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Which polymer is the main chemical constituent of natural rubber?

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The main chemical constituent of natural rubber is polyisoprene.

Specifically, natural rubber consists almost exclusively of the cis-1,4 isomer of polyisoprene, which is a polymer of isoprene (C₅H₈). This material is classified as an elastomer—a rubbery polymer capable of recovering its original shape after being stretched—and is produced in the latex of certain plants, most notably the rubber tree (Hevea brasiliensis).123