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Adding small amounts of ring polymers to a matrix of their linear counterparts is known to increase the zero-shear-rate viscosity because of linear-ring threading. Uniaxial extensional rheology measurements show that, unlike its pure linear and ring constituents, the blend exhibits an overshoot in the stress growth coefficient. By combining these measurements with ex-situ small-angle neutron scattering and nonequilibrium molecular dynamics simulations, this overshoot is shown to be driven by a transient threading–unthreading transition of rings embedded within the linear entanglement network. Prior to unthreading, embedded rings deform affinely with the linear entanglement network and produce a measurably stronger elongation of the linear chains in the blend compared to the pure linear melt. Thus, rings uniquely alter the mechanisms of transient elongation in linear polymers.

A new type of model branched polymer, asymmetric H-shaped polybutadienes, consisting of central crossbars having various combinations of short and long arms attached to the ends of the crossbars, was synthesized using living anionic polymerization and chlorosilane linking chemistry. The linking agent 4-(dichloromethylsilyl)diphenylethylene provides selective reactivity to attach short or long arms on one side or both sides as desired. The samples were characterized thoroughly by size exclusion chromatography with light scattering detection (SEC-LS) and found to exhibit controlled molecular weights, as well as narrow polydispersity indices (PDIs of 1.01–1.06). Temperature gradient interaction chromatography, a method with far superior resolution as compared to SEC, also shows that these materials are well-defined, with minimal and identifiable impurities.

We report on the unusual response of a well-characterized entangled comb polymer in simple shear flow. The polymer with highly entangled backbone (about 16 entanglements) and on average 29 long branches (about 3 entanglements each) has been extensively characterized by interaction chromatography and its rheology carefully studied under controlled conditions using a special cone partitioned-plate geometry. We observe that the start-up shear stress becomes roughly rate independent above a certain critical rate, related to the relaxation time of the branches. Within the rate-independent region, the start-up shear stress displays a double overshoot. We interpret these observations in light of tube-based pompom dynamics. The key idea is that for sufficiently long branches the main stress overshoot, which reflects backbone stretching and orientation, is preceded by the withdrawal of branches into the backbone tube. The excellent quantitative comparison between the simulations and experiments supports the proposed mechanism of the double stress overshoot.

We report a method to directly introduce a hydroxyl group at the omega chain end of polystyrene prepared by atom-transfer radical polymerization. To achieve the quantitative conversion of the bromine group to a hydroxyl group, the transfer reaction of a carbocation with water was exploited. This transfer reaction is a well-known reaction in cationic polymerization. The quantitative conversion and chemical structures of the hydroxyl-terminated PS were characterized using 1H nuclear magnetic resonance spectroscopy, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and high-performance liquid chromatography. In addition, alcohol-based compounds were used to introduce acetonide and propane groups into PS-Br. We introduce a facile method to convert the bromine end of the polymer into a hydroxyl group. For this, bromine-terminated polystyrene (PS-Br) was prepared by atom transfer radical polymerization. The bromine groups of the PS-Br could be directly converted to hydroxyl groups by using Ag+ as the Lewis acid in water/acetone. The conversion yield was investigated by 1H nuclear magnetic resonance spectroscopy, high-performance liquid chromatography, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

We determine experimentally the “dilution exponent” α for entangled polymers from the scaling of terminal crossover frequency with entanglement density from the linear rheology of three 1,4-polybutadiene star polymers that are blended with low-molecular-weight, unentangled linear 1,4-polybutadiene at various star volume fractions, ϕs. Assuming that the rheology of monodisperse stars depends solely on the plateau modulus GN(ϕs) ∝ ϕs1+α, the number of entanglements per chain Me(ϕs) ∝ ϕs–α, and the tube-segment frictional Rouse time τe(ϕs) ∝ ϕs–2α, we show that only an α = 1 scaling superposes the Me(ϕs) dependence of the terminal crossover frequency ωx,t of the blends with those of pure stars, not α = 4/3. This is the first determination of α for star polymers that does not rely on any particular tube model implementation. We also show that a generalized tube model, the “Hierarchical model”, using the “Das” parameter set with α = 1 reasonably predicts the rheological data of the melts and blends featured in...

Different types of polymer chains generated during the nitroxide-mediated polymerization of styrene are separated for the first time, and their molecular weight distribution (MWD) is investigated. Living and dead chains are monitored during the reaction; specifically, two types of living chains derived from the initiation of the alkoxyamine (RT) and the self-initiation of styrene and dead chains present in the as-prepared polystyrene (PS). To distinguish between each polymer species, different numbers of hydroxyl groups are introduced onto the T and R groups of the alkoxyamine (one and two groups, respectively). Each living and dead chains is resolved according to the distinct number of hydroxyl groups on its chain-end using high-performance liquid chromatography. Molecular structures of the fractionated PS are characterized using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and 1 H nuclear magnetic resonance spectroscopy, and the results of which show two distinct initiation paths: one originating from RT and the other from the self-initiation of styrene. Molecular weight and MWD are measured using size-exclusion chromatography and reveal a narrow MWD for the living chains derived from RT. Contrastingly, a broad and skewed MWD is observed for the other living chains derived from the self-initiation of styrene and the dead chains.

