Thermoplastic elastomers free radical copolymerization

Free radical copolymerization is used to produce ionomers that are used commercially as thermoplastic elastomers. There are two types of TPE ionomers copolymers of ethylene and methacrylic acid, and copolymers of ethylene and acrylic acid. The mole fraction of the acid monomer is typically 5% or less. The property difference between the two types of copolymers is... 

Ethylene can be free radically copolymerized with vinyl acetate. Copolymerization with 0%-35% vinyl acetate is carried out in bulk at 1000-2000 bar, that of 35%-100%at 100-400 bar in /-butanol, and that of 60%-100%at 1-200 bar in emulsion. Products with vinyl acetate contents of over 10% give shrinkable films those with up to 30% vinyl acetate give thermoplastic films, and those with over 40% vinyl acetate give clear films. Products of still higher vinyl acetate content are elastomers, fusion, and solvent adhesives or modifiers for PVC. The products can be cross-linked with lauroyl peroxide on the addition of, for example, triallyl cyanurate. Copolymers of ethylene and ethyl acrylate have similar properties. 

Ethylene reacts by addition to many inexpensive reagents such as water, chlorine, hydrogen chloride, and oxygen to produce valuable chemicals. It can be initiated by free radicals or by coordination catalysts to produce polyethylene, the largest-volume thermoplastic polymer. It can also be copolymerized with other olefins producing polymers with improved properties. Eor example, when ethylene is polymerized with propylene, a thermoplastic elastomer is obtained. Eigure 7-1 illustrates the most important chemicals based on ethylene. 

Before BASF investigated this product, Quirk and Hsieh [1], Yuki and coworkers [2,3] and Fischer [4] carried out investigations with this monomer. The first two used the anionic polymerization mechanism and Fischer tried to copolymerize this monomer using free radical polymerization. In the latter case the yields were very low. The use of S/DPE blocks in thermoplastic elastomers [5] has also been briefly described. Some of the work carried out at BASF has been published in a recent review article [6], Owing to the enhanced thermal properties of this copolymer in comparison with atactic polystyrene - the glass transition temperature increases up to 180 °C, depending... 

Other commercial fluoropolymers (all made by free-radical mechanisms) include polychlorotrifluoroethylene (Kel-F), which is similar to PTFE but which can be moulded at temperatures 300 °C. Polyvinylidene difluoride (PVDF) is a thermoplastic (T 160°C) and films of this material show piezoelectric behaviour. When copolymerized with hexafluropropene a very chemically resistant elastomer is obtained (Viton). Polyvinylfluoride (PVF) is another highly crystalline polymer (T 197°C) which is used for high-performance protective coatings. 

---