SANS/WANS time-resolving neutron scattering studies of polymer phase transitions using NIMROD

We use new neutron scattering instrumentation to follow in a single quantitative time-resolving experiment, the three key scales of structural development which accompany the crystallisation of synthetic polymers. These length scales span 3 orders of magnitude of the scattering vector. The study of polymer crystallisation dates back to the pioneering experiments of Keller and others who discovered the chain-folded nature of the thin lamellae crystals which are normally found in synthetic polymers. The inherent connectivity of polymers makes their crystallisation a multiscale transformation. Much understanding has developed over the intervening fifty years but the process has remained something of a mystery. There are three key length scales. The chain folded lamellar thickness is ~ 10nm, the crystal unit cell is ~ 1nm and the detail of the chain conformation is ~ 0.1nm. In previous work these length scales have been addressed using different instrumention or were coupled using compromised geometries. More recently researchers have attempted to exploit coupled time-resolved small-angle and wide-angle x-ray experiments. These turned out to be challenging experiments much related to the challenge of placing the scattering intensity on an absolute scale. However, they did stimulate the possibility of new phenomena in the very early stages of crystallisation. Although there is now considerable doubt on such experiments, they drew attention to the basic question as to the process of crystallisation in long chain molecules. We have used NIMROD on the second target station at ISIS to follow all three length scales in a time-resolving manner for poly(e-caprolactone). The technique can provide a single set of data from 0.01 to 100Å-1 on the same vertical scale. We present the results using a multiple scale model of the crystallisation process in polymers to analyse the results

Ring-Opening Co- and Terpolymerization of Epoxides, Cyclic Anhydrides, and l‑Lactide Using Constrained Aluminum Inden Complexes

Seven constrained aluminum inden complexes having different substituents and diamine backbones were developed for the ring-opening copolymerization (ROCOP) of epoxides and bulky cyclic anhydrides giving alternating polyesters with Tg ranging from 49 to 226 °C. Among several catalyst/cocatalyst screenings, the aluminum inden complex having a rigid phenylene backbone coupled with 4-dimethylaminopyridine showed the best performance giving linear polyesters. In the case of cyclohexene oxide (CHO) and succinic anhydride (SA), the linear poly(CHO-alt-SA) could be transformed to cyclic polymer when the polymerization was left under prolonged reaction time to induce intramolecular transesterification. The kinetic studies of the ROCOP revealed a zeroth-order dependence on cyclic anhydride and a first-order dependence on epoxide and the catalyst. The catalysts can be extended efficiently to the one-pot CHO/PA/l-lactide terpolymerization giving uncommon tapered copolymers of poly(CHO-alt-PA) and PLA via switchable polymerization

Antioxidant and Anticancer Potential of Bioactive Compounds from Rhinacanthus nasutus Cell Suspension Culture

The potential benefits of natural plant extracts have received attention in recent years, encouraging the development of natural products that effectively treat various diseases. This is the first report on establishing callus and cell suspension cultures of Rhinacanthus nasutus (L.) Kurz. A yellow friable callus was successfully induced from in vitro leaf explants on Murashige and Skoog medium supplemented with 1 mg/L 2,4-dichlorophenoxyacetic acid and 1 mg/L 1-naphthalene acetic acid. A selected friable callus line was used to establish the cell suspension culture with the same medium. The antioxidant assays showed that the leaf- and ethanolic-suspension-cultured cell (SCC) extracts exhibited high antioxidant potential. In addition, the in vitro cytotoxicity revealed by the MTT assay demonstrated potent antiproliferative effects against the oral cancer cell lines ORL-48 and ORL-136 in a dose-dependent manner. Several groups of compounds, including terpenoids, phenolics, flavonoids, quinones, and stilbenes, were identified by UHPLC–QToF–MS, with the same compounds detected in leaf and SCC extracts, including austroinulin, lucidenic acid, esculetin, embelin, and quercetin 3-(2″-p-hydroxybenzoyl-4″-p-coumarylrhamnoside). The present study suggests the value of further investigations for phytochemical production using R. nasutus cell suspension culture

