Linear Multiblock Copolymers Research Articles

Self-Assembly of Rod–Coil Multiblock Copolymers: A Strategy for Creating Hierarchical Smectic Structures

We extended self-consistent field theory to explore self-assembly behavior of linear multiblock copolymers consisting of alternative rod and coil blocks. Such rod-coil multiblock copolymers are found to be capable of self-assembling into hierarchical smectic microstructures. For the copolymers with long rod end block, lamellae-in-lamellar structures containing two smectic C phases at small and large length scales were observed. It was found that the hierarchical smectic structures exhibit not only double periodicities in overall structure but also double orientational orders of rod blocks. Additionally, these hierarchical smectic structures can be tailed by tuning the relative length of the coil blocks. For the copolymers with long coil end block, the multiblock copolymers can self-assemble into hierarchical lamellar structures with smectic phases only at the small length scale. The findings gained through the present study may offer valuable information for understanding the self-assembly behavior of complicated rod-coil copolymers and designing polymeric materials with advanced properties.

Quadruple click reactions for the synthesis of cysteine‐terminated linear multiblock copolymers

AbstractSynthesis of cysteine‐terminated linear polystyrene (PS)‐b‐poly(ε‐caprolactone) (PCL)‐b‐poly(methyl methacrylate) (PMMA)/or poly(tert‐butyl acrylate)(PtBA)‐b‐poly(ethylene glycol) (PEG) copolymers was carried out using sequential quadruple click reactions including thiol‐ene, copper‐catalyzed azide–alkyne cycloaddition (CuAAC), Diels–Alder, and nitroxide radical coupling (NRC) reactions. N‐acetyl‐L‐cysteine methyl ester was first clicked with α‐allyl‐ω‐azide‐terminated PS via thiol‐ene reaction to create α‐cysteine‐ω‐azide‐terminated PS. Subsequent CuAAC reaction with PCL, followed by the introduction of the PMMA/or PtBA and PEG blocks via Diels–Alder and NRC, respectively, yielded final cysteine‐terminated multiblock copolymers. By 1H NMR spectroscopy, the DPns of the blocks in the final multiblock copolymers were found to be close to those of the related polymer precursors, indicating that highly efficient click reactions occurred for polymer–polymer coupling. Successful quadruple click reactions were also confirmed by gel permeation chromatography. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

A study for the static properties of symmetric linear multiblock copolymers under poor solvent conditions

We use a standard bead-spring model and molecular dynamics simulations to study the static properties of symmetric linear multiblock copolymer chains and their blocks under poor solvent conditions in a dilute solution from the regime close to theta conditions, where the chains adopt a coil-like formation, to the poorer solvent regime where the chains collapse obtaining a globular formation and phase separation between the blocks occurs. We choose interaction parameters as is done for a standard model, i.e., the Lennard-Jones fluid and we consider symmetric chains, i.e., the multiblock copolymer consists of an even number n of alternating chemically different A and B blocks of the same length N(A) = N(B) = N. We show how usual static properties of the individual blocks and the whole multiblock chain can reflect the phase behavior of such macromolecules. Also, how parameters, such as the number of blocks n can affect properties of the individual blocks, when chains are in a poor solvent for a certain range of n. A detailed discussion of the static properties of these symmetric multiblock copolymers is also given. Our results in combination with recent simulation results on the behavior of multiblock copolymer chains provide a complete picture for the behavior of these macromolecules under poor solvent conditions, at least for this most symmetrical case. Due to the standard choice of our parameters, our system can be used as a benchmark for related models, which aim at capturing the basic aspects of the behavior of various biological systems.

