Material Management without Material Masters is it possible?

Current we manage/procure materials with and without Material Masters. While we utilise a MM for items held within the Stores, the vast majority of materials purchased are through free text purchase orders, credit cards and catalogues without any sort of naming convention. Materials within our store are either linked to a contract or use of an info record and form the basis for our catalogue, MRP and PO processes. My concerns stem around all the materials without a master record. Creating a catalogue difficult to navigate, material categories/contracts difficult to scope, poor reporting and spend analysis, off contract spend and loss of buying power through purchasing de-centralisation.

Have you seen a pure external catalogue model work with SAP with/without any material master?

Any feedback or examples would be appreciated.

Regards