Primer compositions

A primer composition which comprises

• (a) 100 parts by weight of an organopolysiloxane of substantially linear molecular structure represented by the average unit formula ##EQU4## where R.sup.1 is a substituted or unsubstituted monovalent hydrocarbon group substantially free from aliphatic unsaturation and a is a positive number in the range from 0.98 to 2.01, and having a viscosity larger than 100,000 centistokes at 25.degree. C.,
• (b) from 5 to 100 parts by weight of a vinyl-containing organopolysiloxane represented by the average unit formula ##EQU5## where R.sup.2 is a substituted or unsubstituted monovalent hydrocarbon group and b is a positive number in the range from 1.9 to 2.3, from 0.03 to 1 of the groups represented by R.sup.2 per silicon atom in a molecule being vinyl groups, and having a viscosity from 5 to 10,000 centistokes at 25.degree. C.,
• (c) from 5 to 100 parts by weight of an organopolysiloxane resin represented by the average unit formula ##EQU6## where R.sup.3 is a substituted or unsubstituted monovalent hydrocarbon group and c is a positive number in the range from 0.5 to 1.7,
• (d) from 0.5 to 200 parts by weight of an organosilane compound represented by the general formula
• R.sup.4 Si(OR.sup.5).sub.3,
• where R.sup.4 is an aliphatically unsaturated monovalent hydrocarbon group and R.sup.5 is a monovalent group selected from the class consisting of alkyl groups having 1 to 5 carbon atoms, 2-methoxyethyl and 2-ethoxyethyl groups,
• (e) from 5 to 100 parts by weight of a silica filler having a specific surface area of at least 100 m.sup.2 /g,
• (f) from 0 to 10 parts by weight of an organic peroxide, and
• (g) from 0.5 to 50 parts by weight of a condensation catalyst.