappearance of unstable intermediate. One of the major differences between linear and hyperbranched polymers is the availability of large number of accessible terminal groups in the latter. Several properties of the hyperbranched polymers are known to be influenced by the nature of the peripheral groups. Of the many methods that have been designed to functionalize the periphery of HBPs, AB2 + A type copolymerization is one of the most readily implementable. Figure 3. (a) Peripheral modification of hyperbranched polydithioacetal using trans-thiocetalization; (b) schematic representation of the sulphur rich hyperbranched polythioacetal having C-22 alkyl chains on its periphery and (c) TEM images of gold nanoparticle synthesized and stabilized via C-22 functionalized hyperbranched polythioacetal. In chapter 3, the synthesis of a defect-free hypebranched polymer via trans-thiocetalization method was described; these polymers possessed only two kinds of units, namely terminal dimethylacetal groups and dendritic dithioacetal units. Because of the difference in reactivity between the dendritic (D) and terminal (T) units, the terminal groups alone was completely transformed, under acid-catalyzed conditions, to a dithioacetal unit by reaction with a variety of thiols, (Figure 3a) such as dodecanethiol, benzyl mercaptan, ethyl, 3-mercaptopropionate etc.; this transformation of the periphery was shown to be quantitative. One unique feature of this hyperbranched polydithioacetal is the high sulfur content; in order to exploit this aspect, the periphery was selectively transformed with docosyl (C-22) segments, and these sulfur-rich hydrophobically capped hyperscaffolds were utilized to stabilize gold nanoparticles in non-polar solvents (Figure 3b and 3c.) The Au-NPs, thus prepared, were characterized by UV-Visible spectroscopy and transmission electron microscopy; it was shown that, typically particles of about 4-5 nm were produced and they could be dried and readily re-dispersed in organic solvents. In the final chapter of the thesis, the first synthesis of photodegradable hyperbranched polyacetals via a melt trans-acetalization polymerization method is described. The AB2 monomer was designed to carry a dimethyl acetal unit, and a nitro group placed ortho to a hydroxymethyl group (Figure 4a). Self-condensation of this AB2 monomer under melt polymerization conditions gives rise to a hyperbranched polyacetal wherein each repeat unit contains a 2-nitrobenzyl linkage which is susceptible to photolytic degradation upon exposure to 365 nm light. Figure 4. (a) Synthesis of photodegradable hyperbranched nitro polyacetal; (b) scanning electron micrograph of the positive pattern obtained from hyperbranched nitro-polyacetal; (c) synthesis of alkyne-azide clickable hyperbranched nitro polyacetal; and (d) clicking onto the reactive micropatterns. Irradiation with UV light causes the photodegradation of the polymer leading to the formation of 2-nitroso terephthalaldehyde and other low molecular weight oligomeric species. Exploiting this photodegradability, the use of this HBP as a positive photoresist to generate micron-size patterns has been demonstrated (Figure 4b); furthermore, changing the terminal groups from dimethyl acetal to dipropargyl acetal (Figure 4c), permitted the generation of patterned substrates that can be clicked with any desired functionality using the azide-yne click reaction. This last feature is unprecedented and provides a potentially quick handle to create functionalizable patterned surfaces.

The highly branched hyperbranched polymers (HBPs) possess large inner space among the irregular branches and the inter-chain contacts inside the globular HBPs can be greatly inhibited. With the unique structural features, HBPs have good solubility in common organic solvent and reduced possibility to form excimer and aggregated species. On the other hand, the wholly aromatic polyquinolines are reported to have excellent thermal and oxidative stability. With the above superior properties, HBPs and polyquinolines are commonly used as emitting materials in light-emitting diodes (LEDs). Therefore, quinioline moiety was implanted into HBPS in this study to prepare materials with superior properties to be used in LED pplications. Four polyquinoline HBPs with different branching densities (designated as HBP-1 to -4 from low to high densities) were prepared and their optical, thermal, electrochemical properties and device performance were measured and analyzed. The rigid, wholly heterocyclic polyquinolines HBPs have excellent thermal stability with a high Tg (> 245 ¢J) and high decomposition temperature starting at 571 ¢J. The solution and the solid samples have similar UV-vis absorption and PL emission spectra. The resultant samples have high quantum efficiencies with the measured values ranged from 0.68 to 0.74. Most importantly, thermal annealing at high temperatures (> 200 ¢J) resulted in no changes on the corresponding photoluminescent and electroluminescent emission spectra, which indicates the high thermal and spectral stabilities of all HBP polyquinolines in this study.

