Hybrid macrocycles, which chimerically integrate multiple chemical compositions and architectures, provide an effective way to impart new properties to polymers that are not found in their linear or homocyclic analogues. This dissertation addresses the incorporation of hydrophilic blocks into hydrophobic polymer, as either a poly(dimethyl siloxane)-block-poly(oxyethylene) (PDMS-POE) tadpole with a hydrophobic head and a hydrophilic tail or as a diblock poly(styrene)-block-diethylene glycol (PS-DEG) hydrophobic-hydrophilic macrocycle. The supramolecular association properties of both kinds of cycles were studied: the PDMS-POE tadpoles in forming micelles, and the PS-DEG macrocycles in threading with linear polymer to form polyrotaxanes. For the PDMS-POE macrocycle, linear alpha,omega-dihydroxy PDMS was cyclized under dilute conditions with dichloromethylhydrosilane as a linking group to produce hydrosilane-functionalized cyclic PDMS. This was joined to alpha-methoxy,omega-allyl POE via a free radical hydrosilylation reaction to produce the hybrid tadpole macrocycle, which was analyzed by GPC, DSC, and 1H, 13C, and 29Si NMR spectroscopy. Supramolecular aggregation consisting of the formation of micelles under both polar and nonpolar conditions was studied by surface tensiometry and quasielastic light scattering. For the PS-DEG macrocycle, linear alpha,omega-dihydroxy PS was prepared by ATRP polymerization of styrene, followed by reaction with KOH to give hydroxyl endgroups. The linear PS was then cyclized under dilute conditions with diethylene glycol ditosylate, and the product was analyzed by GPC, MALDI-TOF MS, DSC, and 1H, 13C and DOSY NMR spectroscopy. The macrocycle was then statistically threaded with linear PS to give the supramolecular structure poly(styrene)-rotaxa-cyclo[poly(styrene)-block-diethylene glycol]. Characterization was performed with DOSY NMR to verify that the product was threaded, and 1H NMR was collected to determine that the product was 13% macrocycle by weight. DSC showed only one Tg, indicating that the linear and cyclic species were present in the same phase.

Biomaterials have evolved over the years from the passive role of mere biocompatibility to an increasingly active role of presenting instructive cues to elicit precise responses at the molecular and cellular levels. Various characteristics common to synthetic biomaterials in vitro and extracellular matrices in vivo, such as immobilized functional or peptide groups, mechanical stiffness, bulk physical properties and topographical features, are key players that regulate cell response. The dynamics in the cell microenvironment and at the cell adhesive interface trigger a web of cell-material and cell-cell information exchanges that have a profound impact in directing the ultimate cell fate decision. Therefore, comprehension of cell substrate interactions is crucial to propel forward the evolution of new instructive biomaterials. Combinatorial biomaterials that encompass a wide range of properties can help to recapitulate the complexity of a cell microenvironment. The objective of this research was to fabricate combinatorial biomaterials with properties that span wide ranges in both surface chemistries and mechanical moduli. These materials were based on polydimethyl siloxane (PDMS), an elastomeric silicone biomaterial with physiologically relevant stiffness. After developing these mechano-chemical gradient biomaterials, we conducted high throughput screening of cell responses on them to elucidate cell substrate interactions and material directed behaviors. Our central hypothesis was that materials encompassing monotonic gradients in mechanical elastic modulus and orthogonal surface chemistry gradients could be engineered using the soft biomaterial, polydimethyl siloxane (PDMS) and that these gradient biomaterials would evoke a varied cell response. Furthermore, we expected high throughput screening of cell-material interactions using these materials would elucidate patterns and thresholds of synergy or antagonism in the overall cell response to the increased complexity presented by combinatorial materials. First, reproducible gradients in surface chemistry were generated on PDMS through surface modification techniques. Cell response to PDMS surface chemistry gradients was then screened in a rapid high throughput manner. Additionally, characteristics of the adhesive interface were probed to understand its role in cell response. Finally, a 2D combinatorial gradient with a gradient in mechanical elastic modulus and an orthogonal gradient in surface chemistry was fabricated with PDMS. High throughput screening of the synergistic influence of the varied mechanical and biochemical extracellular signals presented by the combinatorial biomaterial on cell response was conducted in a systematic manner. This research demonstrates the fabrication of combinatorial biomaterials with a wide range of mechanochemical properties for rapid screening of cell response; a technique that will facilitate the development of biomaterial design criteria for numerous biomedical engineering applications including in vitro cell culture platforms and tissue engineering.