Analysis of the static properties of cluster formations in symmetric linear multiblockcopolymers

We use molecular dynamics simulations to study the static properties of a single linearmultiblock copolymer chain under poor solvent conditions varying the block lengthN, the numberof blocks n, and the solvent quality by variation of the temperatureT. We study the most symmetrical case, where the number of blocks of monomers of type A,nA, equals that ofmonomers B, nB (nA = nB = n/2), the length of all blocks is the same irrespective of their type, and the potentialparameters are also chosen symmetrically, as for a standard Lennard-Jones fluid. Underpoor solvent conditions the chains collapse and blocks with monomers of the same typeform clusters, which are phase separated from the clusters with monomers ofthe other type. We study the dependence of the size of the clusters formed onn,N andT. Furthermore, we discuss our results with respect to recent simulation data on the phasebehaviour of such macromolecules, providing a complete picture for the clusterformations in single multiblock copolymer chains under poor solvent conditions.

Microphase separation in linear multiblock copolymers under poor solvent conditions

Molecular dynamics simulations are used to study the phase behavior of linear multiblock copolymers with two types of monomers, A and B, where the length of the polymer blocks NA and NB (NA = NB = N), the number of the blocks nA and nB (nA = nB = n), and the solvent quality varies. The fraction f of A-type monomers is kept constant and equal to 0.5. Whereas at high enough temperatures these macromolecules form coil structures, where each block A or B forms rather individual clusters, at low enough temperatures A and B monomers from different blocks can join together forming clusters of A or B monomers. The dependence of the formation of these clusters on the varied parameters is discussed in detail, providing a full understanding of the phase behavior of linear multiblock copolymers, at least for this symmetrical case.

Hyperbranched poly(ether sulfone)s: preparation and application to ion-exchange membranes

Hyperbranched polymers possess unique characteristics such as low viscosity, high solubility in organic solvents and a high degree of functionality at the terminal position. However, hyperbranched polymers also possess weak mechanical properties. In this study, hyperbranched poly(ether sulfone)s (HBPES) possessing sulfonic acid moieties at the terminal position were prepared by reacting electrophilic sulfonium ions with electron-rich benzene rings from two kinds of AB2 monomers. To address the weakness of HBPES, hybrid materials containing linear and hyperbranched PES were investigated. Linear and hyperbranched multiblock copolymers were successfully prepared by reacting oligomeric linear PES and AB2 monomers. From the multiblock copolymers, linear and hyperbranched PES blends were prepared and applied as ion-exchange membranes for fuel cells. Films containing various ratios of linear and hyperbranched PES terminated by sulfonyl chloride groups were prepared via casting from a solution of DMAc. The results indicated that tethers between linear and hyperbranched polymers were important for controlling the size of the phases and for preventing the dissolution of HBPES in water; thus, linear and hyperbranched polymers were crosslinked by simply heating blends of both films. Finally, hybrid films containing sulfonic acid groups were obtained by hydrolyzing the sulfonyl chloride moieties. The resultant films showed ion-exchange capacities that were comparable to that of a Nafion 117 membrane (Dupont, Tokyo, Japan). Hyperbranched poly(ether sulfone)s (HBPES) possessing sulfonic acid at the terminal point were prepared by the electrophilic reaction of sulfonium ions to electron-rich benzene rings starting two kinds of AB2 monomers. First, linear and hyperbranched multiblock copolymers were successfully prepared by the reaction of oligomeric linear PES and AB2 monomer. Next, from these multiblock copolymers, a linear and hyperbranched PES blend was prepared and applied as ion-exchange membranes for fuel cells. The blend films showed comparable ion-exchange capacity with Nafion 117 membrane.

