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The molecular dynamics of a series of biomedical poly(dimethylsiloxane)(PDMS)-based thermoplastic polyurethane nanocomposites (TPU) containing low and high aspect ratio organosilicates was investigated using broadband dielectric spectroscopy (DRS). The microphase separated morphology and degrees of separation, extensively characterized in a previous publication, were used to aid the interpretation of the molecular dynamics. Three relaxations were identified in dielectric spectra of the neat host TPU and nanocomposites over the measured temperature and frequency range: the low temperature process associated with local motion of the PDMS phase (α1), the higher temperature process which is associated with the mixed phase segmental motion (α2), and Maxwell –Wagner – Sillars (MWS) interfacial polarization (α3) process. The incorporation of organoclays has previously been shown to influence the morphology of these TPU systems, consequently affecting their dielectric behaviour. In this work the segmental relaxation time and temperature of 1 , 2 , and 3 process of the TPU are significantly altered by the presence of the low aspect ratio organo -hectorite. These significant changes in the TPU dynamics were due to very strong interactions between the exfoliated organo-hectorite and the TPU matrix, with the low aspect ratio nanofiller effectively acting as an interfacial compatibilizer. The dielectric spectroscopy data confirmed the existence of phase mixing in the E5-325 TPU containing organo-hectorite

Synthetic polymer leaflets in prosthetic cardiac valves hold the potential to reduce calcification and thrombus, while improving blood flow, durability, and device economics. A recently developed siloxane poly(urethane‐urea) (LifePolymer, LP) exhibits properties essential for heart valve leaflets, including low dynamic modulus, high tensile strength, minimal creep, and excellent biostability. LP's properties result from carefully designed “linked co‐macrodiol” chemistry that maximizes silicone content and virtual crosslinks between soft and hard phases. Characterization of multiple commercial batches demonstrates a robust synthesis process with minimal variation. Extensive ISO 10993–based biocompatibility testing results in no observable toxicity or other adverse reactions. An ex vivo AV shunt thrombogenicity investigation reveals nearly undetectable levels of platelet attachment and thrombus formation on LP surfaces. Chronic ovine implantation of prototype heart valves with LP leaflets shows no differences in thrombogenicity or systemic tissue response when compared to a clinically standard tissue‐based valve. Toxicological risk assessment, based on extractables and leachables analysis of LP‐based heart valves, confirms minimal toxicological risk. Lastly, 24‐week, strain‐accelerated in vivo LP biostability testing confirms previous favorable in vitro biostability findings. These studies demonstrate that this newly developed elastomer exhibits ideal biomaterial properties for the flexible leaflets of a totally synthetic heart valve replacement.

Broadband dielectric spectroscopy is used to investigate the segmental dynamics and ionic conduction in lithium perchlorate(sub 4) / poly vinyl methyl ether complexes with Li/O from 0.1/100 to 10/100, at the temperatures from T(sub g) to approximately T(sub g)+80 degree Celsius. The strong correlation between the ionic conduction and the slow segmental relaxation supports the idea that hopping from one segment to another is probably giving rise to macroscopic conduction.

The dynamics of miscible blends of poly(p-(hexafluoro-2-hydroxyl-2-propyl)styrene) (PolyHFS) with poly(vinyl methyl ether) (PVME) and poly(2-vinylpyridine) (P2VPy) were investigated via broadband dielectric relaxation spectroscopy (DRS). The HFS moiety forms strong intermolecular associations with proton-accepting polymers, while the steric shielding provided by the two CF3groups minimizes the number of self-associations. The local, glassy state relaxations of PolyHFS and PVME (or P2VPy) are suppressed in the mixtures due to the strong intermolecular hydrogen bonding. When the number of PolyHFS segments is approximately equal to the number of PVME segments, the local relaxation of PVME is undetectable by DRS. Reduced functional group accessability in P2VPy blends lessens the suppression of local relaxations. A single, broadened dynamic glass transition (α relaxation) is observed for each blend. At temperatures above the α process, an additional relaxation is observed, α*, which is assigned to the breaking and re-forming of hydrogen bonds as the chain relaxes. The temperature dependence of this process is related to the strength of the hydrogen bonding and the approximate fraction of intermolecularly associated segments. [ABSTRACT FROM AUTHOR]

