Thermodynamic and mechanical properties of polymer-solvent systems

This work presents the results of theoretical and experimental characterization of thermodynamic, mechanical and transport properties in polymer solvent systems. The polymer solvent pairs considered ranged to those in which the polymer is rubbery, to those in which the initially glassy polymeric matrix is plasticized by the action of the low molecular weight species. Advanced Equation of State models have been adopted for thermodynamic modeling,along with a rigorous procedure that enables to extend their applicability to the non equilibrium, glassy region. Mass sorption kinetics had been modeled with phenomenological models and with advanced kinetic models.

Novel prototypes of electro-activated molecular machines

The work presented in this thesis deals with the investigation of new prototypes of molecular machines, based on rotaxane and pseudorotaxane architectures, by means of voltammetric and spectroscopic techniques. The discussion is divided in two parts. Part I concerns the investigation of electro-switchable molecular muscles, based on mechanically interlocked molecules. This study is performed on systems of increasing complexity, starting from [2]rotaxanes and arriving to polymers. In Chapters 3 and 4, [2]- and [3]rotaxanes, characterized by the presence of three stations for the macrocycle(s), are investigated. In both systems, the macrocycle(s) movement can be controlled through a combination of stimuli, resulting in a processive and directional motion. In Chapter 5, daisy chain rotaxanes, dimers of the [2]rotaxanes discussed in Chapter 3, are investigated. These systems can be switched between an extended and a contracted conformation, and they represent the monomeric units for the realization of polymeric molecular muscles. In Chapter 6, the properties of electro-switchable polymeric molecular muscles, composed by the daisy chains investigated in Chapter 5, are discussed. The repeating units of these poly-daisy chains contract and extend upon electrical stimulation, and this motion is expected to be transmitted to the polymer itself, resulting in an amplification of the effect. Part II concerns the investigation of rotaxanes and pseduorotaxanes based on heteroditopic calix[6]arenes and cationic guests. In Chapters 8 and 9, novel calix[6]arene macrocycles, functionalized with thiourea or dansyl units, and their related pseudorotaxanes are investigated. In both cases, the calix[6]arene functionalization adds new features to the pseudorotaxane. In Chapters 10 and 11, the influence of orientational isomerism on the properties of [2]- and [3]rotaxanes is investigated. The [3]rotaxanes discussed in Chapter 10 display similar properties, while the [2]rotaxanes described in Chapter 11, characterized by a calix[6]arene and a stilbazolium unit, exhibit distinct photophysical and photochemical properties.

Development of molecular-level switches and implementation into novel nanostructures and smart materials

The work presented in this thesis deals with the design, synthesis and investigation of (supra)molecular switches, and their implementation into novel nanostructures and smart devices. Part A deals with investigation of fundamental properties of Donor Acceptor Stenhouse Adducts (DASAs) as well as their implementation into polymer matrices in order to construct novel smart materials. Part B deals with the implementation of azobenzene photoswitches into pseudorotaxanes and the investigation of the effect of light-driven isomerization on the self-assembly and disassembly processes.