Dendrimers are highly branched macromolecules which are prepared by a stepwise procedure. The presence of a well-defined core, discrete generations and a large number of terminal groups in dendrimers make them structurally very interesting and potentially useful for a wide variety of applications.1 Hyperbranched polymers,2 on the other hand, do not possess a unique core or discrete generations and they contain a large number of statistically distributed defects. Despite the presence of structural imperfections, studies have indicated that hyperbranched polymers capture many of the essential features of dendrimers, such as adoption of a compact conformation and the presence of a large number of readily accessible terminal functional groups. The first chapter of this thesis provides a brief introduction to hyperbranched polymers, with an emphasis on different methods for synthesizing them, followed by a discussion of the various approaches to control their molecular structural features, such as molecular weight, polydispersity, degree of branching, branching density, terminal end-groups, etc. One of the main objectives of the present study is to develop a simple synthetic strategy to generate peripherally functionalized (or functionalizable) hyperbranched polymers (HBP) that could potentially exhibit core-shell type behavior; in other words, polymers that carry segments of distinctly different solubility preferences within the core-region and the peripheral shell. To this end, in chapter 2 we describe the use of the melt-transetherification process,3 using an AB2 monomer along with a mono-functional A-R type comonomer, to directly generate core-shell type hyperbranched structures in a single step.4 Given that an AB2 monomer carries one equivalent excess of B functionality, copolymerization with an A-R type molecule bearing a single A functional group, readily permits the decoration of the periphery of the hyperbranched structures with these R-units. Thus, hyperbranched polyethers having polyethylene glycol (PEG) segments at their molecular periphery were prepared by a simple procedure wherein an AB2 type monomer was melt-polycondensed with an A-R type monomer, namely heptaethylene glycol monomethyl ether (HPEG). The presence of a large number of PEG units at the termini rendered a lower critical solution temperature (LCST) to these copolymers, above which they precipitated out of an aqueous solution.5 In an effort to understand the effect of various molecular structural parameters on their LCST, the length of the hydrophobic spacer segment within the hyperbranched core and the extent of PEGylation, were varied. Increase in the size and hydrophobicity of the hyper-core resulted in a continuous lowering of its LCST, while an increase in the level of PEGylation, increases the LCST, for a given size of the hyper-core. Additionally, linear analogues that incorporates pendant PEG segments were also prepared and comparison of their LCST with that of the hyperbranched polymer clearly revealed that the hyperbranched topology leads to a substantial increase in the LCST, highlighting the importance of the peripheral placement of the PEG units as shown in figure 1.5 This observation also provided an indirect evidence for the development of core-shell type topology in these peripherally functionalized hyperbranched structures. Figure 1. Transmittance of a 0.4 wt % aqueous solution of the linear and hyperbranched polymers as a function of temperature, measured at 600 nm. Such core-shell type HBPs could be also exploited both as unimolecular micelles and reverse micelles by suitably modifying the nature of the AB2 and A-R type monomers4. In the third chapter, the preparation and dye-encapsulation properties of unimolecular micelles as well as reverse micelles based on core-shell HBPs have been presented. In case of micelle forming polymers, an AB2 monomer carrying a decamethylene spacer was used along with heptaethylene glycol monomethyl ether (HPEG) as the A-R type comonomer. One the other hand, for the preparation of reverse micelle forming polymers, an AB2 monomer containing an oligo(oxyethylene) spacer was used along with cetyl alcohol as the A-R type comonomer as shown in scheme 1. The former was readily soluble