about 40 000 the radiation sensitive a group should be present to the extent of from 1 unit for 20 ch 2 o units especially in low molecular weight polymers to 1 for 1000 ch 2 o units preferably 1 unit per 100 500 formaldehyde units the concentration of the a groups can be conveniently determined by ultraviolet spectroscopy using the molar extinction coefficient of the aromatic substituents which can be obtained from the dioxane or dioxolane starting materials or their glycol antecedents for o nitrophenyl groups a band at 267nm is employed having an extinction coefficient u03b5 4 500 transparent films of the intercalated polymers can be obtained by melt pressing the polymer at elevated temperatures preferably 170 u00b0 180 u00b0 c at 300 2000 psi precautions should be taken to prevent exposure of the polymer to air at these elevated temperatures to prevent oxidation and formation of bubbles additions of known antioxidants or thermal stabilizers to prevent chemical or physical decomposition during the molding operation is sometimes desirable films of the polymers may also be obtained by solution casting the novel 1 3 dioxolanes and 1 3 dioxanes required as starting materials for the intercalated polymers are prepared from the corresponding glycols by procedures well known in the art for example reaction of the glycol with an aldehyde or ketone in the presence of an acid catalyst preferably in an inert solvent readily gives the corresponding 1 3 dioxolane or dioxane i e str8 excess aldehyde or ketone may be employed to force the reaction to completion alternatively the water formed in the reaction may be removed by azeotropic distillation.