Styrene-butadiene rubber crosslink distributions

Problem 2.37 A styrene-butadiene rubber with 23.5 mol% styrene in the polymer is vulcanized with sulfur, (a) Calculate the stress at 20% elongation of the vulcanizate in which 1.4% of the butadiene units are crosslinked. (b) What would be the corresponding stress if 2% of the butadiene units are crosslinked Assume random distribution of styrene and butadiene units in the polymer chain. [Density of vulcanizate (without filler) = 0.98 g/cm at 25°C.)... 

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