Thesis (Ph. D.)--Lehigh University, 1997. / Includes vita. Includes bibliographical references.

Ce travail de thèse porte sur la synthèse et la caractérisation d’élastomères réticulés réversiblement à base de polyisoprène et polybutadiène en vue de leur possible recyclage. Pour se faire, de longues chaines de polydiènes 1,4-cis ont été dégradées de manière contrôlée afin d’obtenir des polymères à faible viscosité. Dans un second temps, ces polydiènes ont ensuite été modifiés chimiquement soit le long ou soit aux extrémités des chaines afin d’obtenir des fonctions réactives de type alcool. Ces fonctions hydroxyles ont ensuite servi de point d’ancrage pour le greffage de fonctions furanes. L’addition d’un composé de type bis-maléimide au polymère liquide a alors conduit à la formation d’élastomère réticulé thermo-réversiblement grâce à la réaction de Diels-Alder entre les groupements furanes et maléimides. Les matériaux ainsi obtenus se comportement comme un élastomère réticulé stable dans une large gamme de température (- 80 °C à + 130 °C). Les propriétés mécaniques de ces élastomères (module de Young, contrainte/élongation à la rupture, module caoutchoutique) peuvent être facilement modulées en modifiant plusieurs paramètres comme la longueur des chaines, la densité de réticulation ou le lieu de réticulation (bout des chaines ou le long des chaines. La recyclabilité des matériaux a ensuite été montrée, aucune perte de propriétés n’a été observée même après 5 cycles de recyclage. Enfin, en changeant le type de liens réversibles par des groupements ureidopyrimidinones (UPy), nous avons observé que le matériel réticulé réversiblement par liaisons hydrogène obtenu possédait une organisation supramoléculaire particulière, induite par l’assemblage des groupements UPy. / This work focuses on the synthesis and characterization of reversibly crosslinked polyisoprene and polybutadiene and their potential recyclability. To this end, long chains of 1,4-cis polydienes have been degraded in a controlled manner in order to obtain telechelic polymers with low viscosity. In a second step, these low molar mass polydienes were chemically modified either along the backbone or at the chain-end of the polymer in order to obtain reactive functions. The thus obtained hydroxyl functions have been used as an anchor point for the grafting of furan functions. The addition of a bis-maleimide compound to the liquid polymer led to the formation of thermo-reversibly crosslinked elastomer thanks to the Diels-Alder reaction between the furan and the maleimide groups. The obtained materials have the behavior of a crosslinked elastomer, stable in a wide temperature range (-80 °C to + 130 °C). The mechanical properties of these elastomers (Young's modulus, strain / elongation at break, rubber modulus) can be easily modulated by modifying several parameters such as chain length, crosslinking density or crosslinking site along the chains. The recyclability of the materials was shown as no properties loss was observed even after 5 cycles of recycling. Finally, by changing the furan groups by ureidopyrimidinone groups (UPy), the reversibly crosslinked material obtained through hydrogen bonds possessed a totally different behavior with a particular supramolecular organization, induced by the assembly of the UPy groups.

