Polymer Chains In Solution Research Articles

Toward Synthetic Intrinsically Disordered Polypeptides (IDPs): Controlled Incorporation of Glycine in the Ring-Opening Polymerization of N-Carboxyanhydrides.

Intrinsically disordered proteins (IDPs) do not have a well-defined folded structure but instead behave as extended polymer chains in solution. Many IDPs are rich in glycine residues, which create steric barriers to secondary structuring and protein folding. Inspired by this feature, we have studied how the introduction of glycine residues influences the secondary structure of a model polypeptide, poly(l-glutamic acid), a helical polymer. For this purpose, we carried out ring-opening copolymerization with γ-benzyl-l-glutamate and glycine N-carboxyanhydride (NCA) monomers. We aimed to control the glycine distribution within PBLG by adjusting the reactivity ratios of the two NCAs using different reaction conditions (temperature, solvent). The relationship between those conditions, the monomer distributions, and the secondary structure enabled the design of intrinsically disordered polypeptides when a highly gradient microstructure was achieved in DMSO.

Form II to form I transition in solution-crystallized isotactic polybutene-1.

Different polymer chains in a solution or melt have different conformations with corresponding entropy at each moment, which would be confined after crystallization. Equilibrium concept-based conformation or conformational entropy depends on chain dynamics, which is related to the effect of energy on conformational changes in polymer chains. Herein, an isotactic polybutene-1 (iPB-1) crystal was crystallized from solution by adding a precipitant at various temperatures. The solution-crystallized iPB-1 crystal was heated to 100 °C to obtain form II at different heat rates and the transition of form II was characterized. It was found that the form II to form I transition was not only related to the precipitation temperature but also to the heating rate of the solution-crystallized iPB-1. Thus, both precipitation temperature and heating rate determine the formation temperature of form II, i.e., form II that crystallized at lower temperature would transform faster. The results indicate that the conformation or conformational entropy of the amorphous region in iPB-1 is important to understand crystal transition.

Effectiveness of DPD Simulations to Predict the Dynamics of Polymer Chains in Solutions at Equilibrium and Steady Shear Flows

AbstractThe suitability of dissipative particle dynamics simulations is investigated to predict the dynamics of polymer chains in dilute polymer solutions. The authors find that the predictions depend on the value of the repulsive parameter for bead‐bead pairwise interactions used in the DPD simulations (aij). For all systems, the chain sizes and the relaxation time spectrum are analyzed. For aij = 0, theta solvent behaviour is obtained, whereas the dynamics at equilibrium agrees well with the predictions of the Zimm model. For higher values of aij, the static properties of the chain show good solvent behaviour. However, the scaling laws for the chain dynamics at equilibrium show wide variations, with consistent results obtained only at an intermediate value of aij = 25. At higher values of the repulsive parameter (aij ⩾ 25), the simulations are also able to predict the abrupt cut‐off in the relaxation spectrum, which has been observed earlier in experiments of dilute solutions. To verify further, the chain dynamics in shear flow using DPD simulations is studied. Specifically, the variation of the chain is analysed stretch and end‐over‐end tumbling with shear rates. Overall, the trends obtained from DPD simulations agree well with those observed in earlier BD simulations.

Influence of solvent quality on the swelling and deswelling and the shear modulus of semi-dilute solution cross-linked poly(vinyl acetate) gels.

We systematically examine the influence of varying temperature (T) over a large range in model poly(vinyl acetate) gels swollen in isopropyl alcohol. The theta temperature Θ, at which the second virial coefficient A2 vanishes, is found to be equal to within numerical uncertainty to the corresponding high molecular mass polymer solution value without cross-links, and we quantify the swelling and deswelling of our model gels relative to their size at T = Θ, as customary for individual flexible polymer chains in solutions. We also quantify the "solvent quality" dependence of the shear modulus G relative to G(T = Θ) and compare to the hydrogel swelling factor, α. We find that all our network swelling and deswelling data can be reduced to a scaling equation of the same general form as derived from renormalization group theory for flexible linear polymer chains in solutions so that it is not necessary to invoke either the Flory-Huggins mean field theory or the Flory-Rehner hypothesis that the elastic and mixing contributions to the free energy of network swelling are separable to describe our data. We also find that changes of G relative to G(T = Θ) are directly related to α. At the same time, we find that classical rubber elasticity theory describes many aspects of these semi-dilute solution cross-linked networks, regardless of the solvent quality, although the prefactor clearly reflects the existence of network defects whose concentration depends on the initial polymer concentration of the polymer solution from which the networks were synthesized.

