A model semicrystalline polymer, poly(ethylene naphthalate) (PEN), was used to examine how morphological factors inhibit chain segment relaxations that contribute to dielectric loss. This was achieved by manipulating the extent of crystallization and the crystalline microstructure through a combination of annealing and uniaxial drawing and investigating the effects on dielectric performance. Varying crystallization conditions influenced the dynamic Tg and extent of rigid amorphous fraction formation but had only a moderate effect on loss magnitude. Film orientation, however, greatly reduced loss through strain-induced crystallization and the development of oriented amorphous mesophasic regions. Postdrawing annealing conditions were capable of further refining the crystal microstructure and, in turn, the dielectric properties. These findings demonstrate that the semicrystalline polymer morphology can have a very significant influence on amorphous chain relaxations that contribute to dielectric loss, and understanding how processing conditions affect morphology is critical to the rational design of polymer dielectrics.

Dielectric relaxation spectroscopy is employed to investigate charge transport properties of two polyester ether ionomers in the bulk state and when confined in unidirectional nanoporous membranes (average pore diameter = 7.5 nm). Under nanometric confinement in nonsilanized pores, the macroscopic transport quantities (dc conductivity and characteristic frequency rate) are lower by about 1.4 decades compared to the bulk. The remarkable decrease of transport quantities in nonsilanized nanoporous membranes can be quantitatively explained by considering the temperature dependence of the interfacial layer between the ionomer and the silica membrane surfaces. On the other hand, an enhancement of dc conductivity is observed when the surfaces of the pores are treated with a nonpolar organosilane. This effect becomes more pronounced at lower temperatures and is attributed to slight changes in molecular packing density caused by the two-dimensional geometrical constraint.

•Orientation induced by uniaxial drawing alters dynamics of fluoropolymer film.•Strain-induced crystallization induces formation of rigid amorphous fraction.•The induced crystallization only occurs when drawing above the glass transition.Fluorinated semi-crystalline polymers are attractive for dielectric film applications due to their chemical inertness and high thermal stability. In the present investigation we explore the influence of orientation induced by uniaxial drawing on the crystalline microstructure and relaxation processes of poly(ethylene-tetrafluoroethylene) (ETFE), in order to ascertain how morphological control can benefit polymer dielectric design. When drawn below or near the Tg, the crystallinity of the drawn films is unchanged, and oriented amorphous structures and crystalline microfibrils form at high draw ratios. This orientation slows segmental relaxation, reflected by an increase in the dynamic Tg. When drawing above Tg, the films undergo strain-induced crystallization at high draw ratios. For these films, an increase in dynamic Tg is also observed, in addition to a second segmental relaxation process, appearing as a shoulder on the primary process. We propose that this represents a contribution from a rigid amorphous fraction, having slowed chain dynamics.

•Uniaxial drawing of fluoropolymer films imparted significant changes to microstructure and thermophysical properties.•Achieved higher crystallinity and very high crystal orientation (fc > 0.9) through drawing.•Segmental relaxations were greatly impeded by orientation.This paper presents an investigation of semi-crystalline poly[tetrafluoroethylene -co-(perfluoropropylvinylether)] (PFA) films uniaxially drawn at two temperatures. The extent of crystal unit cell orientation increased significantly with drawing at both draw temperatures as expected, but crystallinity was found to increase with draw ratio only at the lower draw temperature, remaining unchanged at the higher temperature. Considering the evolution of small-angle X-ray scattering patterns as a function of deformation, a model for the changes in PFA lamellar microstructure on drawing was developed. The observed mechanical α and γ relaxations of PFA were assigned to relaxation of rigid and mobile amorphous segments, respectively. Drawing at 200 °C to a draw ratio of 7 leads to a ∼40 °C increase in the α transition temperature compared to the unoriented film, and the findings support the key role of molecular orientation in suppressing the cooperative motions of non-crystalline segments in drawn polymers.