Récemment, une nouvelle technique pour renforcer les élastomères acryliques non chargés a été développée. L'élastomère a été préparé par séquences de gonflement par du monomère acrylique et polymérisation radicalaire en faisant des réseaux interpénétrés. Le prétirement des chaines du premier réseau créent des liaisons sacrificielles qui améliorent de manière significative les propriétés mécaniques de l’élastomère sans modifier sa Tg. Il est donc intéressant d’étendre cette méthode à d’autres familles d’élastomères. Ainsi, dans cette étude, la stratégie des réseaux interpénétrés a été appliquée à deux matériaux intéressants. Premièrement, un élastomère silicone a été synthétisé en utilisant une polymérisation par polycondensation par réaction d'hydrosilylation qui est significativement différente de la polymérisation utilisée pour les réseaux acryliques. Les réseaux multiples ont été ensuite synthétisés en gonflant ce réseau avec des précurseurs de petite masse et un faible pourcentage de réticulant D4H. Ces réseaux multiples en silicone ont les propriétés d’un élastomère classique, avec une énergie de rupture améliorée d’environ 100%. Deuxièmement, des particules coeur-ecorce formés de copolymères dibloc amphiphiles de poly(acide acrylique)-b-poly(acrylate de n-butyle) ou PAA-b-PBA ont été synthétisés par auto-assemblage simultané par polymérisation RAFT et préparés sous la forme de films. Ensuite, les films ont été utilisés comme des charges polymères en poly (acrylate de butyle) en utilisant une technique de réseau interpénétrés multiples. Nous avons réussi pour la première fois à renforcer l'élastomère par des particules de latex. Grâce à cette stratégie d'interpénétration qui distribue des particules de latex de manière très homogène dans l’élastomère, les films interpénétrés montrent de bonnes caractéristiques mécaniques, une résistance à la fracture et une ténacité extrêmement élevées en utilisant moins de 1% de PAA vitreux et pas de réticulant ajouté dans la particule renforçante. / Recently, a new technique to reinforce unfilled acrylic elastomers has been established. The elastomer was prepared by sequential free radical polymerization and swelling of acrylic monomers making interpenetrated networks. By introducing sacrificial bonds, the elastomer had significantly enhanced mechanical properties without changing the Tg of the material. We extended this method to two different elastomeric system to probe its generality. First, a silicone elastomer was synthesized by using polycondensation polymerization via a hydrosilylation reaction which is significantly different from the free radical polymerization used for acrylic networks. The multiple networks were synthesized by sequential swelling and polymerization steps with low molecular weight preducrosrs and a small amount of D4H crosslinker. The resulting silicone multiple networks were fully elastic elastomer with a mechanical toughness improved by about 100%. Second, core-shell latexes made of amphiphilic diblock copolymers Poly(acrylic acid)-block-poly(butyl acrylate) or PAA-b-PBA were synthesized by RAFT polymerization induced self-assembly and prepared into thin films. Different types of core-shell latexes and crosslinked latexes were synthesized and characterized both in the aqueous state and in the dry film state. The films were then used as a polymeric filler to a poly(butyl acrylate) by using the interpenetrated network technique. We succeeded for the first time to reinforce elastomers by latex particles. Thanks to interpenetrated networks strategy which distributed homogenously latex particles though the entire material, the interpenetrated films show extremely enhanced mechanical characteristics, fracture energy and toughness by using less than 1 % of glassy PAA content and no crosslinker in the reinforcing particles.

Carbon nanotubes (CNT) and graphene have been one of the noticeable research areas in science and technology. In recent years, the assembly of these carbon nanostructures is one of the most interesting topic to the scientific world due to its variety of applications from nano to macroscale. These bulk nanostructures to be applicable in shock absorbers, batteries, sensors, photodetectors, actuators, solar cells, fuel cells etc. The present work is motivated to study the detailed compressive behavior of three dimensional cellular assemblies of CNT and graphene. The CNT foams are synthesized by chemical vapor deposition method. It is interesting to study the compressive behavior of CNT foam in the presence external magnetic field applied perpendicular to CNT axis. The peak stress and energy absorption capability of CNT foam enhances by four and nearly two times in the presence of magnetic field as compared to the absence of the magnetic field. In the absence of magnetic field the deformation of CNT foam is obtained elastic, plateau and densification regions. Further CNT foam is loaded with iron oxide nanoparticles of diameter is ~ 40nm on the surface and detailed study of the compressive behavior of the foam by varying iron nanoparticles concentration. The peak stress and energy absorption capability of CNT foam initially decreases with increasing the intensity of the magnetic field, further increases the intensity of the magnetic field the maximum stress and energy absorption capability increases which is due to magnetic CNT and particles align in the direction of the magnetic field. CNT surfaces were further modified by fluid of different viscosities. The mechanical behavior of CNT foam filled with fluids of varying viscosities like 100%, 95% and 90% glycerol and silicone oil are 612, 237, 109 and 279 mPa-s respectively. The mechanical behavior of CNT foam depends on both the intensity of magnetic field and fluid viscosity. The non linear relation between peak stress of CNT and magnetic field intensity is σp(B, η) = σ0 ± α(B-B0) where σ0 is the peak stress at B = B0 , η is the fluid viscosity, parameter α depends on properties of the MR fluid and B0 is an optimum magnetic field for which peak stress is maximum or minimum depending on the fluid viscosity. Graphene is assembled into a three dimensional structure called graphene foam. The graphene foam is infiltrated with polymer and study the detailed compressive behavior of graphene foam and graphene foam/PDMS at different strains of 20, 40, 60 and 70%. The maximum stress and energy absorption capability of graphene foam/PDMS is six times higher than the graphene foam. Also the graphene foam/PDMS is highly stable and reversible for 100 cycles at strains of 30 and 50%. The mechanical behavior of CNT, graphene foam, CNT/PDMS and graphene foam/PDMS is compared. Among all the foams, graphene foam/PDMS has shown the highest elastic modulus as compared to other foams. This behavior can be attributed to the wrinkles formation during the growth of graphene and a coupling between PDMS and interfacial interactions of graphene foam. Therefore it suggests potential applications for dampers, cushions and electronic packaging. Furthermore, the interaction between nanoparticles and polymer in a novel architecture composed of PDMS and iron oxide nanoparticles is studied. The load bearing capacity of uniform composites enhanced by addition of nanoparticles, reaching to a maximum to 1.5 times of the PDMS upon addition of 5wt.% of nanoparticles, and then gradually decreased to 1/6th of PDMS upon addition of 20wt.% of nanoparticles. On the other hand, the load bearing capacity of architectured composites at high strains (≥40%) monotonically increased with addition of nanoparticles in the pillars.