Multiblock copolymers of styrene and isoprene. II. Microstructure and dilute solution properties

Dilute solution properties of linear (SI)₃ six-block copolymers of styrene and isoprene are compared to those of random, two-block, and three-block copolymers of the same system. All the copolymers were prepared with sec-butyllithium in benzene. The microstructure of the polyisoprene blocks is close to that of homopolyisoprene prepared under the same conditions. In contrast, the random copolymer shows a larger amount of trans-1,4 isoprene units. The intrinsic viscosities of the copolymers in methylisobutyl ketone, a poor solvent for both polystyrene and polyisoprene, and in toluene, a good solvent for both homopolymers, are examined on the basis of the Fox–Flory relation for homopolymers. All the copolymers behave similarly in each solvent. In methylisobutyl ketone, the viscosity results indicate a random coil conformation with a small expansion owing to the extra repulsive interactions between the dissimilar units. In all cases, the heterocontact repulsive interactions are small and can be characterized by an interaction parameter χ_ab close to 0.025. In toluene, the perturbation caused by the heterocontacts becomes negligible and the expansion factor α_η can be predicted from a weighted average of those of the parent homopolymers of the same molecular weight as the copolymer.     

Conformational behavior of styrene–dymethylsiloxane block copolymers in dilute solution

To determine the behavior of a copolymer is dilute solution, a viscosity study has been performed on a polystyrene–polydimethylsiloxane block copolymer in three solvents presenting different thermodynamic conditions. The results are discussed in relation to a mixture of homopolymers and a segregated model. The unperturbed dimensions, obtained by the Stock–mayer–Fixman method, are intermediate between those of the parent homopolymers. The intrinsic viscosity measured in a good solvent, toluene, was close to the weighted averages of those of the corresponding homopolymers of equal molecular weight, but higher in decalin and in butanone, θ solvents for PS and PDMS, respectively. According to the low value obtained for the interaction parameter, the chain is slightly expanded as a result of the interactions between the unlike monomer units. Both segregation and random conformation would probably occur, depending on the quality of the solvent.     

Solution properties of styrene-p-chlorostyrene diblock copolymers—I. Conformational behaviour in dilute solutions

The conformational behaviour of styrene-p-chlorostyrene diblock copolymers in dilute solutions was studied and compared with that of the corresponding triblock copolymers. Eight styrene-p-chlorostyrene diblock copolymers, of almost equimolar composition but with different molecular weights, were prepared using an anionic polymerization technique. The intrinsic viscosities of the copolymers were measured in non-selective solvents, such as toluene and 2-butanone, and in a selective solvent, cumene. The osmotic second virial coefficients of the diblock copolymers were measured in toluene. The data were analysed on the basis of two parameter theories. The unperturbed dimensions for the diblock copolymers can be expressed as a composition average of those for the parent homopolymers and the long-range interaction parameters of the diblock copolymers in toluene, 2-butanone and cumene are smaller than those of the triblock copolymers of the same composition. It means that the diblock copolymer chains in these 3 solvents had a more compact conformation than the triblock copolymers of the same composition and molecular weight.     

On the measurement of the χ-parameter under the zero average contrast condition

Several methods for measuring directly the interaction parameter X as a function of polymer concentration are presented. These methods are applied to symmetric ternary mixtures of homopolymers and copolymers in solution under the zero average contrast condition. They can be used for an arbitrary concentration from dilute solution to the bulk and at any value of the scattering wavenumber q. Possible combinations of static and dynamic measurements are presented. © 1992 John Wiley & Sons, Inc.     

Styrene-methyl acrylate copolymers and acrylate homopolymers in solution

Molecular weight determinations by light scattering and osmometry and intrinsic viscosity measurements were made in various solvents on fractions of styrene–methyl acrylate copolymers with different compositions and on acrylate homopolymers prepared by free-radical reaction. Relations between intrinsic viscosity [η] and molecular weight M thus established are compared with those reported by other authors. 2-Methylcyclohexanol was found to be a theta solvent for the copolymers and both parent homopolymers, and isoamyl acetate was a theta solvent for poly(methyl acrylate). From theta point viscosity data obtained with these solvents, unperturbed chain dimensions were estimated. The results are compared with the unperturbed dimensions estimated from the [η]–M relations obtained in good solvents. On the basis of the experimental data it was found that the unperturbed dimension depends linearly on the copolymer composition, in contrast to the case of styrene–methyl methacrylate copolymers. Composition dependences of the theta temperature and of the parameter describing the long-range interactions between nonadjacent segments in polymer chains were investigated. The result implies that long-range interactions between monomeric units never disappear even when those between the same monomeric units vanish. The Huggins constant for copolymer is discussed in terms of the excluded volume variable.     

