Blends peroxidation chain mechanism

Very recently, attempts have been made to develop PP/EOC TP Vs. In order to make TPVs based on PP/EOC blend systems, phenolic resin is ineffective because the latter needs the presence of a double bond to form a crosslinked network structure. Peroxides can crosslink both saturated and unsaturated polymers without any reversion characteristics. The formation of strong C-C bonds provides substantial heat resistance and good compression set properties without any discoloration. However, the activity of peroxide depends on the type of polymer and the presence of other ingredients in the system. It has been well established that PP exhibits a (3-chain scission reaction (degradation) with the addition of peroxide. Hence, the use of peroxide only is limited to the preparation of PP-based TPVs. Lai et al. [45] and Li et al. [46] studied the fracture and failure mechanism of a PP-metallocene based EOC based TPV prepared by a peroxide crosslinking system. Rajesh et al. 

Returning to Vollmert s patent (18), we apply the more complete spectrum of operations to his example 1. In this case butyl acrylate and acrylic acid are dissolved in acetone with azoisobutyronitrile (initiator) and dodecyl mercaptan (chain transfer agent), polymerized, and the acetone is evaporated to form polymer 1. Separately, styrene and 1,4-butanediol monoacrylate are bead polymerized with benzoyl peroxide to form polymer 2. Polymers 1 and 2 are mechanically blended with the simultaneous addition of 1,4-butanediol followed by heating to promote grafting and crosslinking. These steps can be represented in some detail by ... 

Co-reaction of blends to improve the performance has for decades been a practice in the rubber industry. In high-shear mixers some of the chains in rubbers are broken and are reformed by the free-radical mechanism. A similar phenomenon occurs during intensive mixing of polyolefins (see Table 4.34). To enhance this process, sometimes a free-radical source, e.g., peroxides, can be added. 

Kolesov, I. S., and Radusch, H. J. 2008. Multiple shape-memory behavior and thermal-mechanical properties of peroxide cross-Unked blends of Unear and short-chain branched polyethylenes. eXPRESS Polymer Letters 2 461—473. 

---