The microstructure and dynamics of semicrystalline, melt-miscible poly(ethylene oxide)/poly(vinyl acetate) (PEO/PVAc) blends were investigated using small-angle X-ray scattering (SAXS) and broadband dielectric relaxation spectroscopy, respectively. PEO/PVAc blends with selected compositions were crystallized, and SAXS was used to determine the location of the noncrystallizable PVAc in the structure. Values of the microstructural parameters indicate that little, if any, PVAc is incorporated into interlamellar regions under these crystallization conditions, but PVAc diffuses to interfibrillar regions during the crystallization process. For crystalline blends, a dielectric relaxation appears in the same location as the neat PEO α-process, indicating the presence of relatively mobile amorphous segments consisting almost entirely of PEO, in blends with compositions having as much as 50% PVAc. Considering the findings from the SAXS experiments, we attribute αPEOin the blends to the segmental process of the mobile portion of the interlamellar PEO segments. The shape of an observed higher temperature dielectric relaxation, particularly for blends with 30% and 50% PVAc content, suggests that it consists of multiple overlapping processes. The evidence suggests that these are a Maxwell−Wagner−Sillars (MWS) interfacial polarization process (similar to the one observed for neat PEO), a slow segmental process associated with amorphous interfibrillar regions, and possibly a second MWS relaxation. [ABSTRACT FROM AUTHOR]

A molecular level understanding of the properties of polymer electrolytes can only be obtained through an identification of the types of ionic structures formed in these materials and their relationship to the motion of ions in these systems. Vibrational spectroscopy has proved to be a powerful tool in characterizing such local structures, and a detailed study of the infrared spectrum of a set of sulfonated PEO/aromatic polyesters is presented here. An analysis of the symmetric SO3−stretching mode revealed no detectable amounts of “free” SO3−ions in any of the ionomers, but bands due to ion pairs and aggregates were identified. The band due to aggregates increased in intensity relative to the band due to ion pairs as the temperature increased. Vibrational modes due to the poly(ethylene oxide) segments of the copolymers were characteristic of chains in the amorphous state. However, bands due to sequences of trans and gauche O−C−C−O−C−C−O conformations characteristic of the ordered state appeared to be favored upon complexation with ions. The interaction between cations and PEO portions of the chain “locks” the segments in their preferred structure to a large degree, so that compared to non-sulfonated copolymers there are relatively small changes in the relative intensities of conformationally sensitive bands with temperature. [ABSTRACT FROM AUTHOR]

This paper considers high-quality conductivity data for plasticized ionomers in the context of polymer local and segmental processes. Dielectric spectroscopy was conducted on a neat PEO-based ionomer and six mixtures containing 6 wt % plasticizer with a wide range of dielectric constants. Conductivity increased dramatically but remained Vogel Fulcher Tamman (VFT)-like for all plasticized ionomers, indicating that the mechanism of ion transport was unchanged. Relaxation times of the polymer local and segmental processes were analyzed for the plasticized ionomers, providing activation energies and relaxation strengths for the process and VFT fitting parameters for the process. The glass transition temperature Tgof the mixtures was found to be the critical characteristic governing conductivity, based on four criteria:  VFT-like behavior of conductivity, decrease in the conductivity-segmental coupling index upon the addition of plasticizer, statistical insignificance of solvent quality (dielectric constant, donor number, and viscosity) on conductivity, and the creation of a conductivity master curve as a function of Tg-normalized temperature. [ABSTRACT FROM AUTHOR]

The dynamics of sulfonated polystyrene ionomers were investigated by using broadband dielectric relaxation spectroscopy. Dynamic mechanical analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry, and small-angle X-ray scattering were employed in a complementary role. Sulfonated polystyrene ionomers were prepared from the precursor sulfonic acid polystyrene, having 1 and 7 mol % sulfonic acid, by exchanging the protons of the acid functionality with Na, Cs, and Zn cations. Three dielectric relaxations were observed above the glass transition temperature:  the segmental process and relaxations associated with Maxwell−Wagner−Sillars interfacial polarization and electrode polarization. The low-frequency broadening of the transition is related to constraints imposed by the ionic aggregates. A relaxation in the glassy state was observed for the precursor sulfonic acid polystyrene and ionomers and attributed to the local motion of sulfonated phenyl groups. The relaxation strengths of the processes of the ionomers were suppressed by interaction with the cations that create physical cross-links, and the relaxation times decreased with increasing strength of the electrostatic interaction of the ion pairs. [ABSTRACT FROM AUTHOR]