Size exclusion chromatography (SEC) is the most widely employed chromatographic separation technique for characterization of synthetic polymers. SEC separates polymer molecules according to their chain size utilizing size-dependent pore accessibility of polymer molecules. Since the polymer chain size depends on not only molecular weight (MW) but also other molecular characteristics such as composition, chain architecture, and microstructure, SEC cannot separate, for instance, nonlinear homopolymers according to MW or copolymers according to their composition. In contrast to SEC, interaction chromatography (IC) fractionates polymers according to the interaction strength between the polymer molecules and the sorbent. As a result, IC separation is sensitive to chemical nature and MW of polymers unlike the size-sensitive SEC. Furthermore, one can access to the chromatographic critical condition by adjusting the solute interaction strength with the sorbent until the exclusion and interaction contributions to the solute retention are exactly compensated. At the critical condition, polymers of different MW coelute. Therefore liquid chromatography (LC) at the critical condition (LCCC) is a unique tool for LC separation of polymers since the peak dispersion of polymers due to their MW distribution can be suppressed for effective analyses of other molecular characteristics. Recently, polymer separations using two-dimensional LC by various combinations of SEC, IC, or LCCC are increasingly used for the characterization of polymers with multivariate distributions. For effective IC separations, solute interaction strength needs to be controlled judiciously during the elution. For this purpose, either solvent gradient or temperature gradient elution is often used. In this chapter, principles and applications of IC and LCCC separation methods of synthetic polymers are reviewed with an emphasis on the temperature gradient elution method.

A polyring capable of reversible growth and dissociation is synthesized from a tricyclic polystyrene (PS) prepared by combining atom transfer radical polymerization of a 4-arm star-shaped PS and azide–alkyne click reactions. In the preparation of the tricyclic PS, a coupling agent containing a disulfide linkage is used in the click cyclization reaction. The reduction of the disulfide linkage in the tricyclic PS results in an 8-shaped PS with thiol groups which on oxidation leads to a high molecular weight polyring. The topology transformation between the polymers occurs via reversible redox reaction of disulfide/thiol. The high molecular weight of the polyring is realized due to the formation of flexible S–S linkage between the 8-shaped PSs. Their structures are confirmed by FT-IR, 1H NMR, SEC, and MALDI-TOF MS analyses. In addition, molecular weight control of the polyring according to polymer concentration has been confirmed through SEC analysis.

Cyclic polymers synthesized by ring-closure method from linear precursors contain some of linear contaminates. In this work, the origin of linear contaminates in cyclic polystyrenes ( c -PS) is demonstrated by the coupling of liquid chromatography at the critical condition (LCCC) with matrix-assisted laser desorption/ionization time-of-flight mass spectra. The linear contaminates are revealed to be the “dead” chains during ATRP by chain termination, the unreacted linear polystyrene ( l -PS) precursors, and the dimers by the imperfect ring-closure reaction. The c -PS are purified by LCCC fractionation, and the results show the LCCC fractionation at the critical adsorption point (CAP) of c -PS is more efficient than that at the CAP of linears for low molecular weight ( c -PS with high purity (>99.6%) via the tandem-coupled LCCC fractionation at the CAP of l -PS and at the CAP of c -PS.

The critical adsorption point (CAP) of linear and star-shaped polymers was investigated by normal phase and reversed phase liquid chromatography (NPLC and RPLC) and computer simulation. Three sets of polystyrenes (PS) differing in chain architecture and chemically distinct groups were prepared: linear PS (sec-butyl and hydrogen end group), 2-arm PS (linear, two sec-butyl end groups and one silyl group in the middle of the chain) and 4-arm star-shaped PS (four sec-butyl end groups and one silyl group in the center of the star). It was found that the column temperature at CAP, TCAP (linear PS) = TCAP (2-arm PS) > TCAP (4-arm PS) in both RPLC and NPLC which can be attributed to the variation in chain architecture. However, the elution times at CAP of three polymers are all different: In NPLC, tE,CAP (linear) > tE,CAP (2-arm PS) > tE,CAP (4-arm PS) while in RPLC, tE,CAP (4-arm PS) > tE,CAP (2-arm PS) > tE,CAP (linear). The variation of tE,CAP can be explained by the contribution of the chemically distinct gro...

Covalent fixed multicyclic polystyrene conformers were synthesized from inconvertible polystyrene conformers based on p-tert-butylthiacalix[4]arene by azidation and subsequent click coupling. Selective 1D NOESY analyses confirmed that the spatial structures of star polystyrene precursors and multicyclic polystyrenes were preserved during the azidation and click coupling processes. The conformation of star polymers affected degree of decrease in the hydrodynamic volume after cyclization but had little effect on glass transition behavior. The rigid core of star polymer increased the Tg but in the case of multicyclic polymer, this influence of core structure was reduced. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017.

Size exclusion chromatography (SEC) coupled with triple detection (TD) method is widely used for branching analysis of polymers. However, there is an inherent limitation of SEC-TD method that SEC separates polymers according their hydrodynamic size. The SEC resolution of branched polymers is not high since the hydrodynamic size of branched polymers does not change as much as linear polymers with molecular weight (MW), let alone the serious band-broadening in SEC. As a solution of the problem, we propose temperature gradient interaction chromatography (TGIC)-TD method taking advantage of TGIC's characteristics of separating branched polymers according to their MW with much higher resolution than SEC. The potential of the method was demonstrated using regular star-shaped polybutadienes prepared by anionic polymerization. They were characterized by both SEC-TD and TGIC-TD methods. Detailed analysis of branch distribution was possible for narrow MW fractions in TGIC-TD while SEC-TD only provides with average branch number for SEC fractions.

