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Development of a mass spectrometry imaging system utilizing t-SPESI and its application to lipid imaging of tissue sections. The effects of solvent properties on the extraction-ionization process and the spatial resolution of ion images are discussed.

Reversible cross-links by non-covalent bonds have been widely used to produce supramolecular hydrogels that are both tough and functional. While various supramolecular hydrogels with several kinds of reversible cross-links have been designed for many years, a universal design that would allow control of mechanical and functional properties remains unavailable. The physical properties of reversible cross-links are usually quantified by thermodynamics, dynamics, and bond energies. Herein, we investigated the relationship between the molecular mobility and mechanical toughness of supramolecular hydrogels consisting of two kinetically distinct reversible cross-links

Polymerized ionic liquids (PILs) are a special class of ion-containing polymers with ionic liquid structures. The viscoelastic properties of PILs in IL solutions are expected to be influenced by both polymer–polymer interaction and charge screening by IL ions, which becomes complex at high IL concentrations due to strong ionic correlations. In this work, we aim to understand the effect of the ionic correlations on the shear rheology of PIL in IL solutions in the semidilute unentangled (SU) polymer regime, with moderate polymer–polymer interactions. We conducted systematic rheological characterization of a PIL, poly(1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide), in a mixture of an IL, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and a non-ionic solvent, dimethylformamide, to evaluate the specific viscosity ηsp and the longest relaxation time λ with varying IL concentrations cIL, at a fixed polymer concentration. We found that both ηsp and λ initially decreased with the increasing cIL, following the scaling theory of polyelectrolyte solutions in the low salt concentration regime. However, these values exhibited an upturn at high cIL. We explained the observed non-monotonic viscoelastic behavior by proposing a charge screening model for SU solutions, accounting for both modified screening length in concentrated IL solutions and complete charge screening. Our results demonstrate how the strong ionic correlation in concentrated IL solutions modifies the electrostatics of PILs and their corresponding viscoelastic properties in the presence of moderate polymer–polymer interactions.

The impact of the chemical structure on ion transport, nanoscale morphology, and dynamics in polymerized imidazolium-based ionic liquids is investigated by broadband dielectric spectroscopy and X-ray scattering, complemented with atomistic molecular dynamics simulations. Anion volume is found to correlate strongly with Tg-independent ionic conductivities spanning more than 3 orders of magnitude. In addition, a systematic increase in alkyl side chain length results in about one decade decrease in Tg-independent ionic conductivity correlating with an increase in the characteristic backbone-to-backbone distances found from scattering and simulations. The quantitative comparison between ion sizes, morphology, and ionic conductivity underscores the need for polymerized ionic liquids with small counterions and short alkyl side chain length in order to obtain polymer electrolytes with higher ionic conductivity.

Stretching vibrations of aliphatic C-D bonds at the chain end and midchain site of partially deuterated polystyrene (PS) were determined by Fourier transform infrared (FT-IR) spectroscopy. It was first found that the stretching vibration at the chain end is more rapid compared to that at the midchain site in the glassy bulk state. The difference in the frequencies of the stretching vibrations at the chain end and midchain site changed little even when the PS was dissolved in toluene. Moreover, the DFT vibrational frequency calculations showed that the C-D bonds at the end site intrinsically have higher vibrational frequency because of lower intramolecular interactions at the chain end. From these results, it was concluded that the main origin for the local rapid stretching vibration at the chain end is not intermolecular effects but reduced intramolecular interactions induced by the discontinuity of the repeating unit at the chain end.

Dynamic viscoelasticity and dynamic birefringence of a microgel system were investigated around the liquid–solid transition concentration to clarify the molecular origin of the viscoelastic response of the microgel system. The complex modulus showed viscoelastic liquid-like behavior at concentrations, c, below a threshold cⱼₐₘₘᵢₙg for random close packing of the microgels, whereas viscoelastic solid-like behavior at c > cⱼₐₘₘᵢₙg. The imaginary part of the complex strain-optical coefficient changed its sign with increasing angular frequency ω in a liquid-like regime, suggesting that the stress and birefringence involved three relaxation mechanisms. Utilizing the stress-optical rule, SOR, for each relaxation process, the complex shear modulus at c cⱼₐₘₘᵢₙg, the ordinary SOR held well with a single stress-optical coefficient, C, implying that only one stress origin is dominant, which can be attributed to the orientational stress of densely packed microgels in permanent contact. The strain-optical coefficients evaluated using the Onuki–Doi theory reproduced the measurements qualitatively and supported these assignments.