Crystal Structure and Hirshfeld Surface Analysis of Bis(Triethanolamine)Nickel(II) Dinitrate Complex and a Revelation of Its Characteristics via Spectroscopic, Electrochemical and DFT Studies Towards a Promising Precursor for Metal Oxides Synthesis

Metal complexes with chelating ligands are known as promising precursors for the synthesis of targeted metal oxides via thermal decomposition pathways. Triethanolamine (TEA) is a versatile ligand possessing a variety of coordination modes to metal ions. Understanding the crystal structure is beneficial for the rational design of the metal complex precursors. Herein, a bis(triethanolamine)nickel (II) dinitrate (named as Ni-TEA) crystal was synthesized and thoroughly investigated. X-ray crystallography revealed that Ni(II) ions adopt a distorted octahedral geometry surrounded by two neutral TEA ligands via two N and four O coordinates. Hirshfeld surface analysis indicated the major contribution of the intermolecular hydrogen-bonding between —OH groups of TEA in the crystal packing. Moreover, several O–H stretching peaks in Fourier transformed infrared spectroscopy (FTIR) spectra emphasizes the various chemical environments of —OH groups due to the formation of the hydrogen-bonding framework. The Density-functional theory (DFT) calculation revealed the electronic properties of the crystal. Furthermore, the Ni-TEA complex is presumably useful for metal oxide synthesis via thermal decomposition at a moderate temperature (380 °C). Cyclic voltammetry indicated the possible oxidative reaction of the Ni-TEA complex at a lower potential than nickel(II) nitrate and TEA ligand, highlighting its promising utility for the synthesis of mixed valence oxides such as spinel structures

Polymerization of ε‑Caprolactone Using Bis(phenoxy)-amine Aluminum Complex: Deactivation by Lactide

Polymerizations of biodegradable lactide and lactones have been the subjects of intense research during the past decade. They can be polymerized/copolymerized effectively by several catalyst systems. With bis­(phenolate)-amine aluminum complex, we have shown for the first time that lactide monomer can deactivate the aluminum complex during the ongoing polymerization of ε-caprolactone to a complete stop. After hours of dormant state, the aluminum complex can be reactivated again by heating at 100 °C without the addition of any external chemicals still giving polymer with narrow dispersity. Studies using NMR, in situ FTIR, and single-crystal X-ray crystallography indicated that the coordination of the carbonyl group in lactyl unit was responsible for the unusual behavior of lactide. In addition, the unusual methyl-migration from methyl lactate ligand to the amine side chain of the aluminum complex was observed through intermolecular nucleophilic-attack mechanism

Structure–Activity Correlation for Relative Chain Initiation to Propagation Rates in Single-Site Olefin Polymerization Catalysis

We have determined what makes the first monomer insertion (initiation) facile or slow for many homogeneous olefin polymerization catalysts. Specifically, we have developed the first comprehensive and mechanistically detailed quantitative structure–activity relationship (QSAR) that successfully predicts relative chain initiation to propagation rates for a large series of group 4 single-site olefin polymerization catalysts. This QSAR correctly predicts (a) whether initiation is facile or slow and (b) the <i>k</i>_i/<i>k</i>_p ratio for a catalyst family with slow initiation. Monomer concentration versus time profiles were measured for batch polymerization of 1-hexene catalyzed by 27 Cp′Ti­(OAr)­Me₂ and Cp*Zr­(OC₆H-2,3,5,6-Ph₄)­J₂ (J = Me, CH₂Ph) complexes activated with B­(C₆F₅)₃. Comparison of DFT calculations to experimental data revealed that the underlying cause of slow versus facile initiation is the difference in docking site opening sizes between the initiation kinetically dominant ion pair (i-KDIP) and the propagation kinetically dominant ion pair (p-KDIP). Specifically, initiation is facile if the i-KDIP and p-KDIP have similar docking site opening sizes or the i-KDIP docking site opening is not small but slow if the i-KDIP has a small docking site opening and the p-KDIP has a much larger docking site opening. The ion pairing dynamics was strongly influenced by (a) the choice of solvent, (b) whether or not the catalyst exhibits opportunistic ligand coordination, and (c) the type of initiating group. DFT-computed transition states for selected systems confirmed the underlying chemical mechanism that gives rise to this QSAR

