A study of absorption coefficient spectra in a-Si:H films near the transition from amorphous to crystalline phase measured by resonant photothermal bending spectroscopy

Optical absorption spectra of a widegap hydrogenated amorphous silicon film have been estimated by resonant photothermal bending spectroscopy. It is found that excess absorption exists over the photon energy region of 1.2–1.6 eV. This excess absorption decreases by light illumination and does not recover through thermal annealing. The decrease in the excess absorption may be due to oxidization of the film by light illumination.     

Lipase‐Catalyzed transformation of Poly(trimethylene carbonate) into Cyclic Monomer,Trimethylene Carbonate: A New Strategy for Sustainable Polymer Recycling Using an Enzyme

The enzymatic degradation and polymerization using an enzyme were carried out with respect to the establishment of a sustainable chemical recycling system for poly(trimethylene carbonate) [P(TMC)] which is a potentially biodegradable synthetic plastic. The enzymatic transformation of P(TMC)s having an M_n of 3000~48000 using Candida antarctica lipase (lipase CA) in acetonitrile at 70 °C afforded the corresponding cyclic monomer, trimethylene carbonate (TMC: 1,3‐dioxan‐2‐one), in a yield of up to 80%. Thus obtained TMC readily polymerized again using both fresh lipase CA and recovered lipase CA.     

Chain-growth polycondensation of potassium 3-cyano-4-fluorophenolate derivatives for well-defined poly(arylene ether)s

Polycondensation normally proceeds in a step-growth reaction manner to give polymers with a wide range of molecular weights. However, the polycondensation of potassium 2-alkyl-5-cyano-4-fluorophenolate ( 1 ) proceeded at 150°C in a chain polymerization manner from initiator, 4-fluoro-4′-trifluoromethyl benzophenone ( 2 ), to give aromatic polyethers having controlled molecular weights and low polydispersities (M_w/M_n ⩽ 1.2). The resulting polycondensation of 1 had all of the characteristics of living polymerization and displayed a linear correlation between molecular weight and monomer conversion, maintaining low polydispersities. Sulfolane was a better solvent for chain-growth polycondensation of 1 than other aprotic solvents. The polyether from 1 with a low polydispersity showed higher crystallinity than that with a broad molecular weight distribution, obtained by the conventional polycondensation of 1 without 2 .     

Organic Solvent‐Free Enzymatic Transformation of Poly(ϵ‐caprolactone) into Repolymerizable Oligomers in Supercritical Carbon Dioxide

The enzymatic transformation of poly(ϵ‐caprolactone) (PCL) into repolymerizable oligomers in supercritical carbon dioxide (scCO₂) using an enzyme was carried out in order to establish a sustainable chemical recycling system for PCL, which is a typical biodegradable synthetic plastic. The enzymatic conversion of PCL beads having an M̄_n of 110 000 using Candida antarctica lipase (lipase CA) in scCO₂ containing small amounts of water quantitatively afforded CL oligomers at 40°C. The CL oligomers were readily repolymerized using the same enzyme to produce high‐molecular weight PCL.