We investigated the dynamics of the topological network formed by rotaxane-type movable crosslinks consisting of a poly(ethyl acrylate) backbone threaded through peracetylated cyclodextrins, which ...

For bottlebrush-type polystyrene polymacromonomer consisting of a polyisoprene main chain and polystyrene side chains (PI-PS-bPM), dynamic birefringence and viscoelasticity measurements were conduc...

For linear high-cis polyisoprene having a monofunctionally associative carboxyl group at the chain head (PI30-COOH; M = 30.5 × 103), linear viscoelastic and dielectric behavior was examined in its ...

Functional polymeric materials based on reversible noncovalent bonds have attracted much attention due to their mechanical and responsive properties. In particular, the association/dissociation of the reversible bond is widely known to improve the fracture energy of polymeric materials. Herein, we aimed to establish a general strategy for designing tough materials and investigated the relation between the lifetime of reversible bonds and the toughness of the material. We experimentally demonstrated the fracture energy in relation to the viscoelastic relaxation time (τ) of the reversible bonds and the observation time scale. We prepared supramolecular hydrogels cross-linked by inclusion complexes between α-cyclodextrin (αCD) and alkyl chains modified with cation units. τ varied widely in response to the kinetics of the threading/dethreading of the αCD unit. The viscoelastic behaviour of the reversible cross-linking points, which could be tuned by τ and the tensile rate, improved the fracture energy of the supramolecular hydrogels.

Phase equilibrium and dielectric relaxation were examined for mixtures of liquid-crystalline (LC)-forming 4-cyano-4'-pentylbiphenyl (5CB) with dilute dimethyl phthalate (DMP). The mixtures were in an isotropic one-phase state at high temperatures T but were separated into nematic and isotropic phases at low TTIN (isotropic-to-nematic transition temperature), and the isotropic phase disappeared and a nematic one-phase state was realized on a further decrease of T below another transition temperature . These TIN and data (phase diagram) were described considerably well by a simple model of free energy contributed from a Flory-Huggins type mixing entropy (no enthalpic contribution) and a Landau-de Gennes type nematic interaction. This success of the model, not expected for ordinary (not LC-forming) components exhibiting enthalpically-driven phase separation, suggested that the phase separation in the DMP/5CB mixtures was triggered by the nematic transition of 5CB (possibly governed by the packing entropy) and thus the orientation fluctuation of 5CB molecules was coupled with the composition fluctuation. This coupling was expected to affect the dielectric relaxation detecting the rotational dynamics of 5CB molecules, the major component in the mixtures. This expectation was examined for a representative mixture having the DMP content of wDMP = 3.1 wt% and TIN ≅ 27.0 °C. In a high-T asymptote (TTIN + 10 °C), the dielectric relaxation of this mixture was close to that of pure 5CB, which suggested no significant effect of the above coupling on 5CB dynamics in the mixture at such high T. Nevertheless, in a significantly wide range of T between TIN and TIN + 10 °C, the dielectric relaxation time τε of the isotropic one-phase mixture increased on cooling much more significantly compared to τε in that high-T asymptote. The kinematic viscosity ν of the mixture exhibited a qualitatively similar increase in the same range of T, but this increase was weaker than that of τε. This difference between the dielectric τε and the rheological ν was attributed to coupling of the orientation and the composition fluctuations mentioned above. Namely, the composition fluctuation enhances the orientation fluctuation in the mixture thereby providing τε (reflecting the orientation fluctuation) with an extra increase. Pure 5CB exhibited similar increases of τε and ν (stronger for the former) but only in a close vicinity of (within 2-3 °C), because the orientation fluctuation in pure 5CB is coupled with the density fluctuation, not with the composition fluctuation being absent in the pure 5CB system. This behavior of pure 5CB in turn suggests an importance of the coupling of orientation and composition fluctuations in the mixture.

