“Radiation Induced Structural Modifications on Polymers and Copolymers of Ethylene and Propylene”

ENRIQUE M. VALLÉS

Termas de Catillo, Chile

Conferencia; V Coloquio de Macromoléculas de la Sociedad Chilena de Química; 2010

Sociedad Chilena de Química

RADIATION INDUCED STRUCTURAL MODIFICATIONS ON POLYMERS AND COPOLYMERS OF ETHYLENE AND PROPYLENE Enrique Vallés Planta Piloto de Ingeniería Química (Universidad Nacional del Sur – Consejo Nacional de Investigaciones Científicas y Técnicas) , CC 717, Bahía Blanca 8000, BA, Argentina. valles@plapiqui.edu.ar Irradiation is a useful tool for post-reactor polymer modifications. This process induces changes in the structural and the physicochemical characteristics of the polymeric materials. Specifically, the interaction of radiation with polymers stimulate the formation of macroradicals that can lead to scission reactions, crosslinking with other macroradicals to generate branched structures, generation of unsaturations in the polymer chains and grafting of different functional groups. These reactions affect important structural variables of the polymer molecules and, in turn, the physical properties of the treated material. In this way, some polymer properties can be improved by irradiation, making the modified material more appropriate for a wider range of commercial, medical and industrial applications. For example, polymer irradiation has been extensively used in the biomedical and food industries as the last process after packaging to control pathogenic and spoilage organisms. The type of structural modifications induced by irradiation depends on several factors, like the particular chemical structure of the repeated units that form the polymer chain, the intensity of the radiation source, the temperature and the environmental conditions prevailing at the moment of the irradiation and on the post irradiation treatment. In particular, crosslinking prevails in polyethylene, increasing the elasticity of the melt and improving the resistance to of the modified polymer to high temperatures and solvents. On polypropylene, the dominant reaction after formation of the macroradicals is -scission, which induces a molar mass decrease and appearance of terminal double bonds. The subsequent addition of double bonds to the formed macroradicals results in the formation of chain branches with the corresponding raise in molecular weight. The development of metallocene catalysts in the field of polyolefins enabled the production of ethylene and propylene copolymers with homogeneous comonomer distribution, different comonomer concentration and narrow polydispersities, allowing the synthesis of new polymers with a wide range of applications. The response of these novel materials to radiation is varied and subject of current research. In the course of this presentation recent studies of our group on this area will be presented and discussed.