| Polymers display amazing physical properties compared to smaller molecules. Some, like poly(N-isopropylacrylamide) are studied for many years because they undergo a phase separation in aqueous medium when the temperature is raised above the transition temperature. They are soluble in cold water and phase separate when temperature is raised above a critical value. Even if this polymer has caught the attention of scientists, there are others that behave similarly. It is the case with poly(N,N-diethylacrylamide) which is the subject of this thesis.; The synthesis and characterization of homopolymers with N,N-diethylacrylamide has been done to study the influence of the molecular weight on the phase transition temperature and thermodynamic parameters. Fractionation of the polymer has been done in order to obtain samples having molecular weights ranging from 10 000 to 1 000 000 g/mol. Transition temperatures were measured using turbidimetry and differential scanning calorimetry. The results show a decrease in the transition temperature, enthalpy and entropy of mixing when the molecular weight increases. The influence of the concentration has also been studied.; Other studies have been done on PDEA using rheology, dynamic light scattering and a new technique of two dimensions Fourier transform rheology named LASSO (Large Amplitude Step Shear Oscillation). These techniques have allowed us to observe the coil-to-globule transition occurring at the phase transition. The globules can then aggregate and precipitate if the concentration and the molecular weight are high enough. Two dimensional Fourier transform rheology was used to measure and understand nonlinear rheological phenomena in such a system. |
