Erythrodisyndiotactic polymer

All four diisotactic polymers (cis and trans, erythro and threo) are chiral and possess optical activity. Each of the four disyndiotactic polymers possesses a mirror glide plane and is achiral. For symmetric 1,4-disubstituted 1,3-butadienes (R = R ), only the cis and transthreo-diisotactic structures are chiral. Each of the erythrodiisotactic and threodisyndiotactic polymers has a mirror glide plane. Each of the erythrodisyndiotactic polymers has a mirror glide plane. 

Based on the mechanisms known from a-olefin polymerization, Ci-symmetric [Ph2C(Cp)(Flu)] ZrCl2 (3, Flu = 9-fluorenyl) should produce an erythrodisyndiotactic polymer and therefore favor the formation of the rac-hydrodimer, whereas C2-symmetric rac-[Me2Si(Ind)2]ZrCl2... 

SCHEME 16.2 Stereochemistry during the polymerization of a prochiral cycloolefin such as norbornene nsing Cs- (A) and C2-symmetiic (B) catalysts. Independent of the relative topicities of the single insertion events (contrasted by pathways a and b), apphcation of the mechanisms known from a-olefin polymerization predict an erythrodisyndiotactic polymer to be formed by C -symmetric catalysts and an erythrodiisotactic polymer to be formed by C2-symmetric catalysts. 

This polymer cannot be expressed as erythrodisyndiotactic or as threodisyndiotactic. Instead ABHHHHHH AHHHHBHH... 

Explain what is meant by erythrodiisotactic, threodiisotactic and polymers. Illustrate. Do the same for erythrodisyndiotactic and threodisyndiotactic. 

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