Dynamics Of Poly Research Articles

Slow polymer dynamics in poly(3-hexylthiophene) probed by muon spin relaxation

Slow polymer dynamics in poly(3-hexylthiophene) probed by muon spin relaxation

New Insights into the Dynamics of Poly(amidoamine) Dendrimers with Amino Surface Groups from Segmental Relaxation and Ionic Conductivity

New Insights into the Dynamics of Poly(amidoamine) Dendrimers with Amino Surface Groups from Segmental Relaxation and Ionic Conductivity

Structure and dynamics heterogeneity in poly(vinyl acetal)s: The effect of side group length

Understanding on the structure and dynamics of poly(vinyl acetal)s is insufficient due to the complicated chemical structure and amorphous nature of this type of polymers. In this work, we investigate the effect of side group length on structure and dynamics heterogeneity at different length scales spanning from side group, segment, and polymer network by combing dynamic mechanical analysis (DMA), dielectric relaxation spectroscopy (DRS), solid-state NMR, and differential scanning calorimetry analysis (DSC). By increasing the length of acetal side group, its intrinsic dynamics slows down. Taking into account the scale of segment and networks, with the increase of acetal group length, the formation of cross-linking sites formed by the hydroxyl-rich domain is suppressed, the relaxation distribution of the segment widens, and the volume fraction of rigid component decreases. The effect of side group length on the structure and dynamics heterogeneity of poly(vinyl acetal)s at different scales results in significant changes in material properties such as the non-monotonic change in loss factor value (tan δ) and a monotonous reduction in glass transition temperature (Tg).

Differential Poly(A) Tail Length Analysis Using Nanopore Sequencing.

The poly(A) tail is a sequence of several adenosine nucleotides added to the 3' end of RNA molecules transcribed by polymerase II. The dynamics of poly(A) tail length play a significant role in regulating post-transcriptional gene expression by regulating the stability, translation, and decay of messenger RNAs. As a result, an accurate measurement of poly(A) tail length changes is important for understanding its regulatory function in different cellular contexts. Here, we outline a method for using nanopore sequencing and linear mixed models to analyze differences in poly(A) tail length across conditions.

Polymer architecture effect on rheology and segmental dynamics in poly (methyl methacrylate)-silica nanocomposite melts.

Architecturally different polymer chains lead to fundamentally different rheological responses and internal dynamics, which can be utilized to rationalize advanced thermoplastic nanocomposites with tunable mechanical behavior. In this work, three model poly (methyl methacrylate) (PMMA) polymers with linear, bottlebrush, and star architectures with the same total molar mass were investigated in their neat form, and nanocomposites with well-dispersed silica nanoparticles using rheology and broadband dielectric spectroscopy (BDS). The master curves of the dynamic moduli obtained by time-temperature superposition (TTS) over the entire range from the Rouse regime to the terminal flow and a sequence of significantly different relaxation modes were observed for the samples with linear and branch chains. While linear chains form an entangled polymer network, the branched bottlebrush, and star chains show a viscoelastic response with no sign of rubbery entanglement plateau and a weak arm relaxation regime between Rouse and terminal flow, akin to other branched polymers. Moreover, branched chains showed a higher fragility index (m = 3.46 for the bottlebrush and 5.36 for the star) compared to linear chains (m = 3.29) due to dynamical heterogeneities induced by arm relaxation. The addition of nanoparticles affects only the terminal relaxation regime, where the whole chain motion is hindered by the attractive nanoparticles. The dynamics of the polymer segment were investigated by performing broadband dielectric spectroscopy (BDS) at a frequency range from 10-2 Hz to 107 Hz. The results revealed more than 10 times slower segmental relaxation for the star homopolymers and a slowdown in the α-relaxation process for all three architectures in their composite form. The dynamical slowdown in the composites is temperature dependent and more pronounced at low temperatures (leading to approximately equal to 80 times slower dynamics for nanocomposite with bottlebrush PMMA at 150 °C) due to prolonged relaxation of the interfacial polymer compared to the matrix chains. The results from this study have practical applications in fields such as gas separation and polymeric electrolyte membranes, where simultaneous improvement of segmental mobility and mechanical moduli is highly desired.

