Search

Living and dead chains of a polystyrene synthesized by atom transfer radical polymerization were separated and characterized by high performance liquid chromatography (HPLC), size exclusion chromatography (SEC), NMR, and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The bromine end group in the living chain was quantitatively converted to a hydroxyl end group via first azidation and subsequent copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction with propargyl alcohol. The living chains bearing a polar end group are fully resolved from the unmodified dead chains by HPLC separation using a bare silica stationary phase. Molecular weight distributions (MWD) of the living and dead chain are characterized by SEC and MALDI-MS. The MWD of the living chains is close to a Poisson distribution. Interestingly, the elution peak of the living chains in the HPLC separation split into two. The peak split is attributed to the diastereomeric structure of the chain end by NMR and MALDI-MS analyses.

We investigated the microphase in thin films of polystyrene-b-polyisoprene showing cylinder morphology to elucidate the orientation mechanism of the cylinder phase during solvent vapor annealing (S...

We report on the chromatographic separation and characterization of living chains in polystyrene prepared by reversible addition–fragmentation chain-transfer (RAFT) polymerization. To achieve full ...

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.

The morphology of well-purified triblock terpolymers was investigated by X-ray scattering and transmission electron microscopy after solvent vapor annealing (SVA) and compared with that developed a...

We present here a systematic investigation on the glass transition temperature (Tg) for a series of highly purified cyclic polystyrene (c-PS) samples with molecular weight (MW) varying from 3300 to 13,400. Compared with their linear counterparts, c-PS samples show much higher Tg and exhibit weak Tg-MW dependence. By blending linear polystyrenes with c-PS, the linear polymer contamination effect on the Tg of c-PS was systematically investigated. It was found that the measured Tg of the mixtures increases with the decrease of linear polymer content and the relationship is consistent with Fox equation. These results are helpful to understand the origin of previously reported different Tg-MW relationship for c-PS.

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.

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.

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.

An exact polystyrene-graft-polyisoprene (PS-g-PI) synthesized by iterative anionic polymerization and graft reaction using diphenylethylene functional groups was characterized by liquid chromatography. As-prepared graft copolymer contains various byproducts other than the target PS-g-PI. After the fractionation by size exclusion chromatography (SEC), the PS-g-PI appears quite homogeneous by SEC analysis, but the temperature gradient interaction chromatography (TGIC) separation with respect to the PI branch number showed a significantly wide distribution in the number of PI grafts. The resolved TGIC peaks were fractionated, and the molecular weight of each block (backbone or branches) was estimated by liquid chromatography at critical condition (LCCC) analysis at the critical adsorption condition of the opposite block. The composition determined by LCCC analysis and 1H NMR analysis yielded a reasonably self-consistent result. Through this study, we demonstrated that SEC analysis of this type of branched co...

The intrinsic viscosity of cyclic polystyrenes (C-PS) and linear polystyrenes (L-PS) with molecular weight (MW) ranging from 16K to 370K was measured in THF using size exclusion chromatography coupled with a triple detection system. The C-PS samples were prepared by a ring-closure reaction of telechelic linear precursor synthesized by anionic polymerization. As-synthesized C-PS samples after the ring-closure reaction contain various byproducts, and they were fractionated by liquid chromatography at the critical condition to obtain highly pure C-PS. While the intrinsic viscosity of L-PS agrees well with the literature data, C-PS shows significantly lower value than the literature values. The Mark–Houwink exponent of C-PS is 0.67, somewhat lower than 0.70 for L-PS in the good solvent over the MW range examined. Therefore, the ratio of the intrinsic viscosity of C-PS to L-PS (g′ = [η]C/[η]L) in THF is not MW independent but decreases as MW increases (0.63 ≥ [η]C/[η]L ≥ 0.57). The trend of intrinsic viscosity agrees well with the computer simulation result. The discrepancy in [η]C from the literature values can largely be attributed to the contamination of linear byproducts in the earlier studies.

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.

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.

