Crystallization of Molecular Brushes with Block Copolymer Side Chains

A series of three cylindrical molecular brushes with poly(epsilon-caprolactone)-b-poly(n-butylacrylate) side chains were investigated with regard to the effect of the intramolecular confinement on the crystallization behavior of the PCL core block. While the length of the PCL block was maintained (n(PCL) = 50), the degree of polymerization of the PBA corona block, prepared by atom transfer radical polymerization, was varied from n(PBA) = 0 (PCL brush) to n(PBA) = 52 and 163. The crystallization behavior of the studied polymers was shown to be different in thin films and bulk samples. In thin films, the brushlike macromolecules were fully extended and remained segregated due to the steric repulsion of the adsorbed PBA corona. Under the constraint of the backbone extension, crystallization of the PCL core led to formation of a characteristic spinelike morphology. In bulk samples, the core-shell confinement did not prohibit breakout crystallization, leading to the formation of a spherulitic morphology similar to linear and brushlike PCL. However, the crystallization process of the PCL-b-PBA brushes was significantly slower as compared to the linear and brushlike counterparts as it evolved through a transition from the molecularly segregated core-shell morphology to a lamellar organization of multiple molecules. Drawing of fibers containing nascent crystallites resulted in the final morphology composed of crystalline lamellae parallel to the fiber axis with the PCL blocks oriented perpendicular to the axis. The lamellae thickness was shown to decrease with the length of the amorphous PBA block.