On the polymerization of crystalline 1,4‐diethynylnaphthalene, 2 The reaction mechanism

Abstract

Crystalline 1,4-diethynylnaphthalene (1) is photochemically polymerized in the solid state by a radical mechanism. Only the chain initiation step is induced by light, whereas chain propagation also occurs in the dark. The polymerization is controlled by diffusion processes within partially melted domains of the crystal, ultimately leading to a completely disordered system. The reaction rate, however, also depends on the packing of the monomer in the crystal lattice and-in the beginning of the reaction-the polymer chains have a preferential orientation with regard to the crystal axes of the monomer. Radical polymerization in solution indicates that -due to the lack of effective chain termination steps-1 can be polymerized rather effectively as compared to other acetylenes. The photochemically induced polymerization is approximately of second order with regard to monomer concentration.

Metal-Free on-Surface Photochemical Homocoupling of Terminal Alkynes

“…Previous reports show that monomer solutions of aromatic acetylenes undergo UV-induced polymerization and coupling reactions that occur in low yield and with low specificity . A test was performed in order to exclude the occurrence of the homocoupling reaction in solution (Figure S4).…”

Crystal structures and solid-state reactivities of 1,4- and 1,2-bis(5-hydroxypenta-1,3-diynyl)benzenes and 1-(5-hydroxypenta-1,3-diynyl)-4-ethynylbenzene

“…On the basis of the molecular arrangement, the solid-state polymerization of 3 by the ethynyl moiety is expected to proceed, similarly to the case of 1,4-diethynylbenzene. 1, 18 Thus, with respect to the crystals of 3, the monomer arrangement is suitable for solid-state polymerization not only by the diacetylene moieties but also by the ethynyl groups. The distance between the reacting carbons is shorter for the ethynyl groups than for the diacetylene moieties.…”

“…In our previous study, 1,2 1,4-diethynylbenzene did not polymerize upon heating below the melting point, 94-95 ЊC, whereas it polymerized upon irradiation with γ-rays 1 and UV light. 18 The ethynyl groups attached to aromatic rings are considered to be inert in the thermal polymerization in crystalline states, since the melting points of various aromatic acetylenes have been determined. 18…”

“…18 The ethynyl groups attached to aromatic rings are considered to be inert in the thermal polymerization in crystalline states, since the melting points of various aromatic acetylenes have been determined. 18…”

Selective dimerization by a radical chain reaction in γ-irradiated crystals of 1,3-bis(3-acetoxyprop-1-ynyl)-4-methoxy-6-methylbenzene

“…1-3 Crystals of 1,4diethynylnaphthalene, 1,4-diethynylbenzene 2 and their analogues have also been reported to polymerize upon UV irradiation. 4, 5 One of the ethynyl groups participates in the…”