Block polymer morphology

The compositional and two-phase morphological relationships of "A-B" blocks, the "A-B-A" and starblocks have been studied intensively. It has been demonstrated that there is a substantial difference between random copolymers and block polymers, and this difference is based solely on the architectural arrangement of the monomeric units. One of the most important differences is that one Tg is observed in the random copolymer, which is related to the overall composition of the polymer. The block polymer has been shown to have two Tg s - one for polystyrene and one for the polydiene segment, and that these Tg s are not affected by the composition of the block copolymer. Since we can now synthesize large quantities of these pure block polymers, more detailed physical studies can be carried out. The two Tg s observed in... 

Figure 6. Conceptual morphological structure of two-phase SIS block polymers.

When a chemical variety of a linear block copolymer is increased to three different components, an intricate diversity of structures becomes possible [188, 189], This is due to considerable increase in the number of involved polymer-polymer and polymer-surfaces interaction parameters. The studies on thin film behavior of ABC terpolymers are rare, even though they may potentially be more versatile than binary block copolymer morphologies due to the increased complexity. 

Many polymer blends or block polymer melts separate microscopically into complex meso-scale structures. It is a challenge to predict the multiscale structure of polymer systems including phase diagram, morphology evolution of micro-phase separation, density and composition profiles, and molecular conformations in the interfacial region between different phases. The formation mechanism of micro-phase structures for polymer blends or block copolymers essentially roots in a delicate balance between entropic and enthalpic contributions to the Helmholtz energy. Therefore, it is the key to establish a molecular thermodynamic model of the Helmholtz energy considered for those complex meso-scale structures. In this paper, we introduced a theoretical method based on a lattice model developed in this laboratory to study the multi-scale structure of polymer systems. First, a molecular thermodynamic model for uniform polymer system is presented. This model can... 

FIGURE 2.6. Block copolymer morphologies obtainable via phase separation. The exact structure will depend on the relative volume fractions of the two blocks, as well as /N (where / is the interaction parameter and N the length of the polymer). 

GPC fractionation and ozonisis of the products, the yield of cyclic polymer was estimated to be ca. 90%. The morphological transition of the cyclic block polymer depends on composition in essentially the same manner as that of the linear triblock copolymers, whereas the domain spacing of polystyrene-block-polyisoprene cyclic block copolymers were all smaller than those of the corresponding SIS linear triblock copolymers, which is attributed to looped chain conformation. 

The block polymer section is headed by an excellent review paper by Mitchel Shen. Covering anionically polymerized styrene-diene block polymers primarily, the eight papers of this section explore relaxation behavior and morphology. Block polymer properties such as transition behavior, deformation characteristics, and blend effects are shown to be related both to polymer chemical structure and to microphase morphology. 

This dependence of block polymer property on casting solvent also is seen in poly(styrene-b-diene) polymers (28). Theoretical work (23) has shown that the thermodynamically most stable morphology for a diblock polymer containing 50% of each component is a lamella morphology. For this reason MEK was chosen for the tests on all other polymers. 

Samples for the viscoelastic experiments were prepared by a conventional slow-solvent-evaporation technique (1) followed by vacuum drying. For ease in handling in certain experiments, some samples were lightly cured using a 30-MRad dose of electrons other experiments were carried out on uncured materials. Transmission electron microscopy (Phillips Model 200) was used to investigate possible morphological features in the block polymers and blends. Details of the various staining techniques used are presented elsewhere (1,11,12,13). 

Extensive use is made in this work of the effects of orientation on mechanical properties in block polymers with cylindrical and lamellar structures. These effects are, in general, known from earlier studies (6,7) they add convincing evidence to the morphological assignments made. 

It should be clear that the conclusions of this work are limited to block polymers isolated from the polymerization solvent (cyclohexane) by evaporation and subsequently processed by conventional thermal mixing and shaping techniques. Obviously, other morphologies could be realized in many instances by casting films from solvents of varying quality for the two block sequences. 

Different block length distributions in SBS and (SB)X block polymers and their mixtures can cause wide changes in domain morphology at constant overall monomer composition, which lead to characteristically different linear viscoelastic properties. 

Failure Morphologies. Ductile failure of notched polycarbonate specimens has long been recognized to occur with shear yielding from the notch tip (6). This occurs for the block polymers for all rates of test. Hull and Owen (5) recently reported from micrographic studies of impact fracture surfaces that the brittle failure of polycarbonate involves the formation and breakdown of a craze at the notch tip. The ductile-... 

Figure 9. Failure morphology of BPFC-DMS block polymer...

Nielsen, L. E., "Morphology and the Elastic Modulus of Block Polymers... 

The behavior observed depends also on the morphology of the block polymer. Thus when the block polymer texture consists of inclusions of poly-B in a continuous matrix of poly-A, addition of homopolymer A will result only in its... 

The introduction of functional groups at the end(s) or along the polymer chain can produce new materials that can be used as models to study and manipulate fundamental phenomena in polymer science, such as association, adsorption, chain dynamics, and block copolymer morphology.61 65 The synthesis of end-functionalized polymers remains a challenging problem in polymer chemistry. Among the different... 

Gratt JA, Cohen RE (2004) The role of ordered block copolymer morphology in the performance of organic/inorganic photovoltaic devices. J Appl Polym Sci 91 3362-3368 Sun S, Fan Z, Wang Y, Haliburton J (2005) Organic solar cell optimizations. J Mater... 

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