Synthesis and micelle behavior of (PNIPAm-PtBA-PNIPAm)m amphiphilic multiblock copolymer

A linear amphiphilic multiblock copolymer (PNIPAm-PtBA-PNIPAm)m was successfully synthesized by a two-step reversible addition–fragmentation transfer (RAFT) polymerization in the presence of a cyclic trithiocarbonate as RAFT agent. The micelle behavior of (PNIPAm-PtBA-PNIPAm)m multiblock copolymer in aqueous solution was then investigated by means of normal TEM, cryo-TEM, static and dynamic light scattering. The morphology, size, and size distribution of (PNIPAm-PtBA-PNIPAm)m micelles were found to be dependent on the initial concentration of multiblock copolymer in THF. Spherical micelles, associated aggregates of spherical micelles, cage-like micelles, layered structures, and vesicular micelles were experimentally observed, which were in good agreement with the prediction of theory and simulations on linear amphiphilic multiblock copolymer in selective solvent. The (PNIPAm-PtBA-PNIPAm)m micelles also exhibit thermo-sensitive behavior in aqueous solution because of the PNIPAm blocks.

Alternating Amphiphilic Multiblock Copolymers: Controlled Synthesis via RAFT Polymerization and Aqueous Solution Characterization

Four linear amphiphilic multiblock copolymers based on 2-(dimethylamino)ethyl methacrylate (DMAEMA, hydrophilic) and methyl methacrylate (MMA, hydrophobic), bearing from two to five blocks, were synthesized using reversible addition−fragmentation chain transfer polymerization and stepwise monomer additions. The degree of polymerization of each hydrophilic polyDMAEMA block was ∼50, while that of the hydrophobic polyMMA blocks was ca. 20. The stepwise monomer addition procedure secured that each higher multiblock was composed of its immediately lower homologue plus exactly one extra block. The molecular weights (MW) of the synthesized (co)polymers, as measured by gel permeation chromatography (GPC), were close to the theoretically expected. GPC also indicated rather narrow molecular weight distributions which, however, broadened with the number of blocks. The compositions of the copolymers, as determined by proton nuclear magnetic resonance spectroscopy, were also close to the expected values. The cloud poi...

Synthesis and Characterization of Amphiphilic Multiblock Copolymers: Effect of the Number of Blocks on Micellization

Five linear amphiphilic multiblock copolymers based on 2-(dimethylamino)ethyl methacrylate (“D”) and methyl methacrylate (“M”), bearing from two to six blocks, were synthesized using sequential group transfer polymerization. All copolymers were obtained from the same polymerization flask (by the withdrawal of a sufficient amount of sample and appropriate adjustment of subsequent monomer loadings) to ensure better comparison between the various multiblocks. A theoretical degree of polymerization (DPth) of 20 was targeted for all D blocks, whereas a DPth of 10 was aimed for the M blocks. Upon characterization using gel permeation chromatography and 1H NMR spectroscopy, the copolymers were confirmed to have the expected values of molecular weights and compositions. Subsequently, the aqueous micellization behavior of these copolymers was probed using dye solubilization, dynamic light scattering, and small-angle neutron scattering. Dye solubilization experiments indicated that micelles readily formed at low copolymer concentrations equal to or less than 0.03% w/w. The scattering measurements revealed that despite the differences in their overall DPth values, the triblock, the tetrablock, and the pentablock copolymers self-assembled in water to form micelles with radii of gyration and hydrodynamic radii very similar to each other, suggesting chain looping and the formation of flowerlike micelles, which is in agreement with recent Monte Carlo simulations.

Lamellar-in-lamellar structure of binary linear multiblock copolymers

A theoretical description of the lamellar-in-lamellar self-assembly of binary A-b-(B-b-A)(m)-b-B-b-A multiblock copolymers in the strong segregation limit is presented. The essential difference between this binary multiblock system and the previously considered C-b-(B-b-A)(m)-b-B-b-C ternary multiblock copolymer system is discussed. Considering the situation with long end blocks, the free energy of the lamellar-in-lamellar self-assembled state is analyzed as a function of the number k of "thin" internal lamellar domains for different numbers m of repeating (B-b-A) units and different values of the Flory-Huggins chi(AB) interaction parameter. The theoretical predictions are in excellent agreement with the available experimental data.

