208 3 622 320 3 702 765 and 3 929 489 a typical example of such a photocrosslinkable polymer is the polyester prepared from diethyl p phenylenediacrylate and 1 4 bis u03b2 hydroxyethoxy cyclohexane which is comprised of recurring units of the formula str6 other particularly useful polymers of this type are those which incorporate ionic moieties derived from monomers such as dimethyl 3 3 39 sodioimino disulfonyl dibenzoate and dimethyl 5 sodiosulfoisophthalate examples of such polymers include poly 1 4 cyclohexylene bis oxyethylene p phenylenediacrylate co 3 3 39 sodioimino disulfonyl dibenzoate and poly 1 4 cyclohexylene bis oxyethylene p phenylenediacrylate co 3 3 39 sodioimino disulfonyl dibenzoate co 3 hydroxyisophthalate the novel binary acetal polymers described herein are especially useful as binder polymers that are employed in combination with diazo resins in lithographic printing plates however they are also useful in other applications such as solvent thickeners films with high tensile and shear strength and films which have a low dielectric constant they can also be used as a binder for matrices other than coatings the invention is further illustrated by the following examples of its practice 75 0 grams of airvol 523 polyvinyl alcohol were added to a closed reaction vessel fitted with a water cooled condensing column followed by the addition of 225 grams of demineralized water and 450 grams of n propanol with continual stirring the mixture was cooked at 70 u00b0 c for 20 hours after this time the temperature was adjusted to 60 u00b0 c and 6 0 grams of concentrated hydrochloric acid was added over a 2 hour period an admixture consisting of 10 91 grams of.