Ionic transport and segmental dynamics in poly(ethylene oxide) based polymer electrolytes: Dependence on molecular weight of host polymer matrix

We have investigated the ion transport and segmental dynamics in poly(ethylene oxide) (PEO) and sodium tetrafluoroborate (NaBF4) salt based solid polymer electrolytes as a function of molecular weight of PEO polymer matrix at a fixed salt concentration (EO/Na = 18) using broadband dielectric spectroscopy. The molecular weight (Mv) of PEO polymer matrix was varied from 1 × 105 to 6 × 105 g/mol. The ionic conductivity of the PEO based electrolytes obtained from the complex impedance plot showed a correlation with the glass transition temperature, crystallinity and ion diffusion coefficient. The AC conductivity spectra were analyzed by using the universal power law model, except the low frequency region, where the electrode polarization contribution was dominant. The temperature dependence of ionic conductivity and the hopping frequency followed the Vogel-Tammann-Fulcher (VTF) relation, indicating a coupling between the ion transport and the segmental dynamics of polymer chains. The segmental dynamics was investigated using the derivative dielectric constant spectra. The modulus spectra were well described by the Havriliak-Nigami and the Kohlrausch-Williams-Watts functions. The temperature dependence of the conductivity relaxation time also followed the VTF relation. The ion transport in PEO based polymer electrolytes with higher molecular weight was found more cooperative than that of the other polymer electrolytes.

Regulating exchange dynamics in poly(β-hydrazide esters) via push-pull electronic effects towards covalent adaptable networks with fast reprocessing

Poly(β-hydrazide esters), prepared by the aza-Michael addition of a hydrazide to an acrylate moiety, have been used to accelerate the dissociation rates of dynamic aza-Michael adducts via push-pull electronic effects to create covalent adaptable networks (CANs) with faster reprocessing rates. Hydrazide precursors containing aryl groups that can conjugate with the carboxamide functionality can increase the electron density on the terminal amine of the hydrazide (push electronic effect). On the other hand, hydrazide precursors containing alkyl groups that cannot conjugate with the carboxamide will have terminal amines that are more electron-deficient since part of its electron density is donated to the carbonyl group (pull electronic effect). We used small molecule models of the CANs to show that the push electronic effect of the aryl carboxamide group accelerated the dissociation rates of the dynamic aza-Michael adducts and significantly increased the reversibility of the Michael addition. In contrast, the pull electronic effect of the alkyl carboxamide groups reduced the dissociation rates of the dynamic aza-Michael adducts. Likewise, when we examined the reprocessing of the CANs, the poly(β-hydrazide esters) with the push electronic effect had lower stress relaxation times (69–79 s) and reprocessing times than their congeners with the pull electronic effect (182–3760 s). They can be reprocessed at least 10 times when heated to 180 °C for 0.5 h. Regulating the thermal stability of the dynamic aza-Michael adducts can thus reduce the dependence of the reprocessing performance of the CANs on the boiling points of the monomers. In addition, these poly(β-hydrazide esters) show excellent heat resistance (Tg = 113 °C andTd-5% = 279 °C). Thus, the push-pull electronic effect of the carboxamide groups provides a useful strategy to regulate the reversibility of the dynamic covalent bonds to achieve thermosets that can be reprocessed rapidly.

Inter and intra molecular dynamics in poly(trimethylene 2,5-furanoate) as revealed by infrared and Broadband Dielectric Spectroscopies

Infrared spectroscopy (IR) and Broadband Dielectric Spectroscopy (BDS) experiments have been performed in poly(trimethylene 2,5-furanoate)(PTF) and poly(trimethylene terephthalate)(PTT) below their glass transition temperatures. The BDS experiments reveal a richer inter-molecular dynamic for PTT as characterized by a multimodal β relaxation in contrast with the monomodal one exhibited by PTF. The evolution with temperature of comparable IR absorption bands is very similar for PTF and PTT and shows small shifts in wavenumbers towards lower values, with exception of the band related to the stretching mode of the carbonyl group. In addition, a significant difference appears in the shape of the bands associated with the –CO stretching. While for PTT the absorption feature is comprised of a single component, that for PTF exhibits several components suggesting the presence of hydrogen bonds. This effect may be responsible for the monomodal shape of the β relaxation of PTF since a higher degree of intramolecular coupling between the furan ring and the rest of the monomer is expected. Density Functional Theory (DFT) calculations support the experimental results revealing that as temperature increases an increment of the syn conformations of the 2,5-furandicarboxylic acid (FDCA) moiety is likely to occur in the amorphous state. The energy gain from more stable anti to less stable syn isomers can be compensated by the formation of hydrogen bonds between interchain FDCA moieties in syn conformations. This effect may cause additional hindrance to the intermolecular dynamics of the dielectric β relaxation. It is conceivable that the hindrance exhibited by PTF in both intra and inter-molecular dynamics may play a role in the reduction of gas diffusion and permeability of PTF in comparison with PTT.