Anisotropic dynamics of benzonitrile (BzCN) confined in the cocrystalline region of syndiotactic polystyrene (sPS) was studied by means of dielectric spectroscopy. Especially examined was the effect of orientation of the crystalline phase for two types of cocrystals, δ and e clathrates, on the dielectric relaxation behavior. The relaxation time of the BzCN in the δ cocrystal, regardless of its orientation, was found to be longer than that in the e cocrystal, indicating that the δ structure has higher degree of constraint on the guest motion than the e structure. With respect to dielectric intensity Δe due to the guest BzCN relaxation, uniaxial stretching treatment caused different effects in the δ and e cocrystals: Δe increased for the δ cocrystal and decreased for the e crystal by stretching. This observation was attributable to the difference in directionality of anisotropic motion of the guest molecule inside the cavities of these cocrystals. The preferable orientation of the molecular axis of BzCN cor...

Polymerized ionic liquids (PILs) are believed to be ideal solid-state polymer electrolytes, and hence experimental and computational studies have been widely undertaken to understand the relationship between the chemical structure and mechanical/dielectric properties and the ionic conductivity of PILs. However, it is still a challenge to understand the effect of counterion ionic volume on the material properties of PILs. Herein, we demonstrate the effect of the ionic volume ratio of counteranions to side-chain cations on linear viscoelastic response using three imidazolium-based PILs with different counteranions. We show that the elastic modulus is significantly enhanced at temperatures higher than glass transition temperature once the ionic volume of the counteranion exceeds that of the side-chain cation. Our results provide an additional strategy to improve mechanical properties of PILs, while maintaining relatively high ionic conductivity.

Polymerized ionic liquids (PILs) doped with lithium salts have recently attracted research interests as the polymer component in lithium-ion batteries because of their high ionic mobilities and lithium-ion transference numbers. To date, although the ion transport mechanism in lithium-doped PILs has been considerably studied, the role of lithium salts on the dynamics of PIL chains remains poorly understood. Herein, we examine the thermal and rheological behaviors of the mixture of poly(1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide (PC4-TFSI)/lithium TFSI (LiTFSI) in order to clarify the effect of the addition of LiTFSI. We show that the glass transition temperature Tg and the entanglement density decrease with the increase in LiTFSI concentration wLiTFSI. These results indicate that LiTFSI acts as a plasticizer for PC4-TFSI. Comparison of the frequency dependence of the complex modulus under the iso-frictional condition reveals that the addition of LiTFSI does not modify the stress relaxation mechanism of PC4-TFSI, including its characteristic time scale. This suggests that the doped LiTFSI, component that can be carrier ions, is not so firmly bound to the polymer chain as it modifies the chain dynamics. In addition, a broadening of the loss modulus spectrum in the glass region occurs at high wLiTFSI. This change in the spectrum can be caused by the responses of free TFSI and/or coordination complexes of Li and TFSI. Our detailed rheological analysis can extract the information of the dynamical features for PIL/salt mixtures and may provide helpful knowledge for the control of mechanical properties and ion mobilities in PILs.

Dynamic networks constructed by physical cross-links between polymer chains can change their structure through the association and dissociation of cross-linking points. This paper yields experimental data about the transient change of the dynamic storage modulus G′ for a molten random copolymer of vinyl acetate and vinyl alcohol with a vinyl alcohol content of 60 mol%, in which physical cross-links are formed via hydrogen bonding. As the cross-link density depends on temperature, the storage modulus G′ of the system slowly evolves toward equilibrium at the experimental temperature, Ta, after changing the temperature from higher or lower than Ta. The characteristic time scale for the equilibration is on the order of 103~104 s (depending on Ta) and the time evolution curves of G′ are dependent on the thermal history. The ‘memory effect’ (the structure developed at a certain temperature is preserved after changing the temperature) found in the system is discussed in detail. Time evolution behavior is described for a transient network formed via hydrogen bonds in a random copolymer of vinyl acetate and vinyl alcohol. As the cross-link density depends on temperature, the storage modulus G′ of the system slowly evolves toward equilibrium at the experimental temperature, Ta, after changing the temperature from higher or lower than Ta. The ‘memory effect’ (the structure developed at a certain temperature is preserved after changing the temperature) found in the system is discussed in detail.