in water while the latter was soluble in hydrocarbon solvents, like hexane. NMR spectral studies confirmed that both the approaches generated highly branched structures wherein ca. 65-70 % of the terminal B groups were capped by the A-R comonomer. scheme1. Synthesis of the unimolecular micelle and reverse micelle forming polymers using a one step AB2 + A-R type copolymerization. (REFER PDF FILE) One of the approaches commonly used to demonstrate core-shell behavior is to examine the ability of such polymers to encapsulate appropriate dyes from a suitable medium. In the case of the micelle-forming polymer, an aqueous solution of the polymer (6 μM) was sonicated in the presence of excess pyrene for varying periods of time. From the UV-visible spectra (Figure 2) of the aqueous solution (after filtration), it is evident that the saturation uptake is attained in about 7 h. Similar studies were also carried out for reverse-micelle forming polymers in hexane, using methyl orange as the dye. These dye-uptake studies, in conjunction with dynamic light scattering, unequivocally confirmed the formation of unimolecular micelles/reverse micelles. Figure 2. Absorbance as a function of sonication time for micelle-forming polymers (A), and absorbance as a function of the amount of solid dye taken, for reverse micelle-forming polymers (B). (REFER PDF FILE) Another novel approach to generate core-shell systems, using A2 + B3 + A-R type terpolymerization, was also explored in an effort to simplify the synthesis even further. However, dye-uptake measurements revealed that the polymers prepared via the AB2 + A-R approach exhibited a significantly larger uptake compared to those prepared via the A2 + B3 + A-R approach. This suggests that the AB2 + A-R approach generates hyperbranched polymers with better defined core-shell topology when compared to polymers prepared via the A2 + B3 + A-R approach, which is in accordance with previous studies6 that suggest that A2 + B3 approach yields polymers with significantly lower branching levels and consequently less compact structures. In chapter 4, different strategies for functionalization of the core-region and periphery of core-shell type hyperbranched polymers (HBP) using the “click” reaction7 have been explored. For achieving peripheral functionalization, an AB2 + A-R1 + A-R2 type copolymerization approach was used (as depicted in scheme 2), where the A-R1 is heptaethylene glycol monomethyl ether (HPEG-M) and A-R2 is tetraethylene glycol monopropargyl ether (TEG-P). A very small mole-fraction of the propargyl containing monomer, TEG-P was used to ensure that the water-solubility of the core-shell type HBP is minimally unaffected. Scheme 2. Preparation of a hyperbranched polyether having a few percent of propargyl groups at the molecular periphery and further click reaction to place fluorophores at the periphery. Similarly, to incorporate propargyl groups in the core region, a new propargyl group bearing B2-type monomer was designed and utilized in an AB2 + A2 + B2 + A-R1 type copolymerization, such that the total mole-fraction of B2 + A2 is small and their mole-ratio is 1:1 (Scheme 3). Further, using a combination of both the above approaches, namely AB2 + A2 + B2 + A-R1 + A-R2, hyperbranched structures that incorporate propargyl groups both at the periphery and within the core were synthesized. Since the AB2 monomer carries a C-6 alkylene spacer and the periphery is PEGylated, all the derivatized polymers form core-shell type structures in aqueous solutions. In order to ascertain and probe the location of the propargyl groups in these HBP’s, a fluorescent azide, namely azidomethyl pyrene, was quantitatively clicked onto these polymers and their fluorescence properties were examined in solvents of different polarities. Fluorescence spectra in water was unable to differentiate between the fluorophores present at different locations suggesting that the tethered pyrene at the end of a flexible oligoethylene oxide unit is probably tucked within the core-region because of its intrinsic hydrophobic nature. Scheme 3. Preparation of a hyperbranched polyether bearing a few percent of the propargyl groups within the core and further click reaction to place fluorophores in the core-region. The