Opaque polymers

A method for forming an opaque electron-rich polymer comprising the steps: 1) Coating a substrate with an adhesive either having the structure (i) as above ,where F1 is independently selected from, sulphur, silicon, nitrogen, oxygen, phosphorous or boron containing groups and L is selected from linking groups; or is an oxysilane. 2) Applying an electron-rich polymer to the adhesive coated substrate to form an opaque electron-rich layer, the polymer having the structure (ii) wherein E is electron-rich groups and R4 is C1-4 alkanediyl, optionally substituted with one or more halides; or is absent. Step 2 is started within 30 minutes of the end of step 1) The adhesive may be (3-mercaptopropyl)triethoxysilane or preferably (3-mercaptopropyl)trimethoxysilane. The electron rich group is preferably a conjugated group, ideally an aromatic group, more preferably a benzene group and may be selected from the poly(xylylenes). The substrate may be an elastomeric polymer material which may comprise a polysiloxane. Step 1) may be carried out under vacuum at a temperature from 5-100 oC and/or for a period of at least 1.5 hours most preferably at least 2.5 hours. Step 2) may be achieved using chemical vapour deposition. Also included are claims to the product of the method and use of an adhesive for obtaining an opaque electron rich polymer layer.