Polymer, chemical physics

Candidate polymers for biomedical applications must comply with a variety of requirements characteristic of most biomaterials. These requirements arise either from the specific chemical or physical structure of the polymers (chemical, physical, and mechanical criteria) or from the physiological environment where they will be used (biological criteria). Table I summarizes major criteria for the design and selection of polymers as biomaterials. 

Fig. 8.8 The bond fluctuation model. In this example three bcmds in the polymer arc incorporated into a singk effecti bond between effective moncmers . (Figure adapted from Baschnagel J, K Binder, W Paul, M Laso, U Sutcr, I Batouli [N ]ilge and T Burger 1991. On the Construction of Coarse-Grained Models for Linear Flexible Polymer-Chains -Distribution-Functions for Groups of Consecutive Monomers. Journal of Chemical Physics 93 6014-6025.)...

Monte Carlo (MC) techniques for molecular simulations have a long and rich history, and have been used to a great extent in studying the chemical physics of polymers. The majority of molecular modeling studies today do not involve the use of MC methods however, the sampling capabiUty provided by MC methods has gained some popularity among computational chemists as a result of various studies (95—97). Relevant concepts of MC are summarized herein. 

Stabilization of the Cellular State. The increase in surface area corresponding to the formation of many ceUs in the plastic phase is accompanied by an increase in the free energy of the system hence the foamed state is inherently unstable. Methods of stabilizing this foamed state can be classified as chemical, eg, the polymerization of a fluid resin into a three-dimensional thermoset polymer, or physical, eg, the cooling of an expanded thermoplastic polymer to a temperature below its second-order transition temperature or its crystalline melting point to prevent polymer flow. 

J. P. Ibar and co-workers, in Polymer Characterisation Physical Property, Spectroscopic, and Chromatographic Methods, American Chemical Society, Washington, D.C., 1990, p. 167. 

Acrylic Resins. The first synthetic polymer denture material, used throughout much of the 20th century, was based on the discovery of vulcanised mbber in 1839. Other polymers explored for denture and other dental uses have included ceUuloid, phenolformaldehyde resins, and vinyl chloride copolymers. Polystyrene, polycarbonates, polyurethanes, and acryHc resins have also been used for dental polymers. Because of the unique combination of properties, eg, aesthetics and ease of fabrication, acryHc resins based on methyl methacrylate and its polymer and/or copolymers have received the most attention since their introduction in 1937. However, deficiencies include excessive polymerization shrinkage and poor abrasion resistance. Polymers used in dental appHcation should have minimal dimensional changes during and subsequent to polymerization exceUent chemical, physical, and color stabiHty processabiHty and biocompatibiHty and the abiHty to blend with contiguous tissues. 

K. Kremer. Computer simulation of polymers. In M. P. Allen, D. J. Tildesley, eds. Computer Simulation in Chemical Physics. Amsterdam Kluwer, 1993, pp. 397 59. 

N. M. Emanuel and A. L. Buchahenko, Chemical Physics of Polymer Degradation and Stabilization, VNU Science Press, p. 340(1987). 

Chapter 12 discusses the use of the various monomers obtained from a petroleum origin for producing commercial polymers. Not only does it cover the chemical reactions involved in the synthesis of these polymers, but it also presents their chemical, physical and mechanical properties. These properties are well related to the applicability of a polymer as a plastic, an elastomer, or as a fiber. 

Quite naturally, novel techniques for manufacturing composite materials are in principal rare. The polymerization filling worked out at the Chemical Physics Institute of the USSR Academy of Sciences is an example of such techniques [49-51], The essence of the technique lies in that monomer polymerization takes place directly on the filler surface, i.e. a composite material is formed in the polymer forming stage which excludes the necessity of mixing constituents of a composite material. Practically, any material may be used as a filler the use of conducting fillers makes it possible to obtain a composite material having electrical conductance. The material thus obtained in the form of a powder can be processed by traditional methods, with polymers of many types (polyolefins, polyvinyl chloride, elastomers, etc.) used as a matrix. 

The structural varieties of hemicelluloses offer a number of possibilities for specific chemical, physical, and enzymic modifications. Future advancements will be based on the synthesis of hemicellulose-based polymers with new functionalities and with a well-defined and preset primary structure both on the level of the repeating imit and the polymer chain. Hemicelluloses have also started to be attractive to synthetic polymer chemists as... 

Finally, synthetic metals made of polymeric organic molecules may also show the property of ferromagnetism. Organic materials of this kind were first demonstrated in 1987 by Ovchinnikov and his co-workers at the Institute of Chemical Physics in Moscow. The polymer they used was based on a polydiacetylene backbone, which contains alternating double-single and triple-single bonds between the carbon atoms of the molecule (10.2). 