Throughout the study of polymeric Langmuir monolayers at the air/water (A/W) interface, the Wilhelmy plate and Langmuir-Blodgett (LB) techniques along with Brewster angle microscopy (BAM) have been identified as key methods for acquiring structural, thermodynamic, rheological and morphological information. These techniques along with surface light scattering (SLS), a method for probing a monolayer's dynamic dilational rheological properties, will be used to characterize homopolymers, poly(ethylene oxide) (PEO) and poly(ethylene glycol) (PEG), and a new class of novel polymeric surfactants, telechelic (POSS-PEG-POSS) and hemi-telechelic (POSS-PEG) polyhedral oligomeric silsesquioxane (POSS) derivatives of PEG. PEO with number average molar mass, Mn > ~ 18 kg·mol-1 form stable spread Langmuir films at the A/W interface, while oligomeric PEG have ï -A isotherms that deviate from high molar mass PEO. Nonetheless, SLS reveals that the dynamic dilational viscoelastic properties of any Mn PEG(PEO) only depend on ï and not Mn. Likewise, POSS-PEG-POSS telechelics exhibit molar mass dependent ï -A isotherms, where low ï regimes (ï < 1 mN·m-1) have PEG-like behavior, but high ï regimes were dominated by POSS-POSS interactions. SLS studies reveal that the dynamic dilational moduli of POSS-PEG-POSS are greater than either PEO or an analogous POSS compound, trisilanolcyclohexyl-POSS. The ability to control rheological properties and the hydrophilic-lipophilic balance even allows one POSS-PEG-POSS (PEG Mn = 1 kg·mol-1) to form Y-type LB-multilayer films. For POSS-PEG systems, comparisons at comparable POSS:PEG ratios reveal short PEG chains (PEG Mn ~ 0.5 kg·mol-1) yield similar viscoelastic properties as POSS-PEG-POSS (PEG Mn ~ 1 kg·mol-1), while longer PEG chains (PEG Mn ~ 2 kg·mol-1) yield lower modulus films than comparable POSS-PEG-POSS. These differences are attributed to brush-like PEG conformations in short POSS-PEG versus mushroom-like PEG conformations in long POSS-PEG at the A/W interface. These results provide insight for designing PEG-based amphiphilic nanoparticles with controlled interfacial rheology. / Ph. D.

Thesis (MSc (Chemistry and Polymer Science))--Stellenbosch University, 2008. / Reversible addition fragmentation chain transfer (RAFT)-mediated polymerization has emerged as a versatile method for preparing polymers with control over molecular weight and polydispersity. Inherent in its mechanism is the retention of the chain transfer agent, the RAFT agent, at the polymer chain ends. Typically RAFT agents are made up of two parts, the so called R (leaving) and Z (thiocarbonyl thio, stabilizing) groups. These are retained as the a-and the w-end groups of the final polymer, respectively. RAFT polymerization offers a ready method for preparing polymers with well defined end functionalities. The a-end functionality can easily be built into the R group. The Z group, however, is thermally unstable and can impart color and smell to the polymer. Hence, two new methods for Z end group removal were introduced. Both methods take advantage of the facile reaction between thiocarbonyl thio compounds and radicals. By matching the functionalities of the R group (a-end group) with that of the end modified w-chain end, both methods offer an easy route to accessing telechelic functional polymers. End functional polymers have many important uses in industry and in the biomedical field. An alcohol functional xanthate RAFT agent was synthesized and successfully used to conduct the RAFT-mediated polymerization of N-vinylpyrrolidone (NVP). Characterization by NMR and MALDI ToF MS confirmed that a-hydroxyl-w-xanthate-functional PVP was easily produced. In the first end group modification method radicals were generated as in atom transfer radical addition (ATRA). A hydroxyl functional a-haloester was used as the ATRA initiator with a Cu catalyst system. The alkyl radical produced by this ATRA initiator then replaced the Z group giving a telechelic hydroxyl functional polymer. NMR analysis showed that the thiocarbonyl thio end group was completely removed. The hydroxyl functionality was quantified by derivatizing with trichloro acetyl isocyanate and subsequent analysis by NMR. MALDI ToF MS analysis, however, was inconclusive. In the second method the thiocarbonyl thio end group was removed by simply heating the polymer with hydrogen peroxide, thereby replacing the Z group with a hydroxyl end group at the w-chain end, giving a telechelic functional polymer. The telechelic hydroxyl functional polymer was subsequently crosslinked with a trifunctional isocyanate to make a PVP hydrogel. This confirmed that the end-modified polymer was indeed telechelic. The swelling kinetics of this hydrogel were determined in water at 37 oC.

