Modification of Polymers by Additives

Most of the macromolecular substances cannot be processed or used as received from the manufacturing process. This is especially valid for solid polymers. 

Frequently, small amounts of additives have to be admixed as processing aids or to improve the properties of the polymers, before molding compounds or granulated compounds can be made out of them. But also polymers accruing as dispersions have to be converted into a ready-to-use form by additives before they can be applied. 

Depending on the intended application of the polymers the following agents are also admixed  

Unwanted degradation and oxidation processes can be avoided or at least suppressed for some time either by structural modiflcation of the polymer or by special additives. In practice, the addition of so-called antioxidants is particularly effective. Chemical substances that slow down oxidations and the following aging phenomena serve for this purpose. Antioxidants are sufficiently effective even in concentrations below 1 wt% and are added as early as possible to the polymer to be protected, e.g., already during the drying of powdery polymeric materials or during the preparation of granulates. Some of the most important so-called primary antioxidants are sterically hindered phenols and secondary aromatic amines secondary antioxidants are thioethers as well as phosphites and phosphonites. 

Suppression of the Thermo-Oxidative Crosslinking of Polyisoprene by Addition of an Antioxidant 

Conducting additives, e.g., carbon based particles like carbon black or carbon nanotubes, to decrease electrical resistance. 

Flame-proofing agents to decrease inflammability and combustibility, 

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In this paper first results of the solubility and extraction of low molecular weight polymers and plasticizers with supercritical carbon dioxide are presented and compared to the results of phase equilibria measurements. Additionally the formation of sub-micrometer particles during polymerization of acrylic acid and derivatives thereof in scCC are examined and compared with recent works [2], Finally there are some aspects to modification of polymers by absorption of scC02 and reactive components solved therein. 

Chemical modification of polymers by the addition of various flame retardants may have different effects on the ignitability of polymeric materials. Information about such effects helps to explore certain features of the activity mechanism of flame retardants... 

In addition, polymers can be varied by copolymerization. Most important in this context is the modification of polymers by attaching a short second chain or a small number of single groups which drastically differ in their properties from the repeat units of the polymer chain. 

Polyolefins, PO. First impact modification of PO, by addition of elastomers, was patented independently by Bayer A.-G. and Standard Oil Co. in 1937. The isotactic polypropylene, PP, was commercialized in 1957, and its first blends (with polyisobutylene, PIB, and polyethylene, PE) were patented in 1958. In 1960, du Pont started manufacturing ethylene-propylene, EPR, and three years later ethylene-propylene-diene, EPDM, copolymers [Gresham and Hunt, I960]. The first patent on impact modification of PP by addition of EPR dates from 1960. Direct reactor blending of PE/PP/EPR resulting in a thermoplastic polyolefin, R-TPO, dates from 1979. The newest (introduced in 1992) single-site metallocene catalysts generate polymers with controlled tacticity, co-monomer sequences, molecular... 

Reactive extrusion is the chemical modification of polymer while it is being transported in an extruder. In this work, polypropylene is intentionally degraded by the addition of a free radical initiator (a peroxide) during extrusion. The product has improved flow properties because of the removal of the high molecular weight tail and the narrowing of the molecular weight distribution. 

Temperature is an important parameter in radiation degradation, yet remarkably little experimental work has been reported for irradiation at other than ambient temperature. The transition temperatures, Tg and Tm, of the polymer are as important in the radiolysis as they are for the properties. The irradiation temperature can be deliberately varied to enhance the radiation-induced modifications of polymers and should not be regarded as just an environmental property. Similarly, once the sensitization to, or protection from, radiation degradation by small molecule additives is understood — as a function... 

Organofunctional silanes with hydroxy-, epoxy-, acryl-, ester- and carboxy-functions are produced industrially. They are in particular utilized as additives for modification of polymers and for functionalizing silicones for different application sectors. Most of these compounds are manufactured by the addition of appropriately functionalized alkenyl-compounds. 

The most desirable properties for electrically conductive polymeric materials are film-forming ability and thermal and electrical properties. These properties are conveniently attained by chemical modification of polymers such as polycation-7, 7,8, 8-tetracyanoqninodimethane (TCNQ) radical anion salt formation (1-3). However, a major drawback of such a system is the brittle nature of the films and their poor stability (4,5) resulting from the polymeric ionicity. In recent years, polymeric composites (6-8) comprising TCNQ salt dispersions in non-ionic polymer matrices have been found to have better properties. In addition, the range of conductivities desired can be controlled by adjusting the TCNQ salt concentration, and other physical properties can be modified by choosing an appropriate polymer matrix. Thus, the composite systems are expected to have important advantages for use in electronic devices. 

While oxygen-containing polymers have received more attention other heteroatom-containing polymers have also been studied. In addition to homopolymers, copolymers containing more than one monomer has also received attention. Further, modifications of homopolymers by plasticizers, or crosslinking, or grafting to improve the properties of the polymers towards polymer-salt complex formation or increasing the dimensional stability of the materials has also been a focus of research. 

Additives are essential components of plastic formulations that provide maintenance and/or modification of polymer properties, performance, and long-term use. The extension of polymer properties by additives has been playing a substantial role in the growth of plastics, and many polymer applications are accessible only in the presence of a number of ingredients, often only in small quantities, in addition to the polymer itself. 

For a polymer to be useful, it must be able to function properly in a given application. The performance of a polymer is determined primarily by the composition and structure of the polymer molecule. These control the physical, chemical, and other characteristics of the polymer material. Therefore modification of the composition of the structural units represents one of the main approaches to the modification of polymer behavior. In addition to the chemical nature and composition of the structural units that constitute the polymer backbone, molecular architecture also contributes to the ultimate properties of polymeric products. Thus polymer modification can be accomplished by employing one or more of the following techniques ... 

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