Dielectric relaxation spectroscopy in crosslinked polyurethanes based on polymer polyols (original) (raw)
Related papers
Comparative dielectric studies of segmental mobility in novel polyurethanes
e-Polymers, 2004
Molecular dynamics in selected novel linear/low-branched polyurethanes (PUs), based on oligo(oxytetramethylene glycol), 4,4'-diphenylmethanediisocyanate (MDI) or 2,6-toluenediisocyanate (TDI), and unsymmetrical dimethylhydrazine (I) and a derivative of that (II) as chain extenders (CE), were studied by dielectric techniques. Special attention was paid to the investigation of the α relaxation, associated to the glass transition, by dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization currents (TSDC). The TSDC method was used to study the interfacial Maxwell-Wagner-Sillars (MWS) relaxation, related to the accumulation of charges at the interfaces between soft-segment and hardsegment microdomains. The results obtained by DRS and TSDC were in good agreement with each other and in reasonable agreement with results for the microphase separation (MS) obtained by small-angle X-ray scattering and differential scanning calorimetry. TSDC proved to be an attractive complementary technique to DRS for the study of MS in PUs. The results suggest that the position of the MWS band, as well as its separation from the α band, is a good measure of the degree of MS. As regards the PUs studied here, the degree of MS enhances by increasing the mole ratio of CE, and by replacing MDI by TDI or CE I by CE II.
Phase behavior and molecular mobility in polyurethane/styrene-acrylonitrile blends
Journal of Applied Polymer Science, 2001
Differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) techniques, dielectric relaxation spectroscopy (DRS), and dynamic mechanical thermal analysis (DMTA), covering together a wide range of temperatures and frequencies, were employed to investigate molecular mobility and microphase separation in blends of crosslinked polyurethane (PUR) and styrene-acrylonitrile (SAN) copolymer, prepared by reactive blending with polymer polyols. The results by each technique indicate that the degree of microphase separation of PUR into hardsegment (HS) microdomains and soft-segment (SS) microphase increases on addition of SAN. The various techniques were critically compared to each other, with respect to their characteristic time and length scales, on the basis of activation diagrams (Arrhenius plots). The results show that for the dynamic glass transition of the PUR SS microphase the characteristic time scales at the same temperature are similar for DMTA, DSC, and TSDC and shorter for DRS. In terms of fragility, the PUR/SAN blends are classified as fragile systems.
Thermochimica Acta, 2001
The thermal, thermomechanical and thermal-dielectric properties of polyurethane blends based on branched polymer polyol (PUR) and styrene±acrylonitrile (SAN) copolymer were studied by differential scanning calorimetry (DSC), thermomechanical analysis (TMA), thermally stimulated depolarization currents (TSDC) techniques and dielectric relaxation spectroscopy (DRS). Several molecular mobility mechanisms associated with secondary local relaxations, primary (main) relaxations due to the dynamic glass transition and conductivity effects were observed and studied in detail. The use of several molecular mobility techniques, characterized by various spatial and time scales, allowed for several intercomparisons, in particular with respect to the determination of glass transition temperatures and of the temperature dependence of relaxation times which indicate the advantages and the limits of each particular technique. The results by the different techniques suggests in agreement to each other, that on addition of SAN the microphase separation between hard segment (HS) microdomains and soft segment (SS) microphase of PUR is improved. #
Microphase separation in ion-containing polyurethanes studied by dielectric measurements
Acta Materialia, 2004
Ac dielectric relaxation measurements, thermally stimulated depolarization currents (TSDC) measurements, and differential scanning calorimetry (DSC) measurements, were employed to investigate the dielectric properties in relation to the microphase separation in blends of an anion containing polyurethane (PU 1 ) and polyaminourethane (PU 2 ). The temperature at which a-and Maxwell-Wagner-Sillars relaxation appear in the TSDC plots and the magnitude of these relaxations are strongly affected by the degree of microphase separation (DMS) of the ionomer blends. The results, of the various techniques, were compared to each other with respect to their characteristic, and indicate that the DMS decreases on addition of the pure component PU 2 to the blends. Analysis of the a-relaxation, in terms of fragility, indicates that the systems under investigation are fragile. Results indicate a correlation between fragility and DMS. Lower phase mixing suggests higher fragility.
Dielectric relaxations of Acrylic-Polyurethane hybrid materials
Polymer, 2015
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.
