Phase separation, block

Various types of power law relaxation have been observed experimentally or predicted from models of molecular motion. Each of them is defined in its specific time window and for specific molecular structure and composition. Examples are dynamically induced glass transition [90,161], phase separated block copolymers [162,163], polymer melts with highly entangled linear molecules of uniform length [61,62], and many others. A comprehensive review on power law relaxation has been recently given by Winter [164],... 

Groeger, R. 2007. Nano contact printing with afm-controlled phase-separated block copolymer layers. Institut fur Nanotechnologie, Fakultat fur Physik, Universitat Karlsruhe, Karlsruhe, Germany. Report, i-vii, pp. 1-130. 

Figure 6.3 The chemical compositions for macromolecular objects that result from crosslinking within nanodomains of bulk phase separated block copolymers include (a) core-crosslinked spheres (b) core-crosslinked rods (c) mushroom -shaped objects.

Residual Thermal Stress Control of Polyimide Through the Use of Self-Assembled, Phase Separated Block Copolymers. ... 

Thermoplastic Elastomers. A new generation of materials was initiated by the introduction of phase-separated block copolymers which... 

Explicitly developed are models of several theoretical multiphase distributions, with corresponding depth-profile results on thin-film plasma polymers, phase-separated block copolymers, and chemical reactions on fiber surfaces. Ion impact is treated from three points of view as an analytical fingerprint tool for polymer surface analysis via secondary ion mass spectroscopy, by forming unique thin films by introducing monomers into the plasma, and as a technique to modify polymer surface chemistry. 

The living ROMP reactions of norbomene and norbomene derivatives have been used to make a variety of polymers possessing unusual properties. Copolymerization of selected fimctionalized norbomenes with norbomene has been used to synthesize star polymers and side-chain liquid crystal polymers. This chemistry has also resulted in the preparation of phase separated block copolymers that contain uniform sized metal or semiconductor nanoparticles. The... 

If we look at Figure 21.3, we can see that there is an upper limit to the overall styrene content in the polymer if making a polymer to have rubbery properties is the desired outcome [66]. As the styrene content increases, the stress-strain response changes dramatically for these neat SBS polymers. At 53 and 65% styrene content, the polystyrene endblocks form the continuous phase in the phase-separated block copolymer, and these polymers behave more like polystyrene than a rubber at low strain. This low strain behavior is also shown at 39% styrene content, but a rubbery plateau begins to show at lower stress. 

Hydrogenated SBCs are often used to modify polyolefins such as polypropylene, polybutylene and polyethylene. One of the unique characteristics of strongly phase-separated block copolymers such as high molecular weight (>50 000) SEBS and SEPS is their response to shear in the melt. These polymers retain their phase-separated structure well above the Tg of the polystyrene because their order-disorder transition temperatures are above processing temperatures. This phase separation strongly inhibits flow in the absence of shear resulting in infinite viscosity at zero shear rates. The application of shear... 

Fig. 15.5. Schematic depiction of the generalized strategy for preparation of polymeric nanostructures via bulk phase-separated block copolymers.

Fig- 32. Illustration of the aggregation between phase separated blocks of polysulfone and pnBA... 

In many phase-separating block copolymers (especially segmented multiblock copolymers such as polyurethanes where the blocks are usually short), lowering the soft block Mn increases the Tg of the soft phase because of the crosslink-like topological constraints imposed by hard phase domains. 

Polycocyclotrimers were prepared by polycocyclotrimerization of difunctional isocyanates of variable chain length or difunctional isocyanate with monofunctional isocyanate. The stress-strain and viscoelastic properties of resulting polymers were determined. It was found that co-polycyclotrimers prepared from diisocyanates of the variable chain length had typical properties of phase separated block copolymers. 

Nanoparticles Assembled by Phase Separated Block Copolymers Block copolymers serve as templates for the construction of inorganic structures in an organic polymer matrix. Films of block copolymers of 70% styrene and 30%... 

Finally, a different and quite complementary form of crazing occurs on a much larger microstructural scale in diblock copolymers composed of phase-separated blocks of compliant rubbery components such as PB in spherical morphologies or randomly dispersed spheres or wavy rods in a majority component of a stiff polymer such as PS. In such hetero-polymers, under stress the compliant component can be made to cavitate, which triggers plastic expansion of the remaining carcass of the stiff polymer to form a very regular kind of cellular craze matter over substantial parts of the volume and can result in a very tough response. 

Typical phase morphologies of block copolymers are illustrated in Figs. 5.38 0 and 5.79. In the classification of phases, the phase-separated block copolymers are considered to be amphiphilic liquid crystals despite the fact that inside the phase areas the typical liquid-crystalline order is missing (see Sect. 5.5). In this section the question will be addressed what happens when the usually micro- or nano-phase separated block copolymers show solubility, i.e., when the amphiphilic liquid crystal becomes thermotropic, i.e., dissolve at a given temperature. 

Domain A region in a material that has homogeneous properties, e.g., a phase-separated block copolymer where aggregates of blocks of one type are incompatible with blocks of the second type. 

The melt brush (see Fig. la), on the other hand, is free of solvent. Thus, its properties depend significantly less on the presence of a solvent. The melt brush has its main importance in the context of phase separated block copolymers and the often complex morphologies of these systems (for example, lamellar [see Fig. Ic], hexagonal, cubic) are a result of the balance between the interfacial tension and the interactions of the closely packed polymer chains [4-6]. While there is considerable interest in these bulk systems, it has been very advantageous to study polymer brushes as monolayers at flat surfaces. In such a monolayer it is relatively easy to determine and tune the surface concentration of the head groups and to give the system a preferred orientation in space. 

A structural model has been developed to describe the viscoelastic/thermal behavior of phase-separated block copolymers. Success is achieved in fitting the G (T) and G (T) data of five samples (involving three SBS copolymers and three solvents) from -120 C to +100 C, a range which... 

This example conveys much of the basic electrothermodynamics of micro-phase-separated block copolymers in an electric field. The anisotropy arises from shape, and not from molecular anisotropy. (Although there can be a small contribution from the slight stretching of chains, that is not considered here.) The additional feature of block copolymers is that there are a number of microstructure symmetries, and the local composition is continuously varying. To begin, the dielectric constant is expressed as an expansion in the order parameter about the disordered state at equal to zero ... 

Many of the droplets will contain impurities and nucleate relatively early in the experiment however, some will remain amorphous for long times, and, if the rate of nucleation in these droplets is measured, the variation of nucleation rate with temperature can be obtained. If the nucleation is truly homogeneous, and the droplet size is monodisperse, the nucleation rate should, at a particular temperatime, depend only on the sample volume. Recently, similar experiments have been carried out on phase-separated block copolsrmers, in which the crystal-lizable domains are isolated spheres in the hard (or semihard) segregation limit (28,29). An example of data obtained by these two different methods is shown in Figures 3 and 4. 

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