| http://www.w3.org/ns/prov#value | - PEN, however, is a relatively expensive material which is difficult to protect from ultraviolet radiation, and polyethylene terephthalate (PET), a lower index alternative to PEN, cannot easily be suitably oriented with PMMA due to the difference in glass transition temperatures of these materials (about 84??? C. for PET and about 106??? C. for PMMA).
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