Structural relaxation processes in poly(ethylene glycol) methacrylate macromonomers

Abstract

The investigation of the structural relaxation properties of poly(ethylene glycol) methacrylates are of practical interest, due to their ability to work as the inert backbone to which poly(ethylene oxide) oligomers can be attached to obtain highly amorphous polymeric matrices.Two poly(ethylene glycol) methacrylate, PEGMA, macromonomers, with different side chain lengths, are investigated by the dielectric technique, in the frequency range 0.3-300 kHz, and by Brillouin scattering. The analysis of the Brillouin spectra gives evidence for the existence of a relaxation process in both the systems. Furthermore, a comparison of the normalized absorption data with their corresponding classical values (deduced from the shear viscosity data) suggests that what the Brillouin scattering experiment detects is a dissipative relaxational process in which the shear viscosity plays the main role. The comparison of the Brillouin scattering results with the dielectric data shows that what we are observing, in both the systems, is a single relaxation process. The temperature dependences of the relaxation times, observed on more than 10 decades, fail to follow simple Arrhenian behaviours. Both the systems can be interpreted as intermediate between strong and fragile liquids, following the Angell classification, and appear characterized by the existence of a wide variety of local structural environments, triggered by some relaxation process. Such a situation is more clearly evidenced by the macromonomer with longer chain. From the whole body of experimental data, it can be deduced that shorter-sidechain PEGMA macromonomers are better candidates for the formation of highly amorphous comb-branched polymers.

Molecular mobility and fragility in n-ethylene glycol dimethacrylate monomers

“…For the greater TeE-GDMA molecule, the relaxation process is located at lower frequencies/higher temperatures. This same behavior is observed in dielectric measurements of polyalcohols [10], poly(propylene glycol) oligomers [9] and poly(ethylene glycol) methacrylate macromonomers with n ¼ 7 and 12 [29], where the dielectric loss peaks of the higher molecular weight materials are located at higher temperatures. Fig.…”

Structural Relaxation Processes in Polyethylene Glycol/CCl4 Solutions by Brillouin Scattering

“…The low-frequency process is related to micro-Brownian diffusive motions driving the glass transition of the system, whereas the fast process is described in terms of side-group or end-group rotations. [22][23][24][25]33,34 The low frequency process is too slow to contribute to the Brillouin doublet, arising due to the adiabatic pressure fluctuation time correlation function, and only gives rise to a not propagating local contribution to the depolarized Rayleigh scattering, related to the constant pressure density fluctuation (or entropy fluctuations) correlation function. [22][23][24] On this basis, we are confident that the observed process can be related to a local fast conformational structural relaxation of the polymeric chain that splits from the single high-temperature process when a crossover temperature, T C , is approached.…”

“…The observation of a relaxation phenomenon is not an unusual result for moderately viscous molten polymers or for polymeric solutions, ,− and it has been often assigned to the conformational rearrangements of the polymeric chains, triggered by the reorientation of the side groups. To analyze and identify the observed relaxation process, we have to find a theoretical formalism capable of describing the experimental temperature dependencies of the acoustic parameters.…”

Elastic properties of some selected two-monomer systems as studied by Brillouin spectroscopy

“…It seems that there exists an optimum viscosity for a given system at which maximum damping properties are observed. It is interesting, that for compositions containing higher amounts of the diluent, beyond the damping maximum, ˛ values decrease with increasing temperature showing that when the temperature is higher, the damping of the system is lower [10,[22][23][24][25][26][27]. This in turn leads to a conclusion that there exist a phase transition, which depends on system composition and temperature.…”