Thermoplastic apparent interpenetrating polymer networks of polyurethane and styrene/acrylic acid block copolymer: Structure–property relationships

Abstract

Thermoplastic apparent interpenetrating polymer networks (t-AIPNs) of crystallizable polyurethane (CPU) and a styrene/acrylic acid block copolymer (S-b-AA, acid form) of several compositions were prepared by casting from a common solvent. A variety of experimental techniques, including size exclusion chromatography (SEC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), broadband dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization currents (TSDC), and density measurements were employed to investigate structureproperty relationships of the t-AIPNs. Special attention was paid to the investigation of molecular dynamics of the CPU component in the t-AIPNs, by combination of the dielectric DRS and TSDC techniques, as well as from the methodological point of view, to the prospects of morphological characterization by broadband DRS. The results show that the CPU/S-b-AA t-AIPNs studied can be considered as multiphase systems having at least two amorphous and one crystalline phases, as well as regions of mixed compositions. Their properties are determined by the heterogeneity of the individual components, as well as by the heterogeneity caused by the thermodynamic incompatibility of these components. The degree of incompatibility is determined, to a large extent, by the intermolecular hydrogen bonding between the functional groups of the CPU and the S-b-AA components (ester groups and COOH-groups, respectively), which is more effective on addition of small amounts of either of the components.

Dielectric relaxation in polymer–clay nanocomposites

“…Four peaks are observed in Fig. 7.6, all arising from PU (Kanapitsas et al, 2006): in the order of increasing temperature, the local, secondary g and b relaxations in the glassy state, the cooperative, segmental a relaxation in the region of the glass transition, and the interfacial MWs relaxation in the rubbery state. in previous work the g relaxation has been ascribed to crankshaft motion of methylene sequences with participation of adjacent polar groups and the b relaxation to motions of carbonyl groups with attached water molecules (Kanapitsas et al, 2006).…”

“…the systematic study of the MWs peak provides information on microphase separation. More specifically, it has been shown that the difference T MWs -T a increases with increasing degree of microphase separation (DMs) and, thus, T MWs -T a provides a measure for DMs (Kanapitsas et al, 2006). This criterian cannot be, however, rigorously applied here, as additional ions introduced by the clay particles affect conductivity and, thus, the temperature position of the MWs peak.…”

“…Drs data in the following will provide more accurate values of the strength of the a relaxation. the MWs peak is broad, indicating a distribution of relaxation times, which is reasonable in terms of the rather complex morphology of Pus (Kanapitsas et al, 2006), rendering the determination of T MWs less accurate. the systematic study of the MWs peak provides information on microphase separation.…”

“…in previous work the g relaxation has been ascribed to crankshaft motion of methylene sequences with participation of adjacent polar groups and the b relaxation to motions of carbonyl groups with attached water molecules (Kanapitsas et al, 2006). The interfacial MWS peak is typical for PUs and is related to their microphase-separated structure, arising from the accumulation of charges at the interfaces between hard microdomains and the soft microphase and their subsequent relaxation in the depolarization (heating) step (Kanapitsas et al, 2006). Comparative TSDC thermograms on neat PU and the various NCs show that for the secondary g and b relaxations practically neither the peak position (115 and 160 K, respectively) nor the magnitude of the peak change with composition.…”

“…7.6, all arising from PU (Kanapitsas et al, 2006): in the order of increasing temperature, the local, secondary g and b relaxations in the glassy state, the cooperative, segmental a relaxation in the region of the glass transition, and the interfacial MWs relaxation in the rubbery state. in previous work the g relaxation has been ascribed to crankshaft motion of methylene sequences with participation of adjacent polar groups and the b relaxation to motions of carbonyl groups with attached water molecules (Kanapitsas et al, 2006). The interfacial MWS peak is typical for PUs and is related to their microphase-separated structure, arising from the accumulation of charges at the interfaces between hard microdomains and the soft microphase and their subsequent relaxation in the depolarization (heating) step (Kanapitsas et al, 2006).…”