CHAIN FOLDING IN CRYSTALLIZABLE BLOCK-COPOLYMERS

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.