Thermal and dielectric properties of polycarbonatediol polyurethane
Journal of Applied Polymer Science, 2015
The dielectric relaxation behavior of segmented polyurethane has been studied using Broad-Band Dielectric Spectroscopy in the frequency domain, 10 22 to 10 8 Hz, and in the temperature range of 2120 to 140 C. The spectra show three secondary processes (d, c, and b) followed by the a relaxation and conductive processes. The Havriliak-Negami (HN) phenomenological equation was used in order to characterize all the processes. The d, c, and b relaxations are probably associated with (i) local motions of the main chain (ii) motions of the carbonate group in the soft phase and (iii) reorientational motions of water molecules. The microphase separated morphology associated with soft and hard domains is reflected in the dielectric spectra, at high temperatures, by the presence of the Maxwell-Wagner-Sillars (MWS) interfacial polarization process.
Dielectric and hydration properties of segmental polyurethanes
e-Polymers, 2004
Novel polyurethanes (PUs), based on oligo(oxytetramethylene glycol), 4,4'-diphenylmethanediisocyanate and 1,1-dimethylhydrazine as chain extender, were prepared in a two-step process. The ratio prepolymer (PP) to chain extender (CE) was systematically varied in extreme ranges, from 1:1 to 10:1. Dielectric relaxation spectroscopy and thermally stimulated depolarization currents (TSDC) techniques were employed to investigate molecular dynamics and to conclude on microphase separation (MS). In that respect TSDC was proven to be very powerful, in particular as far as the investigation of the interfacial Maxwell-Wagner-Sillars polarization is concerned. Additional information on micromorphology is obtained from water sorption/diffusion measurements. A part of the results suggest that MS improves with increasing the PP:CE ratio. The whole body of results can be explained if, at the same time, it is assumed that a branched structure is developed for samples out of stoichiometry and branching increases with increasing the PP:CE ratio. Preliminary experiments with solutions of the PUs in organic solvents provide support for that assumption.
Polymer, 2009
In this paper we explore the temperature dependence of segregation of hard and soft segments of selected segmented polyurethane copolymers using synchrotron small-angle X-ray scattering (SAXS). The copolymers are composed of the same hard segments but three different soft segment chemistries, of particular interest in biomedical device applications. Hard segments are formed from 4,4 0 -methylenediphenyl diisocyanate and 1,4-butanediol, and soft segments from an aliphatic polycarbonate [poly(1,6-hexyl 1,2-ethyl carbonate)], poly(tetramethylenoxide), or a mixed soft segment synthesized from hydroxyl-terminated poly(dimethylsiloxane) [PDMS] and poly(hexamethylenoxide) macrodiols. The changes in SAXS relative invariants and interdomain spacings are indicative of gradual dissolution of phase separated hard and soft segments with increasing temperature. All copolymers investigated herein, even those containing PDMS soft segments, transform to the single-phase state at a temperature determined by the soft segment chemistry (and hard segment content). The SAXS findings, along with those from parallel temperature-controlled Fourier Transform infrared spectroscopy measurements, also facilitate assignment of the origin of the thermal events observed in the DSC thermograms of these materials.
Journal of Non-Crystalline Solids, 2002
Broadband dielectric relaxation spectroscopy and thermally stimulated depolarization currents techniques were employed to investigate molecular mobility in relation to morphology in semi-interpenetrating polymer networks (semi-IPNs) of linear polyurethane and polycyanurate networks (PCN) and in full sequential IPNs of crosslinked polyurethane and the same PCN. The semi-IPNs are found to be homogeneous at length scales larger than about 2 nm, whereas heterogeneity is suggested at shorter length scales. The full IPNs are characterized by microphase separation. The results are discussed in terms of the formation of chemical bonds between the components. Ó
Molecular dynamics of linear and hyperbranched polyurethanes and their blends
Journal of Non-crystalline Solids, 2005
The molecular dynamics of two polyurethanes with different architecture (linear and hyperbranched) and their blends with compositions 80/20 and 65/35 have been studied by dielectric spectroscopy and dynamic mechanical analysis yielding results complementary to those obtained by differential scanning calorimetry. In pure polyurethanes, relaxation phenomena correlated with glass transitions and with local chain motions are observed. The molecular dynamics in the blends is dominated by the linear component. A significant influence of hyperbranched polyurethane in the blends is observed only in the case of the primary relaxation connected with the high-temperature glass transition. At higher temperatures the dielectric spectra are dominated by conductivity.