conventional melt-transetherification polymerization proceeds by continuous removal of methanol as volatile by product.3 The fifth chapter describes the design and development of a new AB2 monomer that carries two propargyloxy benzyl groups and one hydroxyl group, which underwent melt-transetherification condensation by exclusion of propargyl alcohol (instead of methanol) to generate a hyperbranched polyether containing numerous propargyl ether groups located on their molecular periphery as shown in scheme 4. These propargyl groups were readily “clickable” under very mild conditions with a variety of azides using the copper (I) catalyzed Huisgen type dipolar cycloaddition, popularly known as click reaction,7 to generate a range of functionalized hyperbranched polymers. The simplicity of the monomer synthesis, the solvent-free melt polymerization process and the mild conditions under which quantitative peripheral derivatization is achievable, makes this process ideally suited for the generation of hyperscaffolds onto which a wide range of functionalities could be placed. This turned out to be a rather remarkable extension of the melt transetherification polymerization that permitted the direct generation of peripherally clickable hyperbranched scaffold that, in principle, could be used to generate a wide range of interesting structures. Scheme 4. Synthesis of the hyperbranched polyether with clickable surface in a single step. (For structural formula pl refer pdf file)

Hydrogels have attracted interest as biomaterials due to their similarity to native tissue and extracellular matrix as well as their versatility and tunability. Each of these characteristics allows hydrogels to be used in a wide variety of biomedical applications including drug delivery, tissue engineering, and regenerative medicine. Poly(oligoethylene glycol methacrylate) (POEGMA) has been shown to possess attractive biological and thermoresponsive properties, serving as an alternative to both poly(ethylene glycol) (PEG) and poly(N-isopropylacrylamide) (PNIPAM) depending on the number of ethylene oxide repeat units in the POEGMA side chain. Our group has shown the versatility of POEGMA and has successfully developed hydrazide- and aldehyde-functionalized polymer precursors that form an injectable in situ gelling hydrogel. By engineering the precursor polymer structure and crosslinking density (i.e. number of reactive functional groups in the precursor polymers), the properties of these hydrogels can be tuned. Herein, a hyperbranched structure was incorporated into POEGMA precursors to control the physical and biological properties of hydrogels independent of the chemistry while maintaining gel injectability. By varying the degree of branching (DoB) in these precursors, it was possible to tune the hydrogel properties based on reacting combinations of hyperbranched-linear and hyperbranched-hyperbranched precursor polymers. While it was feasible to tune the mechanical properties of the hyperbranched hydrogels based on the DoB, the hyperbranched-hyperbranched system showed diminished mechanical strength when compared to the hyperbranched-linear system. Overall, the mechanical properties of the whole hydrogel series were comparable to previously reported linear POEGMA hydrogels. In terms of swelling and degradation kinetics, the swelling and degradation rate in both acid-catalyzed conditions and in phosphate-buffered saline (PBS) at physiological temperature (37°C) correlated with DoB and polymer size. The precursor polymers showed minimal cytotoxicity in the presence of 3T3 mouse fibroblasts. Lastly, each of the hyperbranched hydrogels adsorbed higher quantities of protein compared to PEG-based hydrogels, but still relatively low amounts compared to other polymeric biomaterials. We have shown that it is possible to significantly tune the physicochemical properties by slightly changing the polymer precursor chemistry, namely by varying the amount of crosslinker and, thus, the degree of branching in the polymer network. Therefore, hyperbranched POEGMA offers a versatile platform to create tunable hydrogels based on polymer precursor structure for biomedical applications. / Thesis / Master of Applied Science (MASc)

No description available.

