Photooxidation of polyoctenamer: viscoelastic assessment of gel formation

The evolution of viscoelastic properties upon photoageing of polyoctenamer has been monitored using dynamic oscillatory experiments with the aim of comparing with the more usual data obtained by conventional techniques such as FTIR spectroscopy. Our finding is that the average molecular weight increased from the start of the UV exposure, involving rapid cross-linking. At the gel point, a power law frequency dependence of the dynamic storage modulus (G' proportional to omega(n)') and loss modulus (G' proportional to omega(n)") was observed with n' = n " = n = 0.4. Moreover, the gel time was accurely determined, t(gel) = 160 min. Whereas, at the same time, no chemical change was detected by FTIR spectroscopy. Hence, compared to conventional chemical analysis, dynamic rheological measurements consist of an additional method. Its sensitivity for the determination of the molecular structure evolution through photoageing of elastomeric materials has been clearly illustrated. In addition, melt rheology results are in good agreement with the dual processes of photochemical evolution of polyoctenamer previously described from conventional results. (C) 1999 Elsevier Science Ltd. All rights reserved.