Rotational dynamics was examined in detail for four polar aromatic molecules, benzonitrile (BN), p-methylbenzonitrile (p-MBN), o-methylbenzonitrile (o-MBN), and m-methylbenzonitrile (m-MBN), accommodated in a nano-cavity regularly arranged inside the crystalline region (δ-form) of syndiotactic polystyrene (sPS) by means of dielectric relaxation measurements. Except for m-MBN, for which the co-crystalline structure was monoclinic δ-intercalate and no dielectric relaxation process arising from the crystalline region appeared, other three polar guests in the monoclinic δ-clathrate form exhibited the specific dielectric relaxation process. The relaxation times of o-MBN, BN, and p-MBN at room temperature were ranged from 10−7 s to 10−1 s, and in the order of o-MBN

Intrinsic birefringence, Δn 0, is a material constant for the orientational birefringence of polymers, and has been measured by many researchers with various methods. However, the reported values of the same polymer sometimes disagree among the researchers because determination of the orientation degree is somehow complicated. Alternatively, a new method using the modified stress-optical rule (MSOR) was proposed for Δn 0 measurement. In this study, literature data of the Δn 0 for various polymers are assessed and the reliability of Δn 0 estimated via the MSOR is discussed.

A viscoelastic test was made for end-carboxylated polyisoprene (PI-COOH) of the molecular weight M = 30.5 × 103 that underwent the interchain association and dissociation through hydrogen bonding of the COOH groups at the chain end. As a reference, the test was made also for neat PI unimer (with no COOH group at the chain end) and for PI2 dimer (with M = 61.0 × 103), the latter being synthesized through end-coupling of PI– anions (precursor of the PI-COOH sample). The PI-COOH, neat unimer, and dimer samples were diluted in oligomeric butadiene (oB) to a concentration of 10 wt %. The neat unimer and dimer exhibited nonentangled Rouse behavior at this concentration, as expected from their molecular weights. At low temperatures (T ≤ 0 °C) the PI-COOH sample relaxed slower than the reference unimer but faster than the dimer, whereas the relaxation of PI-COOH approached that of the unimer with increasing T > 0 °C, and this change of the relaxation time of PI-COOH was associated with changes in the angular freq...

For nonentangled Rouse chains undergoing head-to-head association and dissociation reaction, the viscoelastic relaxation functions g1(t) and g2(t) were formulated for a case that a given dissociated unimer chain rapidly reassociates with its original partner unimer. The relaxation of the unimer and dimer was essentially determined by ratios ra and rd of the Rouse relaxation time (in the absence of reaction) to the association and dissociation times. For small ra and rd, the reaction was slow so that the unimer and dimer relaxed through respective pure Rouse modes, as naturally expected. However, for most cases in wide ranges of ra and rd, the dimer relaxation was accelerated with increasing rd (>1), and g2 of the dimer was indistinguishable from the pure Rouse relaxation function of the unimer, g1,Rouse. For those cases, g1 of the unimer also coincided with g1,Rouse. These results demonstrate that the motional coupling between the unimer and dimer, occurring through the association/dissociation reaction, ...

Glass transition temperature ( T g ) and vibrational properties at the chain end of polystyrene (PS) were selectively determined by a novel method utilizing Fourier transform infrared (FT-IR) spectroscopy. In this method, PSs having almost the same number average molecular weight ( M n ) but selectively deuterated at different sites, midchain (M-PS, M n = 10.7 kDa) or chain end (E-PS, M n = 10.3 kDa), were synthesized and the asymmetric stretching vibration of the main chain CD 2 ( ν as (CD 2 )) were analyzed in detail. We found that the temperature dependence of the ν as (CD 2 ) frequency shows a clear inflection at the calorimetric T g of PS. The inflection temperature was defined as T g,FTIR , which represents the T g at the local region around the deuterated sites. Although higher segmental mobility at the chain end had been shown above the T g in our earlier work, this study found that the T g,FTIR s of the M-PS and E-PS are the same. From this result, it was concluded that the chain ends move cooperatively with numerous neighboring other segments, averaging out those mobilities at temperatures around the T g . On the other hand, the ν as (CD 2 ) frequency of the E-PS was by a few cm −1 higher than that of the M-PS for any temperature. This was explained in terms of the discontinuity of the repeat unit at the chain end resulting in reduced interactions between repeat units along the chain.