We report on a novel synthetic route to synthesize relatively large quantities of polystyrene (PS) star polymers with targeted arm functionality and molar mass and their theological properties in the molten state. The synthetic route involves grafting styrene monomers onto a modified (aliphatic, alternating) polyketone backbone with a specific number of initiating grafting sites using controlled atom transfer radical polymerization (ATRP). Several polyketone precursors were used. This resulted in a large array of star polystyrenes with nonspherical cores and varying average arm length and number of arms. Their linear viscoelasticity was investigated and discussed in the context of the known response of anionically synthesized stars. Using a powerful characterization toolbox, including state-of-the-art interaction chromatography, rheometry, and tube modeling via the branch-on-branch (BoB) algorithm, we have assessed the viscoelasticity of these star polymers quantitatively. In particular, we have demonstrated a variability in molecular structure, which differs substantially from their anionically synthesized counterparts. Hence, whereas this new family of star polymers is not recommended for fundamental studies of polymer physics such as the molecular origin of relaxation mechanisms without prior extensive fractionation, they could be used in studies of mixtures as well as industrially relevant processing operations that require large amounts of polymeric stars.

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.

HPLC elution behavior of isotopically different block copolymers was investigated. A series of three diblock copolymers of hydrogenous polystyrene and deuterated polystyrene (hPS-b-dPS), in which the length of hPS-block is fixed at 18 kg/mol and the length of dPS-block is varied from 17 kg/mol to 80 kg/mol, was synthesized and their retention behavior in liquid chromatography at critical condition (LCCC) was investigated using a C18 coated silica stationary phase and a mixed solvent of CH2Cl2 and CH3CN. At this LC separation condition, hPS is retained slightly longer than dPS. The LCCC separations were performed at both LCCC conditions of dPS and hPS established with the same stationary and mobile phases, but at different column temperatures. Since the chromatographic retention difference between dPS and hPS is very small, it was possible to elute the block copolymers at both exclusion and interaction modes at the critical condition of each individual block. We found that the block at its critical condition is not fully "invisible" in both cases. In the LCCC separation at the critical condition of dPS, hPS-b-dPS elutes after the injection solvent peak (interaction mode) due to the stronger interaction of the hPS block. Although they have the same hPS block, they do not coelute but elute in the order of decreasing total molecular weight like an elution in exclusion mode. It clearly demonstrates that the dPS block is not "invisible" at the critical condition but influences the retention of the block copolymers. Monte Carlo simulations of the partition coefficient of A-b-B into a slit pore were performed to give insight on the elution behavior of A-b-B at the critical condition of the B block. The simulation shows that a block under the critical condition influences the retention of the other "visible" block whether the "visible" block is eluted in exclusion or interaction mode. When A is eluted in the interaction mode and B is at its critical condition, the partition coefficient is found to decrease with the increase of the "invisible" B block length, conforming to the observed elution behavior in experiments.

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.

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.

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.

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.

The liquid chromatographic retention of polystyrene (PS) oligomer was examined taking the column hold-up volume as an adjustable parameter based on the assumption that Martin's rule is valid, i.e., ln k (retention factor) is proportional to the degree of polymerization (DP). In both bare silica and C18-bonded silica columns, thus determined column hold-up volume is systematically smaller than the elution volume of the injection solvent. When the column hold-up volume was taken as an adjustable parameter, the retention of PS oligomer in organic mobile phase follows Martin's rule (ln k proportional, variant DP) near perfectly. In addition, the enthalpy and entropy changes associated with the solute transfer, determined from the temperature dependence of the PS oligomer retention, also show excellent linear dependence on the degree of polymerization if the adjustable column hold-up volume was used. When we compare the retention behavior of PS and hydroxyl terminated PS, the repeating (styrene) unit exhibits the same enthalpy and entropy change while the end group shows the corresponding difference. All observations conform to Martin's rule regardless of the columns used, but the physical nature of the adjustable column hold-up volume remains to be elucidated.

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.

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 ...

The retention behavior of star-shaped polystyrene (PS) at the liquid chromatographic critical condition of linear PS was investigated. The star-shaped PS samples were prepared by anionic polymerization of styrene and subsequent linking of the polystyryl anions with divinylbenzene. The linking reaction yields a series of star-shaped PS with different number of branches of equal length. Three star-shaped PS samples with different arm molecular weight (MW) were prepared. To investigate the MW (hence the branch number) dependence of the LCCC (liquid chromatography at the critical condition) retention, the two-dimensional liquid chromatography method was used—first separating the polymers with respect to the molecular weight and subsequently separating the effluent by LCCC. Two different pore size columns were used for the LCCC separation to investigate the pore size dependence. The LCCC retention shows a very complex behavior. The retention time of the star-shaped PS shows a strong variation with MW (branch n...