Influence of Polymer Polarity and Association Strength on the Properties of Poly(alkyl ether)-Based Supramolecular Melts

The present work focuses on the impact of polymer polarity and hydrogen-bonding (H-bonding) end groups association strength on the structure and dynamics of poly(alkyl ether)-based supramolecular model polymers studied by means of small angle scattering (SAS), rheology, dielectric relaxation spectroscopy (DRS), and differential scanning calorimetry (DSC). These consist of poly(propylene oxide) (PPO) or poly(ethylene oxide) (PEO) backbone that self-assembly in the bulk via hydrogen bonding (H-bonding). Diaminotriazine (DAT) and thymine-1-acetic acid (THY) as well as 2-ureido-4[1H]-pyrimidinone (UPY) are the H-bonding end groups of choice. Both PPO and PEO bearing either DAT or THY as end groups associate into linear chains, but PPO-THY/DAT forms longer chains in comparison with PEO-THY/DAT. The lower polarity of the backbone results in stronger associations for the same end groups. However, the temperature dependence of the association/dissociation lifetimes for this H-bonding type is independent of the different main chain polarity as these breaking times do not exceed the rouse chain dynamics as expected within the Cates model. PPO-UPY forms a transient network characterized by the interplay between small transient bonds controlled by the characteristic times of association/dissociation between pairs of UPY groups involving probably just two ends, revealed by the similar dielectric spectra with PPO backbone, and a more stable bond type of associate that forms phase separated UPY clusters. The latter are responsible for the physical cross-links in the network and result in the rubbery-like plateau of the rheological spectra. PPO-UPY has similar structure to PEO-UPY, as validated by small angle scattering, but the UPY detachment times in the clusters are longer for PEO-UPY than for PPO-UPY, though the activation energies are very close and match the typical energy barrier specifically imposed by the hydrogen bonds. Moreover, while the segmental relaxation times and the glass transition temperature (Tg) of PPO-UPY is similar to PPO, PEO-UPY has the highest Tg value and a much slower segmental relaxation as compared to PEO and PPO based supramolecular polymers. This seems to indicate that the H-bonding association dynamics of the UPY groups is strongly influenced by the main chain polarity that play a fundamental role in defining the time scale of the association process.

Dynamics of Poly(methyl methacrylate) in Ionic Liquids with Different Concentration and Cationic Structures

Dynamics of Poly(methyl methacrylate) in Ionic Liquids with Different Concentration and Cationic Structures

Understanding the Impacts of Support-Polymer Interactions on the Dynamics of Poly(ethyleneimine) Confined in Mesoporous SBA-15.

Supported amines are a promising class of CO2 sorbents offering large uptake capacities and fast uptake rates. Among supported amines, poly(ethyleneimine) (PEI) physically impregnated in the mesopores of SBA-15 silica is widely used. Within these composite materials, the chain dynamics and morphologies of PEI strongly influence the CO2 capture performance, yet little is known about chain and macromolecule mobility in confined pores. Here, we probe the impact of the support-PEI interactions on the dynamics and structures of PEI at the support interface and the corresponding impact on CO2 uptake performance, which yields critical structure-property relationships. The pore walls of the support are grafted with organosilanes with different chemical end groups to differentiate interaction modes (spanning from strong attraction to repulsion) between the pore surface and PEI. Combinations of techniques, such as quasi-elastic neutron scattering (QENS), 1H T1-T2 relaxation correlation solid-state NMR, and molecular dynamics (MD) simulations, are used to comprehensively assess the physical properties of confined PEI. We hypothesized that PEI would have faster dynamics when subjected to less attractive or repulsive interactions. However, we discover that complex interfacial interactions resulted in complex structure-property relationships. Indeed, both the chain conformation of the surface-grafted chains and of the PEI around the surface influenced the chain mobility and CO2 uptake performance. By coupling knowledge of the dynamics and distributions of PEI with CO2 sorption performance and other characteristics, we determine that the macroscopic structures of the hybrid materials dictate the first rapid CO2 uptake, and the rate of CO2 sorption during the subsequent gradual uptake stage is determined by PEI chain motions that promote diffusive jumps of CO2 through PEI-packed domains.

