Ordered block copolymers copolymer solutions

Hamley, I.W. The effect of shear on ordered block copolymer solutions. Current Opinion in Colloid and Interface Science 2000, 5, 342-350. 

Block Copolymers In solutions, amphiphilic block copolymers self-assemble into a variety of supramolecular micellar nanostructures [163-165]. Micelles form when one block is insoluble or only sparingly soluble in the solvent, whereas the other block is soluble and swollen in the solvent. In order to reduce the interfacial energy of the system, the insoluble block segregates in the core of the micelle. When the... 

Lodge, T. P. Hamersky, M. W. Hanley, K. J. Huang, C.-I (1997) Solvent Distribution in Weakly-ordered Block Copolymer Solutions, Macromolecules, 30, 6139-6149. 

In the presence of a selective solvent, ordered block copolymers form micelles that, at sufficiently high copolymer concentrations, serve to stabilize a diree-dimensional network and promote physical gelation. This study examines the steady and dynamic rheological properties of micellar solutions composed of AB diblock, ABA triblock and bidisperse mfactures of AB and ABA copolymer molecules. Of particular interest is the unexpected improvement in network development upon addition of an AB copolymer to an ABA copolymer at constant solution composition. This behavior is observed for ABA/solvent systems above and below the critical gelation concentration, and is interpreted in terms of the volume exclusion that occurs in bidisperse mixture of grafted chains. 

GopolymeriZation Initiators. The copolymerization of styrene and dienes in hydrocarbon solution with alkyUithium initiators produces a tapered block copolymer stmcture because of the large differences in monomer reactivity ratios for styrene (r < 0.1) and dienes (r > 10) (1,33,34). In order to obtain random copolymers of styrene and dienes, it is necessary to either add small amounts of a Lewis base such as tetrahydrofuran or an alkaU metal alkoxide (MtOR, where Mt = Na, K, Rb, or Cs). In contrast to Lewis bases which promote formation of undesirable vinyl microstmcture in diene polymerizations (57), the addition of small amounts of an alkaU metal alkoxide such as potassium amyloxide ([ROK]/[Li] = 0.08) is sufficient to promote random copolymerization of styrene and diene without producing significant increases in the amount of vinyl microstmcture (58,59). 

The block copolymer and the microsphere were cast from polymer-benzene solution on a Teflon sheet. The solution was gradually dried at room temperature. Film was microtomed vertically at 80 nm thick by the Ul-traCut-N (Reichert Nissei). In order to obtain enough contrast for TEM observation, the P4VP microdomains in the film were stained with OSO4. The film was observed by TEM (JEOL CX-100) at 100 kV. 

Currently, more SBR is produced by copolymerizing the two monomers with anionic or coordination catalysts. The formed copolymer has better mechanical properties and a narrower molecular weight distribution. A random copolymer with ordered sequence can also be made in solution using butyllithium, provided that the two monomers are charged slowly. Block copolymers of butadiene and styrene may be produced in solution using coordination or anionic catalysts. Butadiene polymerizes first until it is consumed, then styrene starts to polymerize. SBR produced by coordinaton catalysts has better tensile strength than that produced by free radical initiators. 

Hashimoto T., Shibayama M., and Kawai H., Ordered structure in block copolymer solution. 4. Scaling rules on size of fluctuations with block molecular weight, concentration temperature in segregation and homogeneous regimes. Macromolecules, 16, 1093, 1983. 

Instead of the familiar sequence of morphologies, a broad multiphase window centred at relatively high concentrations (ca. 50-70% block copolymer) truncates the ordered lamellar regime. At higher epoxy concentrations wormlike micelles and eventually vesicles at the lowest compositions are observed. Worm-like micelles are found over a broad composition range (Fig. 67). This morphology is rare in block copolymer/homopolymer blends [202] but is commonly encountered in the case of surfactant solutions [203] and mixtures of block copolymers with water and other low molecular weight diluents [204,205]. 

PVA Particles. Dispersions were prepared in order to examine stabilization for a core polymer having a glass transition temperature below the dispersion polymerization temperature. PVA particles prepared with a block copolymer having M PS) x 10000 showed a tendency to flocculate at ambient temperature during redispersion cycles to remove excess block copolymer, particularly if the dispersion polymerization had not proceeded to 100 conversion of monomer. It is well documented that on mixing solutions of polystyrene and poly(vinyl acetate) homopolymers phase separation tends to occur (10,11), and solubility studies (12) of PS in n-heptane suggest that PS blocks with Mn(PS) 10000 will be close to dissolution when dispersion polymerizations are performed at 3 +3 K. Consequently, we may postulate that for soft polymer particles the block copolymer is rejected from the particle because of an incompatibility effect and is adsorbed at the particle surface. If the block copolymer desorbs from the particle surface, then particle agglomeration will occur unless rapid adsorption of other copolymer molecules occurs from a reservoir of excess block copolymer. 

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