Nonconventional morphologies in two-length scale block copolymer systems beyond the weak segregation theory

The order-disorder and order-order transitions (ODT and OOT) in the linear multiblock copolymers with two-length scale architecture A(fmN)(B(N2)A(N2))(n)B((1-f)mN) are studied under intermediate cooling below the ODT critical point where a nonconventional sequence of the OOTs was predicted previously [Smirnova et al., J. Chem. Phys. 124, 054907 (2006)] within the weak segregation theory (WST). To describe the ordered morphologies appearing in block copolymers (BCs) under cooling, we use the pseudospectral version of the self-consistent field theory (SCFT) with some modifications providing a good convergence speed and a high precision of the solution due to using the Ng iterations [J. Chem. Phys. 61, 2680 (1974)] and a reasonable choice of the predefined symmetries of the computation cell as well as initial guess for the iterations. The WST predicted sequence of the phase transitions is found to hold if the tails of the BCs under consideration are symmetric enough (mid R:0.5-fmid R:</=0.05); the quantitative agreement between the WST and SCFT phase diagrams is reasonable in a narrow (both in f and chi=chiN) region close to the critical point, though. For mid R:0.5-fmid R:>0.05, a large region of the face-centered cubic phase stability is found (up to our knowledge, first within the SCFT framework) inside of the body-centered cubic phase stability region. Occurrence of the two-dimensional and three-dimensional phases with the micelles formed, unlike the conventional diblock copolymers, by the longer (rather than shorter) tails, and its relationship to the BC architecture is first described in detail. The calculated spectra of the ordered phases show that nonmonotonous temperature dependence of the secondary peak scattering intensities accompanied by their vanishing and reappearance is rather a rule than exception.

Phase behavior and structure formation in linear multiblock copolymer solutions by Monte Carlo simulation

The solution phase behavior of short, strictly alternating multiblock copolymers of type (A(n)B(n))(m) was studied using lattice Monte Carlo simulations. The polymer molecules were modeled as flexible chains in a monomeric solvent selective for block type A. The degree of block polymerization n and the number of diblock units per chain m were treated as variables. We show that within the regime of parameters accessible to our study, the thermodynamic phase transition type is dependent on the ratio of m / n. The simulations show microscopic phase separation into roughly spherical aggregates for m / n ratios less than a critical value and first-order macroscopic precipitation otherwise. In general, increasing m at fixed n, or n at fixed m, promotes the tendency toward macroscopic phase precipitation. The enthalpic driving force of phase change is found to universally scale with chain length for all multiblock systems considered and is independent of the existence of a true phase transition. For aggregate forming systems at low amphiphile concentrations, multiblock chains are shown to self-assemble into intramolecular, multichain clusters. Predictions for microstructural dimensions, including critical micelle concentration, equilibrium size, shape, aggregation parameters, and density distributions, are provided. At increasing amphiphile density, interaggregate bridging is shown to result in the formation of networked structures, leading to an eventual solution-gel transition. The gel is swollen and consists of highly interconnected aggregates of approximately spherical morphology. Qualitative agreement is found between experimentally observed physical property changes and phase transitions predicted by simulations. Thus, a potential application of the simulations is the design of multiblock copolymer systems which can be optimized with regard to solution phase behavior and ultimately physical and mechanical properties.

Vertex functions in the Landau theory of phase transitions in melts of Markovian multiblock copolymers

A modified diagram technique has been developed for obtaining the vertex functions of the Landau free energy of the melt of an m -component linear stochastic multiblock copolymer whose macromolecules are of arbitrary architecture. The derivation of the expressions for the vertex functions by means of this diagram technique for block copolymers with molecular structure distribution described by the Markov chain is considered in detail. Expressions for all contributions to the free energy up to the fourth order and local contributions of the fifth and sixth orders have been found for the first time for the compressible melt of this copolymer. As to nonlocal contributions of these orders, the expressions for the most singular of them have been obtained for the incompressible melt of m -component Markovian copolymers. Some considerations have been made concerning the appearance of the nonlocal contributions of an arbitrary order.