cis-Polyisoprene (PI) chain has the type A dipole parallel along the backbone so that its large-scale (global) motion results in not only viscoelastic but also dielectric relaxation. Utilizing this feature of PI, this paper examined dielectric and viscoelastic behavior of star PI probe chains (arm molecular weight 10–3Ma = 9.5–23.5, volume fraction υ1 = 0.1) blended in a matrix of long linear PI (M = 1.12 × 106). The constraint release (CR)/dynamic tube dilation (DTD) mechanism was quenched for those dilute probes entangled with the much longer matrix, as evidenced from coincidence of the frequency dependence of the dielectric and viscoelastic losses of the probe in the blend. Comparison of the probe data in the blend and in monodisperse bulk revealed that the star probe relaxation is retarded and broadened on blending and the retardation/broadening is enhanced exponentially with Ma. This result in turn demonstrates significant CR/DTD contribution to the dynamics of star PI in bulk. The magnitude of retardation was quantitatively analyzed within the context of the tube model, with the aid of the dielectrically evaluated survival fraction of the dilated tube, φ′(t), and the literature data of CR time, τCR. In the conventional molecular picture of partial-DTD, the tube is assumed to dilate laterally, but not coherently along the chain backbone. The corresponding lateral partial-DTD relationship between φ′(t) and the normalized viscoelastic relaxation function μ(t), μ(t) = φ′(t)/β(t) with β(t) being the number of entanglement segments per laterally dilated segment (that was evaluated from the φ′(t) and τCR data), held for the μ(t) and φ′(t) data of star PI in bulk. Nevertheless, the observed retardation of the star probe relaxation on blending was less significant compared to the retardation expected for the arm motion (retraction) along the laterally dilated tube in bulk PI. This result suggests that the relaxation time of the probe in bulk is governed by the longitudinal partial-DTD that occurs coherently along the chain backbone. In fact, the magnitude of retardation evaluated from the φ′(t) and τCR data on the basis of this longitudinal partial-DTD picture was close to the observation. These results strongly suggest that the star PI chains in monodisperse bulk have two different coarse-grained length scales: the diameter of laterally dilated tube that determines the modulus level and the diameter of longitudinally dilated tube that reflects the path length for the arm retraction and determines the relaxation time. Thus, the star PI chains in bulk appear to move along the longitudinally dilated tube that wriggles in the laterally dilated tube. This molecular scenario is consistent with the previous finding for bulk linear PI

In this work, we discuss the dynamic viscoelasticity of three novolac resins with different molar masses and methylene linkage patterns (para–para′, ortho–ortho′ and ortho–para′ methylene linkages) to clarify the relationship between the structure and viscoelastic properties of novolac resins. The linkage patterns of the novolacs were evaluated using 13C nuclear magnetic resonance spectroscopy. Gel permeation chromatography (GPC) measurements showed that the number density distribution was similar to that predicted for hyperbranched chains. The dependence of the intrinsic viscosity on the molar mass indicated that the three novolacs had a compact branched chain structure similar to that of hyperbranched chains. The glass transition temperatures determined by differential scanning calorimetry (DSC) depended on the molar mass and were less sensitive to the methylene linkage pattern. The viscoelastic spectra obtained by the time–temperature superposition principle for the three resins were similar to each other because the glassy relaxation properties were dominant. Weak polymeric modes originating from the chain connectivity were observed at low frequencies in the composite curve and were well described by the dynamic scaling theory for hyperbranched chains. A clear effect from the linkage patterns on the mechanical properties was not observed. Clarifying the relationship between structure and viscoelastic properties of novolac resins, having different molar mass and different methylene linkage pattern content, by GPC, NMR, rheology and dynamic birefringence analysis.