The use of polymer brushes (long polymer chains anchored at their end to a surface or an interface) as a robust approach to control surface properties has generated significant interest in recent years. The stretched conformation of polymer brushes results in unique aggregation, phase, and dynamic behaviors, therefore, they have been used to stabilize colloidal particles and applied in numerous innovative biomedical applications: targeted magnetic hyperthermia, targeted drug delivery, and genotyping. The main goal of this thesis is to shed light on the key factors that affect the formation of these brushes in solution on solid surfaces. In Chapter 3, attenuated total reflectance infrared spectroscopy (ATR-IR) is used to directly measure the rates of the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions between alkyne-terminated polystyrene and poly(n-butyl acrylate) and azide-functional substrates in the good solvent DMF. Four regimes of behavior are observed: initially, the reaction rate is diffusion-controlled scaling with t^1/2; in the crossover regime at the onset of chain overlap, the rate scales with ln(t); the rate then accelerates briefly; and finally, in the terminal or penetration-limited regime, the logarithm of areal density scales linearly with time. Kinetic behavior in the diffusion-limited, crossover, and penetration-limited regimes corresponds well to the predictions of Ligoure and Leibler. The blob model suggests that the acceleration in rate is due to lateral chain contraction during the mushroom to brush transition. A theory is presented which predicts that the areal density at saturation should scale as Σsaturation ∼ MW^1.2 for good solvents, and experimentally we find MW^(−0.93±0.04) scaling. In Chapter 4, the effect of symmetry of the CuAAC reaction is investigated for the reaction of end-functional polystyrene and solid surfaces modified with self-assembled monolayers (SAMs). The polymer grafting density on azide-functional substrates is about two times higher than the polymer density on alkyne-functional surfaces. This asymmetry in the reaction density is caused by the difference in the mobility of the alkyne groups between the two systems. While the reaction stoichiometry requires one alkyne and one azide, the reaction mechanism involves two alkyne groups and one azide group in the formation of a stable triazole ring. When the alkyne groups are on the surfaces, their mobility is significantly reduced, preventing the formation of the triazole rings and consequently decreasing the amount of polymer grafted. Increasing the alkynes’ mobility by either extending the thickness of the alkyne monolayer or adding free 1-pentyne improves the polymer density on alkyne-functional silica substrates. The presence of free 1-pentyne also increases the polymer density on alkyne-functional wafers containing a preexisting polymer brush. This study shows that the placement of each functional group in the CuAAC reaction is important in surface modification applications. In Chapter 5, a universal model to quantify the amount of tails vs. loops during brush formation of telechelic polymers is proposed. This model involves the synthesis of telechelic polymers bearing a degradable unit in the middle of each chain via ATRP. Several reaction schemes are suggested for the synthesis of the required bi-functional ATRP initiators with degradable units. The amount of singly (tails) vs. doubly (loops) bound chains is quantified by comparing the brush heights, measured by ellipsometry, before and after degradation.

Copolymers are used to increase the interfacial strength of immiscible components and suppress recombination of the minor phase by steric hindrance. The experiments conducted in these studies are designed to investigate in situ polymer loop formation at soft interfaces and functionalized nanotube surfaces. Block copolymers are the most effective type of copolymer for compatibilization because they extend perpendicular to the interface, allowing good entanglement with the homopolymer chains. Multiblock copolymers are more effective than diblock copolymers for strengthening the interface because they can cross the interface multiple times, forming “loops” in each phase that provide entanglement points for the homopolymer. The first part of this dissertation focuses on understanding how telechelic variables influence their effectiveness to compatibilize an immiscible polystyrene (PS)/polyisoprene (PI) homopolymer blend. A fast reacting anhydride and amine telechelic pair (Anh-PS-Anh/NH2-PI-NH2) are compared with a slower reacting epoxy and carboxylic acid pair (Epoxy-PS-Epoxy/COOH-PI-COOH). Different molecular weight pairs are used to investigate the influence of end group concentrations and steric effects. We also investigate how the loading level affects the conversion of one telechelic pair. The PI telechelic has a fluorescent tag, which enables gel permeation chromatography (GPC) with fluorescence detection to be used for determining the amount of tagged PI converted and the molecular weight of the copolymer formed in situ as a function of mixing time. The effectiveness of these telechelic pairs as compatibilizers is quantified by annealing the samples and using scanning electron microscopy (SEM) to measure the domain size of the minor phase as a function of annealing time. The second part of this study investigates the grafting of polymer loops to carboxylated multiwall nanotube (COOH-MWNT) surfaces and determining the reaction rate. These polymer loops will improve the nanotube dispersion by steric hindrance and improve energy transfer by creation of polymer chain entanglements. Fourier transform infrared spectroscopy (FT-IR) is used as a novel technique to measure the quantity of Epoxy-PS-Epoxy grafted to the nanotube surface. In addition, we determined the fraction of telechelics that form loops by further reacting the grafted nanotubes with monocarboxy terminated poly(4-methylstryrene) (COOH-P4MS), which only reacts with unbound Epoxy-PS-Epoxy chain ends.

