Acetal copolymers and use thereof in photosensitive compositions

A polyvinyl acetal copolymer comprising at least one unit of A, at least one unit of B, at least one unit of C and at least one unit of D wherein A is present in an amount of about 0.5 to about 20 weight percent and has the formula

• wherein R is hydrogen or C1-C6 alkyl;
• B is present in an amount of about 10 to about 35 weight percent and has the formula
• C is present in an amount of about 10 to 55 weight percent and has the formula
• wherein R1 is an unsubstituted alkyl groups with up to 4 carbons, an alkyl group with up to four carbons substituted by an acid group, a phenyl group to which an acid group is attached, a phenyl group to which an acid group is attached wherein the phenyl group comprises up to two further substituents selected from the group consisting of halogen, amino, methoxy, ethoxy, methyl and ethyl, or R1 is a group X—NR2—CO—Y—COOH wherein X is an aliphatic, aromatic or an araliphatic spacer group, R2 is hydrogen or an aliphatic, aromatic or araliphatic moiety and Y is a saturated or unsaturated acyclic or cyclic spacer group;
• D is present in an amount of about 5 to about 45 weight percent and has the formula
• wherein each Z is independently selected from the group consisting of O, S and NR5 wherein R5 is selected from the group consisting of hydrogen, C1-C4 alkyl, phenyl and phenyl substituted with up to two substituents selected from the group consisting of halogen, C1-C4 alkoxy and C1-C4 alkyl, R3 and R4 are independently selected from the group consisting of C1-C4 alkyl, phenyl and phenyl substituted with up to two substitutents selected from the group consisting of halogen, C1-C4 alkoxy and C1-C4 alkyl, and wherein m is 0, 1 or 2 and n is 0, 1, 2 or 3 each A being the same or different, each C being the same or different and each D being the same or different.