Nitrogen-free compounds as adhesion promoters for silicon-based scratch-resistant coatings on polycarbonate

In a process for preparing a silicon-based scratch-resistant coating on a polycarbonate substrate comprising applying an adhesion promoter to said polycarbonate and then applying a silicon-based scratch-resistant coating thereto, the improvement wherein said adhesion promoter consists essentially of a nitrogen-free compound corresponding to formula (I) and/or a hydrolysis product or condensation product thereof

• [R1(R2)j]iSiR3k(OR4)4−k−i (I),
• wherein
• i represents the number 1, 2 or 3,
• j represents an integer from 1 to 10,
• k represents the number 0, 1 or 2,
• k+i is ≦3, and
• R1 represents OH, OR, SH, SR, OOC—R, where R represents C1-C10-alkyl or C6-C12-aryl,
• R2 is an unsubstituted, singly substituted, or doubly substituted methylene group,
• R3 is a substituted or unsubstituted C1-C10-alkyl or C6-C12-aryl group,
• R4 represents a C1-C10-alkyl or C6-C12-aryl group, and
• wherein if j represents from 2 to 10, the methylene groups in the chain may optionally be interrupted once or several times by hetero atoms.