Properties of Modified Polymers

Jointing and termination are essential procedures for the efficient and proper transmission and distribution of power through cables. To extend the cable, frequent joints are needed. Also, the end terminations during storage need to be protected. Heat shrinkable and radiation crosslinkable polymeric materials may be used for this purpose. 

Polymers are modified with the multifunctional monomers in an internal mixer and then extruded in the form of a tube. A typical recipe contains polyethylene with 4 parts of TMPTMA irradiated with 200 kGy radiation dose. These are then irradiated in the presence of electron beams followed by passing them through a tube expander. A typical expander contains five sections  

The heat shrinkable properties of these tubes are demonstrated in 

The authors are grateful to the Department of Atomic Energy for helping in the electron beam experiments at various stages and Dr. A.B. Majali. BARC, Bombay and Dr. V. K. Tikku of Nicco corporation Ltd, Calcutta for continuous encouragement. 

Encyclopedia of Polymer science and engineering, Vol.4 John Wiley sons. New York, 1988. p 418. 

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Triazoline-3,5-diones, 4-substituted-ene reactions with polydienes, 220 properties of modified polymers, 220... 

As was mentioned above, four main factors determine the properties of modified polymers the characteristics... 

The properties of the polymers may be modified by mixing abphatic acids or anhydrides with the phthalic anhydride. Many alkyd resins find application in the paint industry. 

Small amounts of specially functionalized monomers are often copolymerized with acryUc monomers in order to modify or improve the properties of the polymer. These functional monomers can bring about improvements either directiy or by providing sites for further reaction with metal ions, cross-linkers, or other compounds and resins. Table 9 Hsts some of the more common functional monomers used in the preparation of acryUc copolymers. 

The neat resin preparation for PPS is quite compHcated, despite the fact that the overall polymerization reaction appears to be simple. Several commercial PPS polymerization processes that feature some steps in common have been described (1,2). At least three different mechanisms have been pubUshed in an attempt to describe the basic reaction of a sodium sulfide equivalent and -dichlorobenzene these are S Ar (13,16,19), radical cation (20,21), and Buimett s (22) Sj l radical anion (23—25) mechanisms. The benzyne mechanism was ruled out (16) based on the observation that the para-substitution pattern of the monomer, -dichlorobenzene, is retained in the repeating unit of the polymer. Demonstration that the step-growth polymerization of sodium sulfide and /)-dichlorohenzene proceeds via the S Ar mechanism is fairly recent (1991) (26). Eurther complexity in the polymerization is the incorporation of comonomers that alter the polymer stmcture, thereby modifying the properties of the polymer. Additionally, post-polymerization treatments can be utilized, which modify the properties of the polymer. Preparation of the neat resin is an area of significant latitude and extreme importance for the end user. 

Rosin is compatible with many materials because of its polar functionaUty, cycloaUphatic stmcture, and its low molecular weight. It has an acid number of ca 165 and a saponification number of ca 170. It is soluble in aUphatic, aromatic, and chlorinated hydrocarbons, as well as esters and ethers. Because of its solubiUty and compatibiUty characteristics, it is useful for modifying the properties of many polymers. 

Rosin ester resins are used as modifiers in the formulation of chewing gum. The rosin derivative modifies the physical properties of the polymer used, providing the desired masticatory properties. The glycerol ester of hydrogenated rosin is the predominant choice, because stabilized materials have improved aging resistance, which extends the shelf life of the gum. 

Rubber-Modified Copolymers. Acrylonitrile—butadiene—styrene polymers have become important commercial products since the mid-1950s. The development and properties of ABS polymers have been discussed in detail (76) (see Acrylonitrile polymers). ABS polymers, like HIPS, are two-phase systems in which the elastomer component is dispersed in the rigid SAN copolymer matrix. The electron photomicrographs in Figure 6 show the difference in morphology of mass vs emulsion ABS polymers. The differences in stmcture of the dispersed phases are primarily a result of differences in production processes, types of mbber used, and variation in mbber concentrations. 

Grafting provides a convenient means for modifying the properties of numerous polymers. It is often required that a polymer possess a number of properties. Such diverse properties may not be easily achieved by the synthesis of homopolymers alone but can be achieved through the formation of copolymers or even terpoly-mers. The formation of graft copolymer with sufficiently long polymeric sequences of diverse chemical composition opens the way to afford speciality polymeric materials. 

There has been much interest in modifying the ion-exchange properties of conducting polymers with substituents or polymeric counter-ions. Cationic substituents, such as ammonium234 and pyridinium235 groups, increase the polymer s anion-exchange capacity and increase anion trans-... 

Plasticizers are very high-boiling liquids that when mixed with polymers like poly(vinyl chloride) modify the properties of the polymer to produce a material with added flexibility without losing other desirable properties such as strength. They are commonly made by reacting phthahc anhydride with a long-chain alcohol (typically eight carbons). 

Wasson, E. A. Nicholson, J. W. (1990). A study of the relationship between setting chemistry and properties of modified glass-poly(alkenoate) cements. British Polymer Journal, 23, 179-83. 

Chemical modifications of PPO by electrophilic substitution of the aromatic backbone provided a variety of new structures with improved gas permeation characteristics. It was found that the substitution degree, main chain rigidity, the bulkiness and flexibility of the side chains and the polarity of the side chains are major parameters controlling the gas permeation properties of the polymer membrane. The broad range of solvents available for the modified structures enhances the possibility of facile preparation of PPO based membrane systems for use in gas separations. 

In order to identify tyrosine derivatives that would lead to polymers that are processible, mechanically strong, and also biocompatible, we initiated a detailed investigation of the structure-property relationships in polyiminocarbonates and polycarbonates. Since the amino and carboxylic acid groups of tyrosine dipeptide (the N and C termini) provide convenient attachment points, selected pendent chains can be used to modify the overall properties of the polymers. This is an important structural feature of tyrosine dipcptide derived polymers. 

Most plastic materials are used because they have desirable mechanical properties at an economical cost. For this reason, the mechanical properties may be considered the most important of all the physical and chemical properties of high polymers for most applications. Thus everyone working with such materials needs at least an elementary knowledge of their mechanical behavior and how this behavior can be modified by the numerous structural factors that can be varied in polymers. High polymers, a few of which have their chemical structure shown in Appendix I, have the widest variety and range of mechanical properties of all known materials. Polymers vary from liquids and soft rubbers to very hard and rigid solids. 

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