Molecular single crystals induce chain alignment in a semiconducting polymer

The blending of π-conjugated molecules with polymeric semiconductors into a composite system is an effective strategy to promote charge carrier mobility because of the transmission path by the conductive polymers through electrical bridge connection of the small organic molecule crystalline domain. In this work, pentacene single crystal was prepared to induce the conjugated polymer chain alignment of polymeric semiconductor PDPP2T-TT-OD to form the semiconducting composite, which led to enhanced field-effect mobility of the organic thin-film transistor (OTFT) by improving the crystallinity due to nucleation and growth phase separation. Besides, with the addition of anti-solvents, the crystallization of the blend film was further improved, 27 times higher than that of a pure polymer semiconductor–based OTFT. That was because the pentacene nuclei induced polymer crystallization through π-π interactions and the addition of anti-solvent promoted the aggregation of polymer chains in solution, enabling the molecular chains packed more closely in solid films. Therefore, the chain arrangement of polymers induced via small molecular single crystals provides a new idea to improve mobility in composite semiconductor thin films for the construction of novel organic optoelectronic devices.

High degree of polymerization of poly(1-pyrenebutyric acid) enables the ultra-trace detection of Cr2O72− in milk

High polymerization degree is critical for polypyrene applying in fluorescent sensing field, which closely related to high sensitivity. However, polypyrene films reported are either insoluble and unprocessable or soluble with few repeat units. In this work, we synthesized a poly(1-pyrenebutyric acid) (PPBA) via electrochemical polymerization in boron fluoride ethyl ether system and the degree of polymerization was up to 43, which showed good fluorescence. The polymer showed high selectivity toward to Cr2O72− among sixteen anions and twenty cations in ethyl alcohol system, and the limit of detection was as low as 1.58 fM. Transmission electron microscope results showed that the quenching mechanism of the PPBA was Cr2O72−-induced inter- and intra-polymer aggregation of polymer chains in solution. Finally, PPBA was successfully applied in milk detection, implying that PPBA can realize the ultra-trace detection of Cr2O72− in practical application.

Charge transfer states impact the triplet pair dynamics of singlet fission polymers.

Polymers are desirable optoelectronic materials, stemming from their solution processability, tunable electronic properties, and large absorption coefficients. An exciting development is the recent discovery that singlet fission (SF), the conversion of a singlet exciton to a pair of triplet states, can occur along the backbone of an individual conjugated polymer chain. Compared to other intramolecular SF compounds, the nature of the triplet pair state in SF polymers remains poorly understood, hampering the development of new materials with optimized excited state dynamics. Here, we investigate the effect of solvent polarity on the triplet pair dynamics in the SF polymer polybenzodithiophene-thiophene-1,1-dioxide. We use transient emission measurements to study isolated polymer chains in solution and use the change in the solvent polarity to investigate the role of charge transfer character in both the singlet exciton and the triplet pair multiexciton. We identify both singlet fluorescence and direct triplet pair emission, indicating significant symmetry breaking. Surprisingly, the singlet emission peak is relatively insensitive to solvent polarity despite its nominal "charge-transfer" nature. In contrast, the redshift of the triplet pair energy with increasing solvent polarity indicates significant charge transfer character. While the energy separation between singlet and triplet pair states increases with solvent polarity, the overall SF rate constant depends on both the energetic driving force and additional environmental factors. The triplet pair lifetime is directly determined by the solvent effect on its overall energy. The dominant recombination channel is a concerted, radiationless decay process that scales as predicted by a simple energy gap law.

A Diarylacetonitrile as a Molecular Probe for the Detection of Polymeric Mechanoradicals in the Bulk State through a Radical Chain-Transfer Mechanism.

Since the beginning of polymer science, understanding the influence of mechanical stress on polymer chains has been a fundamental and important research topic. The detection of mechanoradicals generated by homolytic cleavage of the polymer chains in solution has been studied in many cases. However, the detection of mechanoradicals in the bulk is still limited owing to their high reactivity. Herein, we propose an innovative strategy to detect mechanoradicals visually and quantitatively using a chain-transfer agent that generates relatively stable fluorescent radicals as a molecular probe. Mechanoradicals generated by ball milling of polystyrene samples were successfully detected by using a diarylacetonitrile compound as a fluorescent molecular probe through this radical chain-transfer mechanism. This probe enables the visualization and quantitative evaluation of mechanoradicals generated by polymer-chain scission.

