Polyisoprene energy

These workers found that the overall rate of metalation is proportional to the polybutadiene concentration and to the square root of the n-bu-tyllithium concentration the overall activation energy of metalation was 6.6 and 8.4 kcal/mol for polybutadiene and polyisoprene, respectively. They showed that 9%, and as high as 27%, monomer units were metalated. 

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The bond dissociation energy for the a-scission is 83-94 kcal mol , and for the p-scission is 61.5 - 63 kcal mol . The radical formation is therefore more likely to occur as a p-scission. For polyisoprene decomposition, the methyl scission initiation is also possible, and the bond dissociation energy is similar to that for a-scission. For polymers with more than one methyl group, more than one type of free radical can be formed. 

Pyrolysis of polyisoprene takes place very similarly to that of polybutadiene. The p-chain scission (to the double bond) is the dominant initiation process, and the bond dissociation energy was estimated to be about 61.5-63 kcal mol V The cleavage of the carbon chain backbone has as the final result the elimination of some monomer, linear and cyclic dimers, trimers, etc. The yield of monomer depends on the heating conditions, degree of polymerization, etc. Table 2.1.1 indicates the formation of up to 58% monomer from natural rubber pyrolysis, while Table 7.1.4 shows only about 18% conversion. Some aspects regarding the thermal decomposition mechanism of polyisoprene were discussed in Section 2.1. 

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