Macromolecular network

A model for coal fluidity based on a macromolecular network pyrolysis model has been developed (33). In that model, bond breaking is described as a first-order reaction having a range of activation energies. A variety of lattices have also been used to describe the bonding in coal. In turn these stmctures... 

A predictive macromolecular network decomposition model for coal conversion based on results of analytical measurements has been developed called the functional group, depolymerization, vaporization, cross-linking (EG-DVC) model (77). Data are obtained on weight loss on heating (thermogravimetry) and analysis of the evolved species by Eourier transform infrared spectrometry. Separate experimental data on solvent sweUing, solvent extraction, and Gieseler plastometry are also used in the model. 

Although the basic concept of macromolecular networks and entropic elasticity [18] were expressed more then 50 years ago, work on the physics of rubber elasticity [8, 19, 20, 21] is still active. Moreover, the molecular theories of rubber elasticity are advancing to give increasingly realistic models for polymer networks [7, 22]. 

In this book series, macromolecules containing metal and metal-like elements are defined as large structures where the metal and metalloid atoms are (largely) covalently bonded into the macromolecular network within or pendant to the polymer backbone. 

CNTs own excellent materials properties. DNA is an excellent molecule to construct macromolecular networks because it is easy to synthesize, with a high specificity of interaction, and is conformationally flexible. The complementary base-paring properties of DNA molecules have been used to make two-dimensional crystals and prototypes of DNA computers and electronic circuits (Yan et al., 2002 Batalia et al., 2002). Therefore functionalization of CNTs with DNA molecules has great potential for applications such as developing nanodevices or nanosystems, biosensors, electronic sequencing, and gene transporters. 

One of the dominant issues in coal structure to re-emerge in the past decade is the two-phase concept of coal structure. A very spirited discussion of this topic was a feature of the 1989 symposium (48-52V Peter Given played a central role in the recent work on the two-phase concept, particularly in fostering the usage of the terms "mobile phase" and "macromolecular network" (23.53-551 and in organizing the "debate in print" (54V which has become a landmark papers in coal structure. In particular, the debate in print (24) was cited by all of die contributors to the 1989 discussion of the mobile phase (48-52V Given s work on the mobile phase was a... 

The other view which seems to prevail, is that a significant part of the Lorentzian protons, especially those of lower mobility, may be also associated with fragments of the macromolecular network that can rotate due to a single C-C or C-0 bond linking such fragment to the network. 

The controversy cannot be easily clarified there is no experimental technique available that could isolate all the free molecules and would leave intact the macromolecular network. 

The hypothesis that coals can be considered to consist of two component phases has its origins in observations of coal behaviour as well as deriving from the analysis of coals and attempts to define their structure. The results of extensive studies of untreated, preheated and hydrogenated coals, using analytical and microscopic techniques, have allowed some insight into the association between the so-called mobile phase and macromolecular network, and have provided information upon differences in their chemical properties. 

The concept that coals can be usefully considered to consist of two distinct phases of constituents is not new and has been advanced in different ways since the early part of this century. Its revival in recent times is largely attributable to the efforts of the late Peter Given, to whom is owed the now wide use of the terms mobile phase and macromolecular network (1-3. ... 

In broad terms, the mobile phase comprises the smaller molecules in coals, a portion of which is extractable in solvents. The greater proportion of coals is solvent-insoluble and consists primarily of a three-dimensional crosslinked macromolecular network or matrix. The mobile phase is attached to or held within the network by physical constraints and weak bonds. 

The foregoing observations have direct implications to coal structure. In the present work, the production of liquids is facile below about 15% liquids yield and requires little hydrogen consumption. The processes most probably involve the release of species which are physically trapped or are weakly bonded to the insoluble matrix. At high conversions, the products are derived from the breakdown of the macromolecular network. This phase of conversion requires the cleavage and stabilisation of strong bonds, thereby creating an appreciable demand for hydrogen. 

The results summarise in Table V (271 suggest that removal of some of the mobile phase prior to dry catalytic hydrogenation does not adversely affect chloroform-soluble yields obtained at long reaction times and, in the case of the lignite, the initial rate of conversion may actually be enhanced. Thus, the breakdown of the macromolecular network of coals via catalytic hydrogenation is not strongly dependent on the presence of mobile species. 

The theoretical model describes the break up of the coal macromolecular network under the influence of bond cleavage and crosslinking reactions using a Monte Carlo statistical approach (32-38). A similar statistical approach for coal decomposition using percolation theory has been presented by Grant et al. (39). 

Such statistical methods have been used for the inverse problem in the polymer literature, i.e., the formation of a macromolecular network by polymerization (40-44). The model was used to determine what effect the removal of crosslinks in the network have on thermal decomposition of the network. 

Ziabicki,A., Takserman-Krozer.R. General dynamic theory of macromolecular networks. I. Definitions and classification. J. Polymer Sci. Part A-2 7,2005-2018 (1969). 

Basement membranes (Fig. 1-6)663 function in part as an exoskeleton that helps keep cells positioned. However, the thick basement membranes of the capillary walls of the glomeruli of the kidney provide the ultrafilters that prevent most proteins from entering the urine. Basement membranes contain large amounts of collagen IV, which forms a polygonal network (Fig. 8-33A). A second macromolecular network is formed by the very large 950-kDa crossshaped multisubunit protein called laminin (Fig. 

The polymer networks based on silicon are very suitable for the study of cross-linked systems because of the possibility to synthesize smaller model molecules and macromolecular networks of well defined structure. An additional advantage of silicon polymers is that the resonances arising for different structural units are usually well... 

Sub-glass transitions are generally determined by the molecular (local) scale structure. Their location in the (t, T) space undergoes only a second-order influence of the macromolecular (network) structure through internal antiplasticization effects. By contrast, glass transition is directly under the influence of the network structure (Chapter 10), so that it appears interesting to study the influence of crosslinking on the parameters of the time-temperature relationship (WLF equation) ... 

Fixation in formalin is suitable because the induced protein-protein and protein-nucleic acid cross-links preserve the tissue efficiently while retaining morphology relatively intact. However, the macromolecular network introduced by formalin significantly reduces the access of FISH probes to target DNA. Consequently, the initial steps in a FISH staining must address suitable breakdown of this network. 

Edwards SF (1986) The theory of macromolecular networks. Biorheology 23 589-603 Falkowski PG, Raven JA (1997) Aquatic photosynthesis. 

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