Phase behavior of binary blends of diblock copolymer/homopolymer confined in spherical nanopores

Binary blends of a diblock copolymer (AB) and an incompatible homopolymer (C) confined in spherical cavities are studied using a simulated annealing technique. The phase behavior of the blends is examined for four typical cases, representing the different selectivity of the pore surface to the A, B, and C species. The internal morphology of the spherical polymeric particles is controlled by the homopolymer volume fraction, the degree of confinement, and the composition of the copolymer. Inside a particle, the homopolymers segregate to form one or, under some conditions, two domains; thus, the homopolymers may act as an additional controlling parameter of the shape and symmetry of the copolymer domain. A rich array of confinement-induced novel diblock copolymer morphologies is predicted. In particular, core-shell particles with the copolymers as the shell wrapping around a homopolymer core or a copolymer-homopolymer combined core and Janus-like particles with the copolymers and the homopolymers on different sides are obtained.     

Dilute solution properties of methyl methacrylate—acrylonitrile copolymer (MA2)

This article deals with studies of the dilute solution properties of methyl methacrylate-acrylonitrile (MMA-AN) copolymer of 0.415 mole fraction (mf) of acrylonitrile composition. Mark—Houwink parameters for this copolymer have been evaluated in acetonitrile (MeCN), 2-butanone (MEK), dimethyl formamide (DMF), and γ-butyrolactone (γ-BL). The Mark-Houwink exponent a in all four solvents at all temperatures is larger than the corresponding values of the parent homopolymers. The solvent power is in the order of DMF < γ–BL < MEK < MeCN; [η] decreases with an increase in temperature, which is behavior characteristic of polymers in good solvent. The unperturbed dimensions (K₀) values, obtained by the Stockmayer–Fixman method, are lower than those for the parent homopolymers and depend on solvent as well as temperature. The solute—solvent interaction parameter X₁ values are close to 0.5; X₁ is independent of temperature. The excess interaction parameter X_ABvalues are negative. The results for this copolymer system in regard to low second virial coefficient A₂, large X₁, and high a values suggest that the large extension of these copolymer chains is due to the unusual short-range interactions.     

Lattice Monte Carlo investigations on copolymer systems, 1. Diblock copolymers

Symmetric diblock copolymers in dilute solution were examined by means of Monte Carlo simulations on a cubic lattice with respect to chain- and block dimensions, shape, local structure and number of contacts. The solvent was either a common good one, a common θ-solvent or a selective one for the two blocks. In all cases, repulsive interactions are operative between the blocks. In addition, the underlying homopolymers (athermal and θ) were divided into two parts (and treated as a block copolymer) for comparison. Chain-length was varied from 40 to 1280 segments leading to the expected values for the critical exponent 2v ≈ 1.2 for good solvent quality and 2v ≈ 1.0 for θ-solvent. Copolymers in a selective solvent scale with an intermediate exponent, 2v ≈ 1.13. The deviation of the mean squared dimensions of the copolymers from the sum of those of two homopolymers of the same length and for the same solvent quality as the blocks is largest for block copolymers in a common θ-solvent (where it exceeds 20%), while the blocks themselves have mostly the same dimensions as their underlying homopolymers of equal length. The shape of the copolymers, expressed by the parameter δ (asphericity) becomes more rod-like with increasing chain-length if there are (compact) θ-blocks in the molecule which are subject to mutual repulsive interaction. In these cases, θ exceeds the value of the homopolymers in the limit of infinite chain-length. The number of contacts per segment approaches a limiting value with increasing chain-length which is ≈0.20 for athermal chains and athermal blocks. For θ-chains and θ-blocks, a limiting value is not yet reached within the range of chainlengths investigated. The number of contacts per segment between two different blocks quickly tends to zero with increasing chain-length.     

