Physical structure, polymers

To conclude consideration of the connection between structure (morphology) of polymers and combustion, we included in the last chapter our recent work which describes the new trend in flame retardation - modification of polymer physical structure (morphology) by means of polymer-polymer blends. 

Ogata, N., Jimenez, G., Kawai, H. and Ogihara, T. 1997. Structure and thermal/mechanical properties of poly(Llactide)- clay blend. Journal of Polymer Science, Part B Polymer Physics 35 389-396. 

Chul, M Phillips, R McCarthy, M, Measurement of the Porous Microstructure of Hydrogels by Nuclear Magnetic Resonance, Journal of Colloid and Interface Science 174, 336, 1995. Cohen, Y Ramon, O Kopeknan, IJ Mizrahi, S, Characterization of Inhomogeneous Polyacrylamide Hydrogels, Journal of Polymer Science Part B Polymer Physics 30, 1055, 1992. Cohen Addad, JP, NMR and Statistical Structures of Gels. In The Physical Properties of Polymeric Gels Cohen Addad, JP, ed. Wiley Chichester, UK, 1996 39. 

The present discussion of physical structure and properties is intended to serve merely as a basis for appraising the characteristics of various polymers here surveyed. The nature of the semicrystalline state in polymers and its influence on their physical properties will be dealt with in greater detail in a later chapter. 

Eisenberg, A. King, M. In Ion-Containing Polymers Physical Properties and Structures Academic New York, 1977 Vol. 2, p 169. 

The changes in structure of denatured nuclease as a function of urea concentration (Fig. 3) suggest that, as hydrophobic interactions are weakened and the backbone becomes more highly solvated, the chain expands gradually. The data presented by Millet et al. in this volume suggest that this expansion does not continue asymptotically as predicted by simple polymer physical chemistry. This is the behavior expected for a polypeptide chain trapped in a small region of conformation space. Most, perhaps all, of the conformations accessible in the expanded denatured state may have a native-like topology. 

Recent developments in polymer chemistry have allowed for the synthesis of a remarkable range of well-defined block copolymers with a high degree of molecular, compositional, and structural homogeneity. These developments are mainly due to the improvement of known polymerization techniques and their combination. Parallel advancements in characterization methods have been critical for the identification of optimum conditions for the synthesis of such materials. The availability of these well-defined block copolymers will facilitate studies in many fields of polymer physics and will provide the opportunity to better explore structure-property relationships which are of fundamental importance for hi-tech applications, such as high temperature separation membranes, drug delivery systems, photonics, multifunctional sensors, nanoreactors, nanopatterning, memory devices etc. 

With the discovery of crystalline polypropylene in the early 1950 s, polymer stereochemical configuration was established as a property fundamental to formulating both polymer physical characteristics and mechanical behavior. Although molecular asymmetry was well understood, polymer asymmetry presented a new type of problem. Both a description and measurement of polymer asymmetry were essential for an understanding of the polymer structure. 

HMX and RDX are energetic materials that produce high-temperature combustion products at about 3000 K. If one assumes that the combustion products at high temperature are HjO, Nj, and CO, rather than COj, both nitramines are considered to be stoichiometricaUy balanced materials and no excess oxidizer or fuel fragments are formed. When HMX or RDX particles are mixed with a polymeric hydrocarbon, a nitramine pyrolant is formed. Each nitramine particle is surrounded by the polymer and hence the physical structure is heterogeneous, similar to that of an AP composite pyrolant... 

Disclosed is an ethylene polymer foam structure having enhanced processing and physical properties. The foam structure comprises an ethylenic polymer material and a blowing agent of isobutane and 1,1-difluoroethane. Further disclosed is a process for making the foam structure. 

Surface properties are important to the physical and chemical behavior of polymers. Similar to smaller molecules, polymer surface structures can be determined using a variety of techniques including AES, near-field optical microscopy, electron microscopy, SPM, SIMS, and certain IR and MS procedures. 

The processing of polymeric materials is well advanced in science, engineering, and technology, and continues to advance. The properties of the end product are dependent on the chemical structure, processing, and physical structure. The properties depend on the mesostructure of the particular polymer. 

A more common use of informatics for data analysis is the development of (quantitative) structure-property relationships (QSPR) for the prediction of materials properties and thus ultimately the design of polymers. Quantitative structure-property relationships are multivariate statistical correlations between the property of a polymer and a number of variables, which are either physical properties themselves or descriptors, which hold information about a polymer in a more abstract way. The simplest QSPR models are usually linear regression-type models but complex neural networks and numerous other machine-learning techniques have also been used. 

Cellulose, a polysaccharide consisting of linear 1,4-/ -D-anhydroglucopyra-nose chains laterally associated by hydrogen bonds, is the most abundant and commercially important plant cell wall polymer (1). Consequently, cellulose is also one of the most thoroughly investigated plant cell wall polymers. However, it is enigmatic in the sense that significant elements of cellulose physical structure and the mechanism of cellulose biosynthesis still are not well understood. Since these subjects have been reviewed recently (2-10), this review will update topics covered previously and provide a new analysis of selected topics of contemporary interest. 

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