In the melt state at equilibrium, entangled nonconcatenated ring macromolecules adapt more compact conformations compared to their linear analogs and do not form an entanglement network. We show here that, when subjected to uniaxial stretching, they exhibit a unique response, which sets them apart from any other polymer. Remarkably, whereas both linear and ring polymers strain-harden, the viscosity of the rings increases dramatically (the melt thickens) at very low stretch rates due to the unraveling of their conformations along the stretching direction. At high rates, stretching leads to viscosity thinning similar to that of entangled linear polymers, albeit with subtle differences.

We investigate the influence of the environment on the relaxation dynamics of well-defined H-polymers diluted in a matrix of linear chains. The molar mass of the linear chain matrix is systematically varied and the relaxation dynamics of the H-polymer is probed by means of linear viscoelastic measurements, with the aim to understand its altered motion in different blends, compared to its pure melt state. Our results indicate that short unentangled linear chains accelerate the relaxation of both the branches and the backbone of the H-polymers by acting as an effective solvent. On the other hand, the relaxation of the H-polymer in an entangled matrix is slowed-down, with the degree of retardation depending on the entanglement number of the linear chains. We show that this retardation can be quantified by considering that the H-polymers are moving in a dilated tube at the rhythm of the motion of the linear matrix.

The critical adsorption points (CAP) for ring and linear polymers are determined and compared using Monte Carlo simulations and liquid chromatography experiments. The CAP is defined as the coelution point of ring or linear polymers with different molecular weights (MW). Computational studies show that the temperature at the CAP, TCAP, for rings is higher than TCAP for linear polymers regardless of whether the chains are modeled as random walks or self-avoiding walks. The difference in the CAP can be attributed only to the architectural difference. Experimentally, four pairs of linear and ring polystyrenes (PS) of different MW were synthesized and purified. Care was taken to account for the difference between the end-groups in linear polymers and the linkage unit in ring polymers. Elution of these polymers using a C18 bonded silica stationary phase and a CH2Cl2/CH3CN mixed eluent were studied. The temperature at the coelution point, TCAP, and the coelution time at the CAP, tE,CAP, were determined for both ...

We report herein the effects of solvent, concentration, and molecular weight of α-alkynyl-ω-azido polystyrenes (l-PS-N3) on the synthesis of monocyclic polystyrenes (c-PS) by intra-chain coupling of l-PS-N3 via Cu-catalyzed azide/alkyne cycloaddition method. By using fully end-functionalized l-PS-N3 as precursors, the optimum cyclization conditions to synthesize high purity c-PS (>99% by SEC) are revealed, at concentrations around 7.9 μmol/L in DMF. The c-PS products are fully characterized by SEC, LCCC, 1H NMR, and MALDI-TOF Mass spectrometry. The yield of c-PS decreases with increment of concentration of l-PS-N3 as predicted by Jacobson and Stockmayer's equation. Interestingly, among the three studied PS samples with different molecular weight (∼4k, 9k, 14k Da), the medium one (PS9k) provides the best c-PS yield, while in the three studied solvent (toluene, DMF, cyclohexane), DMF gives the best yied. The results reveal that the PS chain conformation in the solution, which is affected by the solvent and molecular weights, plays an important role in the intra-chain cyclization reaction.

Nonlinear polystyrenes (PS) with similar molecular weights but with different molecular structures having star-, figure-8-, and cage-shaped architectures were synthesized by combining atom transfer radical polymerization (ATRP) and click chemistry. Figure-8- and cage-shaped PS were fractionated by using a gradient normal phase liquid chromatography as confirmed by SEC-LS, MALDI–TOF MS, 1H NMR, and FT-IR spectrometry. Their purities were estimated by using a two-dimensional liquid chromatography (2D-LC). The glass transition temperatures of these topologically different polymers were in the order of cage-, figure-8-, and star-shaped polymers possibly due to the multiple links that constrain the overall molecular diffusivity in the case of multicyclic polymers (figure-8, and cage). Monte Carlo simulation on the glass transition behavior of model system also agreed well with the experimental results.

Poloxamers are low molar mass triblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), having number of applications as non-ionic surfactants. Comprehensive one and two-dimensional liquid chromatographic (LC) analysis of these materials is proposed in this study. The separation of oligomers of both types (PEO and PPO) is demonstrated for several commercial poloxamers. This is accomplished at the critical conditions for one of the block while interaction for the other block. Reversed phase LC at CAP of PEO allowed for oligomeric separation of triblock copolymers with regard to PPO block whereas normal phase LC at CAP of PPO renders oligomeric separation with respect to PEO block. The oligomeric separation with regard to PEO and PPO are coupled online (comprehensive 2D-LC) to reveal two-dimensional contour plots by unconventional 2D IC×IC (interaction chromatography) coupling. The study provides chemical composition mapping of both PEO and PPO, equivalent to combined molar mass and chemical composition mapping for several commercial poloxamers.

