Structure-property relationships in thermoplastic-apparent interpenetrating polymer networks based on crystallizable polyurethane and styrene-acrylic acid copolymer

Abstract

Structure-property relationships in thermoplastic-apparent interpenetrating polymer networks (t-AIPNs), prepared by mechanical blending in a common solvent of crystallizable polyurethane (CPU) and styrene/acrylic acid random copolymer (S/AA), were investigated by means of wide-angle and small-angle X-ray scattering (WAXS and SAXS), dynamic mechanical analysis (DMA), thermally stimulated depolarization currents (TSDC) techniques, dielectric relaxation spectroscopy (DRS), and density, water uptake, deformation, and strength characteristics measurements. Several mechanical and dielectric relaxations of the pure components were characterized, and the effects thereupon induced by blending were followed. The two components show weak affinity to each other. The t-AIPNs can be classified into two groups with high and low contents of CPU, showing essentially the behavior of CPU and of S/AA, respectively. On the other hand, deviations from additivity in several properties indicate interactions between the two components, caused by the formation of H-bonds between their functional groups, and resulting in partial miscibility. In addition, significant changes are observed on some properties of the t-AIPNs on addition of small amounts of either of the components.

Effect of Blending on the Structure of Thermoplastic Interpenetrating Polymer Networks

“…The thermogram of the blend CPU/S-b-AA(K þ ) ¼ 10/90 does not exhibit any melting endotherms, showing that it can be regarded as a wholly amorphous system having a morphology based on the coexistence of microphases of essentially pure S-b-AA(K þ ) and of mixed CPU/S-b-AA(K þ ) microphases. The absence of crystalline BAG in this blend is apparently in contrast with the results of a x-ray scattering study of as-cast t-IPNs based on CPU and S/AA random copolymer (acid form), [24] which showed the existence of BAG crystals in the whole range of compositions from pure CPU to pure S/AA. Besides the structural differences of one of the components (S-b-AA(K þ ) is a block-copolymer), this discrepancy is probably due to the annealing procedure imposed on the present samples (see Section 2) which is expected to favor the formation of the mixed amorphous phase preventing the BAG crystallization.…”

“…This value is consistent with the assignment of this process to crankshaft motions of (CH 2 ) n segments within the amorphous chains. [24,25] It is believed that, in the blend, this process is due to the contributions of g-relaxation within CPU amorphous chains of the mixed phase, whose fraction is enhanced on blending as also observed by calorimetric results.…”

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

“…In previous work, we investigated the structure–property relationships in t‐IPNs prepared from a crystallizable polyurethane (CPU) and a random copolymer of styrene/acrylic acid (S/AA) 10–14. These mixtures were called thermoplastic apparent IPNs, t‐AIPNs, because S/AA was used in the acid form and not in the salt form.…”

“…A better understanding of these relationships is essential for optimizing composition and processing of materials to meet specific end‐use requirements. Both t‐AIPNs prepared by melt mixing of the components13, 14 and by casting from a common solvent10, 12 were investigated. The results by a variety of experimental techniques showed that the t‐AIPNs were microheterogeneous systems with contributions to microheterogeneity from both the heterogeneity of the individual polymers and the thermodynamic incompatibility of the components.…”

“…The results by a variety of experimental techniques showed that the t‐AIPNs were microheterogeneous systems with contributions to microheterogeneity from both the heterogeneity of the individual polymers and the thermodynamic incompatibility of the components. On the other hand, deviations from additivity and significant changes of several properties on addition of small amounts of either of the components indicated partial miscibility, explained by the formation of hydrogen bonds between functional groups of the two components 12, 13…”