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Intramolecular [2+2] cycloadditions on direct irradiation have been observed with four 1-alkene-1,1-dicarbonitriles bearing an additional C&z.dbnd6;C bond positioned in Δ5, Δ6, or Δ7within a flexible chain. The cycloadducts formed are the “parallel” regioisomers. These cycloadditions occur by excitation of an intramolecular charge transfer complex formed by the two double bonds. Triplet sensitisation has also been investigated in one case and found also to lead to intramolecular [2+2] cycloaddition, however furnishing the “crossed” regioisomer. It appears that the triplet cycloaddition path, other than the singlet one, does not involve an exciplex but rather proceeds in two steps via the most stable triplet 1,4-diradical. [Copyright &y& Elsevier]

Copolymerization of ethylene (E) and halogenated styrenes is screened by half-sandwich scandium catalyst 1 and constrained geometry scandium catalysts 2 – 4. The methyl-substituted N -heterocyclic carbene fluorenyl catalyst 3 initiates the E copolymerization with para -fluorostyrene (p FSt), para -chlorostyrene (p ClSt) and para -bromostyrene (p BrSt) to pseudo -random copolymers with an incorporation level of up to 46.3 mol%, 45.1 mol% and 37.5 mol%, respectively. Increasing reaction temperatures from 20 to 60 °C results in an increment of E/ p FSt copolymerization activity from 5.64 × 105 to 8.10 × 105 g mol Sc −1h−1. In contrast, a higher temperature dramatically depresses the E/ p ClSt copolymerization (4.86 × 105 g mol Sc −1h−1 at 20 °C vs 0.90 × 105 g mol Sc −1h−1 at 60 °C). At 20 °C, the E/ p BrSt copolymerization only affords a little pure polyethylene, and the E- p BrSt copolymer with 37.5 mol% p BrSt is obtained at 0 °C. The pseudo -random copolymers of E and halogenated styrenes give one glass transition temperature and decomposition temperature on DSC and TGA curves. Image 1 • Pseudo-random ethylene-halogenated styrene copolymers are synthesized using constrained geometry scandium catalysts. • A positive comonomer effect is found in ethylene copolymerization with halogenated styrenes. • The copolymerization activity is very sensitive to the reaction temperature. [ABSTRACT FROM AUTHOR]