It is commonly believed that cyclic polymers have smaller hydrodynamic radii (Rhs) than their linear counterparts due to the constraint topology. This consensus is based on the results from polymers with high molecular weights (MWs), where the chains are considered as coils. Herein, we investigate the Rhs of low MW cyclic polystyrenes (3000–11,000), cyclic alkanes and their linear counterparts by diffusion ordered NMR spectroscopy. For the first time, a non-free draining effect for small cyclics is revealed, due to the depletion of solvent molecules to pass through the rings, which leads to the increment of hydrodynamic size. With the decrement of polymer MW, this effect becomes more significant and Rhs of cyclic polystyrenes approach that of their linear counterparts. Below a crossover point at MW around 660, Rhs of cyclic polystyrenes are larger than their linear counterparts from the established scaling laws. This is supported by the observed phenomena that cycloalkanes have larger Rhs than their n-alkane counterparts. The results are helpful in understanding the thermodynamic behaviors of small cyclics in solution, especially those bioactive small ring molecules in life science.

A detailed characterization of a commercial polystyrene/polybutadiene block copolymer material (Styrolux) was carried out using two-dimensional liquid chromatography (2D-LC). The Styrolux is prepared by statistical linking reaction of two different polystyrene- block-polybutadienyl anion precursors with a multivalent linking agent. Therefore, it is a mixture of a number of branched block copolymers different in molecular weight, composition, and chain architecture. While individual LC analysis, including size exclusion chromatography, interaction chromatography, or liquid chromatography at critical condition, is not good enough to resolve all the polymer species, 2D-LC separations coupling two chromatography methods were able to resolve all polymer species present in the sample; at least 13 block copolymer species and a homopolystyrene blended. Four different 2D-LC analyses combining a different pair of two LC methods provide their characteristic separation results. The separation characteristics of the 2D-LC separations are compared to elucidate the elution characteristics of the block copolymer species.

Inconvertible p-tert-butylthiacalix[4]arene-core-star-shaped polystyrene conformers were synthesized by atom transfer radical polymerization (ATRP) using initiators of different conformations from p-tert-butylthiacalix[4]arene. 1H NMR and selective 1D NOESY analyses confirmed that the spatial structures of the initiator cores in the 4-arm star polymers were preserved during the polymerization process. While size exclusion chromatography (SEC) analyses revealed a diminishing difference in the hydrodynamic volume of the star polymer conformers as the molar mass increases, reversed phase liquid chromatography distinguishes the 4-arm star polymer having a cone-shaped core from the polymer having a 1,3-alternate-shaped core likely due to their isomeric locations of the hydrophobic tBu groups of the core. This result demonstrates that the inconvertible conformational structures of star polymers having the same composition exhibit distinguishable properties.

We have measured the linear rheology of critically purified ring polyisoprenes, polystyrenes, and polyethyleneoxides of different molar masses. The ratio of the zero-shear viscosities of linear polymer melts η0,linear to their ring counterparts η0,ring at isofrictional conditions is discussed as a function of the number of entanglements Z. In the unentangled regime η0,linear/η0,ring is virtually constant, consistent with the earlier data, atomistic simulations, and the theoretical expectation η0,linear/η0,ring = 2. In the entanglement regime, the Z-dependence of ring viscosity is much weaker than that of linear polymers, in qualitative agreement with predictions from scaling theory and simulations. The power-law extracted from the available experimental data in the rather limited range 1 < Z < 20, η0,linear/η0,ring Z1.2±0.3, is weaker than the scaling prediction (η0,linear/η0,ring Z1.6±0.3) and the simulations (η0,linear/η0,ring Z2.0±0.3). Nevertheless, the present collection of state-of-the-art experimental data unambiguously demonstrates that rings exhibit a universal trend clearly departing from that of their linear counterparts, and hence it represents a major step toward resolving a 30-year-old problem.

Detailed molecular characterization and fractionation were carried out for a polystyrene-block-poly(methylmethacrylate) (PS-b-PMMA) diblock copolymer prepared by linking PS-alkyne and PMMA-azide through a click reaction. PS and PMMA block precursors were prepared by atom transfer radical polymerization and anionic polymerization, and end-functionalized to have alkyne and azide group, respectively. As-synthesized block copolymer was characterized by solvent gradient reversed-phase liquid chromatography (RPLC) with multiple-detection for both separation and identification of byproducts. As-synthesized PS-b-PMMA contains various byproducts including unreacted precursor homo-polymers as well as byproducts formed during the synthesis of precursor polymers. To fractionate pure PS-b-PMMA out, two-step HPLC fractionation was employed. In the first step, PMMA homo-polymer was removed from the as-synthesized polymer using a C18 bonded silica column. In the second step, PS homo-polymer was removed to obtain pure PS-b-PMMA using a bare silica column. In both steps, multiple-injection method was used to facilitate the large scale fractionation procedure. A two-dimensional liquid chromatography method, solvent gradient RPLC for the first dimension and SEC for the second dimension was also conducted to map the molecular characteristics of the block copolymer and its byproducts.

This document defines terms relating to the properties of individual macromolecules, macromolecular assemblies, polymer solutions, and amorphous bulk polymers. In the section on polymer solutions and amorphous bulk polymers, general and thermodynamic terms, dilute solutions, phase behaviour, transport properties, scattering methods, and separation methods are considered. The recommendations are a revision and expansion of the IUPAC terminology published in 1989 dealing with individual macromolecules, macromolecular assemblies, and dilute polymer solutions. New terms covering the principal theoretical and experimental developments that have occurred over the intervening years have been introduced. Polyelectrolytes are not included.