Molecular weight distribution effect on the morphological behavior of polystyrene-block-polyisoprene (PS-b-PI) diblock copolymers was investigated. PS-b-PI samples were prepared by anionic polymerization and further fractionated by HPLC to obtain the fractions of similar average molecular weight and composition but of narrower distributions in both molecular weight and composition. The strategy is to use reversed-phase LC to fractionate the PI block and normal phase LC to fractionate the PS block with a minimal effect on the other blocks. The interfacial thickness, grain size and the phase transition behavior of the unfractionated and fractionated PS-b-PI were compared by X-ray reflectivity, small angle X-ray scattering, transmission electron microscopy and rheological measurements. The fractionated PS-b-PI with more homogeneous molecular weight and composition exhibits a narrower interface, larger grain size and a sharper morphological transition compared to the unfractionated PS-b-PI.

Grazing-incidence X-ray scattering (GIXS) formulas for hexagonally perforated layer (HPL) structures withABCandABstacking sequences were derived, and used in the quantitative analysis of the two-dimensional GIXS patterns of polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer thin films supported on silicon substrates. This quantitative analysis provided detailed information (shape, size and size distribution, packing order, layer packing sequence, and orientation) about the HPL structure of the diblock copolymer films that cannot be easily obtained with conventional X-ray and neutron scattering techniques or with conventional microscopic methods.

We report on mixed surface micellization behavior of two diblock copolymers: PS-b-P2VP (Mw = 56 000, wPS = 50%) and PS-b-PMMA (Mw = 50 000, wPS = 50%). Both diblock copolymers were synthesized by sequential anionic polymerization and have narrow molecular weight distributions. PS-b-P2VP and PS-b-PMMA were spread at the air−water interface in dilute chloroform solution (0.5 mg/mL) by two different methods: (1) spreading of a premixed solution and (2) separate spreading of each block copolymer solutions sequentially. The π−A isotherms were measured at different subphase pH, and the morphology of the surface micelles was investigated by atomic force microscopy after transferring to a Langmuir−Blodgett film onto a silicon wafer. The ionization of the P2VP block induced different morphology at low pH from which the aggregated structure of block copolymers in micelles could be delineated. When PS-b-P2VP and PS-b-PMMA are spread as a premixed solution, two block copolymers form surface micelles sharing a PS co...

We present systematic, unique linear and nonlinear shear rheology data of an experimentally pure ring polystyrene and its linear precursor. This polymer was synthesized anionically and characterized by interaction chromatography and fractionation at the critical condition. Its weight-average molar mass is 84 kg/mol; i.e., it is marginally entangled (entanglement number Z ≈ 5). Its linear viscoelastic response appears to be better described by the Rouse model (accounting for ring closure) rather than the lattice-animal-based model, suggesting a transition from unentangled to entangled ring dynamics. The failure of both models in the terminal region may reflect the remaining unlinked linear contaminants and/or ring–ring interpenetration. The viscosity evolution at different shear rates was measured using a homemade cone-partitioned plate fixture in order to avoid edge fracture instabilities. Our findings suggest that rings are much less shear thinning compared to their linear counterparts, whereas both obey...

High temperature size exclusion chromatography (SEC) has been used widely for the characterization of crystalline polymers, for which high temperature operation above the polymer melting temperature is required to dissolve the polymers. However, this high temperature operation has many advantages in SEC separation in addition to merely increasing polymer solubility. At high temperature the eluent viscosity decreases, which in turn decreases the column backpressure and increases the diffusivity of the analytes. Therefore, many reports on the high temperature operation of high performance liquid chromatography (HPLC) have focused on shortening the analysis time and enhancing the resolution. However, the application of high temperature SEC analysis to exploit the merits of high temperature operation is scarce. In this article, therefore, we report on a new apparatus design for high temperature SEC.

The subphase pH effect on the surface micelles of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymers was investigated by the π−A isotherm and the morphology of the Langmuir−Blodgett...

We investigated the phase transition behavior from the hexagonally perforated layer (HPL) to the gyroid (G) phase in supported thin film of a polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer (Mn = 34.0 kg/mol, wtPI = 0.634) by grazing-incidence small-angle X-ray scattering. After annealing at 120 °C, the PS-b-PI thin film spin-coated on silicon wafer exhibited HPL morphology with its lamellae highly oriented parallel to the substrate up to a thickness as much as 1 μm. The interface-induced orientation allowed us to obtain a well-developed diffraction pattern in the absence of external mechanical strain to align the domains. The comparison with the computer-simulated diffraction pattern revealed that the HPL structure has mosaic grains oriented randomly in-plane with ABC stacking and undetectable amount of AB stacking. Upon heating, the HPL phase undergoes a phase transition to the G phase. The phase transition occurred epitaxially converting the HPL layers to the {121} planes of the G structure main...

A polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) was fractionated by HPLC, and the morphology of surface micelles formed at the air/water interface was investigated. Individual PS and PMMA blocks were fractionated by normal-phase and reversed-phase HPLC, respectively, into three fractions each to obtain nine fractions of narrower distribution in molecular weight as well as in composition. Although the mother PS-b-PMMA was prepared by anionic polymerization and had a narrow molecular weight distribution as characterized by size exclusion chromatography (Mw = 72.8 kg/mol, Mw/Mn = 1.08, PS wt % = 73.7%), the nine fractionated samples showed significant variations in molecular weight (Mw = 63.1−79.5 kg/mol) and in composition (PS wt % = 66.5−76.3%). The fractionated block copolymers formed more uniform surface micelles than the unfractionated mother PS-b-PMMA and exhibited a large variation with respect to the composition. The PS-b-PMMA fraction of the lowest PS content (66.5 wt %) showed circular mi...

The phase behavior of polystyrene-block-poly(n-pentyl methacrylate) copolymers [PS−PnPMA] having various block length ratios was investigated by rheology, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). All of the PS−PnPMA exhibited two transitions: the lower disorder-to-order transition (LDOT) and upper order-to-disorder transition (UODT) occurring at a lower and higher temperature, respectively. Thus, PS−PnPMA is characterized by a closed-loop type of phase behavior. As the volume fraction of PS in PS−PnPMA was decreased from 0.5 to 0.23, the microdomains observed between the LDOT and UODT changed from lamellae (LAM) to hexagonally packed cylinders (HEX) and finally to body-centered-cubic spheres (BCC), similar to other block copolymers exhibiting only an order-to-disorder transition. The rheological properties depended strongly on the type of microdomains within the closed-loop. The storage and loss moduli (G‘ and G‘ ‘) within the closed loop are the highest for a PS−P...

Temperature gradient interaction chromatography (TGIC) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) were applied for the characterization of highly branched polystyrenes (PS) prepared by linking living polystyryl anions using 4-chlorodimethylsilylstyrene. Reversed-phase (RP)-TGIC showed an unexpectedly high resolution according to the number of branches despite significant overlap of the molecular weight as confirmed by MALDI-TOF MS. The enhancement of the resolution is ascribed to the contribution of the nonpolar groups in the branched PS: the dimethylsilyl groups in the branching unit as well as the sec-butyl initiator groups. As the number of branches increases, the number of nonpolar groups increases, which in turn increases the RP-TGIC retention synergistically with increasing molecular weight. In contrast, a poorer resolution was found in normal-phase-TGIC, in which the nonpolar groups reduce the retention. The resolution in RP-TGIC appears superior to that of liquid chromatography at the chromatographic critical condition (LCCC) of PS. It is seemingly due to the synergistic contribution of the incremental PS molecular weight to the functionality in the branched PS in RP-TGIC while only the functionality contributes to the separation in LCCC. This type of resolution enhancement could be utilized efficiently for the analysis of highly branched polymers such as dendrimers or hyperbranched polymers.

We have investigated the evolution of surface morphology with thin-film growth of polystyrene (PS)–polyisoprene (PI) diblock copolymer and fabrication of polymer nano-template by atomic force microscopy (AFM). Well-controlled (PS-b-PI) diblock copolymer (PI weight fraction = 0.16, Mw=85000, and Mw/Mn=1.01) was prepared by living anionic polymerization. Spin coated copolymer film on both the hydrophobic Si and hydrophilic oxide and nitride substrates showed a typical layer-by-layer growth mode. The (PS-b-PI) diblock copolymer film became spontaneously ordered after overnight annealing inside a vacuum oven above their glass transition temperature, giving hexagonal-close-packed (hcp) phase of PI spheres. The well-controlled monolayer film was selectively etched via ozonation to obtain PI sphere voids and then subsequently reacted with CF4+ ions to etch the PS matrix. We obtained the AFM image of the surface morphology of such formed polymer template, whose pattern consisted of 20-nm-size spheres with a periodicity of 45 nm.

