Polyolefins radiation polymerization

NABLO, SAM V. RANGWALLA, IM J. WYMAN, JOHN E. Electron-Initiated Graft Modification of Polyolefins. Radiation Curing of Polymeric Materials, ACS Symposium Series 417, American Chemical Society, Washington, DC (1990) 534-551. 

Thus the incorporation of polyfunctional monomers in polyolefins, followed by radiation polymerization, can improve properties, lower the dose for gelation, or minimize degradation, depending on the polymer. It should be pointed out that a major use of the materials described here is as insulators for electrical wires and cables (Nicholl, 1969). 

Polycondensation pol5mers, like polyesters or polyamides, are obtained by condensation reactions of monomers, which entail elimination of small molecules (e.g. water or a hydrogen halide), usually under acid/ base catalysis conditions. Polyolefins and polyacrylates are typical polyaddition products, which can be obtained by radical, ionic and transition metal catalyzed polymerization. The process usually requires an initiator (a radical precursor, a salt, electromagnetic radiation) or a catalyst (a transition metal). Cross-linked polyaddition pol5mers have been almost exclusively used so far as catalytic supports, in academic research, with few exceptions (for examples of metal catalysts on polyamides see Ref. [95-98]). 

This volume is including information about thermal and thermooxidative degradation of polyolefine nanocomposites, modeling of catalytic complexes in the oxidation reactions, modeling the kinetics of moisture adsorption by natural and synthetic polymers, new trends, achievements and developments on the effects of beam radiation, structural behaviour of composite materials, comparative evaluation of antioxidants properties, synthesis, properties and application of polymeric composites and nanocomposites, photodegradation and light stabilization of polymers, wear resistant composite polymeric materials, some macrokinetic phenomena, transport phenomena in polymer matrix, liquid crystals, flammability of polymeric materials and new flame retardants. 

It Is known that most radiation Initiated polymerization processes are Initiated by Che free radicals created by radlolysls of Che monomers. If a monomer or a mixture of monomers Is Irradiated In Che presence of a polymer, a graft copolymer Is formed which has different physical properties. For example. If a second polymer like polyacrylonitrile or polyvlnylldlne chloride, which possess superior barrier properties against permeation by oxygen, carbon dioxide, water vapor etc.. Is grafted to a polyolefin film like polyethylene, polypropylene, etc., the barrier properties of the composite film are greatly enhanced compared with Che polyolefin film. 

The monomer chosen for this demonstration was acrylonitrile. It Is compatible with the hydrolyzed vinyl benzyl amine silane primer In methanol, and will polymerize and copolymerize with moderate doses of electron beam energy. This study was designated to demonstrate the effectiveness of the new process In radiation grafting of acrylonitrile onto polyolefin films. 

This preliminary study has shown that radiation initiated graft polymerization and co-polymerizatlon on a polyolefin film surface can be achieved using the above described process with electron initiation. This process can be employed with a wide range of monomers. ... 

As all polyolefins, polyethylene is sensitive to UV radiation, although less than polypropylene. For outdoor use polyethylene needs special stabilization against UV light. The light stabilizers for polyethylene are in principle the same as for polypropylene. On accelerated weathering, HALS show much better performance in HDPE tapes than UV absorbers, despite the latter being used in much higher concentrations. The comparison between HALS is, however, in favor of the polymeric HALS-III, which has the same performance when added at a concentration of 0.05% as HALS-I and HALS-II at 0.1%. 

Several ofher cross-linking methods can be applied. For example, acrylonitrile, methyl methacrylate (MMA), and its EO derivatives can be copolymerized and then cross-linked with diisocyanate. A thin gel membrane can be prepared by soaking a polyolefin nonwoven fabric in a solution of reactant(s), which is fhen cross-linked by means of ultraviolet radiation. The thickness of fhis fhin gel membrane is 50-100 pm, and the ionic conductivity is 2-4 X 10 3 S/cm. Compared to the gel polymer electrolyte made from dry PAN, fhis process is much simpler, and the energy consumption is 10% lower. However, there are also disadvantages. For example, imreacted monomer and residual catalyst are difficult to remove from the gel polymer electrolyte, leading to reduced ionic conductivity and stability of the polymer. To overcome these disadvantages, the acrylonitrile monomer is first polymerized in nonaqueous electrolyte, and then the unreacted monomer is removed by vacuum. Finally, a multifunctional monomer is added, and the battery is filled with the mixed solution. It is solidified by heating to get the gel polymer electrolyte. 

Much has been written about the effects of ultraviolet (UV) radiation on polymeric material and in particular polyolefins. While UV radiation still comprises a relatively small portion of the total radiation found in sunlight that reaches the earth s surface, the acceleration of the deterioration in the earth s ozone layer over the last several decades dictates that subsequently outdoor durables will be exposed to even higher doses of UV radiation than previously realized. 

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