Dielectric relaxations of Acrylic-Polyurethane hybrid materials

Abstract

In this work we present a dielectric relaxation study of Acrilyc/Polyurethane polymers synthesized via miniemulsion photo-polymerization. Three different samples, both parts of the synthesized hybrid latex (SOL and GEL fractions) and a full acrylic sample as reference have been considered. Besides dielectric experiments using broadband Dielectric Spectroscopy (BDS) technique, complementary Differential Scanning Calorimetry measurements have been performed. The thermodynamic characterization outcomes evidence very similar characteristics of the glass transition phenomena among the investigated samples without any signature of melting/crystallization. However BDS experiments show three well resolved dielectric relaxation processes above Tg, two of them evidence marked differences among the samples. A detail study allows us to provide a molecular origin for these three dielectric relaxation processes in connection with the sample characteristics. In particular, our results show that the characterization of these hybrid Acrylic/PU by BDS can provide access to some of the structural features that would ultimately influence the adhesives properties.

Dielectric relaxation analysis of hybrid acrylic–polyurethane gels

“…In order to understand the differences exhibited by the network relaxation it is useful to recall the molecular interpretation obtained for the dielectric relaxation of these polymers. It was previously reported [10] that Acrylic-PU samples present mainly three different dielectric relaxations, the α-relaxation, the dangling chain relaxation and the network relaxation. The dipolar entities responsible for the α-relaxation were attributed to segments of the acrylic main chains.…”

“…Finally, the network relaxation process was reported to be originated by the presence of orientationally correlated urethane-segment bundles belonging to PU chains linked by both ends to the acrylic main chain and forming the gel network. The presence of such large molecular entities responsible for the relaxation phenomena was inferred by the high values of both the dielectric strength and the limiting high temperature relaxation time [10]. Now, when comparing the values of τ max obtained for the network relaxation in the three gel samples at 400 K, we see that Gel A and Gel C show both values close to 5 ms and that τ max is nearly a factor of 5 smaller for Gel B (see Figure 4).…”

“…Due to the relative narrow range of time scales available for each relaxation process, the accurate determination of the three parameters of the VFT by a free fitting is not feasible. Thus, we fixed the value of T 0 to that determined previously for the α-relaxation time of Gel B (T 0 = 158 K) [10]. Since, as commented above, the segmental dynamics is not sensitive to the distinct network characteristics of our samples, using the same value of T 0 for all samples is well justified.…”

“…Making use of broadband dielectric spectroscopy (BDS) technique we have already reported a suitable molecular interpretation for the dielectric relaxation phenomena in the gel and sol fractions of a characteristic latex obtained via miniemulsion photo-polymerization [10]. With this information at hand, in this work we study three distinct gel fractions corresponding to hybrid Acrylic-Polyurethane latexes synthesized with different initial conditions.…”

Physical properties and dielectric behavior of the poly(urethane‐urea) based on o‐dianisidine and renewable cross‐linkers

“…39,40 The electrical properties of polyurethanes and poly(urethane-urea) are important and are studied in order to obtain intelligent polymeric materials with electrical properties determined by the frequency and intensity of the applied electric field. 7,41 Previous results 42,43 have indicated that the dielectric constant and the dissipation factor of the polyurethanes are dependent both on the orientation of the dipole of the hard and soft segments, but also on their microstructure. Dielectric spectroscopy is used for the investigation of the molecular dynamics of the polyurethanes and poly(urethane-urea) with polar structure in very broad range of frequencies.…”