A Diarylacetonitrile as a Molecular Probe for the Detection of Polymeric Mechanoradicals in the Bulk State through a Radical Chain‐Transfer Mechanism

AbstractSince the beginning of polymer science, understanding the influence of mechanical stress on polymer chains has been a fundamental and important research topic. The detection of mechanoradicals generated by homolytic cleavage of the polymer chains in solution has been studied in many cases. However, the detection of mechanoradicals in the bulk is still limited owing to their high reactivity. Herein, we propose an innovative strategy to detect mechanoradicals visually and quantitatively using a chain‐transfer agent that generates relatively stable fluorescent radicals as a molecular probe. Mechanoradicals generated by ball milling of polystyrene samples were successfully detected by using a diarylacetonitrile compound as a fluorescent molecular probe through this radical chain‐transfer mechanism. This probe enables the visualization and quantitative evaluation of mechanoradicals generated by polymer‐chain scission.

Controlling Optical and Catalytic Activity of Genetically Engineered Proteins by Ultrasound.

Ultrasound (US) produces cavitation‐induced mechanical forces stretching and breaking polymer chains in solution. This type of polymer mechanochemistry is widely used for synthetic polymers, but not biomacromolecules, even though US is biocompatible and commonly used for medical therapy as well as in vivo imaging. The ability to control protein activity by US would thus be a major stepping‐stone for these disciplines. Here, we provide the first examples of selective protein activation and deactivation by means of US. Using GFP as a model system, we engineer US sensitivity into proteins by design. The incorporation of long and highly charged domains enables the efficient transfer of force to the protein structure. We then use this principle to activate the catalytic activity of trypsin by inducing the release of its inhibitor. We expect that this concept to switch “on” and “off” protein activity by US will serve as a blueprint to remotely control other bioactive molecules.

Non-Debye segmental relaxation of poly-N-vinyl-carbazole in dilute solution

Ultrasonic absorption measurements were carried out for poly-N-vinyl-carbazole in dilute 1,2-dichloro-ethane solution at frequencies from 1 to 50 MHz over a temperature range of 10–45°C with increments of 5°C under constant pressure. For the specific solution a single relaxation process was observed experimentally in the frequency range studied. The relaxation frequency of poly-N-vinyl-carbazole in 1,2-dichloro-ethane solution is comparable to the relaxation frequency observed in vinyl-type polymers despite the structural differences and the corresponding relaxation process is thermal in nature and assigned to the local segmental motions of some monomeric units. From the temperature dependence of the acoustic parameters we were able to estimate the thermodynamic parameters related to the segmental motion of the PVK polymer chains in solution. Furthermore, we performed molecular mechanics calculations on polymeric chains with a relatively low number of monomers to elucidate the mechanism behind the relaxation process and to establish the suggested local segmental motions of the polymer in 1,2-dichloro-ethane solution. The experimental and theoretical results have been compared and discussed in the context of relevant theories of the field.

Impact of Local Stiffness on Entropy Driven Microscopic Dynamics of Polythiophene

We exploited the high temporal and spatial resolution of neutron spin echo spectroscopy to investigate the large-scale dynamics of semiflexible conjugated polymer chains in solutions. We used a generalized approach of the well-established Zimm model of flexible polymers to describe the relaxation mode spectra of locally stiff polythiophene chains. The Zimm mode analysis confirms the existence of beads with a finite length that corresponds to a reduced number of segmental modes in semiflexible chains. Irrespective of the temperature and the molecular weight of the conjugated polymer, we witness a universal behavior of the local chain stiffness and invariability of the bead length. Our experimental findings indicate possibly minor role of the change in π-electron conjugation length (and therefore conjugated backbone planar to non-planar conformational transition) in the observed thermochromic behavior of polythiophene but instead point on the major role of chain dynamics in this phenomenon. We also obtained the first experimental evidence of an existence of a single-chain glass state in conjugated polymers.

Synthesis of spin labeled ethylene glycol based polymers and study of their segmental motion

Understanding segmental dynamics of polymer chains is important to decipher the microscopic behavior in order to modulate the bulk properties of polymers. Study of electron spin resonance (ESR) spectroscopy of polymer chain segments is useful to understand internal dynamics of polymer chains in solution. In this paper, poly(oligoethylene glycol methacrylate-co-2,2,6,6-tetramethyl piperidin-4-yl methacrylate)s, OEG-TMPMs, were synthesized. The synthesized OEG-TMPMs were characterized by nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and thermogravimetric (TG) techniques. The TMPM moiety in OEG-TMPMs was oxidized to 2,2,6,6-tetramethyl-1-piperinidyloxy-4-yl methacrylate (TMP) to generate nitroxide radicals. These nitroxide radical-containing OEG-TMPs were analyzed with Fourier transform-infrared (FT-IR) spectroscopy, cyclic voltammetry (CV) and ESR spectroscopy. The effect of side chain length on the segmental mobility of OEG-TMPs was studied. The results showed that the longer pendent chains as in OEG-TMP-4 imparted higher flexibility to the backbone of the polymer and increased rotational freedom of nitroxide radicals as compared to restricted mobility in the case of shorter polymer side chains.

