The helical conformation of poly(3‐methyl butene‐1)

Abstract

AbstractThe crystal structure of poly(3‐methyl butene‐1) has been investigated by X‐ray methods. The unit cell is tetragonal with a = b = 34.32 Å., c = 6.84 Å., α = β = γ = 90°, and the space group was found to be I41 cd. The experimental density, 0.91 g./ccm., agrees well with the calculated value 0.92 g./ccm., on the assumption of 64 monomeric units. The monomeric units are arranged in 16 different helices, which are of the 41 type, and which pack together in groups of four around each four‐fold screw axis of the unit cell, leading to four four‐helixclusters. The crystal structure proposed for poly(3‐methyl butene‐1) can be described as a four four‐helical cluster which exhibits a high degree of “openness”. This „openness”︁ of the structure is a consequence of the way in which the four clusters of four helices each pack together. Each cluster, however, behaves by itself very much as a distinct unit. The high melting point observed is probably a consequence of the mode of packing of the helices within this unit cell.