Influence of chain length and temperature on UV-Vis absorption and degradation behavior of poly(diethyl dipropargylmalonate) with an alternating cis-trans-1,2-(cyclopent-1-enylene)vinylene structure

Cyclopolymerization of diethyl dipropargylmalonate (DEDPM) with Mo(N-2,6-i-Pr 2 -C 6 H 3 ) (CHCMe 2 Ph)(OC(CH 3 ) 3 ) 2 in the presence of quinuclidine yields poly(DEDPM) with an alternating cis-trans-1,2-(cyclopent-1-enylene)vinylene structure. Poly(DEDPM) n with different degrees of polymerization (n = 5-90) and PDI < 1.4 was prepared. A linear plot of number of monomers (N) added versus molecular weight as determined by light scattering (data were collected at λ = 690 nm) suggests that the cyclopolymerization of DEDPM proceeds in a living manner. A degree of polymerization (DP)-dependent UV-Vis absorption is found. At 25°C, the absorption maximum λ max for poly(DEDPM) n for n ≥ 50 is 591 nm. Thus, a maximum effective conjugation length N eff of 52 can be calculated. Increasing chain length results in a highly resolved fine structure in the UV-Vis spectrum with absorption maxima at 550 and 590 nm and a shoulder at around 513 nm for poly(DEDPM) 70 . In the solid state, absorption maxima were in the range of 478-574 nm for poly(DEDPM) 5-90 . Poly(DEDPM) 10 and poly(DEPM) 90 showed glass transition temperatures of 25.8 and 26.5°C, respectively. The measurement of λ max of poly(DEDPM) 50 solutions in chloroform within a temperature range of 30°C reveals a reversible thermoresponsive behavior with changes in λ max of 8 nm. Poly(DEDPM) is stable under air over months in the solid state, as well as in solution using non-acidic solvents (e.g. CH 2 Cl 2 ). In contrast, values for λ max for poly(DEDPM) solutions in CHCl 3 decrease, if the solutions are exposed to air and light, yet remain constant in the absence of light and air. Changes in molar mass of poly(DEDPM) solutions in CHCl 3 and CH 2 Cl 2 were investigated by SEC measurements using light scattering detection and correlated with their time-dependent UV-Vis absorption behavior. Finally, poly(DEDPM) 10-90 is thermally stable up to 185°C under a helium atmosphere.