Conductivity hysteresis in polymer electrolytes incorporating poly(tetrahydrofuran)

Conductivity hysteresis and room temperature ionic conductivities >10 −3 S/cm were recently reported for electrolytes prepared from blends of an amphiphilic comb copolymer, poly[2,5,8,11,14-pentaoxapentadecamethylene (5-hexadecyloxy-1,3-phenylene)] (polymer I), and a linear multiblock copolymer, poly(oligotetrahydrofuran- co-dodecamethylene) (polymer II), following thermal treatment [F. Chia, Y. Zheng, J. Liu, N. Reeves, G. Ungar, P.V. Wright, Electrochim. Acta 43 (2003) 1939]. To investigate the origin of these effects, polymers I and II were synthesized in this work, and the conductivity and thermal properties of the individual polymers were investigated. AC impedance measurements were conducted on I and II doped with LiBF 4 or LiClO 4 during gradual heating to 110 °C and slow cooling to room temperature. Significant conductivity hysteresis was seen for polymer II, and was similarly observed for poly(tetrahydrofuran) (PTHF) homopolymer at equivalent doping levels. From thermogravimetic analysis (TGA), gel permeation chromatography (GPC) and 1H NMR spectroscopy, both polymer II and PTHF were found to partially decompose to THF during heat treatment, resulting in a self-plasticizing effect on conductivity.

Ideal tetrafunctional amphiphilic PEG/PDMS conetworks by a dual‐purpose extender/crosslinker. I. Synthesis

AbstractThe synthesis of a new type of amphiphilic conetwork (APCN) consisting of well‐defined hydrophilic poly(ethylene glycol) (PEG) and hydrophobic polydimethylsiloxane (PDMS) segments is described. The conetwork is ideal (the lengths of each PEG and PDMS chain segments, respectively, are identical) and tetrafunctional (exactly four chains emanate from each crosslink site). The synthesis of the conetworks was achieved by the use of a novel dual‐purpose extender/crosslinker Y (bis [(dimethylsilyl)oxy]‐[(etoxydimethylsilyl)oxy]phenylsilane, (SiPh(SiH)2OEt)), in two steps: (1) Synthesis of a new linear random multiblock copolymer (MBC) (AY)n(BY)m, where A is the hydrophilic PEG and B is the hydrophobic segment, and (2) Crosslinking the multiblocks by catalytic condensation of the SiOEt groups in the Y units. The extender/crosslinker fulfills two totally different functions: First, it extends two incompatible hydrophilic and hydrophobic prepolymers (PEG and PDMS) to a random MBC, and, subsequently, it cross‐links the multiblocks to the target APCN. The synthesis and characterization of the extender/crosslinker is also presented. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4953–4964, 2005

Theory of chromatographic separation of linear and star-shaped binary block-copolymers

Equations for the distribution coefficient of heteroarm stars are derived by using a model of an ideal chain in a slit-like pore; these equations together with those previously reported for linear block-copolymers are applied to describe chromatography of such copolymers. According to the theory, the retention generally depends on molar mass, composition, and architecture (microstructure and topology) of copolymers, on pore size and on adsorption interaction of chain units A and B. Three special modes of chromatography are studied in detail. (i) If interactions for A and B are close to the critical point of adsorption (CPA), the retention practically does not depend on architecture, and high molar mass copolymers can be separated by composition. (ii) At SEC condition for B and strong adsorption for A, copolymers in principle can be separated by architecture; better separation is expected in wide pores. Retention of linear block-copolymers decreases with increasing of the number of blocks; for heteroarm stars the theory predicts retention decreasing as: AB > StarAAB > StarABB; StarAAAB > StarABBB > StarAABB; StarAAAAB > StarABBBB > StarAAABB > StarAABBB. (iii) At the CPA for B copolymers AB, BAB and heteroarm stars regardless molar mass of B, M(B), can be separated by M(A). The same is true for ABA and ABAB...A in narrow pores. While the retention of AB, BAB, Star AB...B and StarAAB...B is the same, copolymers AB, ABA and linear multiblock-copolymers can be separated, as well as symmetric and very asymmetric triblock-copolymers ABA.

