Positive-working photodefinable polyimide precursors

An acid-labile poly(amic acetal ester) (I) ##STR8## wherein the backbone polyamic acid portion of the poly(amic acetal ester) is derived from a tetracarboxylic acid dianhydride of the structure ##STR9## and a diamine of the structure B(NH.sub.2).sub.2 wherein A is a tetravalent aromatic moiety and B is a divalent aromatic moiety and the acetal ester group (E) is of the formula ##STR10## where R.sup.1 is hydrogen or C.sub.1 -C.sub.6 alkyl;

• R.sup.2 is C.sub.1 -C.sub.18 alkyl;
• and R.sup.3 and R.sup.4 independently are hydrogen or C.sub.1 -C.sub.18 alkyl where the definition of C.sub.1 -C.sub.18 alkyl includes the joining of R.sup.1 and R.sup.2 or R.sup.1 and either R.sup.3 or R.sup.4, or R.sup.2 and either R.sup.3 or R.sup.4 to form a 5-, 6-, or 7-membered ring and n is an integer from about 3 to about 90.