No abstract

A new class of H-bond donating ureas was developed for the ring-opening polymerization (ROP) of lactone monomers, and they exhibit dramatic rate acceleration versus previous H-bond mediated polymerization catalysts. The most active of these new catalysts, a tris-urea H-bond donor, is among the most active organocatalysts known for ROP, yet it retains the high selectivity of H-bond mediated organocatalysts. The urea cocatalyst, along with an H-bond accepting base, exhibits the characteristics of a "living" ROP, is highly active, in one case, accelerating a reaction from days to minutes, and remains active at low catalyst loadings. The rate acceleration exhibited by this H-bond donor occurs for all base cocatalysts examined. A mechanism of action is proposed, and the new catalysts are shown to accelerate small molecule transesterifications versus currently known monothiourea catalysts. It is no longer necessary to choose between a highly active or highly selective organocatalyst for ROP.

Purpose The purpose of this paper is to investigate the knowledge existing in the literature on supply chain resilience for identifying the supply chain practices adopted for securing resilience in given uncertain event. Design/methodology/approach A systematic literature review is conducted to identify 84 conceptual and empirical studies. The research findings are synthesized in categories of uncertain events, supply chain practices and outcomes. Findings A set of propositions linking the uncertain events, mechanisms and supply chain resilience improvement is developed. It was found that the sufficient conditions for resilience under unexpected disasters are substantially different from those required for resilience against disruptions caused by internal practices or complexity. Originality/value Practitioners can benefit from the knowledge of interventions and mechanisms to improve their supply chain resilience in the face of different unpredictable situations. The contribution of this paper is twofold: first, it develops an actionable theory of supply chain resilience by developing testable propositions in the context of supply chains exposed to uncertainties resulting from unexpected disruptions, complexity of supply chains and adoption of certain internal practice; second, the paper highlights the key shortcomings of existing literature and provides opportunities for further research and improvement.

Thiourea (TU)/amine base cocatalysts are commonly employed for well-controlled, highly active “living” organocatalytic ring-opening polymerizations (ROPs) of cyclic esters and carbonates. In this work, several of the most active cocatalyst pairs are shown by 1H NMR binding studies to be highly associated in solution, dominating all other known noncovalent catalyst/reagent interactions during ROP. One strongly binding catalyst pair behaves kinetically as a unimolecular catalyst species. The high selectivity and activity exhibited by these ROP organocatalysts are attributed to the strong binding between the two cocatalysts, and the predictive utility of these binding parameters is applied for the discovery of a new, highly active cocatalyst pair.

The research in this paper is focused on enhancing existing knowledge in cost estimation models at the bidding stage of service support contracts. The difficulty of this task lies in the long lasting contracts, which in some cases may reach even 40 years. The paper first reports the existing knowledge through detailed review of literature. The paper studies different service support contracts and reports the cost modelling techniques used in availability type contracts in the context of defence and aerospace industry. The contribution of this paper is to identify the key areas of improvement and business priorities in the area of cost modelling of availability type service support contracts.