Structure–Activity Correlation for Relative Chain Initiation to Propagation Rates in Single-Site Olefin Polymerization Catalysis

We have determined what makes the first monomer insertion (initiation) facile or slow for many homogeneous olefin polymerization catalysts. Specifically, we have developed the first comprehensive and mechanistically detailed quantitative structure–activity relationship (QSAR) that successfully predicts relative chain initiation to propagation rates for a large series of group 4 single-site olefin polymerization catalysts. This QSAR correctly predicts (a) whether initiation is facile or slow and (b) the <i>k</i>_i/<i>k</i>_p ratio for a catalyst family with slow initiation. Monomer concentration versus time profiles were measured for batch polymerization of 1-hexene catalyzed by 27 Cp′Ti­(OAr)­Me₂ and Cp*Zr­(OC₆H-2,3,5,6-Ph₄)­J₂ (J = Me, CH₂Ph) complexes activated with B­(C₆F₅)₃. Comparison of DFT calculations to experimental data revealed that the underlying cause of slow versus facile initiation is the difference in docking site opening sizes between the initiation kinetically dominant ion pair (i-KDIP) and the propagation kinetically dominant ion pair (p-KDIP). Specifically, initiation is facile if the i-KDIP and p-KDIP have similar docking site opening sizes or the i-KDIP docking site opening is not small but slow if the i-KDIP has a small docking site opening and the p-KDIP has a much larger docking site opening. The ion pairing dynamics was strongly influenced by (a) the choice of solvent, (b) whether or not the catalyst exhibits opportunistic ligand coordination, and (c) the type of initiating group. DFT-computed transition states for selected systems confirmed the underlying chemical mechanism that gives rise to this QSAR

Structure–Activity Correlation for Relative Chain Initiation to Propagation Rates in Single-Site Olefin Polymerization Catalysis

We have determined what makes the first monomer insertion (initiation) facile or slow for many homogeneous olefin polymerization catalysts. Specifically, we have developed the first comprehensive and mechanistically detailed quantitative structure–activity relationship (QSAR) that successfully predicts relative chain initiation to propagation rates for a large series of group 4 single-site olefin polymerization catalysts. This QSAR correctly predicts (a) whether initiation is facile or slow and (b) the <i>k</i>_i/<i>k</i>_p ratio for a catalyst family with slow initiation. Monomer concentration versus time profiles were measured for batch polymerization of 1-hexene catalyzed by 27 Cp′Ti­(OAr)­Me₂ and Cp*Zr­(OC₆H-2,3,5,6-Ph₄)­J₂ (J = Me, CH₂Ph) complexes activated with B­(C₆F₅)₃. Comparison of DFT calculations to experimental data revealed that the underlying cause of slow versus facile initiation is the difference in docking site opening sizes between the initiation kinetically dominant ion pair (i-KDIP) and the propagation kinetically dominant ion pair (p-KDIP). Specifically, initiation is facile if the i-KDIP and p-KDIP have similar docking site opening sizes or the i-KDIP docking site opening is not small but slow if the i-KDIP has a small docking site opening and the p-KDIP has a much larger docking site opening. The ion pairing dynamics was strongly influenced by (a) the choice of solvent, (b) whether or not the catalyst exhibits opportunistic ligand coordination, and (c) the type of initiating group. DFT-computed transition states for selected systems confirmed the underlying chemical mechanism that gives rise to this QSAR