Self-assembly in block polyelectrolytes

The self-consistent field theory (SCFT) complemented with the Poisson-Boltzmann equation is employed to explore self-assembly of polyelectrolyte copolymers composed of charged blocks A and neutral blocks B. We have extended SCFT to dissociating triblock copolymers and demonstrated our approach on three characteristic examples: (1) diblock copolymer (AB) melt, (2) symmetric triblock copolymer (ABA) melt, (3) triblock copolymer (ABA) solution with added electrolyte. For copolymer melts, we varied the composition (that is, the total fraction of A-segments in the system) and the charge density on A blocks and calculated the phase diagram that contains ordered mesophases of lamellar, gyroid, hexagonal, and bcc symmetries, as well as the uniform disordered phase. The phase diagram of charged block copolymer melts in the charge density--system composition coordinates is similar to the classical phase diagram of neutral block copolymer melts, where the composition and the Flory mismatch interaction parameter χ(AB) are used as variables. We found that the transitions between the polyelectrolyte mesophases with the increase of charge density occur in the same sequence, from lamellar to gyroid to hexagonal to bcc to disordered morphologies, as the mesophase transitions for neutral diblocks with the decrease of χ(AB). In a certain range of compositions, the phase diagram for charged triblock copolymers exhibits unexpected features, allowing for transitions from hexagonal to gyroid to lamellar mesophases as the charge density increases. Triblock polyelectrolyte solutions were studied by varying the charge density and solvent concentration at a fixed copolymer composition. Transitions from lamellar to gyroid and gyroid to hexagonal morphologies were observed at lower polymer concentrations than the respective transitions in the similar neutral copolymer, indicating a substantial influence of the charge density on phase behavior.     

Controlling effective interactions and spatial dispersion of nanoparticles in multiblock copolymer melts

The microscopic Polymer Reference Interaction Site Model theory is employed to study, for the first time, the effective interactions, spatial organization, and miscibility of dilute spherical nanoparticles in non‐microphase separating, chemically heterogeneous, compositionally symmetric AB multiblock copolymer melts of varying monomer sequence or architecture. The dependence of nanoparticle wettability on copolymer sequence and chemistry results in interparticle potentials‐of‐mean force that are qualitatively different from homopolymers. An important prediction is the ability to improve nanoparticle dispersion via judicious choice of block length and monomer adsorption‐strengths which control both local surface segregation and chain connectivity induced packing constraints and frustration. The degree of dispersion also depends strongly on nanoparticle diameter relative to the block contour length. Small particles in copolymers with longer block lengths experience a more homopolymer‐like environment which renders them relatively insensitive to copolymer chemical heterogeneity and hinders dispersion. Larger particles (sufficiently larger than the monomer diameter) in copolymers of relatively short block lengths provide better dispersion than either a homopolymer or random copolymer. The theory also predicts a novel widening of the miscibility window for large particles upon increasing the overall molecular weight of copolymers composed of relatively long blocks. The influence of a positive chi‐parameter in the pure copolymer melt is briefly studied. Quantitative application to fullerenes in specific copolymers of experimental interest is performed, and miscibility predictions are made. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1098–1111     

Prediction of miscibility regions in ternary blends of poly(styrene-stat-acrylonitrile), poly(acrylonitrile-stat-methyl methacrylate), and poly(styrene-stat-methyl methacrylate)

The miscibilities of ternary copolymer blends prepared from poly(styrene-stat-acrylonitrile), poly(styrene-stat-methyl methacrylate), and poly(methyl methacrylate-stat-acrylonitrile) were predicted by calculating the interaction parameter, χ_blend, for various blend combinations, from the corresponding binary segmental interaction parameters estimated from previous work. Binodal and spinodal curves were calculated using the Flory-Huggins theory and it was observed that the most accurate estimate of the boundary between miscible and immiscible blends was given by the spinodal. It has also been demonstrated that in some of the ternary blends with fixed copolymer compositions the miscibility of the blend can be altered by changing the ratio of the three components in the mixture. Conditions for miscibility in this ternary system, and possibly a general feature of all such systems, are (a) that at least two of the binary interaction parameters χ_ij are less than the critical value χ_crit, while the third should not be too much larger, that is, one of the copolymers may act as a compatibilizer for the other two copolymers, (b) that the difference Δχ = /χ₁₂ ? χ₁₃/ is small. © 1992 John Wiley & Sons, Inc.     