•Lithium-conducting PEO ionomers were plasticized with PEG600.•We observe the dissolution of ionic aggregates into ion pairs.•Ionic conductivity was improved by two orders of magnitude.•Tg was reduced non-linearly with increasing plasticizer content.Poly(ethylene glycol) plasticizer is blended with a PEO-based single-ion conductor to lower the glass transition temperature of the ionomer and solvate the lithium counterions. With increasing plasticizer content at room temperature, FTIR spectra indicate that the fraction of ions in isolated ion pairs increases relative to those in ionic aggregates, and X-ray scattering data indicate that the ionic aggregates are further apart than expected by dilution alone. Together these data show that the average size of ionic aggregates decreases as PEG plasticizer is added. The dissolution of aggregates into ion pairs promotes ion conduction. Coupled with faster segmental dynamics and ion mobility from the depressed Tg, the ionic conductivity of plasticized ionomers improved by two orders of magnitude at room temperature. Resolving the alpha relaxation of these ionomer blends reveals that the mechanism for ion transport is segmentally-assisted ion motion.

This paper presents the first findings on the molecular dynamics of the remarkable new class of linear and precisely functionalized ethylene copolymers. Specifically, we utilize broadband dielectric relaxation spectroscopy to investigate the molecular dynamics of linear polyethylene (PE)-based ionomers containing 1-methylimidazolium bromide (ImBr) pendants on exactly every 9th, 15th, or 21st carbon atom, along with one pseudorandom analogue. We also employed FTIR spectroscopy to provide insight into local ionic interactions and the nature of the ordering of the ethylene spacers between pendants. Prior X-ray scattering experiments revealed that the polar ionic groups in these ionomers self-assemble into microphase-separated aggregates dispersed throughout the nonpolar PE matrix. We focus primarily on the dynamics of the segmental relaxations, which are significantly slowed down compared to linear PE due to ion aggregation. Relaxation times depend on composition, the presence of crystallinity, and microphase-separated morphologies. Segmental relaxation strengths are much lower than predicted by the Onsager theory for mobile isolated dipoles but much higher than linear PE, demonstrating that at least some ImBr pendants participate in the segmental process. Analysis of the relaxation strengths using the Kirkwood g correlation factor demonstrates that ca. 10–40% of the ImBr ion dipoles (depending on copolymer composition and temperature) participate in the segmental motions of the precise ionomers under study, with the remainder immobilized or having net antiparallel arrangements in ion aggregates.

Anion conducting polyphosphazene ionomer analogues of poly[bis(methoxyethoxyethoxy)phosphazene] (MEEP) were synthesized and their iodide transport properties studied. Polymer bound cations were quaternized with either short alkyl or short ether oxygen chains. X-ray scattering reveals a low q peak near 4 nm–1 arising from the backbone–backbone spacing between polyphosphazene chains, an ion-related peak at 8 nm–1, and a peak at 15 nm–1 corresponding primarily to the amorphous halo of the PEO side chains. Because of the short spacing of the intermediate q peak, the ions are proposed to exist mostly in isolated ion pairs or small aggregates. First-principles calculations combined with dielectric spectroscopy suggest that less than 10% of the ions are in isolated pairs while the remainder participate in quadrupoles or other small aggregates. These ionomers display high values for the high frequency dielectric constant, ε∞ (highest value ε∞ = 11), due to atomic polarization of the iodide anion. These MEEP-based ionomers have room temperature dc conductivity of order 10–6 S cm–1 and show potential for application in iodide conducting solar cells if the segmental mobility could be increased.

Porosity in polymers of intrinsic microporosity (PIMs) is closely related to free volume: it arises from a chain structure combining rigid segments with sites of contortion, producing a large concentration of interconnected pores smaller than 1 nm. Membranes of these polymers are subject to physical aging, which decreases their permeability and reduces their performance in gas separation. In this work, a robust interpretation of PIM X-ray scattering features is developed with support from molecular dynamics simulations. The sensitivity of scattering patterns to time, temperature and film thickness is shown to be qualitatively consistent with physical aging, demonstrating that these high-free-volume, porous polymeric glasses present a unique opportunity to study structural changes during physical aging using scattering methods. Quantitative modeling of PIM scattering patterns remains challenging, and the time resolution required to capture the initial aging stages of a single film is difficult to achieve with laboratory instruments. However, the spectrum of glassy states accessed by varying film thickness and aging temperature raises the possibility that there may be two distinct mechanisms of aging in PIMs.

