Composite materials, block copolymers

These materials, however, as a rule exhibit rather broad chemical composition distribution. Block copolymers may contain important amounts of parent homopolymer(s) [232,244,269], In any case, it is to be kept in mind that practically all calibration materials contain the end groups that differ in the chemical composition, size, and in the enthalpic interactivity from the mers forming the main chain. In some cases, also the entire physical architecture of the apparently identical calibration materials and analyzed polymers may differ substantially. The typical example is the difference in stereoregularity of poly(methyl and ethyl methacrylate)s while the size of the isotactic macromolecules in solution is similar to their syndiotactic pendants of the same molar mass, their enthalpic interactivity and retention in LC CC may differ remarkably [258,259]. 

The intrinsic 3D interfacial curvature in compositionally asymmetric block copolymers provides extra degrees of freedom for the phase behavior in hexagonally structured microdomains. It is now well established that confinement of a cylinderforming block copolymer to a thickness other than the characteristic structure dimension in bulk, together with surface fields, can cause the microstructure to deviate from that of the corresponding bulk material. Surface structures in Fig. 1 are examples of simulated [57-59] and experimentally observed morphologies [40, 49, 60-62] that are formed in thin films of bulk cylinder-forming block copolymers. 

As already shown above in Section 4.7, the composition of block copolymers can be changed in a systematic manner. Stupp and co-workers [36] have used this flexibility to investigate the ability of thin films of such materials to form... 

Volume XVII, Intersdence Publishing, Division of John Wiley Sons, New York. Comment These 15 chapters by individual authors deal with low-pressure ethylene copolymers over a broad range of compositions from elastic materials, block copolymers, and ethylene copolymers with styrene, and copolymers prepared with cationic and anionic methods. Each chapter includes references. 

Similarly, the random introduction by copolymerization of stericaHy incompatible repeating unit B into chains of crystalline A reduces the crystalline melting point and degree of crystallinity. If is reduced to T, crystals cannot form. Isotactic polypropylene and linear polyethylene homopolymers are each highly crystalline plastics. However, a random 65% ethylene—35% propylene copolymer of the two, poly(ethylene- (9-prop5lene) is a completely amorphous ethylene—propylene mbber (EPR). On the other hand, block copolymers of the two, poly(ethylene- -prop5iene) of the same overall composition, are highly crystalline. X-ray studies of these materials reveal both the polyethylene lattice and the isotactic polypropylene lattice, as the different blocks crystallize in thek own lattices. 

Thermoplastic elastomers are often multiphase compositions in which the phases are intimately dispersed. In many cases, the phases are chemically bonded by block or graft copolymerization. In others, a fine dispersion is apparentiy sufficient. In these multiphase systems, at least one phase consists of a material that is hard at room temperature but becomes fluid upon heating. Another phase consists of a softer material that is mbberlike at RT. A simple stmcture is an A—B—A block copolymer, where A is a hard phase and B an elastomer, eg, poly(styrene- -elastomer- -styrene). 

D-TEM was introduced into rubber technology field in 2004 by the authors of this chapter [4]. In a recent review of 3D-TEM applied in materials science field [5], only two papers were cited on polymeric samples—one on block copolymers [6] and the other on rubbery composites with conventional and in situ silica [4]. Starting from the latter, 3D-TEM measurements have been carried out on rubbery nano-composites [7-16], and this recent and very important topic is described in this review. 

Block copolymers of polystyrene with rubbery polymers are made by polymerizing styrene in the presence of an unsaturated rubber such as 1,4 polybutadiene or polystyrene co-butadiene. Some of the growing polystyrene chains incorporate vinyl groups from the rubbers to create block copolymers of the type shown in Fig. 21.4. The combination of incompatible hard polystyrene blocks and soft rubber blocks creates a material in which the different molecular blocks segregate into discrete phases. The chemical composition and lengths of the block controls the phase morphology. When polystyrene dominates, the rubber particles form... 

In this study, the effects of the variations in block sequence and composition (and thus relative block length) on the material properties of two series of triblock copolymers has been investigated. One of the blocks, the hydrogenated polybutadiene (HB), is semicrystalline, and the other block, the hydrogenated polyisoprene (HI) is rubbery at room temperature. Thus in one series, the HBIB block copolymers, the end blocks are semi-... 

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