Increasing lithium extraction performance by adding sulfonated poly (ether ether ketone) into block‐copolymer ethylene vinyl alcohol membrane

AbstractBACKGROUNDHigh efficiency membrane extraction (ME) of lithium from brine has been constrained by membrane mass transfer resistance. We report here a new solvent‐resistant membrane produced from ethylene vinyl alcohol (EVAL) and sulfonated polyether ether ketone (SPEEK).RESULTSThe effect of the SPEEK on the thermodynamics and kinetics of demixing to the membrane morphology was investigated systematically. Addition SPEEK created extra resistance to the movement of the polymer chains in solution which was reflected in the reduced gelation diffusion coefficient. About 0.5 wt% of SPEEK was sufficient to reduce the mass transfer resistance of lithium ions (Li+). Membrane thickness showed linear correlation with Li+ flux, but was limited by its weak mechanical strength. Finally, a composite EVAL/SPEEK membrane supported by a thin loose nonwoven fabric showed a stress of 12.5 MPa, nearly 10‐fold greater than the unsupported membrane, and the highest lithium extraction flux of 4.80 × 10−8 mol cm−2 s−1.CONCLUSIONThe work provides a rationale for developing mechanically stable, high extraction flux membranes for ME. © 2020 Society of Chemical Industry

Review and reproducibility of forming adsorbed layers from solvent washing of melt annealed films.

Recent studies suggest chain adsorption in the melt may be responsible for a number of property changes in thin films by making correlations between the residual adsorbed layer thickness hads(t) measured after a given solvent washing procedure as a function of annealing time t of the film at an elevated temperature prior to this solvent rinse. This procedure, frequently called "Guiselin's experiment", refers to the thought experiment proposed in a 1992 theoretical treatment by Guiselin that assumed chain segments in contact with the surface are irreversibly adsorbed whereby unadsorbed chains could be washed away by solvent without disturbing the adsorbed substrate contact points in the melt. In the present work, we review this recent literature, identifying and experimentally testing a common protocol for forming adsorbed layers hads(t) from solvent washing melt films. We find hads(t) curves to be far less reproducible and reliable than implied in the literature, strongly dependent on solvent washing and substrate cleaning conditions, and annealing at elevated temperatures is unnecessary as densification of films sitting at room temperature makes the glassy film harder to wash off, leaving behind hads of comparable thickness. This review also summarizes literature understanding developed over several decades of study on polymer adsorption in solution, which experimentally demonstrated that polymer chains in solution are highly mobile, diffusing and exchanging on the surface even in the limit of strong adsorption, contradicting Guiselin's assumption. Preformed adsorbed layers of different thicknesses hads are shown to not affect the average glass transition temperature or physical aging of 30 nm thick films. In summary, a number of open questions and implications are discussed related to thin films and polymer nanocomposites.

Synthesis of spin-labelled poly(acrylic acid)s and their segmental motion study

Understanding the segmental dynamics of polymer chains is cardinal to decipher the microscopic behaviour in order to modulate the bulk properties of polymers. The study of electron spin resonance (ESR) spectroscopy of spin-labelled polymers is useful to understand the segmental dynamics of polymer chains in solution. In this paper, poly(acrylic acid)s (PAAs) were spin labelled with 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl radicals. Spin-labelled PAAs (SL-PAAs) were characterised by Fourier-transform infrared spectroscopy, ultraviolet–visible spectroscopy, thermogravimetric analysis, differential scanning calorimetry, cyclic voltammetry (CV), and ESR analyses. The polyelectrolyte complexes of SL-PAAs were prepared by employing poly(diallyldimethylammonium chloride) (PDADMAC) as the polycation and analysed by transmission electron microscopy, dynamic light scattering (DLS), and ESR spectroscopies. The effect of molar mass on the segmental dynamics of SL-PAAs in pristine as well as in the form of polyelectrolyte complexes (PECs) was studied. The results indicated that SL-PAAs show a differential complexation behaviour with PDADMAC in the PECs depending on their molar mass.