Dynamic viscoelasticity and dynamic birefringence of phenolic resins having different cross-linking density were examined to clarify the relationship between structure and viscoelastic properties. Dynamic modulus was found to be insensitive to cross-linking density at a high cross-linking density, where molar mass between the cross-linking points was smaller than the viscoelastic segment size of phenolic resin, whereas the complex strain-optical coefficient reflects more sensitively the cross-linking density. Dynamic viscoelasticity and dynamic birefringence of phenolic resins having different cross-linking density were examined to clarify the relationship between structure and viscoelastic properties. Dynamic modulus was found to be insensitive to cross-linking density at a high cross-linking density, where molar mass between the cross-linking points was smaller than the viscoelastic segment size of phenolic resin, whereas the complex strain-optical coefficient reflects more sensitively the cross-linking density.

cis-Polyisoprene (PI) has the type A dipole parallel along the chain backbone so that the end-to-end fluctuation of PI chains results in slow dielectric relaxation. Comparison of dielectric and viscoelastic data of PI has revealed several interesting features related to the entanglement dynamics, for example, success and failure of the full dynamic tube dilation (DTD) picture for monodisperse linear and star PI, respectively [see a review: Watanabe, H. Polym. J. 2009, 41, 929, for example]. For monodisperse linear PI, recent modeling [Glomann et al. Macromolecules 2011, 44, 7430] and single-chain slip-link simulation [Pilyugina et al. Macromolecules 2012, 45, 5728] suggest that the constraint release (CR) mechanism has negligible influence on the dielectric relaxation time τe in the entangled regime, which appears to disagree with the previous data. Thus, we revisited the classical problem: CR contribution to the dielectric relaxation of PI. Specifically, we made dielectric and viscoelastic measurements f...

Dynamics of 4-pentyl-4’-cyanobiphenyl (5CB) dissolved in several polymers at concentrations of 3 - 7 wt% was examined by dielectric relaxation measurement. Glassy (segmental) mode of the matrix polymer was also investigated by viscoelastic measurements for the same samples. Polystyrene (PS), poly(4-methylstyrene) (P4MS), and poly(4-tert-butylstyrene) (PtBS) were used as host polymers considering that they have the same backbone structure but different side-chain bulkiness. Two dielectric relaxation modes (slow and fast modes) of 5CB component appeared in all the mixtures and the relative intensity of the fast mode increased in the order of PS < P4MS < PtBS, corresponding to the order of the side-chain bulkiness and main chain stiffness. The effects of such chemical structure differences on the two relaxation modes, particularly their temperature dependence were examined in detail. Comparison of relaxation times for the fast mode and the segmental dynamics of the matrix polymer suggests that the fast mode was attributed to the restricted orientational fluctuation, which includes precession motion around the long axis, of 5CB molecule in a confined space formed by slow polymer chains. The dielectric intensity of the fast mode increased with increasing side-chain bulkiness of polymers. This means that the larger side-chain decreases the spatial restriction for the movement of guest 5CB molecules in the glassy state. The slow mode was attributed to the rotational motion of 5CB molecule nearly cooperative with the segmental motion of matrix polymer. The relaxation times of dielectric slow mode and viscoelastic glass mode were compared. Temperature dependence of the slow mode was slightly different from that of the segmental motion of polymer corresponding to the glass mode. From the difference between these relaxation times, the correlation length relevant to the glass mode was determined as functions of temperature for the three polymers.

