Lamella-to-Lamella Transition and Effect of Coil-Stretching on Crystallization in a Rod−Coil Diblock Copolymer Containing Poly(ϵ-caprolactone)

Abstract

We have studied the phase properties of a diblcok copolymer poly(ϵ-caprolactone)-block-poly(2,5-bis[4-methoxyphenyl]oxycarbonyl)styrene) (PCL-b-PMPCS) with a PMPCS volume fraction of ∼59%. The mesogen-jacketed liquid crystalline (LC) PMPCS block was amorphous in the as-cast films; and would transform into a columnar (Φ) LC phase upon the first heating and thereafter serve as rod in the copolymer studied. On the basis of simultaneous measurement of small- and wide-angle X-ray scattering (SAXS and WAXS), we identified that the original microphase-separated lamellar morphology observed in the as-cast films with amorphous PMPCS block could evolve into a new lamellar morphology with a significantly increased long period. This lamella-to-lamella transition was triggered by the amorphous-to-LC transition and was irreversible. WAXS results revealed that the chain axes of the PCL block in crystal and the rod-like PMPCS block in Φ phase were all parallel to the microphase-separated lamellar normal. Since the melting temperature of PCL crystal was well below the glass transition temperature of PMPCS block, crystallization of the PCL block was taken place in one-dimensional confined environment. Compared with those confined by the amorphous PMPCS blocks, the PCL blocks were more stretched in the confinement constructed by the Φ phase of PMPCS blocks, and thus were crystallized faster with increased fold length. This work demonstrated a lamellar phase morphology evolution based on LC phase formation of the rod block, and also indicated an effect of the degree of coil stretching on polymer crystallization.