Synthesis of PMMA‐PTHF‐PMMA and PMMA‐PTHF‐PST linear and star block copolymers

AbstractCombination of cationic, redox free radical, and thermal free radical polymerizations was performed to obtain linear and star polytetramethylene oxide (poly‐THF)‐polymethyl methacrylate (PMMA)/polystyrene (PSt) multiblock copolymers. Cationic polymerization of THF was initiated by the mixture of AgSbF6 and bis(4,4′ bromo‐methyl benzoyl) peroxide (BBP) or bis (3,5,3′,5′ dibromomethyl benzoyl) peroxide (BDBP) at 20°C to obtain linear and star poly‐THF initiators with Mw varying from 7,500 to 59,000 Da. Poly‐THF samples with hydroxyl ends were used in the methyl methacrylate (MMA) polymerization in the presence of Ce(IV) salt at 40°C to obtain poly(THF‐b‐MMA) block copolymers containing the peroxide group in the middle. Poly(MMA‐b‐THF) linear and star block copolymers having the peroxide group in the chain were used in the polymerization of methyl methacrylate (MMA) and styrene (St) at 80°C to obtain PMMA‐b‐PTHF‐b‐PMMA and PMMA‐b‐PTHF‐b‐PSt linear and star multiblock copolymers. Polymers obtained were characterizated by GPC, FT‐IR, DSC, TGA, 1H‐NMR, and 13C‐NMR techniques and the fractional precipitation method. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 219–226, 2004

Design of ABC Triblock Copolymers near the ODT with the Random Phase Approximation

Leibler's random phase approximation for block copolymers, modified so as to be applicable to linear multiblock copolymers, has been quantitatively compared to data from three linear ABC/ACB triblock copolymer melts: poly(cyclohexylethylene-b-ethylene-b-ethylethylene) (CEEE)/CEEE, poly(styrene-b-isoprene-b-ethylene oxide) (SIO)/ISO (Macromolecules 2001, 34, 6994−7008;Macromolecules 2002, 35, 7007−7017), and poly(styrene-b-isoprene-b-dimethylsiloxane) (SID)/ISD (Macromolecules 2002, 35, 3189−3197). The RPA calculation provides the mean-field static structure factor for a disordered block copolymer melt, which can be used to anticipate the scattering behavior and spinodal stability limit temperature (Ts); in the context of mean-field theory, the spinodal should lie near the order−disorder-transition temperature (TODT). We find that the RPA spinodal temperature semiquantitatively matches the magnitude and temperature dependence of the ODT as a function of molecular weight (in CEEE/CEEE) and composition (SIO...

Bridging and looping in multiblock copolymer melts

We apply both self-consistent-field theory (SCFT) and strong-segregation theory (SST) to the lamellar phase of a melt of linear multiblock copolymers. We present a new solution for the SST which now agrees with that obtained for the SCFT. Using both theories, we calculate the distribution of monomers from the center of blocks originating from a single interface, the lamellar spacing, and the fraction of blocks which bridge across lamellae.

Stable and Unstable Phases of a Linear Multiblock Copolymer Melt

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStable and Unstable Phases of a Linear Multiblock Copolymer MeltM. W. Matsen and M. SchickCite this: Macromolecules 1994, 27, 24, 7157–7163Publication Date (Print):November 1, 1994Publication History Published online1 May 2002Published inissue 1 November 1994https://doi.org/10.1021/ma00102a025RIGHTS & PERMISSIONSArticle Views849Altmetric-Citations98LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (821 KB) Get e-Alerts Get e-Alerts