On the compatibility of binary and ternary random copolymers of acrylonitrile with vinyl acetate and/or α-methylstyrene—II: The influence of the time factor

The time dependence of the microscopical aspect, crystallinity, viscosity of the spinning solutions and the thermal and tinctorial properties of films formed from binary, ternary copolymers and binary copolymer mixtures of acrylonitrile with vinyl acetate and χ-methylstyrene have been compared. The characteristics of binary copolymers and incompatible mixtures are stable with time, while those of ternary copolymers and pseudocompatible mixtures evolve towards a limiting state. with phase separation.     

Design of bicontinuous polymeric microemulsions

Recent experiments suggest that thermodynamically stable, bicontinuous microemulsions can be achieved in symmetric ternary blends of two homopolymers and a diblock copolymer by formulating alloys with compositions near mean-field isotropic Lifshitz points. We argue that practical application of this design criterion may require use of homopolymers of unequal molecular weights and block copolymers of different architecture. We demonstrate the existence of, and explicitly locate, mean-field isotropic Lifshitz points in ternary blends with homopolymer molecular weight asymmetry and either AB diblock or ABA triblock copolymer architectures. These calculations considerably expand the parameter space for observing bicontinuous microemulsions and allow for more flexibility in tailoring melt rheological properties and solid-state mechanical properties. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2775–2786, 1997     

Phase behavior and interfacial properties of diblock copolymer-homopolymer ternary mixtures: Influence of volume fraction of copolymers and interaction energy

We use a Monte Carlo method to study the phase and interfacial behaviors of A-b-B diblocks in a blend of homopolymers, A and B, which are confined between two asymmetric hard and impenetrable walls. Our results show that, when the interaction strength is weak, the block copolymersare uniformly distributed in the ternary mixtures under considered concentrations. Under strong interaction strength, distribution region of the block copolymers changes from a single smooth interface to a curved interface or multi-layer interface in the ternary mixtures. Furthermore, our findings show that with increasing volume fraction of A-b-B diblock copolymer(фC), copolymer profiles broaden while фC≥ 0.4, a lamellar phase is formed and by further increasing фC, more thinner layers are observed. Moreover, the results show that, with the increase of фC, the phase interface first gradually transforms from plane to a curved surface rather than micelle or lamellar phase while with the increase of the interaction between A and B segments(ε_(AB)), the copolymer chains not only get stretched in the direction perpendicular to the interface, but also are oriented. The simulations also revealthat the difference between symmetric and asymmetric copolymers is negligible in statistics if the lengths of two blocksare comparable.     

Properties of polystyrene-poly(methylmethacrylate) random and diblock copolymers in dilute and semidilute solutions

Solution properties for random and diblock copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA) have been measured by dynamic and total intensity light scattering in solvents of differing quality. The results are compared with the corresponding properties for PS and PMMA homopolymers of similar molecular weight, in order to determine if interactions between unlike monomers are significant. The hydrodynamic radius (R_h) and diffusion second virial coefficient (k_d) for the random copolymer are found to be larger than the corresponding values for the homopolymers in a solvent which is near-theta for the two homopolymers, whereas no such effect is observed for the block copolymer. This suggests that most intrachain interactions occur a relatively short distance along the chain backbone. In a mutual good solvent R_h and k_d of the random copolymer are comparable to the average of the values for the homopolymers, indicating that in a good solvent monomer/solvent interactions dominate over monomer/monomer interactions. For an isolated diblock copolymer in a mutual good solvent, there is no evidence that interactions between unlike monomers lead to additional expansion of the entire molecule, as measured by R_h, nor expansion of the individual blocks as probed by light scattering with one block optically masked. However, at low but finite concentration there is evidence (the coefficients of the binary interaction terms in the viscosity and the mutual diffusion coefficient, and the second and third virial coefficients) that a weak ordering effect may exist in block copolymer solutions, far from the conditions where microphase separation occurs. Finally, measurements of ternary polymer-polymer-solvent solutions show no dependence on monomer composition or monomer distribution for the tracer diffusion of probe PS-PMMA copolymers in a PMMA/toluene matrix. This indicate that the frictional interaction is largely unaffected by interactions between unlike monomers. However, there is evidence that the thermodynamic interaction is more unfavorable between a random copolymer and the homopolymer matrix than between a diblock and the matrix. © 1994 John Wiley & Sons, Inc.     

