Stereoregularity of fractionally crystallized poly(propylene oxide) samples by 13C-NMR spectroscopy

Several stereoregular poly(propylene oxide) (PPO) samples were synthesized employing either trimethyl aluminum hydrolyzates or Pruitt–Baggett type catalysts. Dilute isooctane solutions of these samples were fractionally crystallized by stepwise cooling from 333 K down to 273 K. The fractions which dissolve at 273 K were noncrystallizable and were further fractionated by GFC. The isolated fractions were characterized by ¹³C-NMR, DSC, and viscometry techniques. Both structural (head-to-head and tail-to-tail linkages) and steric (syndiotactic dyads) irregularities were found in otherwise isotactic chains and their abundance apparently increased as the melting point and the chain length of the fractions decreased.