Hierarchical structure in polymers

Among the numerous challenges faced in understanding the formation and evolution of hierarchical structures in polymer crystallization, we restrict ourselves to explain the essential basic features of folded lamellae. Specihcally, we consider (1) molecular origin of enhanced scattered intensity before any crystallographic features are apparent, (2) spontaneous selection of small lamellar thickness, (3) molecular details of growth front, and (4) formation of shish-kebab structures in the presence of a flow. 

Hierarchical Levels. The hierarchical structure in polymers is well recognized. The implications for new materials have been discussed recently by Bement (12) and Baer et al. (13), who emphasized four levels of structure based on dimension molecular, nanometer, micrometer, and macromolec-ular levels. These authors 12, 13) illustrated these concepts with both syn-... 

Munoz-Bonilla, A., Ibarboure, E., Papon, E., Rodriguez-Hemandez, J. Self-organized hierarchical structures in polymer surfaces self-assembled nanostructures within breath figiues. Langmuir 25, 6493-6499 (2009)... 

The crystallization of homopolymers yields a hierarchical structure in polymer materials, which substantially controls their physical properties. Therefore, the crystalline morphology of homopolymers has been one of the important research subjects in polymer science. In addition, the crystallization of homopolymers spatially confined in various nanodomains, such as micelles, AAO, or microdomain structures, may bring new information on crystallization mechanisms of homopolymers, because it will be possible to highlight a specific crystallization mechanism (e.g., nucleation or crystal growth) in the overall crystallization process consisting of several combined mechanisms. Furthermore, the crystallization in nanodomains has the possibility of providing new polymer materials, and their physical properties should be unique as compared with usual polymer materials. This is because the substantial control of nano-ordered structures formed in polymer materials will be possible by this crystallization, which is never achieved by the crystallization of neat homopolymers. 

Containing himdreds and thousands of monomeric units, the hierarchical structure of polymers also gives rise to their diversity in aggregations—polymers are not distinctly amorphous or crystalline. The aggregation of polymers often has amorphous subdivisions and crystalline parts which make them exhibit combined features of amorphisms as well as crystals. 

Lee, K.-Y.. Bismarck, A. Creating hierarchical structures in cellulosic fibre reinfraeed polymer composites for advanced performance. Natural Fibre Composites, pp. 84—102. Woodhead Publishing, Cambridge (2014)... 

Of course, there are many kinds of natural polymers. Starch and bread are discussed in Section 14.3, and silk fibers in Section 14.4 both are semicrystalline materials. The hierarchical structure of polymers has been reviewed by... 

Several sessions were included in scientific program. The session Bio-inspired Polymers included 11 oral presentations. Self-assembly of an aquaporin mimic, tailoring surface properties with polymer brushes, bioinspired block copolymers, hierarchically structured conjugated polymers via supramolecular self-assembly, natural polymeric composites with mechanical function, macromolecular oxidation catalysts based on miniemulsion polymerization and some other problems were discussed on this session. 

Peng S, Xiong X, Zhang G, Xia N, Chen Y, Wang W (2009) Hierarchical structure in oriented fibers of a dendronized polymer. Macromolecules 42(l) 281-287. doi 10.1021/ma8015932... 

Figure 2.1 Schematic of the hierarchical structure in crystallizable polymers.

Crystallization of a semicrystalline block copolymer quenched from the melt will also be briefly reviewed. Chu and Hsiao [68] comprehensively reviewed recent developments in SAXS where they discussed simultaneous measurements with other techniques. Among recently developed techniques, we will focus on simultaneous SAXSAVAXS (wide-angle X-ray scattering) and/or Hv-SALS (depolarized small-angle light scattering) measurements [69,70] because these are powerful techniques to study crystallization and spherulitic higher-order hierarchical structures in semicrystalline block polymers [71,72]. Current developments will also be reviewed later in the subsection on semicrystalline block polymers. 

The addition of water-soluble polymers such as polyethylene oxide (PEO) or polyvinyl alcohol (PVA) into the synthetic mixture of the C TMAX-HN03-TE0S-H20 system (n = 16 or 18 X = Br or Cl) under shear flow is found to promote uniformity and elongation of rope-like mesoporous silica. The millimeter-scaled mesoporous silica ropes are found to possess a three-level hierarchical structure. The addition of water-soluble polymer does not affect the physical properties of the silica ropes. Moreover, further hydrothermal treatment of the acid-made material under basic ammonia conditions effectively promotes reconstruction of the silica nanochannels while maintaining the rope-like morphology. As a result, a notable enhancement in both thermal and hydrothermal stability is found. 

However, the particular synthetic requirements in the preparation of conjugated polymers have thus far severely limited the number of similarly hierarchically structured examples. Pu et al. reported different types of conjugated polymers with fixed main-chain chirality containing binaphthyl units in their backbone which exhibited, for example, nonlinear optical activity or were used as enantioselective fluorescent sensors [42—46]. Some chirally substituted poly(thiophene)s were observed to form helical superstructures in solution [47-51], Okamoto and coworkers reported excess helicity in nonchiral, functional poly(phenyl acetylenejs upon supramolecular interactions with chiral additives, and they were able to induce a switch between unordered forms as well as helical forms with opposite helical senses [37, 52, 53]. 

These examples serve to highlight that supramolecular self-assembly and topo-chemical diacetylene polymerizations are a perfect match. Topochemical diacetylene polymerizations are an advantageous means of covalent capture for the reasons outlined above. The required order may, on the other hand, be provided by supramolecular self-assembly, which extends the scope beyond singlecrystalline monomers. This aspect becomes particularly important in the case of functional monomers in order to address specific applications. However, in contrast to previous investigations, the targeted preparation of hierarchically structured poly (diace tylene)s with a defined, finite number of strands required the presence of equally well-defined, uniform supramolecular polymers [106] with the propensity to form predictable superstructures, instead of micellar or vesicular ID aggregates. 

Figure 4.11 Schematic representation of the conversion of stranded poly(diacetylene)s with a multiple-helical quaternary the supramolecular polymers into conjugated polymers under structure in the case of A. retention of the hierarchical structure, leading to four-... 

Matsushita Y, Creation of hierarchically ordered nanophase structures in block polymers having various competing interactions, Macromolecules, 2007, 40, 771-776. 

In the final chapter "Principles of Statistical Chemistry as Applied to Kinetic Modeling of Polymer Obtaining Processes" by Semion Kuchanov (Lomonosov Moscow State University, Moscow, Russia), the contemporary problems of bridging models of micro- and macrostructure are discussed. The hierarchical analysis of chemical correlation functions (so-called chemical correlators) is a subject of the author s special interest. These problems are presented conceptually stressing that the problem of crucial importance is revealing the relation between the process mode and the chemical structure of polymer products obtained. 

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