Replicative manufacturing of metal moulds for low surface roughness polymer replication.

Tool based manufacturing processes like injection moulding allow fast and high-quality mass-market production, but for optical polymer components the production of the necessary tools is time-consuming and expensive. In this paper a process to fabricate metal-inserts for tool based manufacturing with smooth surfaces via a casting and replication process from fused silica templates is presented. Bronze, brass and cobalt-chromium could be successfully replicated from shaped fused silica replications achieving a surface roughnesses of Rq 8 nm and microstructures in the range of 5 µm. Injection moulding was successfully performed, using a commercially available injection moulding system, with thousands of replicas generated from the same tool. In addition, three-dimensional bodies in metal could be realised with 3D-Printing of fused silica casting moulds. This work thus represents an approach to high-quality moulding tools via a scalable facile and cost-effective route surpassing the currently employed cost-, labour- and equipment-intensive machining techniques.

p-Benzyne.

A noble gas matrix at low temperature was used to investigate the photochemical behavior of diacetyl terephthaloyl diperoxide and dipropionyl terephthaloyl diperoxide as well as 1,4-diiodobenzene. All three photoreactions formed small quantities of a compound with IR absorption bands at 725 and 980 cm-1 , which disappeared when the matrix was annealed. These bands correspond to the most intense of the calculated bands (B3LYP) for 1,4-didehydrobenzene (p-benzyne) (1). That decomposition of the peroxides in fact leads to 1 is confirmed by vapor-phase pyrolysis experiments in which (Z)-2 was obtained in high yield.

Matrix Isolation of Perfluorinated p-Benzyne.

As the first isolated derivative of 1,4-didehydrobenzene, 1,4-didehydro-2,3,5,6-tetrafluorobenzene (1) was generated from 1,4-diiodotetrafluorobenzene (2) by photolysis at 254 nm in a neon matrix at 3 K. The 4-iodo-2,3,5,6-tetrafluorophenyl radical 3 is formed as an intermediate in this reaction. Both 1 and 3 were characterized by their IR spectra. Compound 1 is photolabile and undergoes a photochemical retro-Bergman reaction to 1,3,4,6-tetrafluorohex-3-ene-1,5-diyne (4) upon broad-band UV irradiation (260-320 nm).

Vibrational spectrum of m-benzyne: a matrix isolation and computational study.

m-Benzyne (2) was generated in low-temperature matrices and IR spectroscopically characterized from four different precursors. To assign the IR absorptions, the perdeuterated derivative 2-d(4) was also investigated. By comparison with CCSD(T) calculations all vibrations between 200 and 2500 cm(-)(1) with a predicted relative intensity >2% could be assigned. All experimental and theoretical results are in accordance with a biradicaloid structure for 2, while there is no evidence for a bicyclic closed-shell structure. While benzyne 2 is stable under the conditions of matrix isolation at low temperature, flash vacuum pyrolysis at high temperatures or UV irradiation results in the rearrangement to cis-enediyne. A mechanism involving ring opening accompanied by hydrogen migration is proposed.