Structure and dynamics of semicrystalline polymer films composed of syndiotactic polystyrene (sPS) and 2-butanone were examined through X-ray diffraction, polarized FTIR, and dielectric relaxation measurements. The X-ray and FTIR measurements revealed its crystal structure to be δ-clathrate containing 2-butanone molecules inside. The carbonyl group of 2-butanone in the crystal was found to orient preferentially parallel to the ac plane of the crystal through the polarized ATR FTIR measurements. Dielectric measurements were also conducted on these film samples to see only the relaxation dynamics of 2-butanone thanks to the high dielectric intensity of 2-butanone compared to sPS. Two relaxation modes denoted by slow and fast modes appeared. The former was assigned to the motion of 2-butanone molecules entrapped in the cavities of the crystalline (δ-form) and the latter to those in the amorphous region. We focused on the slow mode in order to elucidate the specific dynamics of the guest molecule confined in the crystalline region. The relaxation time of the slow mode was about 4 orders of magnitude longer than that of liquid 2-butanone. This suggests that the dynamics of guest molecules is highly restricted due to the high barrier to conformational and/or orientational change of the guest molecule in the cavity of δ-crystal. Furthermore, the dielectric intensity Δε of the slow mode was much smaller than the one calculated from that of bulk liquid 2-butanone and the guest concentration in the crystalline region (the intensity was only 10% of the estimated value from the bulk liquid data). This result also indicates that the free rotational motion of 2-butanone molecules is restricted inside the crystal. This will be consistently related to the weak uniplanar orientation of the carbonyl group of 2-butanone parallel to the ac plane revealed by the X-ray and polarized ATR FTIR measurements.

Dynamic birefringence and viscoelasticity measurements of bottlebrush-like polystyrene polymacromonomers having various branch (side chain) lengths were conducted over a wide frequency region covering from the glass-to-rubber transition zone to the flow zone in order to discuss effects of side chain length on dynamical stiffness of main polymer chain. Strain-induced birefringence at high frequencies was negative, similarly to linear polystyrenes, irrespective of side chain length, while birefringence in the flow zone strongly depended on side chain length. By using the modified stress-optical rule (MSOR), the complex modulus was decomposed into two components, main chain and branch components. With increasing the side chain length, the dynamical stiffness of main chain (number of repeating units per viscoelastic segment) first increased and then leveled off, suggesting that repulsive interaction between branches would be screened out over a certain branch length.

A glass transition temperature, T(g), and a β relaxation temperature, T(β), of spin-labeled polystyrene (PS) having a number average molecular weight (M(n)) of ca. 25 kDa were determined by the microwave power saturation (MPS) method of electron spin resonance (ESR). Spin labeling was selectively carried out at chain ends or midchain segments. This method allowed us to determine the local T(g) and the local T(β) around the spin-labeled sites, selectively. The T(g) determined by the ESR, T(g,ESR), was in good agreement with that determined by differential scanning calorimetry, T(g,DSC); the T(g,ESR) decreased with decreasing M(n) with blending oligomers as well as the T(g,DSC). The T(g,ESR) for the end-labeled PS (PS-E) was equal to that for the midchain-labeled PS (PS-M) irrespective of the M(n). However, we previously reported that the PS-E showed distinctly higher segmental mobility than the PS-M in the temperature range 423-463 K (above T(g)). Therefore, we conclude that the chain ends intrinsically have higher segmental mobility than midchain segments due to the discontinuity of repeat units; however, the mobilities of chain ends and midchain segments are averaged out in the vicinity of T(g) due to the cooperativities with neighboring numerous chain segments. Concerning the β relaxation, the T(β) determined by the MPS was in good agreement with those determined by dielectric and dynamic mechanical spectroscopies and dilatometry. The T(β) of the PS-E was the same with that of the PS-M within experimental uncertainties; the T(β) was insensitive to the M(n) in contrast to the T(g). Therefore, we conclude that the effect of chain end is little on the β relaxation of PS due to its local character. In addition, the effect of annealing at 353 K was found to be the same for the T(β)s of the PS-E and PS-M.

We conducted dielectric and viscoelastic relaxation measurements for polystyrene (PS)/4-pentyl-4′-cyanobiphenyl (5CB) and PS/4-pentyl-4′′-cyanoterphenyl (5CT) mixtures in the miscible state with the weight fractions of 5CB or 5CT from 0.04 to 0.27 to examine the relationship between two-component dynamics in the mixture. Dielectric relaxation measurements mainly probed the dynamics of low-mass molecule (LM), 5CB or 5CT, because of the much larger dipole moment of LMs compared to that of PS. PS/5CB mixtures exhibited bimodal dielectric relaxation, while PS/5CT showed unimodal relaxation. The observed two relaxation modes (slow and fast modes) in PS/5CB were attributed to the full rotational motion and partial rotational motion of 5CB, respectively. The latter motion is allowed in the restricted space surrounded by less mobile PS matrix. In the case of 5CT, the fast mode was suppressed due to the larger size of 5CT molecule, and only the slow mode (rotational mode) appeared. The relaxation times of slow mod...