This paper describes the influence of mixed poly(tetramethylene oxide) (PTMO) soft segments on microphase separation and morphology, hydrogen bonding, and polymer transitions for a series of alternating polyurea copolymers prepared from a single modified diphenylmethane diisocyanate. The fraction of two PTMO soft segments [with molecular weight = 1000 and 250 g/mol] was systematically varied and incorporated during bulk polymerization. ATR-FTIR spectroscopy confirmed that the intended polymers were synthesized and was used to determine the state of the local hydrogen bonding in these copolymers. Systematic changes in hard domain microstructure as a function of soft segment composition were clearly observed in AFM tapping mode phase images: the polyureas become progressively disordered with increasing content of the shorter PTMO. This was confirmed in a quantitative fashion using small-angle X-ray scattering. Results from dynamic mechanical analysis experiments reveal rather significant changes in dynamic segmental relaxations and storage moduli at 25 °C for this series of polyureas, which are in keeping with the findings from other experiments.

Three diisocyanates with different symmetry and planarity (2,6-TDI, 2,4-TDI and MDI) were used to synthesize polyureas with the same oligomeric polyetheramine having a molecular weight of ∼1000 g/mol. The influence of diisocyanate symmetry on the phase separated morphology, hydrogen bonding behavior, and molecular dynamics were investigated. Symmetric diisocyanate structures facilitated self-assembly of hard segments into ribbon-like domains, driven by strong bidentate hydrogen bonding. The hard domains for the 2,6-TDI polymer appear to be continuous in AFM images, while the persistence length of the hard domains in the 2,4-TDI and MDI polymers gradually decrease, and fewer hard domains are apparent with decreasing hard segment symmetry. The extent of hard/soft segment demixing, assessed from small-angle X-ray scattering, was very incomplete for all of the polyureas and is significantly influenced by hard segment structure. For the 2,4- and 2,6-TDI polyureas, two segmental relaxations were observed using dielectric relaxation spectroscopy; one arising from relatively unrestricted motion in the soft segment rich phase, and a slower process associated with segments in the soft phase constrained by their attachment to hard domains.

Dielectric relaxation spectroscopy was used to investigate the molecular dynamics of model segmented polyurethane copolymers having identical hard segments and hard segment weight fractions, but with four different soft segment chemistries of particular interest in biomedical devices. All soft segments have molecular weight ∼1000 g/mol and are composed of either tetramethylene oxide, hexamethylene oxide, aliphatic carbonate, or dimethylsiloxane (PDMS) segments. These microphase-separated materials exhibit rich dielectric relaxation behavior: up to two relaxations in the glassy state, a segmental α relaxation (two for the polymer with predominately PDMS soft segments), and three slower relaxations. The slowest process arises from interfacial (MWS) polarization, and its strength decreases significantly with increasing temperature (over a few tens of degrees) and disappears at a temperature similar to that at which the small-angle X-ray scattering from the phase-separated microstructure disappears.

The role of thermal history on the nanoscale segregated structure of a bulk polymerized polyurea containing oligomeric poly(tetramethylene oxide) soft segments is investigated in the present study. Temperature-dependent unlike segment demixing was explored in two series of experiments: at constant heating (and cooling) rate and on annealing at selected elevated temperatures. Tapping mode atomic force microscopy on the as-polymerized polymer demonstrates that the polyurea hard segments self-assemble into a ribbon-like morphology that is generally preserved on annealing, although ribbon coarsening was observed at the highest annealing temperature. The results from the constant heating rate synchrotron X-ray scattering experiments demonstrate that the nanoscale structure begins to reorganize at temperatures as low as ∼70 °C, and the very significant changes in mean interdomain spacing observed at much higher temperatures are largely retained on returning to ambient conditions. Although there was surprisingly no detectable difference in the degree of hard/soft segment segregation in the longer time annealing experiments, changes in interdomain spacing were detected at the lowest annealing temperature (120 °C) used in this study. In combination with the findings from the synchrotron X-ray experiments, this demonstrates that domain reorganization is clearly both time and temperature dependent. The results from X-ray scattering and AFM experiments are also supported by those from FTIR spectroscopy and thermal analysis.

