Crystal orientation and melting behavior of poly（e-caprolactone） in a diblock copolymer of poly（e-caprolactone）- block-poly（2,5-bis[4-methoxyphenyl]oxycarbonyl）styrene） （PCL-b-PMPCS） was investigated. The degrees of polymerization of the PCL and PMPCS block are 200 and 98, respectively. With the PMPCS in a columnar liquid crystalline phase, the diblock is rod-coil one, which exhibits a lamellar phase morphology with the PCL layer thickness of 15.2 nm. Since the glass transition temperature of PMPCS block is much higher than the melting temperature of PCL, the crystallization of PCL is in a one-dimensionally ＂hard＂ confinement environment. Mainly on the basis of two-dimensional wide-angle X-ray diffraction experiments, we identified the orientation of PCL isothermally crystallized at various crystallization temperatures （Tos）. At high Tcs （To 〉 10 ℃）, the c-axis of the PCL crystal is along the layer normal of the microphase-separated sturcture. Decreasing Tc can result in the tilting of PCL c-axis with respect to the layer normal. The lower the Tc is, the more the c-axis inclines. Meanwhile, the b-axis of PCL remains perpendicular to the layer normal. At a very low Tc of-78 ℃, the orientation of the PCL crystals is completely random. For the samples isothermally crystallized at Tc 〈 10 ℃, double melting behavior can be observed. While the low temperature endotherm reflects the melting of the crystals originally formed at the Tc applied, the high temperature one is associated with the crystals subjected to the process of recrystallization/reorganization upon heating due to the annealing effect.
Using three designed peptides with precisely-controlled charge density and three types of DNAs with different length and flexibility, the effect of charge density on the formation of PEC was studied. Highly charged（KKKK）5 interacts strongly with 21 bp ds DNA to form large complex, followed by precipitation; while the medium charged（KGKG）5 only form complex with 21 bp ds DNA at proper ＋/- charge ratios; and no prominent complex between weakly charged（KGGG）5 and 21 bp ds DNA is observed at the same conditions. Similar trend is observed when the peptides form complex with 2000 bp DNA or 21 nt ssD NA. It is also found that the complex formed by adding peptide to DNA is in random coil conformation, but the complex prepared by the inverse order is in molten globule state. Re-dissolution of the complex occurs only when DNA is added to peptides with similar or shorter length.