We have studied the surface micelle formation of polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) at the air-water interface. A series of four PS-b-P2VPs were synthesized by anionic polymerization, keeping the PS block length constant (28 kg/mol) and varying the P2VP block length (1, 11, 28, or 59 kg/mol). The surface pressure-area (π-A) isotherms were measured and the surface morphology was studied by atomic force microscopy (AFM) after Langmuir-Blodgett film deposition onto silicon wafers. At low surface pressure, the hydrophobic PS blocks aggregate to form pancake-like micelle cores and the hydrophilic P2VP block chains spread on the water surface to form a corona-like monolayer. The surface area occupied by a block copolymer is proportional to the molecular weight of the P2VP block and identical to the surface area occupied by a homo-P2VP. It indicates that the entire surface is covered by the P2VP monolayer and the PS micelle cores lie on the P2VP monolayer. As the surface pressure is increased, the π-A isotherm shows a transition region where the surface pressure does not change much with the film compression. In this transition region, which displays high compressibility, the P2VP blocks restructure from the monolayer and spread at the air-water interface. After the transition, the Langmuir film becomes much less compressible. In this high-surface-pressure regime, the PS cores cover practically the entire surface area, as observed by AFM and the limiting area of the film. All the diblock copolymers formed circular micelles, except for the block copolymer having a very short P2VP block (1 kg/mol), which formed large, non-uniform PS aggregates. By mixing with the block copolymer having a longer P2VP block (11 kg/mol), we observed rod-shaped micelles, which indicates that the morphology of the surfaces micelles can be controlled by adjusting the average composition of block copolymers.

The molecular reorientations and surface morphologies of rubbed films formed from atactic polystyrene (PS) samples with various molecular weights (weight-average molecular weight) in the range 2700−83 000 and narrow polydispersity were investigated in detail by atomic force microscopy, optical retardation analysis, and linearly polarized infrared spectroscopy. We have first discovered previously unknown surface topography features in rubbed films of PS with >9800 : submicroscale groovelike meandering structures composed of fine groovelike pebbles in tens of nanometers are present, oriented perpendicular to the rubbing direction. The unusual surface morphology is a significant departure from the surface topographies observed so far for rubbed PS and other polymer films, for which grooves are usually only found parallel to the rubbing direction. These surface morphology variations might be due to the different deformation responses of the different molecular weight PS films to the shear forces caused by co...

Temperature gradient interaction chromatography (TGIC) was applied for the separation of a complex miktoarm star copolymer which has one polystyrene (PS) arm and three polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer arms. Such miktoarm star polymers are much more difficult to characterize than branched homopolymers since the byproduct, typically polymers with missing arm(s) or coupled products, have not only different molecular weights but also different compositions. TGIC was able to fully separate the byproducts, and the composition of the molecular species corresponding to the different separated elution peaks was determined by two methods, fractionation/NMR and multiple detection (UV and RI). A reasonable agreement between the results of the two methods was obtained. By using the composition found, the corresponding molecular weights were determined by multi-angle light scattering detection. Based on the composition and the molecular weight we were able to identify the structure of the different molecular species.

The chain architecture dependence of the retention behavior of block copolymers in the temperature gradient interaction chromatography (TGIC) and liquid chromatography at the critical condition (LCCC) was investigated. For the purpose, polystyrene (PS)/polybutadiene (PB) diblock (SB), SBS triblock, and BSB triblock copolymers were prepared by sequential anionic polymerization and further fractionated by reversed-phase TGIC to obtain a set of the block copolymers with high purity, narrow distribution, and matched block length. In the TGIC separation with C18 bonded silica stationary phase and a mixture of CH2Cl2/CH3CN mobile phase, retention of the three block copolymers with matched molecular weight and composition shows a significant architecture effect: SBS elutes significantly earlier while BSB or SB elute later at similar retention volume. It indicates that the polymer−stationary phase interaction is less effective for the PB block located at the middle of the chain than the blocks located at the cha...

We have investigated the surfaces of rubbed polystyrene (PS) films in detail using atomic force microscopy and have discovered a previously unknown surface feature: submicroscale meandering groove-like structures composed of gravel-like grooves in tens of nanometers are present, oriented perpendicular to the rubbing direction. This unusual surface morphology is a significant departure from the surface topographies observed so far for rubbed PS and other polymer films, for which grooves are usually only found parallel to the rubbing direction. We also conclude from retardation analysis and linearly polarized infrared (IR) spectroscopy that the phenyl side groups of the PS chains are reoriented perpendicular to the rubbing direction, with para-directions that are nearly normal to the film plane, whereas the vinyl backbones of the PS chains are reoriented along the rubbing direction. This is the first time IR spectroscopic techniques have been used to determine the three-dimensional reorientation geometry o...

