Chemical Modification of Polymeric Materials

Plasma treatment and plasma deposition polymerization provides a unique and powerful method for the surface chemical modification of polymeric materials without altering their bulk properties. (7-5) These techniques offer the possibility to improve the performance of existing biomaterials and medical devices and for developing new biomaterials-(- -6)... 

One possible way of polymer waste management is the chemical modification of polymeric materials. Sulkowski et al. (2013) used expanded polystyrene waste (EPS), as the reference material, which was converted into polymeric flocculants by the sulfonation reaction. Under conventional heating and microwave conditions, poly(styrenesulphonate) acids (EPSS) were obtained from EPS during the sulfonation process with sulfuric acid as the sulfonation agent and Ag SO as the catalyst. It was observed that the sulfonation process performed under microwave irradiation gave same amount of product as in case of conventional conditions but the reaction time was substantially reduced from 1-1.30 h to 15 min. 

Composite Particles, Inc. developed two methods of surface modification of polymeric materials which are used for materials of different shapes and compositions. Here, only the spherical, non-rubber particles are discussed. Further information is included in the section on rubber particles below. One method of surface modification is based on exposing the polymeric powder to a chemically reactive gas atmosphere which oxidizes surface groups to form OH and COOH functionalities. These functionalities are then available for reaction with the components of the matrix into which modified particles are introduced. Vistamer HD and UH are manufactured by this method from polyethylenes of different molecular weights. Two factors can be regulated here the properties of the core particle and the type and density of functional groups on the surface of these particles. Polyethylene is a material, which without this modification, will not be compatible with most systems. The surface modification allows the incorporation of the material into resins. This improves abrasion resistance, tear strength, and moisture barrier properties and reduces the fiiction coefficient. 

In the early stages of ESR application to polymer research, many studies on the identification of free radicals produced by irradiation with ionizing radiation, x-ray, and ultraviolet light were made. Some of the irradiation effects in polymeric materials were considered to originate from the radical processes and, therefore, clear identification of the radicals trapped in irradiated polymers was one of the most important problems at that stage. In this meaning, ESR application was considered to be a very convenient technique for this purpose, because detection and identification of the free radicals bearing unpaired electrons in principle can be done easily by the ESR method without any chemical modification of the materials. 

Surface modification refers to the modification that occurs only on the surface of a polymer material without further internal modification. Surface modifications of polymeric materials include surface chemical oxidation, corona surface treatment, surface flame treatment, surface heat treatment, surface plasma treatment, surface metallization processing, ion implantation, and surface grafting polymerization. Because surface modification occurs only on the surface of materials, the performance does not change uniformly. 

New elastic polymeric materials (resistance to higher stroke or air) can be obtained by using physical modification methods, but using this method, two phases (PS and rubber) in the mixture were formed. Small rubber particles spread as a PS layer and, after awhile, the relationship between the layers decreases and rubber particles gather in the upper layer of the materials. This can be the cause of the loss of resistance of the materials. These material disadvantages have stimulated the polymer synthesis to increase the PS resistance to higher physico-mechanical properties, such as higher temperature and stroke for the chemical modification of PS with various functional modifiers. 

Cross-linked polystyrene and its functional derivatives are widely used in organic syntheses as polymeric reagents and catalysts.28 However, thermal and chemical stability of such materials has to be better. Some improvement in these properties can be achieved by the grafting of styrene with the following chemical modification or grafting of other functional monomers. 

Due to the 3 hydroxyl groups available for oxidation within one anhydroglucose unit and due to the polymeric character of the cellulose a great variety of structural modifications and combinations is possible. As with other types of chemical changes at the cellulose molecule also in this case the oxidation can affect different structural levels differently. Depending on the oxidative stress imposed on the cellulose, the individual hydroxyls within the AGU and within the polymer chain are involved to varying extent and may respond to further treatment and reactions in a specific way. Despite their low concentration in the imol/g range, oxidative functionalities are one of the prime factors to determine macroscopic properties and chemical behavior of cellulosic materials (Fig. 1). 

IR spectroscopy can be used to characterise not only different rubbers, but also to understand the structural changes due to the chemical modification of the rubbers. The chemical methods normally used to modify rubbers include hydrogenation, halogenation, hydrosilylation, phosphonylation and sulfonation. The effects of oxidation, weathering and radiation on the polymer structure can be studied with the help of infrared spectroscopy. Formation of ionic polymers and ionomeric polyblends behaving as thermoplastic elastomers can be followed by this method. Infrared spectroscopy in conjunction with other techniques is an important tool to characterise polymeric materials. 

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