Partially sulfonated polystyrene-b-poly(dimethylsiloxane) (sPS-b-PDMS) block copolymer membranes were prepared using three different polymers with various molecular weights and block ratios. Eleven different products were obtained with controlled degree of sulfonation (DS) of PS block ranging from 22% to 48%, and they were cast into proton exchange membranes (PEMs). Each PEM was rigorously characterized to see the effect of molecular weight and PS content to PEM for direct methanol fuel cells (DMFC). The first set of sPS-b-PDMS with the highest molecular weight and 50% PS block ratio generally showed high mechanical strength and selectivity (proton conductivity/ methanol permeability), and the second set with medium molecular weight and 60% PS ratio showed high proton conductivity. The last PEM with the lowest molecular weight and 80% PS ratio exhibited a poor tensile strength which is not suitable for PEM application. When the membrane/electrode assemblies (MEAs) were fabricated using the sPS-b-PDMS PEMs with moderately high DS (~40%), one from the second set (moderate molecular weight, 60% PS content) showed the best power performance (90 mW/cm2 at 70 °C) in active mode DMFC operation, which was found to be 20% higher than that of Nafion 115 MEA.

Bicyclic polystyrene was prepared by combining atom transfer radical polymerization and click chemistry. The bicyclic polymer was separated from concurrently produced acyclic (branched) polymers through fractional precipitation, and its purity was quantified by two-dimensional liquid chromatography analysis. The structure of bicyclic polymer was characterized by SEC, MALDI–TOF MS, 1H NMR, and FT-IR.

We explored a new synthetic strategy for ultra-high molecular weight long-chain branched (LCB) polymers with equal spacing between adjacent branch points. This method can synthesize LCB polystyrene (LCB-PS) with total molecular weight of 4.9 million g/mole, 16 branches of 140 kg/mole and polydispersity index of 1.5. The introduction of multiple branch points with long side chains allows the LCB-PS to resist the elastic-driven decohesion. Even after a large step extension of stretching ratio λ = 7.4, the specimen would not undergo elastic breakup that occurs in linear PS even at λ = 2.7. These LCB-PSs are also extraordinarily more stretchable during startup uniaxial extension, with the maximum engineering stress emerging at stretching ratio λ max ≈ 4 M bb / M e , where Mbb is the molecular weight of backbone and Me is the molecular weight between entanglements.

In this work, we investigated the peculiar peaks found in the MALDI-TOF mass spectra of polystyrenes (PS) with a bromine end prepared by atom transfer radical polymerization when silver trifluoroacetate (AgTFA) and THF were used as cationization agent and solvent, respectively, in the MALDI sample preparation. In the MALDI mass spectrum, PS with a terminal bromine was not detected but the species with a terminal double bond (U series), and −22 m / z (T series) and +18 m / z (W series) peaks relative to U series appeared as major peaks. While the U species was reported as a result of the elimination reaction of HBr, but the origin and the structure of the other species have not been elucidated. We found that the −22 m / z peak of U n is in fact T n -2 , which is the adduct of THF and the anion of the Ag salt, TFA − (+186 m / z ) to U n -2 . The +18 m / z peak was confirmed to be the species with a terminal OH. All these reactions were catalyzed by Ag salt and the T and W series were not found at all when NaTFA was used as a cationization agent.

We report on the shear flow start-up and the relaxation upon flow cessation of anionically synthesized comb polymers of different chemistries. The experimental data, obtained with a cone partitioned-plate geometry in order to avoid artifacts, showed that the start-up shear flow of combs exhibits systematic dependencies on the branching structure. They were interpreted by invoking dynamic dilution and hierarchical relaxation, which are known to control the linear viscoelastic response. For all combs studied here, the backbones remained entangled after dynamic dilution due to branch relaxation. We combined the important molecular parameters (i.e., the number and molar mass of the branches) into a single parameter, the number of entanglements of the dynamically diluted backbone, ZBBDIL., which we found to be the main scaling parameter for the observed nonlinear flow behavior. The steady viscosities as function of Weissenberg number were less shear-thinning compared to linear analogues, and the higher the amo...

We present a detailed systematic investigation of the transient uniaxial extensional response of a series of well-characterized, anionically synthesized comb polystyrenes and polyisoprenes. The comb architecture consists of a linear chain backbone with multiple branches of equal molar mass, and represents an excellent model branched polymer. The linear viscoelastic response has been studied already in great detail. Our results indicate that the strain hardening becomes more important as the Hencky strain rate is increased. In general, the larger the number of entanglements of the segments between branches and/or of the branches, the stronger the strain hardening and the smaller the characteristic rate for its onset. The key molecular parameter appears to be the number of entanglements per branch. By varying it, one can tailor the amount and onset of strain hardening. This can be rationalized by accounting for the combined effect of backbone tube dilation and extra friction, brought about by the branches. In fact, we define an effective “stretch time” of the comb as the timescale for stretch relaxation along the dilated backbone tube when accounting for the large friction that comes from the branches and suggest that extension hardening occurs at rates equal to or greater than its inverse. The good comparison of this prediction to experimental data is a promising guide toward a universal framework for understanding the effects of branches on extensional rheology, and hence providing some insight into the behavior of long-chain branched polyolefins.