Radiation Degradation of Copolymers. III. Poly(styrene-co-methyl Acrylate)

The distribution of volatile products from γ-irradiation of copolymers of styrene and methyl acrylate is independent of the composition of the copolymer and the same as that obtained from poly(methyl acrylate). The yields are less than proportional to the methyl acrylate content, Indicating a protective effect from the styrene units as observed previously in copolymers of styrene with methyl methacrylate. The flexural strengths of the copolymers, measured at 1°C, decrease with radiation dose for high styrene content, but increase for high methyl acrylate content. Samples irradiated in air have appreciably lower strengths than those irradiated in vacuum. Gel measurements show intermediate behavior for the copolymers between the homopolymers.     

Frictional properties of dilute block-copolymer solutions and homopolymer solutions. Application to molecular weight determination.

An equation for the translational diffusion coefficient of block copolymers in dilute solution has been obtained by modifying Zimm's equation for homopolymers to take into account the existence of dissimilar segments in block copolymers. Illustrative calculations for homopolymers and block copolymers have been made and the results for homopolymers have been compared with experiments and with the calculations of Yamakawa and Fujii. A procedure has been proposed to determine the molecular weight of a block copolymer from measurements of its limiting viscosity number and its sedimentation coefficient or translational diffusion coefficient.     

Design, synthesis, and aqueous aggregation behavior of nonionic single and multiple thermoresponsive polymers

Nonionic water-soluble poly(acrylamide)s and poly(acrylate)s were synthesized by RAFT and ATRP methods. Similar to the synthesized poly(N-isopropylacrylamide) and poly(N-acryloylpyrrolidine), aqueous solutions of statistical acrylate copolymers bearing two different oligo(ethylene oxide) side chains showed a sharp clouding transition upon heating beyond characteristic temperatures. The temperature of the cloud point can be easily fine tuned by the copolymer composition. As for poly(N-isopropylacrylamide) and poly(N-acryloylpyrrolidine), the cloud-point temperatures of these statistical copolymers are rather insensitive to changes in the molar mass or the NaCl content of the solutions. Also, ternary triblock copolymers containing one permanently hydrophilic block and two different thermoresponsive blocks were synthesized, varying the block sequence systematically. Their aggregation in aqueous solution was followed by turbidimetry and dynamic light scattering. Depending on the heating process and the triblock sequence, micellar aggregates of 40 to 600 nm size were found. The thermally induced aggregation behavior depends sensitively on the block sequence but is also subject to major kinetic effects. For certain block sequences, a thermally induced two-step association is observed when heating beyond the first and second cloud points of the thermoresponsive blocks. However, the thermal-transition temperatures of the block polymers can differ from the thermal-transition temperatures of the individual homopolymers. This may be caused by end-group effects but also by mutual interactions of the different blocks in solution, as physical mixtures of the homopolymers exhibit deviations from a purely additive thermal behavior.     

Preparation,fractionation, and dilute-solution behavior of ABA poly(methyl methacrylate-b-α-methylstyrene) block copolymers

The preparation by anionic polymerization of six ABA poly(methyl methacrylate-b-α-methylstyrene) block copolymers and of sixteen poly(α-methylstyrene)s is described. The block copolymers, of similar molecular weight but with different chemical compositions, were fractionated by preparative gel permeation chromatography and their behavior in dilute solution was investigated using viscometry. The results obtained indicate that the intramolecular phase separation does not occur under the conditions utilized, the block copolymers assuming randomcoil configurations in all of the copolymer/solvent systems studied. Consequently the block copolymer molecules are more expanded than homopolymers of the same molecular weight. The series of poly(α-methylstyrene)s covered the molecular weight range 2.7 × 10³–1.3 × 10⁶ and enabled the determination of Mark–Houwink–Sakurada constants for poly(α-methylstyrene) in the solvents chosen for the block copolymer studies.     

Study of copolymer–copolymer interactions and formation of intermacromolecular complexes

Interpolymer complex formation has been studied between methacrylic acid-methacrylamide copolymer and acrylic acid–acrylamide copolymer. The respective co-monomer units of the two copolymers enter into complex formation through H-bonding and ion dipole interactions. The unreacted units in the copolymer complex also interact with homopolymers such as PEO and PVP to form ternary complex. Formation of complexes and replacement reactions could be shown through several experimental techniques, e.g., viscometry, conductometry, and potentiometry.