A series of rigid-rod polyesters with flexible alkoxy side chains of different length has been studied in order to determine the structure and properties of the polymers in various states (solid state, mesophase, melt). Various supermolecular structures can be obtained depending on the length of the side chains and on the preparation conditions of the samples. The relaxation behavior of the polymers has been investigated by dynamic mechanical measurements. Complex relaxation spectra have been observed, and types of molecular motions and structural rearrangements have been assigned to the observed mechanical relaxation transitions. The rheological behavior was studied in the mesophase and in the melt. In some polymers typical liquid-crystalline properties have been observed, as for example the flow-thinning effect. Large deformation of polymer films as well as the structure and mechanical strength of oriented samples have also been studied.
International audienceFree radical polymerization of styrene was monitored in situ by combining Raman spectroscopy to other experimental techniques (gravimetry and rheology). Three different processes were investigated: bulk, emulsion and miniemulsion polymerization. A complete analysis of the evolution of Raman spectrum during the course of reaction showed that a lot of information about molecular dynamics could be extracted and related to chemical phenomena. In addition, we report for the first time the coupling of Raman spectroscopy to a rheometer in order to monitor styrene bulk polymerization both at the scale of chemical bonds and at the scale of macroscopic phenomena (viscosity variation)
Because of the importance of the maltenepolymer interaction for the better performance of polymermodified asphalts, this article reports the effects of the molecular characteristics of two commercial poly(styreneblock-butadiene-block-styrene-block) (SBS) polymers and their partially hydrogenated derivatives [poly{styrene-block[(butadiene) 1Àx -(ethylene-co-butylene) x ]-block-styreneblock} (SBEBS)] on the morphology and rheological behavior of maltene-polymer blends (MPBs) with polymer concentrations of 3 and 10% (w/w). Each SBEBS and its parent SBS had the same molecular weight and polystyrene block size, but they differed from each other in the composition of the elastomeric block, which exhibited the semicrystalline characteristics of SBEBS. Maltenes were obtained from Ac-20 asphalt (Pemex, Salamanca, Mexico), and the blends were prepared by a hot-mixing procedure. Fluorescence microscopy images indicated that all the blends were heterogeneous, with polymer-rich and maltene-rich phases. The rheological behavior of the blends was determined from oscillatory shear flow data. An analysis of the storage modulus, loss modulus, complex modulus, and phase angle as a function of the oscillatory frequency at various temperatures allowed us to conclude that the maltenes behaved as pseudohomogeneous viscoelastic materials that could dissipate stress without presenting structural changes; moreover, all the MPBs were more viscoelastic than the neat maltenes, and this depended on both the characteristics and amount of the polymer. The MPBs prepared with SBEBS were more viscoelastic and possessed higher elasticity than those prepared with SBS.
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