This paper addresses the risks for a main contractor firm's project business that arise from subcontractors' inter-organizational relationships in complex and dynamic project networks. Existing project risk management research neglects the management of such relational risks in networks. This paper discusses this un-researched area by analyzing triads representing sub-networks of three actors in a larger network. The empirical study employed several semi structured interviews in two global contractor organizations. Critical incidents identified in triadic settings were used to explain the logic of how risks arose from subcontractors' inter-organizational relationships. This paper identifies four categories of risk sources characterized by subcontractors' inter-organizational relationships. The four risk source categories are based on subcontractors' relationships with 1) other subcontractors, 2) the contractor's competitor 3) the contractor's client and 4) non-business actors (e.g. a local authority or regulatory body). The empirical study emphasizes the dynamic nature of the risks that business relationships cause in the main contractor's current and future projects and business. Furthermore, the empirical analysis suggests that the risks arising from subcontractors' relationships have an impact on two different layers: a) the temporary project network layer and b) the permanent business network layer. The impacts of risk on the temporary project network layer relate to specific sales and delivery projects, whereas the impacts of risk on the permanent business network layer relate often to changes in the network position of the business players. This paper suggests a novel risk management approach, where risks and opportunities arising from subcontractors' relationships are actively taken into account in subcontractor management.

Summary: The kinetic behaviour of a supported metallocene catalyst in slurry polymerisation of ethylene with 1‐hexene under industrially relevant reaction conditions has been studied. Polymerisation experiments were carried out in a 5‐litre stirred tank reactor in a temperature range from 60 to 80 °C and ethylene partial pressures from 5 to 15 bar. Comonomer and hydrogen amounts were varied as well. The catalyst showed pronounced activation and slow deactivation during runtimes of about 1 hour. Strong influences of 1‐hexene (“hexene effect”) and hydrogen (“hydrogen effect”) on the activity profiles were observed. Based on the experimental results, a kinetic model has been derived in order to describe and predict important polymerisation data such as activity profile, comonomer content and molecular weight distributions with respect to the reaction conditions. The presented kinetic model is able to describe the observed effects of 1‐hexene and hydrogen on the activity profiles, as well as the comonomer incorporation across a broad range of polymerisation conditions. The molecular weight distributions can be simulated with good qualitative agreement to the experimental data.

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