Dispersed Microdomains Research Articles

Fundamental Principles and Emerging Opportunities for Selectively‐Solvated Block Copolymer Networks in Nonpolar Media: A Perspective

AbstractBlock polymers remain an extensively studied class of macromolecules due to their ability to self‐organize spontaneously as a result of microphase separation into a variety of ordered nanostructures, depending on the number of contiguous sequences (“blocks”) present and their sequential arrangement. These polymers are classified as multifunctional since they exhibit two or more different property sets during application. In this work, the focus is on bicomponent block copolymers composed of soft and hard segments arranged as linear triblock or higher‐order multiblock copolymers and possessing the properties of a thermoplastic elastomer (TPE). Of particular interest are selectively‐solvated TPEs, designated as TPE gels (TPEGs), with precisely‐ and composition‐tunable properties. An important aspect of TPEs and their TPEG analogs is their elasticity, which reflects the ability of the soft block(s) to form a contiguous molecular network connected by dispersed microdomains composed of the hard block. Here, the origins of microphase separation and network formation in styrenic TPEs and TPEGs are explored, and experimental, theoretical, and simulation results are examined to elucidate chemistry‐structure‐property‐processing (CSPP) relationships in these self‐networking materials. Once such relationships are established, several unconventional technologies that can directly benefit from TPEGs, along with TPEGs fabricated from TPEs possessing different chemical moieties, are likewise considered.

Toughened Blends of Polystyrene and Ethylene-Styrene Interpolymers

Ethylene-styrene interpolymer (ESI) resins prepared using a constrained geometry catalyst have been found to make toughened blends with polystyrene (PS). At a low level in the blend, an ESI resin forms dispersed micro-domains of sub-micron size in polystyrene. At 40 %, an ESI resin makes a co-continuous blend that is both stiff and ductile. The toughening effect increases as the styrene content in the ESI resin increases peaking at an approximately 70 wt % of styrene. The results indicate that ESI resins are compatible with polystyrene and the compatibility increases as the styrene content in the resin increases.

Synthesis and characterization of non-covalent liquid crystalline diblock copolymers

Poly(dimethylaminoethylmethacrylate)-b-poly(sodium methacrylate) diblocks, (polyDMAEMA-b-polyMA), were synthesized as precursors of liquid crystalline (LC) copolymers. These LC copolymers were prepared by proton-transfer between a carboxylic acid-containing mesogen (A) and the dimethylamino substituent of the polyDMAEMA block and by electrostatic interactions between the polyMA subunits and an ammonium-containing mesogen (B). When mesogen A is complexed with DMAEMA units, a dramatic enhancement of the mesophase stability is noted. The mesogenic properties of these LC copolymers were compared to those ones of the parent LC homopolymers, in relation to the copolymer composition. The supramolecular organization of the LC diblock copolymers was studied by small-angle X-ray scattering (SAXS), and smectic mesophases were observed in some LC (co)polymers. For samples containing a major LC block, a smectic mesophase coexists with microphases formed by the second amorphous block. Different organizations, including a body-centered lattice of spheres and a hexagonal array of cylinders, were observed, depending on the investigated copolymers and their composition. When the LC block is the minor component, it forms microdomains too small for a liquid crystalline order to emerge. Moreover, no supramolecular organization of these dispersed microdomains was detected by SAXS. A homogeneous smectic mesophase was observed when the two blocks are bearing liquid crystalline moieties.

A two-phase model for controlled drug release from biphasic polymer hydrogels

A comprehensive two phase model is developed to describe the sustained release of a solute or drug from a biphasic hydrogel substrate. Such a material consists of a continuous hydrophilic phase (polymer backbone in water) and a dispersion of spherical microdomains made of the hydrophobic side chains of the polymer organised in a micelle like fashion. The solute or drug is assumed to be encapsulated within the dispersed microdomains, and to diffuse from the interior to the surface of the microdomain where it exchanges following a Langmuir isotherm. Mass transfer to the bulk phase occurs by desorption of the drug from the surface through a driving force that is proportional to the difference of surface and bulk concentration. Accordingly the drug is released to the surroundings by diffusion through the bulk. Depending on the values of the Langmuir constant and assuming well stirred behaviour in the interior of the microdomain, the present model results in either of the two asymptotic models developed in previous studies. The results of a parametric study show that the desired steady state flux of a specific drug to the surroundings may be obtained given appropriate values of structural properties of the material. This conclusion is further supported when using this model to simulate earlier experimental results. The polymer structural properties can be manipulated easily during the fabrication of dispersed-phase networks, as indicated by preliminary experiments.

Mathematical model of mass transport through dispersed‐phase polymer networks

AbstractA mathematical model of mass transport through dispersed‐phase networks to be used for the sustained release of drugs or other solutes at steady rates is presented. The drug is assumed to be encapsulated within the dispersed microdomains and transported to the bulk by diffusion across the interface. A drug is released to the surroundings by diffusion through the bulk. The results show that the desired steady flux of a drug to the surroundings may be obtained given appropriate values of structural properties of the network. These properties may be manipulated easily in the fabrication of dispersed‐phase networks reported previously.

Electrically conductive semiinterpenetrating polymer networks of poly(3-octylthiophene)

Electrically conducting semi-IPNs were synthesized from soluble poly(3-octylthiophene), styrene monomer, and a cross-linking agent. By controlling the level of cross-linking of the polystyrene component, it was possible to create semi-IPNs with highly dispersed microdomains of the conjugated polymer. For example, semi-IPN samples containing 20% poly(3-octylthiophene) (P3OT) and 10% divinylbenzene (DVB) exhibit very finely dispersed P3OT domains on the order of 1000 A. This particular cross-linking level also produced semi-IPNs with a very low percolation threshold