Crystallization behavior and chain folding manner of cyclic, star and linear poly(tetrahydrofuran)s

The number of crystalline stems per molecule was estimated for cyclic, star and linear poly(tetrahydrofuran)s (PTHF) with relatively small molecular weights Mn of 3000-10,000 (in the star, Mn of arm chains), by comparison between experimental crystalline thickness and calculated crystalline stem length. The number of stems in cyclic PTHF was only even numbers, 2 and 4, depending on the molecular weight, as expected, while 2, 3 and 4 for linear PTHF. For the star polymers, the number of stems obtained experimentally deviated from integral stem numbers in the lower molecular weights. The number of chain folds per molecule was estimated for cyclic polymers, and it was concluded that the molecular arrangement was not monolayer but bilayer structure for the cyclic polymer having four folds. Nucleation was much enhanced for cyclic and star PTHFs, while their growth rates of spherulites were reduced. Equilibrium melting temperature was lower for the cyclic than for the star and linear. The reduced growth rate for cyclic PTHF was attributed to the restricted molecular arrangement into the lamella including the amorphous part, based on the results for the folding manner and the melting temperature. In the blends of star and linear PTHFs, nucleation was much enhanced in the star-rich compositions, while the spherulite growth rate varied linearly with the blend composition.