Atactic polystyrene (PS) has the type-B dipole perpendicular to the chain backbone so that its local, segmental motion activates the dielectric relaxation. For monodisperse oligostyrene (OS) and PS samples of various molecular weights M, details of this motion were examined at temperatures T well above Tg through comparison of the complex modulus, G* = G′ + iG′′, and the complex dielectric permittivity, e* =e′ – ie′′, measured as functions of the angular frequency ω. For the OS samples, G*(ω) and e*(ω) fully relaxed through the segmental dynamics thereby exhibiting respective terminal relaxation tails (low-frequency tails), G′(ω) ∝ ω2, G′′(ω) ∝ ω, Δe′(ω) ≡ e′(0) – e′(ω)∝ ω2, and e′′(ω) ∝ ω, at ω below the segmental relaxation frequency ωs. For the PS samples, G*(ω) relaxed partly through the segmental dynamics and then exhibited the polymeric full relaxation characterized by the Rouse-like behavior followed by the terminal flow behavior (with/without intermediate entanglement plateau depending on M). In c...

Viscoelastic, dielectric, and rheo-optical behavior was examined for miscible blends of high-M cis-polyisoprene (PI) and poly(p-tert-butylstyrene) (PtBS). The slow dielectric relaxation of the blends was exclusively attributed to the global motion of the PI chains having the type-A dipoles. The PI and PtBS chains behaved as the fast and slow (low- and high-friction) components and were well entangled with each other. The dynamics of these chains changed significantly with temperature T. At high T, the blend exhibited two-step entanglement plateau of the storage modulus G′(ω), and the plateaus at high and low angular frequencies (ω) were attributed, with the aid of the dielectric data, to the entanglement among all component chains and that between the PtBS chains, respectively. The entanglement length a characterizing the high-ω plateau was well described by a simple mixing rule based on the number fraction n of the Kuhn segments of the components, a = nPIaPIbulk + nPtBSaPtBSbulk. This result was consiste...

Poly(vinyl acetate)/poly(methyl glycidyl ether) (PVAc/PMGE) blends were found to be miscible in wide ranges of temperature and composition. We made dielectric relaxation measurements for this miscible blend at several compositions to examine the degree of dynamic heterogeneity. Two α-relaxation peaks were observed in both temperature and frequency dependencies of dielectric loss curves. These two relaxation modes were attributed to the segmental motion of each component. From the temperature dependence of each segmental relaxation time, we determined two effective glass transition temperatures (TgeffPVAc and TgeffPMGE) as functions of the blend composition. Existence of the intrinsic Tgeff of the components, which were different more than 20K, indicates that the PVAc/PMGE blend is ‘dynamically heterogeneous’. We found that the self-concentration model could semiquantitatively explain the composition dependence of each Tgeff.

Effects of solvents on segmental dynamics of polystyrene (PS) at the chain end have been studied by the site-specific spin-label method of electron spin resonance (ESR). PS’s having similar number-average molecular weight (ca. 25 kDa) but labeled with a nitroxde at the chain end (E-PS) or midchain segments (M-PS) individually were used for the measurements. Toluene and dioctyl phthalate (DOP) which are good and theta solvents, respectively, for PS were selected as solvents. The temperature variation of ESR spectra was simulated based on the “macroscopic order with microscopic disorder” model to determine the segmental mobility of the labeled segment. The E-PS showed obviously and slightly higher mobility compared to the M-PS in the bulk PS and in the concentrated PS/DOP (50/50) solution, respectively. On the other hand, the E-PS showed the same mobility with the M-PS within experimental uncertainties in the dilute PS/toluene (1/99), concentrated PS/toluene (60/40), and dilute PS/DOP (3/97) solutions. Name...