Effect of Ring Rigidity on the Statics and Dynamics of Linear Catenanes

We used molecular dynamics simulations to investigate the statics and dynamics of poly[n]catenanes for different bending rigidities of the constituent rings. We show that stiffer rings yield catenanes with more extended and, at the same time, more flexible backbones. The softening of the backbone reflects the decreasing steric interactions of catenated rings as their shape becomes more oblate due to increased rigidity. The internal dynamics of catenanes is affected too. Going from flexible to rigid rings causes a several-fold slowing of different processes, from segmental rotations and size fluctuations to Rouse modes. Finally, by considering the statics and dynamics of crowded solutions of catenanes, we isolate another emergent property controlled by the rigidity of the rings. Specifically, we show that catenanes with rigid rings hinder each other’s motion more than those with flexible rings. Thus, in equally crowded solutions, the diffusion coefficient is smaller for catenanes with stiffer rings.

Dynamics of Poly(cyclohexene carbonate) as a Function of Molar Mass

Stereoregular poly(cyclohexene carbonate) (PCHC) homopolymers were prepared via copolymerization of cyclohexene oxide and carbon dioxide (CO2) using (R,R)-(salcy)-CoCl and bis(triphenylphosphine)iminium chloride as a catalyst. The homopolymers had molar masses in the range of 4800–33,000 g mol–1 and relatively narrow dispersity after careful fractionation, as required for the molecular dynamics investigation. We employed differential scanning calorimetry and dielectric spectroscopy, the latter as a function of temperature and pressure, for investigating the thermal properties and the molecular dynamics, respectively. The segmental dynamics in the vicinity of the liquid-to-glass temperature was very complex. The dual segmental processes were inseparable by decreasing the temperature or by increasing the pressure. Based on DFT calculations of the dipole moment, they were ascribed to different stereo sequences of the PCHC backbone. The limiting glass temperature, Tg, for very high molar masses was ∼125 °C. The high Tg value obtained herein well justifies its application as a CO2-based alternative for polystyrene (PS) in a variety of materials based on block copolymers. Moreover, fragility increased with increasing molar mass with values intermediate to poly(styrene) and poly(cyclohexyl methacrylate). The flexible cyclohexyl group in PCHC undergoing intramolecular chair-to-chair conversion increases the packing ability and consequently decreases the fragility. PCHC is a brittle material because it lacks entanglements even for the higher molar masses investigated herein, which is relevant for application as a PS substitute. Within the investigated range of molar masses, the dependences of the terminal relaxation times, τΝΜ, and of the zero-shear viscosity, ηο, on the molar mass, M, are τΝΜ/τSM ∼ M3.2 and ηο ∼ M1.4, revealing an intermediate behavior between Rouse and entangled chains.

Effects of Nanometer Confinement on the Self-Assembly and Dynamics of Poly(γ-benzyl-l-glutamate) and Its Copolymer with Poly(isobutylene)

Effects of Nanometer Confinement on the Self-Assembly and Dynamics of Poly(γ-benzyl-<scp>l</scp>-glutamate) and Its Copolymer with Poly(isobutylene)

Dielectric relaxation and glassy dynamics in poly(diisopropyl fumarate) and its copolymers with acrylate segments

Dynamical behavior and glass transitions in copolymers of diisopropyl fumarate (DiPF) with 1-adamantyl acrylate (AdA) or n-butyl acrylate (nBA) are investigated by dielectric relaxation spectroscopy (DRS) to elucidate the effect of structural constraint due to the absence of a CH2 spacer on the dynamics. DRS measurements revealed that the two copolymers exhibit three dynamical processes: α-, β-, and γ-processes. The relaxation time of the β-process can be described by the Vogel-Fulcher-Tammann (VFT) law in addition to the α-process. Hence, two glass transition temperatures, Tg, can be evaluated from α- and β-processes. The AdA and nBA fraction dependence of Tgs is consistent with that obtained by dynamical mechanical analysis. The Vogel temperature of the α-process is nearly equal to that of the β-process for the PDiPF homopolymer. With the increase in the AdA fraction, the difference in the Vogel temperature between the α- and β-processes increases. This result suggested that there is an intrinsic correlation between the α- and β-processes for PDiPF, and the correlation changes with the AdA fraction. From the nBA fraction dependence of the β-process, the β-process of PDiPF can be related to the segmental motion of the main chain. Nevertheless, PDiPF exhibits a solid-like property up to the Tg, which is related to the α-process. The physical origins of other processes also were discussed.

2H NMR Study of Polymer Segmental Dynamics at Varying Cross-Linking in Poly(N-isopropylacrylamide) Microgels.