The influence of poly(tetramethylene oxide) (PTMO) soft segment length on the phase-separated microstructure, state of hydrogen-bonded associations, and molecular dynamics was investigated in polyureas polymerized from the bulk. For higher PTMO molecular weights (1000 and 650 g/mol) hard segments self-assemble into ribbon-like domains, while incorporation of a 250 g/mol soft segment leads to a predominately mixed segment material. The degree of microphase separation of the hard and soft segments, however, is rather incomplete for polymers synthesized from 1000 and 650 g/mol PTMO and decreases with decreasing soft segment molecular weight. Broadband dielectric relaxation spectroscopy reveals two segmental relaxations: a soft segment rich (α) and slow segmental (α2) process. When the molecular weight is reduced from 1000 to 650 g/mol the mobility of these processes is reduced, consistent with findings from differential scanning calorimetry and dynamic mechanical analysis.

Polyureas, formed by the rapid reaction between isocyanates and diamines, are attractive for various applications due to their outstanding mechanical properties, which can be tuned by varying component chemistry, molecular weight, and stoichiometry. Polyureas synthesized from a modified methylene diphenyl diisocyanate (Isonate 143 L) and polytetramethylene oxide-di-p-aminobenzoate (Versalink P1000) are widely utilized and investigated for energy absorbing applications such as impact mitigation and ballistic protection. In order to develop a more complete understanding of their mechanical response, we explore the effect of uniaxial strain on the phase separated microstructure and molecular dynamics. We utilize wide- and small-angle X-ray scattering to investigate amorphous segment and hard domain orientation, and broadband dielectric spectroscopy for interrogation of the dynamics. Uniaxial deformation was found to significantly perturb the phase-separated microstructure and chain orientation and result in a considerable slowing down and broadening of the polyurea soft phase segmental relaxation.

The dynamics of three main-chain liquid crystalline polysiloxanes were investigated using broadband dielectric relaxation spectroscopy. The liquid crystalline polymers (LCP) differ regarding the substituents on the rigid mesogens, and the nature of the substituents is found to influence the relaxation behavior. Within the temperature and frequency range examined, five relaxations are observed; two glassy state processes are associated with motions of the spacer segments (γγ relaxation) and the substituted phenyl rings (ββ relaxation). The segmental (αα) relaxation time changes with the nature of the mesogen substituent. A relaxation assigned to interfacial polarization between domain boundaries was observed, which disappears at the LCPs clearing temperature.

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 CF3 groups 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.

Two series of styrene/n-butyl acrylate (S/nBA) gradient copolymers and block copolymers are prepared with a range of molecular weights to investigate the effect of increasing interphase on relaxation time distributions and to relate these to measurements of glass transition breadth using differential scanning calorimetry and dielectric relaxation spectroscopy (DRS). This is the first time DRS has been used in the study of gradient copolymers. The segmental relaxation associated with the dielectrically active component of the block copolymers (nBA) resembles that of poly(n-butyl acrylate) in behavior but becomes broader as the system shifts from highly segregating to moderately segregating. In contrast, the gradient copolymer segmental relaxation largely resembles that of a random copolymer with similar composition but with broader relaxation time distributions. The one exception is the most phase-segregated of the gradient copolymers, for which the relaxation response appears as two overlapping contributions representing regions of high nBA content and low nBA content. The breadth in relaxation time achieved by this gradient copolymer is comparable to or exceeds that of a weakly segregated block copolymer.

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 αPEO in 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.

The dynamics of intermolecularly hydrogen-bonded polymer blends of poly(p-(hexafluoro-2-hydroxyl-2-propyl)styrene) with poly(vinyl acetate), poly(ethylene[30]-co-vinyl acetate[70]) and poly(ethylene[55]-co-vinyl acetate[45]) are investigated by broadband dielectric relaxation spectroscopy and Fourier transform infrared spectroscopy. Each blend component exhibits a glassy state (β) relaxation, and these relaxations are affected by the formation of intermolecular associations. The glassy state behavior of the blends can be modeled using the Painter−Coleman association model. All blends exhibit a single Tg and a single dielectric segmental (α) relaxation, indicative of strong segmental-level coupling. The fragility of the glass-formers depends on the volume fraction of intermolecularly associated segments, and the association model predicts which compositions have the highest fragilities. A relaxation related to the breaking and reforming of hydrogen bonds is observed at temperatures above the α process, and its temperature dependence varies systematically with ethylene content.

