Crystallization Behavior and Crystal Orientation of Poly(ε-caprolactone) Homopolymers Confined in Nanocylinders: Effects of Nanocylinder Dimension

Abstract

The crystallization behavior and crystal orientation of poly(ε-caprolactone) (PCL) homopolymers and PCL blocks spatially confined in identical nanocylinders have been investigated using differential scanning calorimetry (DSC) and two-dimensional wide-angle X-ray diffraction (WAXD) as a function of cylinder diameter D. The PCL homopolymers confined in nanocylinders were prepared using microphase separation of PCL-block-polystyrene (PCL-b-PS) copolymers with a photocleavable o-nitrobenzyl group (ONB) between PCL and PS blocks and the subsequent cleavage of ONB by irradiating UV light. The time evolution of PCL crystallinity χ PCL showed a first-order kinetics for both PCL blocks and PCL homopolymers confined in all the nanocylinders investigated. However, the D dependence of crystallization rates for PCL blocks was more drastic than that for PCL homopolymers, and consequently various Ddependent interrelations were observed between crystallization rates of PCL blocks and PCL homopolymers. The crystal orientation was also dependent on D; the b-axis of PCL crystals oriented parallel to the cylinder axis both for PCL blocks and PCL homopolymers confined in the nanocylinder with D = 13.0 nm, whereas the (110) plane of PCL crystals was normal to the cylinder axis in the nanocylinders with D ≥ 14.9 nm. The difference in the degree of crystal orientation was not detected between PCL blocks and PCL homopolymers confined in nanocylinders with D ≥ 14.9 nm.

Crystallization of polymer chains confined in nanodomains

“…12), whereas it improves slightly for PCL blocks, yielding a moderate difference in the degree of crystal orientation at higher T c -->(>À45°C) between PCL blocks and PCL homopolymers. This difference in the degree of crystal orientation reduces between PCL blocks and PCL homopolymers with increasing D PCL , which will be intimately related to the crystal growth direction in each nanocylinder [76].…”

“…Thus, we could prepare block chains and homopolymers both confined in identical nanospheres, nanocylinders, or nanolamellae (Fig. 9), and examined the substantial difference in crystallization behavior and crystal orientation between them as a function of nanodomain shape, size, or crystallization temperature [74][75][76][77][78]. …”

“…By using the method described above, we prepared PCL blocks and PCL homopolymers both confined in identical nanospheres or nanocylinders provided by the microphase separation of PCL-b-PS copolymers [74][75][76][77], where the vitrification of PS blocks prevented macrophase separation between PCL and PS homopolymers after photocleaving ONB. The crystallization behavior and crystal orientation were examined as function of nanodomain size and crystallization temperature to clarify the effects of chain confinement on the crystallization.…”

“…The crystal orientation of PCL blocks and PCL homopolymers confined in identical nanocylinders was also examined as a function of D PCL [76], and results are schematically summarized in Fig. 11, where the crystal orientation depends significantly on D PCL ; when D PCL is small ($13.0 nm), the b-axis of PCL crystals (i.e., fastest growth axis) is oriented parallel to the long axis of nanocylinders both for PCL blocks and PCL homopolymers, namely, PCL crystals predominantly grow one-dimensionally in smaller nanocylinders (Fig.…”

Effect of block asymmetry on the crystallization of double crystalline diblock copolymers

“…3 The crystallization of diblock copolymer with one crystallizable block has been extensively studied in last few decades. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] However, the complexity associated with the crystallization of double crystalline diblock copolymer is poorly understood. In crystallinecrystalline diblock copolymer, the final crystal morphology is driven by the competition between two blocks towards crystallization along with microphase separation.…”