The crystallization of oxyethylene/oxybutylene (E/B) diblock copolymer
s has been studied by simultaneous SAXS and WAXS. The copolymers cryst
allized from their melts (disordered, lamellar, or hexagonal) with fol
ded E blocks. Rapid crystallization (quench) of lamellar melts was acc
ompanied by a change in length scale and led to structures with multip
ly-folded E blocks and the B blocks slightly stretched from their melt
conformation. Quenching the hexagonal melts gave no change in length
scale and led to structures with multiply-folded E blocks and the B bl
ocks unstretched from their melt conformation. These metastable folded
structures formed during rapid crystallization did not unfold on heat
ing but could be self-seeded to grow equilibrium once-folded (or multi
-folded) structures. The folded states are discussed in terms of contr
ibutions to the Gibbs energy of crystallization from E-block folding a
nd B-block stretching.