Process for the manufacture of a substrate made of transparent organic glass and substrate thus obtained

Process for the manufacture of an optical or ophthalmic item comprising a substrate made of transparent organic glass, which comprises:

• 1) partially polymerizing a polymerizable composition in order to form a prepolymer;
• 2) bringing at least one surface of the prepolymer into contact with a polymerization inhibitor and diffusing the polymerization inhibitor into the prepolymer in order to form at least one inhibited thin surface layer in the prepolymer, having a thickness of 30 to 200 .mu.m;
• and
• 3) resuming the polymerization of the prepolymer in order to obtain the substrate made of transparent organic glass containing at least one thin surface layer having a thickness of 30 to 200 .mu.m polymerized to a degree of progression which is significantly lower than that of the remainder of the substrate.

Process for the manufacture of an optical or ophthalmic item comprising a substrate made of photochromic transparent organic glass which comprises:

• producing a substrate by a method which comprises:
• (a) introducing into a mould a composition which is polymerizable into a transparent organic glass;
• and
• (b) polymerizing the composition under conditions such that the resulting substrate made of transparent organic glass has at least one thin surface layer polymerized to a degree of progression and/or of crosslinking which is appreciably lower than that of the remainder of the substrate
• bringing at least the surface adjacent to the thin surface layer with a lower degree of progression and/or of crosslinking into contact with a photochromic substance and diffusing the said photochromic substance into the said thin surface layer.