The authors are thankful to Dr. P. Sadhukhan (Bridgestone/Firestone Research, Akron, OH) for different rubber samples Dr. T. Medintseva (the Semenov s Instimte of Chemical Physics, Moscow, Russia) for TPV samples Dr. N. Dutta (University of South Australia, Adelaide, Australia) for the samples of SEBS filled with oil Dr. Z. Petrovich (Kansas Polymer Research Center, Pittsburg State University, Pittsburg, KA) for PU samples, and NIST/ATP Award 70NANB4H3055 for financial support. 

Lyman, D. J., and Knutson, K., Chemical, physical, and mechanical aspects of blood compatibility, in Biomedical Polymers... 

Altenberger, AR TirreU, M, On the Theory of Self-Diffusion in a Polymer Gel, Journal of Chemical Physics 80, 2208, 1984. 

Altenberger, AR TirreU, M Dahler, JS, Hydrodynamic Screening and Particle Dynamics in Porous Media, SemidUute Polymer Solutions and Polymer Gels, Journal of Chemical Physics 84,5122, 1986. 

Baumgartner, A Muthukumar, M, Polymers in Disordered Media, Advances in Chemical Physics 94, 625, 1996. 

Zimm, BH, Dynamics of Polymer Molecules in Dilute Solution Viscoelasticity, Flow Birefringence and Dielectric Loss, Journal of Chemical Physics 24, 269, 1956. 

This difference in spatial characteristics has a profound effect upon the polymer s physical and chemical properties. In thermoplastic polymers, application of heat causes a change from a solid or glassy (amorphous) state to a flowable liquid. In thermosetting polymers, the change of state occurs from a rigid solid to a soft, rubbery composition. The glass transition temperature, Tg, ... 

Permissions granted by the following journals and publishers are gratefully acknowledged Academic Press, Inc., Annual Reviews, Inc., Canadian Journal of Research, Chemische Berichte, Die Makromoleku-lare Chemie, India Rubber World, Industrial and Engineering Chemistry, Interscience Publishers, Inc., Journal of the American Chemical Society, Journal of Applied Physics, Journal of Chemical Physics, Journal of the Chemical Society (London), Journal of Colloid Science, Journal of Polymer Science, Journal of Research of the National Bureau of Standards, Transactions of the Faraday Society, Williams and Wilkins Company, and Zeitschrift fur physikalische Chemie. 

In the past decades, polymer materials have been continuously replacing more traditional materials such as paper, metal, glass, stone, wood, natural fibres and natural rubber in the fields of clothing industry, E E components, automotive materials, aeronautics, leisure, food packaging, sports goods, etc. Without the existence of suitable polymer materials progress in many of these areas would have been limited. Polymer materials are appreciated for their chemical, physical and economical qualities including low production cost, safety aspects and low environmental impact (cf. life-cycle analysis). 

Nature of the polymer matrix (physical and chemical properties of the polymer determine how the additives can be separated, if at all)... 

These enhance the appearance of the polymer, but play no role in the chemical, physical or mechanical properties of the base polymer. The main difficulty is that if the finished assembled article is made from different grades of the same polymer or from different polymers, then, particularly with different polymers, the combination must be uniform. For example, bathroom suites are often made from different materials, e.g., ceramics, baths (polyacrylates), trimmings (PVC, PP). The colorants therefore have to undergo different processing conditions and it is essential that in the final products the colour is the same. 

As already mentioned, a network can be obtained by linking polymer chains together, and this linkage may be either physical or chemical. Physical linking can be obtained by (i) absorption of chains onto the surface of finely divided particulate fillers, (ii) formation of small crystallites, (iii) coalescence of ionic groups, or (iv) coalescence of glassy sequences in block copolymers. 

N.M. Emanuel and A.L. Buchachenko, Chemical Physics of Molecular Destruction and Stabilization of Polymer, VNU Science Press, Utrecht, Netherlands, 1987. 

Since the chemical structure and monomer composition of a specific polymer are the most important factors in determining the polymer s physical and material properties, a short recapitulation of typical representatives of microbially synthesized poly(hydroxyalkanoates) is presented in this section. A more detailed overview on this issue is available from References [19-21], but is not within our scope here. The monomer composition of PHAs depends on the nature of the carbon source and the microorganisms used. This way, numerous monomers have been introduced into PH A chains [3-9]. PHAs have been divided roughly into two classes [19]. 

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