Telechelic polyesters have successfully been synthesized with lipase-catalyzed polymerization. The produced telechelics had a high degree of di­functionalization, high purity (requiring little or no workup) and controlled degree of polymerization. The syntheses were performed in one-pot one-step reaction systems. The use of protection/deprotection chemistry was not necessary, since the lipase selectivity was utilized in the syntheses. Two different types of lipase-catalyzed polymerizations were applied – ring-opening polymerization and polycondensation. In ring-opening polymerization telechelics were produced by a combination of initiation, α-functionalization, and linking through termination, w-func­tionalization. In polycondensation different types of end-cappers were used to synthesize telechelics. Several exampels of functional groups were used for end-functionalization - epoxide, methacrylate and tetraallyls. Enzyme kinetic schemes describing the different functionalization met­hods of polyesters are presented and discussed. Stoichiometry and different reaction conditions have been studied to understand the effects these functions have on the final structure of the synthesized telechelics. Polyesters are classified as biodegradable, and can also be synthesized from materials that can be extracted or fermented from renewable sources like plants. Lipase-catalysts have several beneficial attributes, like high selectivity, they are renewable and biodegradable, are non-toxic and metal-free and can operate under mild reaction conditions. The focus of this thesis has been on lipase-catalyzed syntheses and characterization of the produced telechelics, in addition some materials have been produced. Some uses of telechelics are surface modification, materials for block co-polymers, functional films and biomedical applications. / QC20100726

No description available.

Octafluorobiphenylene-linked bis(cyclopentadienone) was prepared bearing one perfluoro-4-tolyl and one tert-butyl substituent on the terminal diene rings. Polymerizations with 1,4- and 1,3-diethynylbenzene afforded linear Diels-Alder polyphenylenes (DAPPs) having lateral tert-butyl and perfluoro-4-tolyl substituents. The perfluoro-4-tolyl-substituted DAPPs are thermally stable, glassy solids (Tg ~ 230 deg C) that could not be cast into stable films (Mn ~ 10kDa, DPn ~ 10). New compounds perfluoro(1-phenyl-1-octanone) and perfluoro(1,1-diphenyl-1-octanol) were prepared from pentafluorophenylmagnesium bromide and perfluorooctanoyl chloride by nucleophilic acyl substitution and addition reactions. Diels-Alder reactions of 1,2-bis(nonafluorobiphenyl-4-yl)-4-tert-butylcyclopentadiene (CPD-1) with N-(4-fluorophenyl)maleimide (FMI) were explored as models for cyclopentadiene-maleimide-based Diels-Alder polymerizations. Mixtures of five endo/exo adducts were obtained, dependent upon CPD-1 tautomers present at reaction temperatures. The thermodynamic adduct (B3LYP/6-31G* geometry optimizations) was found to be the exo DA adduct of FMI and 2,3-bis(nonafluorobiphenyl-4-yl)-5-tert-butylcyclopentadiene. Five of the six possible isomers were observed and characterized including two by single-crystal X-ray diffraction. Parallel reactions of FMI and 1,2-bis(pentafluorophenyl)-4-tert-butylcyclopentadiene yielded three crystallographically characterized isomers, and with 1H NMR and 19F NMR spectrometry, including 1-D NOE, allowed five isomeric products to be identified. Diene CPD-1 is reactive toward nucleophiles (such as potassium 4-methylphenoxide) at the 4-positions of the C12F9 groups. Using this reactivity pattern, CPD-1 was polymerized with bis(phenol) A (BPA) and bis(phenol-A-6F) (BPAF) to form linear poly(arylene ethers) (Mn ~35 kDa) containing backbone cyclopentadienes. These polymers are glassy solids (Tg ~ 220 deg C) with good thermal stability (Td ~ 290 deg C), and they form stable, creaseable films cast from chloroform solutions. Treatment with 1.5-5.0% of 1,6-bis(N-maleimido)dodecane in N,N-dimethylacetamide (DMAc) at 165 deg C gave insoluble, solvent-swellable networks confirmed using ATR-FTIR. CPD-1 was also used as a cyclopentadiene-based linking group for chain extension of phenol-terminated methyl-PEEK oligomers (PEEKMOHs) with Mn values of 2, 5, and 10 kDa. These polymers are glassy solids (Tg ~ 156 deg C) with good thermal stability (Td ~ 400 deg C), that form stable, creaseable films from chloroform. Segmented polymers were treated with FMI in NMP, and showed functionalization density of approximately 50% by 19F NMR. Segmented polymers were also cross-linked by reaction of 1,6-bis(N-maleimido)hexane (cyclopentadiene to maleimide functional group ratio of 1:1) in NMP at 140 deg C. / Ph. D.

