In Fig. 4(a, b),
the dimensionless elongational at break and elastic modulus
as a function of the photo-oxidation time and representative about 82 C and +123 C, respectively; after UVB exposure, the Tg for PB units shifts from 82 C to higher value, at about 70 C, suggesting the occurrence of crosslinking reactions. As known, the formation of locally rigid structures through macromolecular aggregations and/or crosslinking, reduces the mobility of polymeric segments causing the increase of the Tg value