Polyolefins chemical modification

The synthesis of new polymeric materials having complex properties has recently become of great practical importance to polymer chemistry and technology. The synthesis of new materials can be prepared by either their monomers or modification of used polymers in industry. Today, polystyrene (PS), which is widely used in industrial applications as polyolefins and polyvinylchlorides, is also used for the production of plastic materials, which are used instead of metals in technology. For this reason, it is important to synthesize different PS plastic materials. Among the modification of PS, two methods can be considered, viz. physical and chemical modifications. These methods are extensively used to increase physico-mechanical properties, such as resistance to strike, air, or temperature for the synthesizing of new PS plastic materials. 

A good example of a reactive modifier which has been used (14) to enhance properties of polyolefins is maleic anhydride (MA). The formation of maleic adduct in polypropylene (PP), for example, can be used to effect several modifications e.g. to improving hydrophilicity, adhesion and dyeabflity. Moreover, the polymer-maleic adduct has an availabla additional functionality to effect other chemical modifications for achieving the desired material design objectives. Reactions of MA with polymers in solution are described in the patent literature (15). 

In general, there are two ways to functionalise polyolefins via direct copolymerisation of an olefin with a polar monomer and via chemical modification of preformed polymers [508 514]. 

Thermoplastic materials often have a lower surface energy than do thermosetting materials. Thus, physical or chemical modification of the surface is necessary to achieve acceptable bonding. This is especially true of the crystalline thermoplastics such as polyolefins, linear polyesters, and fluoropolymers. Methods used to increase the surface energy and improve wettability and adhesion include... 

The earliest data on solution of stabilizer permanency problems by means of polymerization of functionalized monomers having double bonds C=C were published in the late 1960s. They deal with results concerning stabilization of rubber [50-53] (experience from the chemical modification of rubber were successfully exploited in this case) and with light stabilization of polyolefins [54]. 

Halogenated polyolefins form another class of polymers. Some of the polymers from this class have important practical applications. Among these are poly(vinyl chloride), poly(vinylidene chloride), and polytetrafluoroethylene. Several unusual polymers such as poly(vinyl bromide) also are included in this class. Most halogenated polymers are obtained by the polymerization of a halogenated monomer. However, chemical modification (e.g. chlorination) of a preexistent polymer also can be applied to obtain partially halogenated materials. 

Specifically, PVC blends with polyethylene, polypropylene, or polystyrene could offer significant potential. PVC offers rigidity combined with flammability resistance. In essence, PVC offers the promise to be the lowest cost method to flame retard these polymers. The processing temperatures for the polyolefins and polystyrene are within the critical range for PVC. In fact, addition of the polyolefins to PVC should enhance its ability to be extruded and injected molded. PVC has been utilized in blends with functional styrenics (ABS and styrene-maleic anhydride co-and terpolymers) as well as PMMA offering the key advantage of improved flame resistance. Reactive extrusion concepts applied to PVC blends with polyolefins and polystyrene appear to be a facile method for compatibilization should the proper chemical modifications be found. He et al. [1997] noted the use of solid-state chlorinated polyethylene as a compatibilizer for PVC/LLDPE blends with a significant improvement in mechanical properties. A recent treatise [Datta and Lohse,... 

Nevertheless, the lack of reactive groups limit some of their end uses, particularly where adhesion, dyeability, paintability, printability, or compatibility are needed. Consequently, the chemical modification of polyolefins has been an area of increasing interest as a route to higher value products. ... 

New Options via Chemical Modifications of Polyolefins Part 1. Synthesis and Properties of Novel Phosphonium lonomers From Poly(Isobutylene-co-4-Bromomethylstyrene)... 

Chemical modification of polyolefins is a broad and rapidly growing field of science. Such modification, often times, is done to introduce either subtle or gross changes that enhance the attributes of the original polymer. For example, introduction of ionic interactions in polymers provides a means of controlling polymer structure and properties. As would be expected, ion-containing polymers, otherwise known as ionomers , display properties which are dramatically different from those of the parent polymer. Therefore, a broad spectrum of material properties may be created by varying the ion content, type of counter ion, and extent of neutralization. 

The bonding of a viscoelastic material (a film of glue) onto a solid surface can only be expected, then, when the surface tension of the liquid is lower than the critical surface tension 7. of the solid body. According to equation (13-3), these two quantities are related to the contact angle S and the interfacial surface tension between solid and adhesive film. Since a chemical variation in the surface can also cause the surface tension to change, it is often possible to obtain better bonding through chemical modification of a surface. An example of this is the oxidation of the surface of polyolefins [see the critical surface tensions of poly(ethylene) and poly-(vinyl alcohol) in Table 13-3]. 

The interactions and adhesion involved is basically a surface phenomena, and the nature and characteristics of interfaces and interphases are of prime importance. They can be promoted by use of proper compatibilizing agents (5) or directly, by modifying surface properties (6). Permanent chemical modification of polymer surfaces is a rather difficult task, and for polyolefins, which are poorly reactive this difficulty is even greater. On the other hand, if activated, polyolefins can react with oxygen of the atmosphere easily which is a chain reaction with... 

Natural fibres are hydrophilic in nature as they are lignoceUulosic, which contain strongly polarized hydroxyl groups. These fibres, therefore, are inherently incompatible with hydrophobic thermoplastics, such as polyolefins. The major limitations of using these fibres as reinforcements in such matrices include poor interfacial adhesion between polar-hydrophUic fibres and non-polar-hydrophobic matrix, and difficulties in mixing due to poor wetting of the fibres with the matrix. Hence, it is imperative that natural fibres should be subjected to chemical modification to increase the compatibility and adhesion between fibres and matrix. 

The evaluation of thermal degradation may be suggestively done by the comparison between chemiluminescence and oxygen uptake measurements (Figs. 22a and b) which both of them are based on the chemical modifications caused by oxygen diffusion. They similarly allow to order several polymeric materials based on their stability. Ozawa s group found for some polyolefins the following sequence of stability [9001] ... 

Polyolefins can be functionalized either by chemical modification of preformed polymersi or by copolymerization of olefins with suitable polar comonomers. ... 

Polyolefins, especially polyethylene and polypropylene, are used in a wide range of applications, since they incorporate an excellent combination of mechanical, chemical and electronic properties and processibility. Nevertheless, deficiencies, such as the lack of reactive groups in the polymer structure, have limited some of their end uses, particularly those in which adhesion, dyeability, paintability, printability or compatibility with other functional polymers is paramount. Accordingly, the chemical modification of polyolefins has been an area of increasing interest as a route to higher value products and various methods of functionalization (1-3) have been employed to alter their chemical and physical properties. 

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