Structure-property relationships via complementary hydrodynamic approaches: Poly(2-(dimethylamino)ethyl methacrylate)s

Here we present a combined analytical study of a homological series of poly(2-(dimethylamino)-ethyl methacrylate)s (DMAEMA) and their corresponding with methyl iodide quaternized versions poly[2-(methacryloyloxy) ethyl] trimethyl-ammonium iodide]s (QDMAEMA) in a wide range of molar masses (~7 to ~300kDa) and low dispersities (~1.1 to ~1.3). The polymers were studied predominantly in 0.2MNaCl in water at T=20.0°C applying mutually reinforcing's set of hydrodynamic methods, such as, viscometry, analytical ultracentrifugation, dynamic light scattering, isothermal diffusion and size exclusion chromatography. The manuscript provide compulsory discussions on the evaluation of physically sound values of the molar masses, hydrodynamic sizes and conformations of the macromolecules in solution. Special attention is paid to the investigation of ion-specific interactions and their influence on the hydrodynamic and molecular characteristics. The conformation of polymer chains in solution was validatedvia the classical scaling equations showing θ-conditions – [η]=0.055M0.47±0.04;s=0.006M0.50±0.02;D=1200M-0.50±0.02 for the initial DMAEMAs polymer chains and thermodynamically good ones for the quaternized macromolecules characterized by [η]=0.002M0.80±0.04;s=0.0133M0.45±0.02;D=1665M−0.55±0.02. The equilibrium rigidity was found to be visibly influenced by the overall electrostatic interactions and the presence of closely associated iodine ions to the quaternized polymer chains giving A=4.4nm in comparison to A=2.4nm for the initial macromolecules.

In−situ monitoring Poly(3-hexylthiophene) nanowire formation and shape evolution in solution via small angle neutron scattering

The crystallization of poly(3-hexylthiophene) (P3HT) to form nanowires has attracted considerable interest because this process significantly increases the hole mobility when compared to amorphous P3HT, leading to improved performance in photovoltaic and other organic electronic devices. However, full characterization of the crystallization self-assembly of the polymer chains in solution has not been achieved yet, due to limited use of in−situ not destructive techniques. Here, we investigate the ageing-driven formation and evolution of regioregular (rr) P3HT nanostructures in chlorobenzene solution using small angle neutron scattering (SANS) and UV–Vis spectroscopy. We have monitored how the shape of the rr-P3HT aggregates evolves. The initial states for rr-P3HT chains are the random coils, which straighten to form rods. These subsequently π - π stack to form 2D lamellae, which further stack to create nanowires. The formation of nanowires is promoted both by the length of ageing and by low temperatures (4∘C). Temperatures above >40∘C reverse the formation of nanowires. Additionally, atomic force microscopy (AFM) and grazing incidence wide angle x-ray scattering (GIWAXS) reveal that the nanowires can be successfully aligned during deposition by off-axis spin coating. Finally, the anisotropic conductivity of the aligned rr-P3HT nanowire films is reported. This is significant for applications such as gas sensing or organic thin film transistors, where increased conductivity and controlled nanostructure are desirable.

Exploring the role of relaxation time, bond length and the length of the polymer chain in the end-to-end looping kinetics of a long polymer chain in solution. An exact analytical model

A Smoluchowski-like equation is accounted for modeling the end-to-end looping kinetics. The phenomenon of looping is represented by a Dirac delta function sink of finite strength, placed at a point where the end-to-end distance between the monomers is zero. The sink is a physical quantity determining the possibility of looping at that point. We formulate two different rate constants, showing arrhenius type behaviour, which are obtained using the Green’s function method. The long term rate constant depends directly on relaxation time and inversely on the bond length and for shorter polymer constructs, the end-to-end looping is faster than the longer one.

Mechanistic study of the nucleation and conformational changes of polyamines in presence of phosphate ions

Polyamine Phosphate Nanoparticles (PANs) have great potential for the delivery of large therapeutics, such as plasmids and/or siRNAs. The formation of PANs by complexation of Poly(allylamine hydrochloride) (PAH) and phosphate ions from Phosphate Buffer (PB) was studied here, and how it is affected by the presence of phosphate ions from PB and ionic strength. From Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS) the critical PB concentration for PANs formation was determined. Below this critical point, Small Angle X-ray Scattering (SAXS) studies revealed that small PAH-phosphate aggregates coexist with not complexed or weakly complexed polymer chains in solution and that the presence of the phosphate ions increases the Kuhn length of the polymer chains until that only spherical aggregates are present in solution. TEM, DLS and SAXS showed the increase of PANs size with ionic strength up to 250 mM NaCl. At higher NaCl concentrations, PANs disassemble into smaller aggregates. Isothermal Titration Calorimetry (ITC) showed that PAN formation is an exothermic process and the association of phosphates below the critical PB concentration is entropically controlled.