TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The polymer composition further contains photo-acid generator. Preferred Position: The alkenyl group in the component (a) exists in the terminal of molecule. Preferred Components: The alkenyl group in the component (a) is allyl group. The hydrolyzable silyl group in the component (b) is alkoxy silyl group. The component (c) is siloxane compound or cyclosiloxane compound. The photo-acid generator is onium salt.    TECHNOLOGY FOCUS - POLYMERS - Preferred Method: The isobutylene-type polymer (a) is manufactured by living cationic polymerization. The polymer composition is manufactured such that ratio of number of alkenyl group in component (a) and hydrosilyl group of component (c) is less than 1 to 50, ratio of number of alkenyl group in component (b) and alkenyl group in component (c) is less than 0 to 20, and ratio of number hydrosilyl group of component (c) and alkenyl group in component (b) is less than 1 to 50. EXAMPLE - 1,3,5,7-tetramethyl cyclotetrasiloxane (9.6 g), EP200-A (RTM: isobutylene polymer) (20 g) having number average molecular weight of 5000, ethylcyclohexane (40 g), and Pt-VTSC-3.0X (RTM: platinum vinyl siloxane complexes) (5 mu L) were reacted at 60 degrees C, solvent was distilled off and unreacted components was again dissolved in ethylcyclohexane (40 g). A LS-815 (RTM: trimethoxy vinylsilane) (4.3 g) was dripped to the reaction solution, reacted at 60 degrees C for 7 hours, solvent and unreacted components were distilled off, and obtained polymer. A WPI-116 (RTM: photo-acid generator) (0.02 g) was added to the obtained polymer (1 g), to obtain polymer composition. The obtained polymer composition was diluted with toluene (1 g) of toluene, obtained solution was coated on a glass substrate by spin coat method, and irradiated with ultraviolet ray, to obtain cured material. The obtained cured material had thickness of 10 mu m, transmittance of 95% at 400 nm, 1% weight reduction temperature of 257 degrees C, moisture-permeable coefficient of 6.8x 10-13 g.cm/(cm2.second.Hg(mercury)), and excellent heat resistance and transparency.