Polymers macromolecular nature

The mechanism of polyoondensation reactions is thought to parallel that of the low-molecular-weight analogs. As a result of their macromolecular nature, polymers would be expected to have retarded mobility. It was therefore predicted, purely on theoretical arguments, that the chemical reactivity of polymers should be low. 

The polymer in natural rubber consists almost entirely of ci -poly(isoprene) (1.6). The molecules are linear, with relative molar mass typically lying between 300 000 and 500 000. The macromolecular nature of rubber was established mainly by Staudinger in 1922, when he hydrogenated the material and obtained a product that retained its colloidal character, rather than yielding fragments of low relative molar mass. 

The views of Staudinger, on the one hand, and Meyer and Mark, on the other, actually were not so far apart as the tenor of their polemics might indicate. Their agreement on the essential macromolecular nature of high polymers appears to have contributed materially to the rejection of the simple cyclic formulas widely accepted up to that time. 

Probably the most promising polymeric drug carrier system involves polysaccharide molecules. These are natural polymers and are often biodegradable to products that are useful to the host or easily eliminated by the host. Dextrans have been the most extensively used polysaccharide for macromolecular prodrug preparations (79). These materials are biocompatible and the in vivo fate is directly related to their molecular weight. Moreover these macromolecules can be easily targetted to the hepatocytes with D-mannose or L-fucose (20). 

The most relevant property of stereoregular polymers is their ability to crystallize. This fact became evident through the work of Natta and his school, as the result of the simultaneous development of new synthetic methods and of extensive stractural investigations. Previously, the presence of crystalline order had been ascertained only in a few natural polymers (cellulose, natural rubber, bal-ata, etc.) and in synthetic polymers devoid of stereogenic centers (polyethylene, polytetrafluoroethylene, polyamids, polyesters, etc.). After the pioneering work of Meyer and Mark (70), important theoretical and experimental contributions to the study of crystalline polymers were made by Bunn (159-161), who predicted the most probable chain conformation of linear polymers and determined the crystalline structure of several macromolecular compounds. 

The present chapter deals with molecular characteristics of synthetic polymers. Numerous natural polymers such as the most polysaccharides can be tentatively incorporated into this group of macromolecular substances because their behavior in many aspects resembles that of the synthetic polymers and also because they are often chemically modified to adjust their utility properties. The typical example is cellulose, the most abundant organic polymer on earth. 

The effects mentioned in the last sub-section are all local ones and do not depend upon the macromolecular nature of the material. A more important group of properties comprises those that are affected by the changes that LCB produces in the space-filling behaviour of polymer molecules under conditions in which they are free or relatively free from conformational constraints, that is in solution or in the melt, or in the amorphous state below 7. ... 

On the basis of the separation mechanism, restricted-access media can be classified into physical or chemical diffusion barrier types. The limited accessibility of the former type is due to the pore structure of the support that represents physical diffusion barriers for macromolecular compounds. The restricted access of the latter type is due to covalently or adsorptively bonded synthetic or natural polymers that cover the support surface, preventing macromolecules from being adsorbed on or denatured by the column packing material. 

Peculiarities of Thermotropic Liquid-Crystalline Polymers Related to Their Macromolecular Nature... 

Mucoadhesives are generally macromolecular organic polymers made from natural (gelatin, agarose, chitosan, hyaluronic acid) or synthetic polymers (polyvinylpyrrolidone (PVP), polyacrylates, polyvinyl alcohol, cellulose derivates). They possess hydrophilic groups that can... 

Macromolecular chemistry covers a particularly wide field which includes natural polymeric material, such as proteins, cellulose, gums and natural rubber industrial derivatives of natural polymers, such as sodium carboxymethyl cellulose, rayon and vulcanised rubber and the purely synthetic polymers, such as polythene (polyethylene), Teflon (polytetrafluoroethylene), polystyrene, Perspex (poly (methyl... 

Blackwell, J. (1982) The macromolecular organization of cellulose and chitin. In Cellulose and Other Natural Polymer Systems, Brown, R. M.,Jr. (Ed.), p. 403. Plenum, New York. 

In 1968, already back in Italy, Vittorio was called as full professor to the University of Trieste, where he founded the Macromolecular Chemistry Laboratory, leading a number of young scientists who still are active in the field of carbohydrate and polysaccharide chemistry. His main interest during this period was investigations on the polyelectrolytic properties of synthetic and natural polymers, including the very poorly studied ionic polysaccharides. 

Product information is presented for Amina T 100, a newly developed polymer from Creavis GmbH with antimicrobial action. Its crucial advantages lies in its macromolecular nature. In contrast to other polymers provided conventionally with biocides, there is no wash-out of low molecular toxic components. The starting materials are not antimicrobially active, and the antimicrobial action develops only in the polymer. Product properties are listed, its spectrum of activity is identified, and kinetics of reduction are charted. 

Within the specific context of this chapter, renewable resources represent the obvious answer to the quest for macromolecular materials capable of replacing their fossil-based counterparts [2, 3]. This is not as original as it sounds, because, apart from the role of natural polymers throughout our history evoked above, the very first synthetic polymer commodities, developed during the second half of the nineteenth century, namely cellulose esters, vulcanized natural rubber, rosin derivatives, terpene resins , were all derived from renewable resources. What is new and particularly promising, has to do with the growing momentum that this... 

Staudinger spent the next twenty or so years building up macromolecular chemistry and helping to lay the foundation for today s multibillion-dollar polymer industry. He retired in 1951 and received the 1953 Nobel Prize in chemistry for his work on polymers. He died on September 8, 1965. SEE ALSO Polymers, Natural Polymers, Synthetic. 

A number of reviews cover what has been achieved over the past 20 years in the field of soluble polymers as potential drug carriers.The polymers selected for preparing macromolecular prodrugs can be categorized according to (1) the chemical nature (vinylic or acrylic polymers, polysaccharides, poly(a-amino acids)) (2) the back bone stability (biodegradable polymers, stable polymers) (3) the origin (natural polymers, synthetic polymers) and (4) the... 

The macromolecular nature of polymers and the existence of molecular weight distribution (polydis-persity) lead to a broadening of T. ... 

Because of the macromolecular nature of polymers and the conformational changes associated with melting, the process of melting in polymer is more rate sensitive than that in simple molecules. 

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