We have recently shown that Grubbs' type catalysts can be used to enable the breakdown of butyl rubber into oligomeric fragments without high energy input or elevated temperature. Before such a route can be be viable for a stage in rubber recycling it is necessary to establish the limit of minimal catalyst loading (to reduce cost) and the efficicacy of additives used to assist the breakdown of large polymers by inserting chain ends. In this proposal we build on our original chemistry and rheology by using in-situe SANS to follow the metathesis catalysed breakdown of rubbery polymers. Because ring polymers and linear polymers have slightly different structure factors, we also aim to test our original hypothesis that the breakdown product can be predominantly include ring, rather than linear polymers.