Rheological modification is frequently cited as a key application for hyperbranched polymers. However, the high degree of branching in these polymers restricts entanglement and the resultant mechanical properties suffer. Longer distances between branch points may allow entanglements. Highly branched polymers, where linear units are incorporated between branch points, are synthesized with an oligomeric A2 plus a monomeric B3. Higly branched polymers differ from traditional hyperbranched polymers in that every monomeric repeating unit of a hyperbranched polymer is a potential branch point, which is not true for highly branched polymers. The oligomeric A2 plus B3 synthetic methodology was used for the synthesis of highly branched ionenes and polyurethanes. Highly branched ionenes, which have a quaternary ammonium salt in the main chain, were synthesized with a modified Menshutkin reaction. The oligomeric A2 was comprised of well-defined telechelic tertiary amine endcapped poly(tetramethylene oxide). Reduced mechanical properties were observed for highly branched polymers compared to linear counterparts. Highly branched polyurethanes were synthesized with polyether soft segments including poly(ethylene glycol), poly(tetramethylene glycol), and poly(propylene glycol). Degree of branching was determined via a novel 13C NMR spectroscopy approach, which is described herein. The classical degree of branching was supplemented with an alternative degree of branching equation, which was tailored for highly branched architectures. The melt and solution viscosities of highly branched poly(ether urethane)s were orders of magnitude lower than the linear analogs. For the first time, the presence of entanglements was confirmed for highly branched polymers. Doping the highly branched polyurethane with lithium perchlorate, a metal salt, resulted in a significantly higher melt viscosity. The ionic conductivity of the highly branched polyurethane when doped with a metal salt was orders of magnitude higher than the linear analog. Soybean oil was oxidized for synthesis of soy-based polyol monomers. Three regimes were determined, and for the first time, a correlation between hydroxyl number and a resonance from the double bonds of soybean oil in 1H NMR spectroscopy was described. The relationship was used to accurately describe oxidation of soybean oil with time, temperature, and air flow rate. Soybean oil oxidation was catalyzed, and tack-free films were formed. / Ph. D.

Poly(ethylene terephthalate) (PET) is an important commercial polyester and widely used as fibers, packagings, containers and engineering materials. It is believed that the incorporation of a low level of ionic groups into PETs dramatically improves the mechanical performance and compatibility with other substrates. However, polymers containing ionic groups always exhibit complicated behavior due to the presence of ionic aggregates in the organic matrix, and this thesis investigates the effect of backbone architectures on the properties of PET ionomers in detail. Three series of random and telechelic PET ionomers with equivalent molecular weights and ionic contents were synthesized using conventional melt polymerization. Solid state sodium NMR spectroscopy and melt rheological analysis demonstrated that the stability of ionic aggregates of telechelic ionomers decreased dramatically with an increase in temperature. A slightly branched structure resulted in high molecular weight ionomers bearing more than two ionic end groups. However, when the level of the branching reagent was lower than 3 mol%, the ionomers with flexible backbone (poly (ethylene terephthalate-co-ethylene isophthalate)) tended to form a high fraction of intramolecular aggregates at high temperatures. When the level of branching agent was higher than 3 mol%, the compact structures led to strong intermolecular aggregates. PEG endcapped PET and PET random ionomers were synthesized to investigate the effect of PEG end groups on the morphology and rheology of PET and PET ionomers. A small fraction of incorporated PEG end groups increased PET crystallization rate dramatically. Moreover, the PEG endgroups tended to aggregate on the surface of PET to result in a PEG rich layer, which improved the biocompatibility and decreased protein adhesion. The PEG end groups also plasticed the ionic clusters of PET ionomers to decrease melt viscosity, and resulted in a water soluble polyester. Hyperbranched polymers contain a well-defined plurality of peripheral functionalities. These functionalities subsequently serve as sites for further chemical modification or as templates for noncovalent intermolecular association. In most cases, hyperbranched polymers are prepared using a one-step polymerization process involving ABn monomers. A novel AB2 monomer, 4-(fluorophenyl)-4',4"-(bishydroxyphenyl) phosphine oxide, was synthesized. The monomer was successfully polymerized to a modest molecular weight with various catalysts, including K₂CO₃ and Cs₂CO₃/Mg(OH)₂. Moreover, an efficient approach to hyperbranched polyarylates via the polymerization of A2 and B3 monomers without gelation was also developed. A dilute bisphenol A (A2) solution was added slowly to a dilute 1,3,5-benzenetricarbonyl trichloride (B3) solution at 25 °C to prepare hyperbranched polyarylates in the absence of gelation. / Ph. D.

