Propylene polymers are used widely throughout the world in a diverse range of applications such as agriculture, construction, fibre technology, health and hygiene, and packaging. Common propylene polymers include polypropylene and random and heterophasic polypropylene copolymer which can incorporate ethylene and possibly other comonomers.
Propylene polymers such as polypropylene are generally manufactured in large scale reactors. Depending upon their intended application, a given propylene polymer may be manufactured in different grades such that it exhibits a variety of processing properties. For example, polypropylene may be manufactured with a relatively low MFI (typically characterised by a high average molecular weight and a broad molecular weight distribution) for use in blow-moulding applications, or with a relatively high MFI (typically characterised by a lower average molecular weight and a narrower molecular weight distribution) for use in injection moulding applications.
However, there is generally insufficient flexibility in large scale manufacturing operations to prepare the numerous grades of propylene polymers required by downstream converters. Some grades of propylene polymers are therefore produced by tailored post-reactor modification processes using a base resin that is produced on mass. For example, propylene polymers such as polypropylene may be reacted with organic peroxides in a post-reactor modification melt mixing process to prepare grades of polypropylene having a higher MFI and lower polydispersity than the base resin.
The use of organic peroxides is invariably complicated by the formation of peroxide-derived by-products which can present problems due odour or toxicity and can limit the use of the product particularly in food contact applications.
While other processes have been developed for producing post-reactor modified propylene polymers, an opportunity remains to address or ameliorate one or more disadvantages or shortcomings associated with existing processes, or to at least provide a useful alternative process.