NMR determination of crystalline polymer conformation

The 31-helical,. ..tgtgtgtg... conformation is adopted by i-PP chains in all four of its crystalline polymorphs, while s-PP chains adopt the 4 -helical,. ..ttggttgg... conformation in its prevalent, most stable polymorph. Each crystalline CH2 carbon in i-PP is trans in one direction along the backbone 

Syndiotactic polystyrene (s-PS) can be crystallized into two polymorphs [26], forms I and II. The alUtrans, planar zigzag conformation is adopted by the chains in form I crystals, while in form II crystals the s-PS chains adopt the same 4i-helical. ttggttgg... conformation found for the prevalent form of crystalline s-PP. Notice the CH2 carbon resonances [26] in form II 

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