We report here an easy method for the synthesis of dendrimer-like polymers with high branching functionality (1 → 8). The synthetic process involves iterative grafting reactions in a divergent way. A multi-functional core containing short segments of polyisoprene (PI), either as a star-like block copolymer of isoprene and styrene or as a linear triblock copolymer of isoprene, styrene and isoprene (coded G1), is epoxidized on the double bonds and grafted with a living block copolymer, polyisoprene-b-polystyrenyllithium (PI-b-PSLi), again with a short PI segment, through the ring-opening reaction of oxirane by polymeric anions. The resulting graft polymer, G2, possesses a definite number of PI segments at the periphery. These PI segments are further epoxidized followed by the ring-opening addition of PI-b-PSLi, affording G3. Repeating the process leads to the synthesis of a dendrimer-like polystyrene up to 5th generation with a polydispersity lower than 1.21, as measured by SEC. A feature of the process is the easily accessible high chain density in the final product, although defects exist due to steric hindrance in the reactions of high generations. The solution properties of the dendritic products are investigated using viscometry and dynamic and static laser light scattering on the molecular conformation. The results support a compact globular conformation model for the dendrimer-like products. In addition, the chain density of the products from the star-like core is higher than that of products from a linear triblock core. AFM results show that the dendritic products adopt flattened conformations and tend to form lateral sphere-like aggregates on mica substrate.

We present a systematic investigation of well-characterized, experimentally pure polystyrene (PS) rings with molar mass of 161 000 g/mol in dilute solutions. We measure the ring form factor at θ - and good-solvent conditions as well as in a polymeric solvent (linear PS of roughly comparable molar mass) by means of small-angle neutron scattering (SANS). Additional dynamic light scattering (DLS) measurements support the SANS data and help elucidate the role of solvent quality and solution preparation. The results indicate the increase of ring dimensions as the solvent quality improves. Furthermore, the experimental form factors in both θ -solvent and linear matrix behave as ideal rings and are fully superimposable. The nearly Gaussian conformations of rings in a melt of linear chains provide evidence of threading of linear chains through rings. The latter result has implications for the dynamics of ring-linear polymer mixtures.

Low-temperature anionic ring-opening homopolymerizations and copolymerizations of two glycidol derivatives (allyl glycidyl ether (AGE) and ethoxyethyl glycidyl ether (EEGE)) are studied using a metal-free catalyst system, 3-phenyl-1-propanol (PPA) (an initiator) and 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris-(dimethylamino)phosphoranylidenamino]-2Λ5,4Λ5-catenadi(phosphazene) (t-Bu-P4) (a promoter) in order to obtain well-defined functional linear polyethers and diblock copolymers. With the aid of the catalyst system, AGE is found to successfully undergo anionic ring-opening polymerization (ROP) even at room temperature (low reaction temperature) without any side reactions, producing well-defined linear AGE-homopolymer in a unimodal narrow molecular weight distribution. Under the same conditions, EEGE also undergoes polymerization, producing a linear EEGE-homopolymer in a unimodal narrow molecular-weight distribution. In this case, however, a side reaction (i.e., chain-transfer reaction) is found to occur at low levels during the early stages of polymerization. The chemical properties of the monomers in the context of the homopolymerization reactions are considered in the design of a protocol used to synthesize well-defined linear diblock copolyethers with a variety of compositions. The approach, anionic polymerization via the sequential step feed of AGE and EEGE as the first and second monomers, is found to be free from side reactions at room temperature. Each block of the obtained linear diblock copolymers undergoes selective deprotection to permit further chemical modification for selective functionalization. In addition, thermal properties and structures of the polymers and their post-modification products are examined. Overall, this study demonstrates that a low-temperature metal-free anionic ROP using the PPA/t-Bu-P4 catalyst system is suitable for the production of well-defined linear AGE-homopolymers and their diblock copolymers with the EEGE monomer, which are versatile and selectively functionalizable linear aliphatic polyether platforms for a variety of post-modifications, nanostructures, and their applications.

In the branching analysis by size exclusion chromatography (SEC)/triple detection (concentration, light scattering, and viscosity detectors) method, the branch number is calculated from the extent of chain size contraction due to chain branching relative to the linear polymer of the same molecular weight (MW). A problem can arise from the fact that polymer chain size depends on both MW and chain branching. Since SEC separates polymers according to the chain size, an SEC fraction of randomly branched polymers may contain polymer species heterogeneous in both MW and chain architecture in general. As a solution of the problem, we propose a separation of polymers by interaction chromatography according to MW first and then measure the chain size distribution of polymers in the homogeneous MW fraction by SEC/triple detection. The analysis scheme is successfully established by online two-dimensional liquid chromatography combining temperature gradient interaction chromatography and SEC/triple detection.

