Phase and crystallization behaviors determined by self-organization, crystallization, and vitrification in crystalline-amorphous diblock copolymers

The phase behavior of diblock copolymers has been one of the most active research topics in polymer physics in the past twenty years. Poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymer has been chosen as a model compound to investigate the phase and crystallization behaviors of crystalline-amorphous diblock copolymers. PEO is crystallizable with an equilibrium melting temperature ($T°m$) ∼ 68.9°C, and PS is amorphous with a glass transition temperature (T_g) ∼ 100°C. By careful macromolecular design and control, it is possible to study phase relationships among self-organization, crystallization, and vitrification by controlling three temperature parameters, i.e., the order-disorder transition temperature of the diblock copolymer ( T_ODT), the crystallization temperature of the crystallizable block (T_c), and the glass transition temperature of the amorphous block ($Tag$).; In a PEO-b-PS (11.0k–5.2k) diblock copolymer, the T_ODT is determined to be below the glass transition temperature of the PS-rich phase ($TPS-richg$ = 44.0°C), and thus crystallization of the PEO blocks takes place from the disordered state. Using time-resolved simultaneous small angle X-ray scattering (SAXS) and wide angle X-ray diffraction (WAXD) techniques, it has been found: (1) when $Tc>TPS\; -richg$, the initial composition-fluctuation-induced disordered phase morphology is destroyed by the crystallization of the PEO blocks to form a crystalline lamellar structure; (2) when the T_c is near the $TPS-richg$, although the PS-rich phase has become almost hard solid, the PEO crystallization can still manipulate the phase morphology by gradually expanding the phase morphology; and (3) when , the crystallization becomes constrained by the vitrification of the PS-rich phase. Overall crystallization rate, crystal melting behavior, and overall crystallinity results further confirm the competition between crystallization and vitrification at different temperature regions.; In a lamellar-forming PEO-b-PS (8.7k–9.2k), the $TPSg$ is determined to be 62°C, and the $TPEOm$ is ∼51°C for T_c < 40°C. The T_ODT of this diblock copolymer is determined by SAXS to be 160°C. The PEO blocks thus crystallize within a lamellar confined environment between two PS layers. The crystal (the c-axis) orientation shows changes from random to perpendicular to the lamellar surface normal (nˆ), to inclined, and finally to parallel to nˆ, solely depending upon increasing T_c. An analysis of the mean crystallite size shows that the crystal growth changes from one-dimensional (1D) to two-dimensional (2D) with increasing T_c. It is observed by time-resolved simultaneous 2D SAXS and WAXD that the specific crystal orientation is formed in an early stage (crystallinity less than 5 wt%) of the crystallization of the PEO blocks. Self-seeding experiments show that the specific crystal orie...