A miktoarm star-shaped copolymer, with one polystyrene arm (M w = 198 kg/mol) and three polyisoprene arms (M w = 51 kg/mol) (PSPI 3 ), was rigorously characterized by temperature gradient interaction chromatography (TGIC). The polymer was prepared by linking active chain ends of precursor polymers to tetrachlorosilane as the linking agent, and the precursor polymers were prepared by anionic polymerization. The crude product was purified by fractional precipitation to remove the byproducts and the excess reagents. Size exclusion chromatography (SEC) analysis shows a narrow single elution peak whose molecular weight and composition are in good agreement with the predicted values in experimental precision. Therefore, it appears on the basis of conventional characterization using SEC, light scattering, and NMR that the fractionated mother represents a high-purity PSPI 3 miktoarm star copolymer. However, TGIC analysis reveals the presence of significant amount of byproducts, most significantly PSPI 2 , which amounts to about 20% of the fractionated sample. This result clearly indicates that the analysis results utilizing conventional polymer characterization tools such as SEC, light scattering, osmometry, and viscometry are insufficient to establish the purity of polymers with complex architecture. It seems preferable to carry out a more detailed analysis such as that described in this work, in particular for polymers with complex architectures, if rigorous proof of structural purity is required.

The reaction products of polystyryllithium with air were characterized by size-exclusion chromatography, temperature gradient interaction chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Polystyryllithium was prepared by anionic polymerization of styrene initiated with sec-butyllithium in cyclohexane under an Ar atmosphere. It was confirmed that polystyryl ketone, polystyryl alcohol, and directly coupled polystyrene were the major products in addition to the normally terminated polystyrene, which is consistent with the results in the literature. We could also identify the presence of methoxy and carboxylic acid end capped polystyrenes as well as dipolystyryl ether as minor products. Among the minor products, dipolystyryl ether has not been reported yet.

In this study we fractionated polystyrene-block-polyisoprene diblock copolymers (PS-b-PI) prepared by anionic polymerization into fractions which have a narrower distribution in molecular weight as well as in chemical composition. The strategy was to use two-dimensional HPLC: reversed phase HPLC to fractionate PI block and normal phase HPLC to fractionate PS block with a minimal effect of the other block. The working principle of the separation method was confirmed for a low molecular weight PS-b-PI (2.4 kg/mol). With the aid of matrix assisted laser desorption/ionization mass spectrometry, we found that the separation method could resolve each mer of the PS-b-PI. We extended the application to a high molecular weight diblock copolymer (24 kg/mol) and established the method as a promising tool to further fractionate block copolymers into molecular species better defined in molecular weight as well as in composition. We observed a significant variation in average molecular weight as well as in composition...

Model comb-shaped polystyrene (PS) samples are synthesized by anionic polymerization and the as-prepared PS heterogeneous combs are further fractionated by temperature gradient interaction chromatography (TGIC) to obtain well-defined random combs with 1–4 branches at random positions on a backbone. Size exclusion chromatography-triple detection and TGIC-triple detection analyses are carried out with the fractionated PS random combs in a good and a theta solvent, respectively. The experimentally observed geometric contraction factor (g), the ratio of the mean square radius of gyration and the hydrodynamic contraction factor (g′), and the ratio of the intrinsic viscosity are compared. It is observed that the two contraction factors follow the relationship of g′ = ge reasonably well and the exponent e of the PS combs is found as ∼1 in a good solvent and ∼0.66 in a theta solvent. Furthermore, it is found that the theoretical grw is not in good agreement with the experimental results.

Chromatographic retention of linear and ring polystyrene was investigated near the chromatographic critical condition. Reversed phase silica columns of four different pore sizes were employed to examine the pore size dependence. Adjusting the column temperature, the critical condition for linear polystyrene was searched for each column with a mixed mobile phase of CH2Cl2/CH3CN (57/43 v/v). It was practically impossible to establish an unambiguous critical condition with a single pore size column for a wide molecular weight range of polystyrenes, in particular with narrow pore size columns. At the best available condition, retentions of nine different molecular weight ring polystyrenes were measured relative to their linear precursors for each pore-sized column. As predicted theoretically, the partition coefficient (K) of ring polymers vs the size ratio of polymer chain to pore (R/d) shows a good linear relationship in the large pore regime (R/d ≪ 1). This linearity is found to be universal for all the por...