It has been a long held ambition of both industry and academia to understand the relationship between the often complex molecular architecture of polymer chains and their melt flow properties, with the goal of building robust theoretical models to predict their rheology. The established key to this is the use of well-defined, model polymers, homogeneous in chain length and architecture. We describe here for the first time, the in silico design, synthesis, and characterization of an architecturally complex, branched polymer with the optimal rheological properties for such structure-property correlation studies. Moreover, we demonstrate unequivocally the need for accurate characterization using temperature gradient interaction chromatography (TGIC), which reveals the presence of heterogeneities in the molecular structure that are undetectable by size exclusion chromatography (SEC). Experimental rheology exposes the rich pattern of relaxation dynamics associated with branched polymers, but the ultimate test is, of course, did the theoretical (design) model accurately predict the rheological properties of the synthesized model branched polymer? Rarely, if ever before, has such a combination of theory, synthesis, characterization, and analysis resulted in a "yes", expressed without doubt or qualification.

We report the synthesis and characterization by temperature gradient interaction chromatography (TGIC) and rheometry of a symmetric H-shaped polybutadiene (PBd) that we call “HA20B40”, and of a symmetric star-shaped synthetic precursor of HA20B40, and the use of these characterization data to test and validate advanced tube models (the hierarchical and, to a lesser extent, the BOB models) for long-chain branched polymers. Furthermore, by deliberately adding additional well-characterized linear and star-branched polymers into HA20B40, we mimic the effect of impurities in the sample to test the ability of the hierarchical model to account for the effect of similar such impurities, which are detected by TGIC. Our modeling predictions for HA20B40 and its blends with star and linear polymers show very good agreement with measured rheological data, indicating that the modeling validation is successful for the symmetric H-shaped polymers. We then test the hierarchical model further using literature data for symm...

Polystyrene-b-polyisoprene-b-poly(methylmethacrylate) (PS-b-PI-b-PMMA) triblock copolymer was synthesized by sequential anionic polymerization. The as-synthesized triblock copolymer contains side products of inadvertently terminated PS and PS-b-PI precursors. The side products can be effectively removed by semi-prep scale liquid chromatography using multiple injection method to obtain pure PS-b-PI-b-PMMA. It was found that the removed side product contains another polymer species, coupled PS-b-PI, which could not be recognized by size exclusion chromatography (SEC) analysis since the elution peak of the coupled product overlaps with that of PS-b-PI-b-PMMA. This study demonstrates that the size based separation of SEC is often not good enough to characterize complex polymers precisely and interaction chromatography can render unique advantage over SEC analysis.

We demonstrate a simple route for preparing various micellar nanostructures, like spheres, cylinders, and vesicles, by spin-coating or drop-casting process of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) copolymer solutions in pure tetrahydrofuran (THF), THF/water, and THF/ethanol mixture. Upon drying, a solvent selectivity plays an important role in determining micellar nanostructures in thin films. In solution, micellar sizes and shapes of these PS-b-P4VP copolymers were investigated by dynamic and static light scattering. Immediately after spin-coating the polymer solutions, surface and internal morphologies of the films were observed by atomic force microscopy and transmission electron microscopy. As the polymer concentration in THF or the amounts of water or ethanol added in THF solutions was varied, a remarkable difference in the PS-b-P4VP micellar morphologies was observed, from which spherical or cylindrical or vesicular micelles were developed. These micellar films were used as scaffolds or templates for fabricating metal nanodots or nanowires arrays.

The structural details of a set of highly entangled H-shaped polybutadienes (PBDs) prepared by anionic polymerization were examined in detail by three reputable laboratories using size exclusion chromatography (SEC) and temperature gradient interaction chromatography (TGIC). While SEC data indicated that samples having the desired structures (i.e., nearly monodisperse H-shaped polymer) had been produced, additional SEC data from other laboratories showed that the samples were structurally more complex than originally thought. TGIC data revealed that while the samples did not contain high molecular weight byproducts, they did contain low molecular weight byproducts. To discern these structural details of the branched PBDs, small amounts of sample were fractionated by TGIC. By combining knowledge of the polymerization process with the TGIC data of fractionated samples, it was possible to work out the detailed compositions of the samples and the branching structures of each component.

A new model describing the retention in temperature gradient interaction chromatography of polymers is developed. The model predicts that polymers might elute in temperature gradient interaction chromatography in either an increasing or decreasing order or even nearly independent of molar mass, depending on the rate of the temperature increase relative to the flow rate. This is in contrast to solvent gradient elution, where polymers elute either in order of increasing molar mass or molar mass independent. The predictions of the newly developed model were verified with the literature data as well as new experimental data.

Poly[bis(9H-carbazole-9-ethyl)dipropargylmalonate] (PCzDPM) is a novel pi-conjugated polymer bearing carbazole moieties that has been synthesized by polymerization of bis(9H-carbazole-9-ethyl)dipropargylmalonate with the aid of molybdenum chloride solution as the catalyst. This polymer is thermally stable up to 255 degrees C under a nitrogen atmosphere and 230 degrees C in air ambient; its glass-transition temperature is 147 or 128 degrees C, depending on the polymer chain conformation (helical or planar structure). The charge-transport characteristics of PCzDPM in nanometer-scaled thin films were studied as a function of temperature and film thickness. PCzDPM films with a thickness of 15-30 nm were found to exhibit very stable dynamic random access memory (DRAM) characteristics without polarity. Furthermore, the polymer films retain DRAM characteristics up to 180 degrees C. The ON-state current is dominated by Ohmic conduction, and the OFF-state current appears to undergo a transition from Ohmic to space-charge-limited conduction with a shallow-trap distribution. The ON/OFF switching of the devices is mainly governed by filament formation. The filament formation mechanism for the switching process is supported by the metallic properties of the PCzDPM film, which result in the temperature dependence of the ON-state current. In addition, the structure of this pi-conjugated polymer was found to vary with its thermal history; this change in structure can affect filament formation in the polymer film.

