ABSTRACT
Polymers and copolymers in this group have unsaturated the chain backbones; most result from polymerization of a 1,4-diene [1], such as 1,4-butadiene or isoprene (2-methyl-1,4-butadiene). This produces a polymer with a double bond between the second and third carbons of the repeat unit:
where X may be a hydrogen atom, a methyl group, or a chlorine atom. Polynorbomene {VI-B-6}:
is formed by a ring-opening methathesis polymerization (ROMP) [2]. The monomer units in these elastomeric polymers can occur in either cis-or trans-configurations; the polymers may be predominantly cis-, predominantly trans-, or a mixture. Polybutadiene (PBd) (see Structure A with X= H) {VI-A-l, VI-A-lH, VI-A-2, VI-A-2H} is often blended with synthetic or natural rubber to improve wear resistance. cis-Polyisoprene (see Structure A with X= CH3) {VI-B-1, VI-B-lH} is chemically identical to the most prevalent type (hevea) of natural rubber; trans-polyisoprene {VI-B-2, VI-B-2H} is similar to less common natural forms (balata or gutta percha). Polychloroprene (see Structure A with X = Cl) {VI-B-5, VI-B-5H}, a synthetic material, is employed when improved chemical resistance is needed [1]. The 13C chemical shifts for some common polydienes are summarized in Table VI-1.