A microscopic understanding of the internal structure and dynamics of poly(N-isopropylacrylamide) (PNIPAM) chains, in microgel colloids, is developed using deuterium NMR (2H NMR) to study deuterated PNIPAM suspensions as functions of temperature and pressure for four cross-linker molar fractions (f). The PNIPAM polymers were labeled with deuterons at the backbone (d3-PNIPAM) or on side chains (d7-PNIPAM). 2H NMR spectra of the d3-PNIPAM suspensions for all cross-linker molar fractions indicated freely moving chains at low temperature and a nearly immobilized fraction above ∼35 °C. Polymer segments in the collapsed phase of the d3-PNIPAM suspension were more mobile than those in the dry powder. This is direct microscopic evidence that the polymer remains significantly hydrated in the collapsed phase, consistent with strong, indirect evidence from recent light scattering and rheology measurements from our laboratory. However, the observation of a small fraction of immobilized segments in the swollen phase for higher cross-linker molar fraction suggests that, particularly for high levels of cross-linking, some polymer is nonhydrated even in the swollen phase. Finally, variable-pressure NMR (up to 90 MPa) showed a slight increase in transition temperature with pressure for lower cross-linker molar fractions and a larger increase in transition temperature with pressure for higher cross-linker molar fractions. This is consistent with a previously reported dependence of collapse transition enthalpy on cross-linker molar fraction.

Sub-Rouse Dynamics in Poly(isobutylene) as a Function of Molar Mass

We report on the molar mass dependence of the segmental, sub-Rouse, and terminal relaxation processes of poly(isobutylene). For this purpose, seven samples were synthesized with molar masses in the range from 2.8 to 172 kg·mol–1 and investigated by temperature-modulated differential scanning calorimetry, dielectric spectroscopy, and rheology. Rheology provided access to the terminal times that were found to scale as τterm ∼ Μ3.2. On the other hand, the sub-Rouse dielectric process shows a very weak molar mass dependence (τsub – Rouse/τSM ∼ M0.1), that is, distinctly different from the Rouse and terminal dynamics. We infer that the sub-Rouse mode has a lengthscale intermediate to the statistical segment length (∼1.25 nm) and the length of an entanglement strand (∼2.3 nm).

Ultrafast Dynamics Experienced by Carbon Dioxide Diffusing through Polymer Matrices.

Fourier transform infrared, pump-probe polarization anisotropy, and two-dimensional infrared spectroscopies were used to study the steady-state and time-dependent behavior of carbon dioxide dissolved in three different polymer systems. Gas reorientation dynamics in poly(methyl methacrylate), poly(methyl acrylate), and poly(dimethylsiloxane) were sensitive to the nature of chemical interactions between the gas and polymer, as well as whether the polymer was in a glassy or rubbery phase. The homogeneous dynamics experienced by the asymmetric stretching vibration were found to be fastest for rubbery polymers with weak, nonspecific gas-polymer interactions. Spectral diffusion was absent for the carbon dioxide vibrational mode in glassy poly(methyl methacrylate) but was activated for the chemically similar but rubbery poly(methyl acrylate). The vibrational dynamics are shown to have a direct correlation with the diffusivity of carbon dioxide through the polymer matrices.

Ultrafast Fluorescence Depolarization in Conjugated Polymers.

We report on large-scale simulations of intrachain exciton dynamics in poly(para-phenylenevinylene). Our theoretical model describes Frenkel exciton coupling to both fast, quantized C-C bond vibrations and slow, classical torsional modes. We also incorporate system-bath interactions. The dynamics is simulated using the time evolution block decimation method, which avoids the failures of the Ehrenfest approximation to describe decoherence processes and nonadiabatic interstate conversion. System-bath interactions are modeled using quantum trajectories and Lindblad quantum jump operators. We find that following photoexcitation, the quantum mechanical entanglement of the exciton and C-C bond phonons causes exciton-site decoherence. Next, system-bath interactions cause the stochastic collapse of high-energy delocalized excitons into chromophores. Finally, torsional relaxation causes additional exciton-density localization. We relate these dynamical processes to the predicted fluorescence depolarization, extract the time scales corresponding to them, and thus interpret the observed sub-ps fluorescence depolarization.

Swelling dynamics of Poly (N, N- Dimethylacrylamide - co- Crotonic acid) Hydrogel and Evaluation of its Potential for Controlled Release of Fertilizers

Swelling dynamics of Poly (N, N- Dimethylacrylamide - co- Crotonic acid) Hydrogel and Evaluation of its Potential for Controlled Release of Fertilizers