Effects Of Chain-Ends Tethering On The Crystallization Behavior Of Poly(Epsilon-Caprolactone) Confined In Lamellar Nanodomains

We have investigated the effects of chain-ends tethering at nanodomain interfaces on the crystallization behavior of poly(e-caprolactone) (PCL) chains spatially confined in lamellar nanodomains. The PCL chains tethered at both chain-ends (T2-PCL), one chain-end (T1-PCL), and no chain-end (i.e., PCL homopolymers) (T0-PCL) were prepared from polystyrene-block-PCL-block-polystyrene (PS-b-PCL-b-PS) triblock copolymers having a photodeavable o-nitrobenzyl (ONB) group at either or both of block junctions. The lamellar nanodomain was provided by the microphase separation of PS-b-PCL-b-PS copolymers, in which T2-PCL was inherently confined. Subsequently, the ONB group was cleaved by the irradiation of ultraviolet light to yield T1-PCL or T0-PCL from T2-PCL without perturbing the lamellar nanodomain. T2-PCL showed an extremely low melting temperature and crystallinity as compared with T1-PCL and T0-PCL, indicating that the crystallization was significantly affected by chain mobility imposed by chain tethering at both ends to yield immature PCL crystallites. All the PCL chains exhibited a sigmoidal time evolution of crystallinity during isothermal crystallization, implying that their crystallization was driven by a conventional nucleation and growth mechanism. However, the crystallization rate at a same temperature depended largely on the state of chain tethering; T0-PCL crystallized moderately faster than T1-PCL, whereas T2-PCL crystallized extraordinarily slower than T1-PCL. The crystallization kinetics of these PCL chains confined in lamellar nanodomains is qualitatively discussed.