‘Reworkable polymers'' are readily removable from substrates and hence facilitate reusing and recycling substrates. This helps economic as well as environmental aspects as recycling substrates enables an efficient use of substrates. The thermally degradable acetalester group was incorporated into a norbornene monomer for preparing as reworkable polymer system based on ''thiol-ene'' photo-curing. The photo-curable formulations consist of norbornene acetalester monomer, TMPTSH as a tri-functional ''thiol'' and TANTA or TAOTA, as a tri-functional ''ene'' with HCPK as a photo-initiator. The mixture was UV-irradiated to render flexible transparent film coatings. The photo-curing process was finished within a minute the spectral changes were first observed by DPC and FT-IR. During the DSC measurement, thermal degradation of the photo-cured films were observed at low temperatures (~225 ℃) as a result of thermally cleavable acetal ester groups in the cross-linked polymer chains. Gel content measurements were also carried out in THF as a solvent. In the gel content measurements, the photo-cured films showed higher than 95 % values confirming nearly complete photo-curing. On the contrary, the values remarkably decreased to less than 70 % by thermal treatment at 220 ℃ for 10 min. The thermal degradation of the acetal ester groups in the cross-linked polymer chains were also identified by FT-IR spectral analysis and DSC analysis.The properties of photo-cured films were also characterized by thermal analysis with TGA. The TGA results proved to be inconsistent with DSC because the weight loss of acetal ester degradation was not clearly detectable in the TGA measurement. To characterize the degradation, USANS (KIST-USANS) & SANS (18mSANS of HANARO) were measured to observe the polymer size and behavior.