Organocatalyzed chemoselective ring-opening polymerizations

Abstract

A novel metal-free and protecting-group-free synthesis method to prepare telechelic thiol-functionalized polyesters is developed by employing organocatalysis. A scope of Brønsted acids, including trifluoromethanesulfonic acid (1), HCl.Et2O (2), diphenyl phosphate (3), γ-resorcylic acid (4) and methanesulfonic acid (5), are evaluated to promote ring-opening polymerization of ε-caprolactone with unprotected 6-mercapto-1-hexanol as the multifunctional initiator. Among them, diphenyl phosphate (3) exhibits great chemoselectivity and efficiency, which allows for simply synthesis of thiol-terminated poly(ε-caprolactone) with near-quantitative thiol fidelity, full monomer conversion, controlled molecular weight and narrow polydispersity. Kinetic study confirms living/controlled nature of the organocatalyzed chemoselective polymerizations. Density functional theory calculation illustrates that the chemoselectivity of diphenyl phosphate (3) is attributed to the stronger bifunctional activation of monomer and initiator/chain-end as well as the lower energy in hydroxyl pathway than thiol one. Moreover, series of tailor-made telechelic thiol-terminated poly(δ-valerolactone) and block copolymers are efficiently generated under mild conditions.

Layer dependent antiferromagnetism in the Sr4Ru3O10 ruthenate at the metamagnetic-like transition

“…If the magnetic coupling in the ab plane was of ferromagnetic nature, then the magnetic contribution to the Bragg reflections would be comparable for the 004 and for the 002 reflection since for ferromagnetic modes in the ab plane (irreducible representations 3 and 4, see Table T1 and T2) the magnetic structure factor would be modulated with l according to the periodic form cos[lπ(z1+z2)]*cos[lπ(z1-z2)]. Our measurements i zero field ( Figure 2) show however that this is not the case, on the contrary at around T* the reflection 002 is much more intense than the 004 which is in fact vanishing, and this difference is well beyond the attenuation of the magnetic scattering by the magnetic form factor at these two close scattering vectors [20]. propagation vector k = (0,0,0), calculated with BasIreps.…”

“…Given the diversity of the inner and outer ruthenium atoms, we can speculate that the different sites be responsible for the two observed transitions at TC=105 K and at T*=50K. In a recent report [20], neutron scattering experiments have been able to ascertain the presence of a magnetic signal in the ab plane about T*, based on the observation of additional intensity in the 002, 006 and 008 reflections. The hyphothesis of a ferromagnetic axis sligtly tilted in the ab-plane at around T* has been put forward to explain the occurrence of magnetism in the ab plane, however no explanation has been provided for the absence of the 004 reflection.…”

“…The clear anomaly at T*=50 K that we observed in the temperature dependence of the Bragg peaks [17] was not interpreted in terms of an additional magnetic phase due to the absence of convincing magnetic signal in the ab plane within our experimental conditions. More recently, the hyphothesis of a ferromagnetic component in the ab-plane at around T* has been put forward by Zhu and collaborators, based on the observation of a sizable neutron magnetic scattering in the ab plane [20]. However the proposed model does not fit entirely our previous experimental observations [17], especially the lack of intensity in some specific reflections.…”

Resolving 500 nm axial separation by multi-slice X-ray ptychography

“…For general sample systems where different elements are not separated in the beam propagation direction, the decoupling of low-spatial-frequency features would rely on choosing the proper imaging mechanisms available in the multi-modality measurement scheme that best represents the structural properties of the sample. For example, the smallangle-scattering signal can be used for distinguishing materials with similar texture and electron density (Liebi et al, 2015;Zhu et al, 2018), and the Bragg diffraction can select crystal grains with different orientations (Huang et al, 2015b;Yau et al, 2017). Meanwhile, recent algorithm development shows that combining multi-slice ptychography with tomography and exploiting the redundant measurements at different angles helps the decoupling of low-spatial-frequency features.…”

Synthesis, characterization and sustainable drug release activity of drug bridged diblock copolymer

“…Terzopoulu et al [3] reported the ROP of CL using SO as a catalyst and initiator. Similarly, other novel initiators such as benzylalcohol [4,5], gelatin [6], lipase [7], mercaptohexanol [8], diethyleneglycol [9], bisphenolate ligand [10] and mPEG [11] were used for the ROP of CL. Due to the bio-degradability and bio-compatibility of PCL, it is used as a drug carrier material.…”