No description available.

RESUM Les reïnes epoxi constitueixen un dels polímers més emprats en el món de la industria, si bé presenten una sèrie d’inconvenients, els més importants dels quals són: la seva inherent fragilitat, la seva excessiva resistència tèrmica que en dificulta l’eliminació d’un substrat un cop finalitzada la seva vida útil i l’encongiment que experimenten durant el procés de curat. Per tal de reduir o eliminar aquests problemes aquesta tesi proposa l’ús de polímers hiperramificats així com polímers estrella i copolímers lineal-hiperramificat de bloc com a modificants químics de reïnes comercials. Amb aquesta estratègia s’han aconseguit millorar la tenacitat degut a efectes flexibilitzants o a separacions de fase del modificant en la matriu epoxídica, així com reduir l’encongiment en el curat o la degradabilitat de les reïnes, sense afectar altres propietats de la reïna com la seva Tg o la seva duresa. / ABSTRACT Epoxy resins are one of the most used polymers in the field of technological applications. However, they present some drawbacks being the most important the following: they are inherently brittle materials; they present excessive thermal resistance that limits their reworkability; and the shrinkage they experiment during curing. To overcome these problems this thesis proposes the use of hyperbranched polymers, as well as star polymers and lineal-hyperbranched block copolymers as chemical modifiers of commercially available epoxy resins. With this strategy tougher materials have been obtained due to either a flexibilizing effect or a phase separation of the modifier within the epoxy matrix. Moreover, the shrinkage on curing and the degradability of the thermosets have been improved without compromising other properties of the resin such as its Tg or its hardness.

The overall emphasis of this doctoral dissertation is on the design, synthesis, detailed characterization and application of amphiphilic hyperbranched fluoropolymers (HBFPs) crosslinked with poly(ethylene glycols) (PEGs) in complex polymer coatings as anti-biofouling surfaces. This dissertation bridges synthetic polymer chemistry, materials science and biology to produce functional coatings capable of fouling prevention, demonstrating thermo-controlled healing and acting as a benchmark surface to understand component:property relationships prior to increasing formulation complexities. A two-dimensional array of HBFP-PEG coatings was produced by the co-deposition of uniquely composed HBFPs with varying weight percentages of PEG. Bulk and surface properties were evaluated and assigned to formulation trends. Based on these findings, the most viable candidates were replicated and their fouling responses were assessed against three marine fouling organisms. An active mode of biofouling resistance was covalently grafted onto the surface of HBFP-PEG. The presentation of the settlement-deterrent molecule noradrenaline (NA) works in tandem with the highly-complex surface, to act as a dual-mode, anti-biofouling coating NA-HBFP-PEG. Secondary ion mass spectrometry (SIMS) was employed to quantify the extent of NA substitution. Biological assays against oyster hemocytes confirmed the activity of the grafted NA and cyprid settlement assays supported that the overall anti-biofouling ability of NA-HBFP-PEG was increased by 75%. Thermally-reversible crosslinks were installed as healable units throughout the framework of the networks, with the goal of generating coatings that could possess a greater resistance to mechanical failure. Small molecule and linear polymer models were probed by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC) to demonstrate the controlled reversibility of the crosslinks. Optical microscopy was employed to visualize surface scratch healing and fluorescence microscopy was used to identify the adsorption behavior of fluorescently-labeled proteins. A benchmark, anti-biofouling surface was generated through thiol-ene crosslinking of a linear fluoropolymer with pendant alkenes (LFPene) with pentaerythritol tetrakis(3-mercaptopropionate) (PETMP). Core constituents were evaluated spectroscopically and surfaces of LFPene-PETMP, along with two model surfaces that largely expressed a single component, were analyzed to understand how individual elements and blending contributed to the physical, mechanical and anti-biofouling properties to generate a performance baseline to compare against future generations.