amorphous copolymers of perfluoro - 2 , 2 - dimethyl - 1 , 3 - dioxole with at least one fluoro comonomer selected from one or more of ten defined classes having a recited minimum mole proportion of perfluoro - 2 , 2 - dimethyl - 1 , 3 - dioxole , in no event less than 65 %, have high glass transition temperatures of 140 ° c . or higher , low indices of refraction , and good physical properties , and low dielectric constants , which make them suitable for cladding optical fibers as well as for many electronics applications , including the manufacture of substrates for circuit boards . they all are soluble at room temperature in perfluoro , which makes it practical to apply them as coatings from solution .