Block and alternating copolymer chains of styrene–vinylmethylether and styrene–methylmethacrylate by molecular dynamics simulation (original) (raw)
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Macromolecules, 1990
Ordered microdomain structures for binary mixtures of a poly(styrene-b-isoprene) diblock copolymer (SI) with homopolystyrenes (HS) were investigated as a function of molecular weight of HS ( M h o ) under conditions where the majority of HS can be solubilized into the polystyrene microdomains. For a given fraction of HS, the interdomain distance D was found to increase with Mhomol and a unique morphological transition from cylinders to lamellae was also found with increasing Mhomo. These results imply that HS is generally not miscible with the polystyrene (PS) block chains confined in the microdomain space, although they are chemically identical. The higher the value h&o,,,o, the lower the miscibility with the block PS chains. As a consequence, HS with higher Mbmo tends to cause the PS microdomains to swell less uniformly, resulting in segregation more toward the middle of the PS microdomains. Here the conformational entropy loss upon mixing plays a dominant role in the miscibility of HS and block PS and hence on solubilization of HS into PS microdomains. Thus the miscibility of the confined chains is distinctly different from that of the corresponding free chain.
Extension of Rod-Coil Multiblock Copolymers and the Effect of the Helix-Coil Transition
Physical Review Letters, 2000
The extension elasticity of rod-coil mutliblock copolymers is analyzed for two experimentally accessible situations. In the quenched case, when the architecture is fixed by the synthesis, the force law is distinguished by a sharp change in the slope. In the annealed case, where interconversion between rod and coil states is possible, the resulting force law is sigmoid with a pronounced plateau. This last case is realized, for example, when homopolypeptides capable of undergoing a helix-coil transition are extended from a coil state. PACS numbers: 61.25.Hq, 61.41. + e, 87.15.He With the advent of single molecule mechanical measurements it became possible to study the force laws characterizing the extension of individual macromolecules [1]. In turn, these provide a probe of internal degrees of freedom associated with intrachain self-assembly or with monomers that can assume different conformational states. A molecular interpretation of the force laws thus obtained requires appropriate theoretical models allowing for the distinctive "internal states" of each system. The formulation of such models is a challenging task in view of the complexity and diversity of the systems investigated. These include DNA [2], the muscle protein titin [3] and the extracellular matrix protein tenascin [4], the polysaccharides dextran [5] and xanthan , as well as the synthetic polymer poly(ethelene-glycol) .
Self-assembly of rod-coil block copolymers from weakly to moderately segregated regimes
The European Physical Journal E, 2007
Abstract.We report on the self-assembly behaviour of two homologue series of rod-coil block copolymers in which, the rod, a π -conjugated polymer, is maintained fixed in size and chemical structure, while the coil is allowed to vary both in molecular weight and chemical nature. This allows maintaining constant the liquid crystalline interactions, expressed by Maier-Saupe interactions, ω , while varying the tendency towards microphase separation, expressed by the product between the Flory-Huggins parameter and the total polymerization degree, χN . Therefore, the systems presented here allow testing directly some of the theoretical predictions for the self-assembly of rod-coil block copolymers in a weakly segregated regime. The two rod-coil block copolymer systems investigated were poly(DEH-p-phenylenevinylene-b-styrene), whose self-assembly takes place in the very weakly segregated regime, and poly(DEH-p-phenylenevinylene-b-4vinylpyridine), for which the self-assembly behaviour occur...
The Journal of Physical Chemistry B, 2011
The phase behavior of binary blends of rodÀcoil diblock copolymers and coil or rod homopolymers is studied by the self-consistent field theory (SCFT). The rod blocks are modeled as wormlike chains and the corresponding SCFT equations are solved using a hybrid method, in which the orientation-dependent functions are discretized on a unit sphere, while the positional space-dependent functions are treated using a spectral method. Phase diagrams of the blends are constructed as a function of the homopolymer volume fraction and phase segregation strength. It is discovered that the phase behavior of the system depends on the flexibility of the homopolymers. The addition of coil-homopolymers stabilizes the smectic phases. Low-molecular weight coil-homopolymers tend to mix with the coil-blocks, whereas high-molecular weight coilhomopolymers are mostly localized at the center of the coil-domains. On the other hand, the addition of rod-homopolymers strongly affects the orientation ordering of the system, leading to transitions between monolayer smectic-C, monolayer smectic-A and bilayer smectic-A phases.
Macromolecules, 1999
We show that polymeric materials characterized by two length scales are obtained if diblock copolymers are mixed with amphiphilic selective solvents, leading to self-organization which combines the "block copolymer length scale" with a much shorter "nanoscale". In this work, the amphiphilic compound is 3-n-pentadecylphenol (PDP) which is hydrogen-bonded to the pyridine group of polystyreneblock-poly(4-vinylpyridine), i.e., PS-b-P4VP. The molecular architecture resembles comb-coil diblock copolymers A-block-(B-graft-C) but is obtained using the supramolecular assembly route. The structures were determined with a combination of transmission electron microscopy and small-angle X-ray scattering. On the block copolymer scale (300 Å range), the PS blocks are microphase-separated from the P4VP-(PDP) x blocks, where x denotes the ratio between the number of phenol and pyridine groups. For PS-b-P4VP block copolymers having a spherical morphology and P4VP as the minority component, the structure of PS-b-P4VP(PDP)x changes from spherical to hexagonal and further to lamellar as a function of the amount of PDP added. For all comb-coil diblock copolymer morphologies, the P4VP(PDP)x domains are further "nanophase-separated" into lamellar structures due to microphase separation of the comb copolymer-like complex between P4VP and PDP. The morphology diagram is presented for stoichiometric conditions (x) 1), using a range of different PS-b-P4VP block copolymers.
