Tailored rheology of a metallocene polyolefin through silane grafting and subsequent silane crosslinking

Polymer modification through silane grafting and its subsequent crosslinking allows the rheological properties of a polymer to be tuned from those of a viscous melt to those of a crosslinked elastic network. In this study, a metallocene polyolefin resin is grafted with vinyl trimethoxy silane (VTMS) using dicumyl peroxide (DCP) as the initiator and is subsequently crosslinked in an oxidative environment. Dynamic rheological experiments are conducted to elucidate the effects of DCP and VTMS concentrations on the grafting and ensuing crosslinking processes. We find that the addition of VTMS alone to the polymer produces no grafting. In contrast, the presence of DCP by itself leads to direct crosslinking between polymer chains as suggested by an increase in elastic modulus and complex viscosity. Samples containing both DCP and VTMS undergo silane grafting, with the extent of grafting increasing with increasing DCP concentration. This conclusion is borne out by both rheological and Fourier transform infrared measurements. The grafted samples undergo silane crosslinking only in an oxidative environment and at temperatures equal to or greater than 190 °C. During crosslinking, the samples undergo a transition from a viscous melt with frequency‐dependent moduli to a gel exhibiting frequency‐independent moduli with the elastic modulus exceeding the viscous modulus. However, the kinetics of crosslinking and the extent of the modulus increase are a function of the DCP concentration, with both exhibiting a maximum at a specific DCP and VTMS combination. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2468–2479, 2000     

Catastrophe Theory Applied to Neuropsychological Data: Nonlinear Effects of Depression on Financial Capacity in Amnestic Mild Cognitive Impairment and Dementia

Financial incapacity is one of the cognitive deficits observed in amnestic mild cognitive impairment and dementia, while the combined interference of depression remains unexplored. The objective of this research is to investigate and propose a nonlinear model that explains empirical data better than ordinary linear ones and elucidates the role of depression. Four hundred eighteen (418) participants with a diagnosis of amnestic MCI with varying levels of depression were examined with the Geriatric Depression Scale (GDS-15), the Functional Rating Scale for Symptoms of Dementia (FRSSD), and the Legal Capacity for Property Law Transactions Assessment Scale (LCPLTAS). Cusp catastrophe analysis was applied to the data, which suggested that the nonlinear model was superior to the linear and logistic alternatives, demonstrating depression contributes to a bifurcation effect. Depressive symptomatology induces nonlinear effects, that is, beyond a threshold value sudden decline in financial capacity is observed. Implications for theory and practice are discussed.     

Towards a Stronger Halogen Bond Involving Astatine: Unexpected Adduct with Bu3PO Stabilized by Hydrogen Bonding

The halogen bond is a powerful tool for the molecular design and pushing the limits of its strength is of major interest. Bearing the most potent halogen-bond donor atom, astatine monoiodide (AtI) was recently successfully probed [Nat. Chem. 2018 , 10, 428–434]. In this work, we continue the exploration of adducts between AtI and Lewis bases with the tributylphosphine oxide (Bu₃PO) ligand, revealing the unexpected experimental occurrence of two distinct chemical species with 1:1 and 2:1 stoichiometries. The 1:1 Bu₃PO⋅⋅⋅AtI complex is found to exhibit the strongest astatine-mediated halogen bond so far (with a formation constant of 10^(4.24±0.35)). Quantum chemical calculations unveil the intriguing nature of the 2:1 2Bu₃PO⋅⋅⋅AtI adduct, involving a halogen bond between AtI and one Bu₃PO molecular unit plus CH⋅⋅⋅O hydrogen bonds chelating the second Bu₃PO unit.     

The influence of monomer chemistry on radical formation and secondary reactions during electron-beam polymerization

The vast majority of industrial electron-beam (EB) polymerizations are initiated via radical mechanism. Because radicals drive EB polymerization, understanding their formation and secondary reactions can provide insight into polymerization kinetics and property development. Primary and initiating radicals were quantified by measuring G(R^•) and G(M^•) , respectively, for various acrylate and methacrylate monomers. Monomer chemistry was shown to impact primary radical formation; however, increased primary radical concentration did not necessarily correlate to increased conversion. Despite exhibiting high values of G(R^•) , methacrylates achieved very little conversion and had G(M^•) values near zero. Acrylates achieved much higher G(M^•) values and rates of polymerization compared to their methacrylate counterparts. Additionally, the efficiency of primary radicals converting to initiating radicals, f(M^•) , for each acrylate monomer was shown to be a good predictor of the amount of gel fraction formed during polymerization. Understanding radical formation and secondary radical reactions can help guide the structure/processing conditions/properties relationships that are currently underdeveloped for EB reactions.     

Sequential Formation of Heteroternary Cucurbit[10]uril (CB[10]) Complexes

The globular and monocationic guest molecule trimethyl-azaphosphatrane ( AZAP , a protonated Verkade superbase) was shown to form a host:guest 1 : 1 complex with the cucurbit[10]uril (CB[10]) macrocycle in water. Molecular dynamics calculations showed that CB[10] adopts an 8-shape with AZAP occupying the majority of the internal space, CB[10] contracting around AZAP and leaving a significant part of the cavity unoccupied. This residual space was used to co-include planar and monocationic co-guest ( CG ) molecules, affording heteroternary CB[10]⋅ AZAP ⋅ CG complexes potentially opening new perspectives in supramolecular chemistry.