Segmented polyurethane (PU) block copolymers were synthesized using 4,4′-methylenediphenyl diisocyanate and 1,4-butanediol as hard segments and oligomeric ethoxypropyl polydimethylsiloxane (PDMS) as the soft segments, with hard segment contents ranging from 26 to 52 wt%. The microphase separated morphology, phase transitions, and degrees of phase separation of these novel copolymers were investigated using a variety of experimental methods. Like similar copolymers with mixed ethoxypropyl PDMS/poly(hexamethylene oxide) soft segments, PU copolymers containing only ethoxypropyl PDMS soft segments were found to consist of three microphases: a PDMS matrix phase, hard domains, and a mixed phase containing ethoxypropyl end group segments and dissolved short hard segments. Analysis of unlike segment demixing using small-angle X-ray scattering demonstrates that degrees of phase separation increase significantly as copolymer hard segment content increases, in keeping with findings from Fourier transform infrared spectroscopy measurements.

Three series of chemically well-defined polyurethanes were synthesized with the same hard segments but different soft-segment chemistries of interest in biomedical applications. The multiblock polyurethanes have soft segments composed of either an aliphatic polycarbonate [poly(1,6-hexyl 1,2-ethyl carbonate)], polytetramethylenoxide, or a mixed macrodiol of polyhexamethylenoxide and hydroxyl-terminated poly(dimethylsiloxane) and the same hard-segment chemistry [4,4′-methylenediphenyl diisocyanate and 1,4-butanediol]. Analysis using small-angle X-ray scattering and other methods demonstrates that demixing of the hard and soft segments varies greatly between the three series of copolymers. For example, the PDMS/PHMO-based copolymers exhibit a three-phase, core−shell morphology, while the other two series exhibit a typical two-phase structure. In addition to quantitative measurements of hard/soft-segment demixing for the two-phase copolymers, FTIR spectroscopy was used to assess inter- and intracomponent hydrogen bonding, and tapping mode AFM was used to characterize the nanoscale morphology.

•Uniaxial drawing alters crystalline microstructure and segmental dynamics of ETFE.•Annealing near or above Tg relaxes oriented amorphous segments, but has no significant effect on lamellar orientation.•Dielectric breakdown strength increases with uniaxial orientation to values as high as 870 MV/cm.In the present investigation, we explore the influence of uniaxial orientation and subsequent thermal annealing on semi-crystalline poly(ethylene-tetrafluoroethylene) (ETFE) microstructure and dynamics, and the connection to dielectric breakdown strength. Understanding the influence of crystalline microstructure on dynamics and breakdown, and in turn how processing influences microstructure, is critical for establishing rational design of polymer dielectrics. When drawn below the glass transition temperature (Tg), the Weibull breakdown strength decreases compared to that of the undrawn precursor film, but increases on thermal annealing near or above Tg. This behavior is associated with the formation and elimination of drawing-induced microvoids, respectively. When drawn above Tg, the breakdown strength increases to ∼870 MV/cm, dominated by orientation of amorphous segments, and decreases on thermal annealing above Tg to near that of the undrawn film.

Porosity in polymers of intrinsic microporosity (PIMs) is closely related to free volume: it arises from a chain structure combining rigid segments with sites of contortion, producing a large concentration of interconnected pores smaller than 1 nm. Membranes of these polymers are subject to physical aging, which decreases their permeability and reduces their performance in gas separation. In this work, a robust interpretation of PIM X-ray scattering features is developed with support from molecular dynamics simulations. The sensitivity of scattering patterns to time, temperature and film thickness is shown to be qualitatively consistent with physical aging, demonstrating that these high-free-volume, porous polymeric glasses present a unique opportunity to study structural changes during physical aging using scattering methods. Quantitative modeling of PIM scattering patterns remains challenging, and the time resolution required to capture the initial aging stages of a single film is difficult to achieve with laboratory instruments. However, the spectrum of glassy states accessed by varying film thickness and aging temperature raises the possibility that there may be two distinct mechanisms of aging in PIMs.

The segmental and local chain dynamics as well as the transport of Na+ and Li+ cations in a series of model poly(ethylene oxide)-based polyurethane ionomers is investigated using dielectric relaxation spectroscopy. A physical model of electrode polarization is employed to separately determine mobile ion concentration and ion mobility in these single-ion conductors. A model including unpaired ions, separated ion pairs, and contact ion pairs is used to reconcile the very small fraction of free ions obtained using the electrode polarization model with those of previous studies of ion association in polyether-based single-ion conducting and salt-containing systems.