Progress in Polymer Science, 2003
The solid-state supramolecular organization of block copolymers containing one p-conjugated block and one nonconjugated block is elucidated with a joint experimental and theoretical approach. This approach combines atomic force microscopy (AFM) measurements on thin polymer deposits, which reveal the typical microscopic morphologies, and molecular modeling, which allows one to derive the models for chain packing that are most likely to explain the AFM observations. The conjugated systems considered in this study are based on aromatic building blocks (i.e. phenylene, phenylene ethylene, fluorene, or indenofluorene), substituted with alkyl groups to provide solubility; they are attached to non-conjugated blocks such as polydimethylsiloxane, polyethylene oxide, or polystyrene. Films are prepared from solutions in solvents which are good for both blocks, in order to prevent aggregation processes in solution. Therefore, the morphology observed in the solid state is expected to result mostly from the intrinsic self-assembly of the chains, with little specific influence of the solvent. In such conditions, the vast majority of compounds show deposits made of fibrilar objects. Closer examination of single fibrils on the substrate surface indicates that the objects are ribbon-like, i.e. their width is significantly larger than their height, with typical dimensions of a few tens of nanometers and a few nanometers, respectively. These results suggest that a single type of packing process, governed by the p-stacking of the conjugated chains, is at work in those block copolymers. This prevalence of such a type of packing is supported by the theoretical simulations. Molecular mechanics/dynamics calculations show that the conjugated segments tend to form stable p-stacks. In these assemblies, the block copolymer molecules can organize in either a head-to-tail or head-to-head configuration. The former case appears to be most likely because it allows for significant coiling of the non-conjugated blocks while maintaining the conjugated blocks in a compact, regular assembly. Such supramolecular organization is likely responsible for the formation of the thin, 'elementary' ribbons, which can further assemble into larger bundles. The issue of chain packing in fluorene-based systems has been modeled separately, since in these compounds, the alkyl groups attached to sp 3-hybridized sites inherently accommodate out of the plane of the conjugated backbone, which can disturb the chain packing. Various possibilities of chain packing have been explored, starting from short alkyl substituents and extending the size of the side groups to n-octyl. The calculations indicate that, when in zigzag planar conformation, linear alkyl side groups can orient in such a way that close p-stacking of the conjugated chains is preserved. In contrast, branched alkyl groups are too bulky to allow close packing of the conjugated backbones to take place. This difference is consistent with the presence or absence of fibrilar structures observed in thin deposits of the corresponding polymers; it can also account for the differences observed in the optical properties.
Effect of Sequence Distribution on Copolymer Interfacial Activity
Macromolecules, 2005
Interfacial segregation of diblock, gradient, and random copolymers was measured using forward recoil spectrometry. The polymers were synthesized by a ring-opening metathesis polymerization, allowing a high degree of control over the sequence distribution. The norbornene-based monomers have reactivity ratios close to unity, which makes them ideal for facile tailoring of different gradient copolymer profiles. The copolymers form a good weakly segregating model system for which we can obtain an estimate of the interaction parameter . Mean-field theory was used to describe the interfacial segregation results and to relate the measured quantities to the detailed molecular structure of the interface. The diblock copolymer forms a monolayer at the interface and significantly reduces the interfacial tension, while the random copolymer forms an interfacial wetting layer. The gradient copolymer exhibits intermediate behavior, forming a monolayer with a larger interfacial width than that of the diblock copolymer.
Double-gyroid network morphology in tapered diblock copolymers
2011
We report the formation of a double-gyroid network morphology in normal-tapered poly (isopreneb-isoprene/styrene-b-styrene) [P(I-IS-S)] and inverse-tapered poly(isoprene-b-styrene/isoprene-bstyrene) [P(I-SI-S)] diblock copolymers. Our tapered diblock copolymers with overall poly(styrene) volume fractions of 0.65 (normal-tapered) and 0.67 (inverse-tapered), and tapered regions comprising 30 volume percent of the total polymer, were shown to self-assemble into the double-gyroid network morphology through a combination of small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The block copolymers were synthesized by anionic polymerization, where the tapered region between the pure poly(isoprene) and poly(styrene) blocks was generated using a semi-batch feed with programmed syringe pumps. The overall composition of these tapered copolymers lies within the expected network-forming region for conventional poly(isoprene-b-styrene) [P(I-S)] diblock copolymers. Dynamic mechanical analysis (DMA) clearly demonstrated that the order-disorder transition temperatures (T ODT 's) of the network-forming tapered block copolymers were depressed when compared to the T ODT of their non-tapered counterpart, with the P(I-SI-S) showing the greater drop in T ODT . These results indicate that it is possible to manipulate the copolymer composition profile between blocks in a diblock copolymer, allowing significant control over the T ODT , while maintaining the ability to form complex network structures.