A novel group transfer polymerization of 1-trimethylsiloxy-benzocyclobutene via hetero Diels-Alder reaction

A novel group transfer polymerization via hetero-Diels-Alder reaction is described. When 1-trimethylsiloxybenzocyclobutene ( 1 ) was treated with a catalytic amount of p-anisaldehyde (4-methoxybenzaldehyde) and TASF (tris(dimethylamino)sulfonium difluorotrimethylsilanide) at room temperature for 0.5 h, poly[1,2-phenylene-1-(trimethylsiloxy)ethylene] was obtained quantitatively. The number-average molecular weight of the polymer was M̄_n = 2000 and the molecular weight distribution was narrow (ratio of weight-to number-average molecular weights M̄_w/M̄_n = 1.18). Structural characteristics suggested a polymerization mechanism involving isomerization of 1 to o-quinodimethane and successive hetero-Diels-Alder reaction leading to poly[1,2-phenylene-1-trimethylsiloxy ethylene]. The living-like nature of the polymerization was supported by a monomer addition experiment in which the molecular weight increased according to the increase of the added monomer.     

Structure of chain-ends in polybutadiene produced with the CoBr2(PPh3)2/MgCl2/SiPh2(OCH3)2-Al(CH3)3 catalyst system

Polymerization of 1,3-butadiene with the CoBr₂(PPh₃)₂/MgCl₂/SiPh₂(OCH₃)₂-Al(CH₃)₃ catalyst system was conducted in the presence of ethylene. It was found that addition of ethylene causes a marked decrease in the molecular weight of polybutadiene although ethylene is not incorporated at the chain-end. The structure of chain-ends was analyzed using very low molecular-weight polybutadiene produced in the presence of ethylene, which led to the conclusion that 1,2 and 2,1 insertion reactions predominate at the initiation and propagation steps, respectively.     

Molecular orbital study on the mechanism of radical polymerization of spiro-orthocarbonates bearing exo-methylene groups

Molecular orbital studies were carried out to compare the easiness of ring-opening in the radical polymerization of spiro-orthocarbonates bearing exo-methylene groups at α-position of the ether oxygen, spiro[2,4-benzodioxepine-4′-methylene-3,2′-[1,3]-dioxolane] ( 1 ), and at β-position of the ether oxygen, spiro[2,4-benzodioxepine-5′-methylene-3,2′-[1,3]-dioxane] ( 2 ). The formation energy suggests that 1 would show a degree of ring-opening larger than 2 , contrary to the experimental result. Therefore, a reverse relation in activation energy was suggested, i. e., the kinetic factor surpasses the thermodynamic factor in the ring-opening reaction of 1 and 2 . Although the calculation of the activation energy of the radical ring-opening reaction was not successful, the result extracted from the perturbation energy calculations of vinyl polymerizations of 1 and 2 agree well with their radical vinyl polymerizability. Namely, 1 was confirmed to have a larger vinyl polymerizability than 2 , which agrees well with the smaller ring-opening polymerizability of 1 compared with 2 . The real HOMO and LUMO (highest occupied and lowest unoccupied molecular orbitals) of 1, 2 and their intermediates for the radical addition were confirmed not to correspond to the apparent HOMO and LUMO from the detailed analysis of their coefficients of atomic orbitals (AOs). The frontier electron density of 1 and 2 agrees well with the fact that the β-carbon of their exo-methylene group has a higher reactivity toward radical species than the α-carbon.     

Diacetylene-containing polymers IV. Novel diacetylene-containing polyamides and copolyamides

New monomers, bis(3-ethynyl)dianilides, were synthesized from 3-ethynylaniline and different diacid dichlorides and were polymerized by oxidative polycoupling to give soluble high molecular weight film forming diacetylene-containing polyamides. UV-induced and thermal cross-linking of the polymer were studied. A correlation was found between the chain flexibility and the absoprtion peaks of visible spectra of cross-linked polymer films. Third order nonlinear optical susceptibility (χ⁽³⁾) of the polymer films was in the range of 10⁻¹⁰-10⁻⁹ esu.