Novel poly(ethylene isophthalate) (PEI) and poly(ethylene terephthalate) (PET) polymers containing terminal units derived from sodio 3-sulfobenzoic acid (SSBA) were synthesized using catalyzed melt polymerization techniques. Various concentrations of the ionic end group, SSBA, were successfully incorporated in a telechelic fashion. For comparison, polyesters containing telechelic alkyl groups with controllable molecular weights were also synthesized. Furthermore, ionic copolymers of dimethyl isophthalate and trans-cyclohexane dicarboxylate, dimethyl isophthalate and dimethyl terephthalate were synthesized to study the influences of polarity and rigidity of the polymer chain backbone on material properties. Novel branched polyester ionomers using trimellitic anhydride were also prepared. In addition to modifying the polymer compositions, PET ionomers were blended with zinc stearate to investigate the effect of plasticizer on the melt processibilty of the ionomers. FTIR spectroscopy, which was used to quantify the sulfonate end groups for all of the ionomers, indicated an absorbance peak for the S-O stretching mode between 600-700 cm⁻¹. ¹H NMR spectroscopy was used to confirm the structure of the ionic and non-ionic polyesters, as well as to verify the presence of the terminal groups. By systematically varying the chemical structure of these ionomer model systems (i.e., altering the contents of ionic functional groups), detailed characterizations were carried out, wherein the ionic interactions/aggregations in the ionomers were found to play an important role in the resulting material properties. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) measurements were performed to study the effects of ionic groups and oligomer composition on the thermal properties of the polyesters. The glass transition temperatures of the ionomers revealed that the ionic interaction helped to maintain the structural integrity of the polymer chains, thus limiting their mobility. The dilute solution viscosity behavior of the ionomers exhibited upward curvature, which is a key characteristic of an ionomer. In PEI ionomers, the ionic aggregates formed at lower temperatures (<150 °C), while at higher temperatures (>150 °C), the ionic aggregations dissociated and behaved similarly to oligomers with lower molecular weights. Dodecanol was used as an effective end-capper to control the molecular weight of the non-ionic polyesters. In addition to telechelic ionic PEI and PET homopolymers, copolymers of poly(ethylene isophthalate-co-trans-1,4-cyclohexane dicarboxylate) (PEI-co-trans-CHDC) and poly(ethylene isophthalate-co-terephthalate) (PEIT) telechelic ionomers were also synthesized and characterized. Introducing trans-1,4-cyclohexane dicarboxylate into PEI ionomers decreased the polarity and packing regularity of the polymer chains. Also, the kinked-structure of dimethyl isophthalate reduced the regularity of the polymer chains in PET ionomers, thus reducing their propensity for rapid crystallization. Crystallization kinetics were studied for both ionic and alkyl telechelic polyesters, and resulting data revealed that the nature of the endgroup had a dramatic effect on crystallization from the melt state. The catalyst residue in the polymers also affected the crystallization rate for both ionic and non-ionic polyesters. With regard to the ionomers, antimony catalyst interacted with ionic aggregates, further increasing the crystallization rate. Branched PEI and PET ionomers showed an increase in melt strength. After blending with zinc stearate, the melt viscosity of the PET ionomers dropped dramatically. / Master of Science