In this article, we have investigated a temperature-rise fractionation procedure for poly(3-hexyl thophene) (P3HT) and poly(3-octyl thophene) (P30T) that provides well-defined molecular weight (MW) fractions with improved molecular weight distributions (MWD) when compared with Soxhlet extraction. This process involves dispersing the material over C18-boned silica stationary phase in a jacketed column and using incremental rises in column temperature (T col ) to gradually improve solvent quality and selectively dissolve higher molecular weight samples with a narrow polydispersity (PDI). Fractionation of P3HT with ΔT col = 5 °C in methylene chloride (MC) yielded 7 fractions ranging from M p of 20 to 53 kg/mol with an average PDI of 1.80 compared with a mother sample of 3.10. Predominant recovery of P3HT was acquired for fractions with T col > 20 °C (30 wt %). Subsequent separation of P30T in methylene chloride, with a reduced ΔT col of 3 °C per fraction, due to increased solubility from the longer alkyl chain, generated 8 fractions with a weight range of M n = 22 to 57 kg/mol with an mean PDI of 1.23 with the mother sample having PDI = 2.34, demonstrating the tunability of this method.

In recent years, two-dimensional liquid chromatography (2D-LC) has been used increasingly for the analysis of synthetic polymers. A 2D-LC analysis provides richer information than a single chromatography analysis at the cost of longer analysis time. The time required for a comprehensive 2D-LC analysis is essentially proportional to the analysis time of the second dimension separation. Many of 2D-LC analyses of synthetic polymers have employed size exclusion chromatography (SEC) for the second-dimension analysis due to the relatively short analysis time in addition to the wide use in the polymer analysis. Nonetheless, short SEC columns are often used for 2D-LC analyses to reduce the separation time, which inevitably deteriorates the resolution. In this study, we demonstrated that high temperature SEC can be employed as an efficient second-LC in the 2D-LC separation of synthetic polymers. By virtue of high temperature operation (low solvent viscosity and high diffusivity of the polymer molecules), a normal length SEC column can be used at high flow rate with little loss in resolution.

Four homopolymer films (poly(methyl methacrylate) (PMMA), poly(4-vinylpyridine) (P4VP), polystyrene (PS), and poly(alpha-methyl styrene) (PAMS)) with different interactions with native Si oxide on Si wafers and three random copolymer films (PS-ran-PMMA) with different mole fractions were investigated with the X-ray reflectivity (XRR) method. The electron density profile of each film was obtained by fitting the results of the XRR measurements. A new data correction technique that uses the vertical real beam profile and a fitting method that uses the distorted wave Born approximation were combined to overcome the sensitivity limitations of XRR analysis. The results show that the chemical structures of polymer pendant groups and the interactions between the polymer films and the native Si oxide layer are strongly correlated with the density profiles of the films near the surfaces and interfaces. Two general types of electron density profiles were found that are characterized by the polarity of the pendant group of the polymer. The reproducibility and credibility of the fitting technique were also thoroughly tested.

This paper reports for the first time the programmable digital memory characteristics of the nanoscale thin films of a fully π-conjugated polymer, poly(diethyl dipropargylmalonate) (pDEDPM) in the ...

The evaporation of sessile droplets placed on polymer surfaces was studied by microscopic observation of the changes in shape of aqueous solution droplets in which the alkyl lengths and the initial concentrations of sodium n-alkylates were varied. Although the initial contact angles of the droplets were not significantly different, the evaporation process varied significantly with the alkyl length of the sodium n-alkylate employed. For the sodium dodecanoate (C 12), showing the highest surface activity, the concentration was found to have a significant effect on the evaporation process of the droplets. In the evaporation of water droplets, variations in the three distinct stages were caused by the different concentration of solutes distributed near or at the air/water interface. It is revealed that the concentration of droplet solute near the air/water interface requires not only solvent evaporation but also some affinity of the solute for the interface. The initial C 12 concentration-dependence of the evaporation of C 12 solution droplets is discussed with particular emphasis on the sudden spreading or sudden contraction of the contact area near the end of evaporation. It is suggested that the cluster formation by C 12 molecules at the air/liquid interface during the evaporation causes Marangoni instability in an evaporating droplet, and the clusters are expected to move dynamically, depending on the droplet concentration of C 12, from the droplet center to the contact line and vice versa, showing Marangoni flow along the air/water interface.

We present the synthesis of polystyrene combs via an improved procedure, which allows the average number of arms to be small (3−5) but well controlled. It is shown that temperature gradient interaction chromatography (TGIC) proves to be a highly effective method for the analysis of these combs, providing directly the distribution of the number of arms on the synthesized comb molecules. We use this arm-number distribution to model the linear rheology of an entangled melt of such combs, via our previously published algorithm [Das et al. J. Rheol. 2006, 50, 207−234], and demonstrate that this compares favorably with the measured linear rheology. A comparison is also made with the predicted rheology for two alternative assumptions about the distribution of arms on the comb, (i) where it is assumed that the addition of arms is an ideal random process and (ii) where there is a fixed number of arms per comb. These predictions also agree well with the experimental results, thus supporting the validity of simpler ...