Hydrogen removal by annealing from C-doped InGaAs grown on InP by metalorganic chemical vapor deposition

Hydrogen removal from C-doped InGaAs grown on InP substrate by metalorganic chemical vapor deposition is discussed based on the dependence of hole concentration on various annealing conditions. It is revealed that the hydrogen removal rate becomes higher as the annealing temperature is higher and the activation energy of hydrogen removal is about 1.9 eV regardless of C-doped layer thickness. The hydrogen removal rate is also found to be inversely proportional to C-doped layer thickness, suggesting that the hydrogen removal reaction is mainly governed by hydrogen diffusion.     

Lipase‐Catalyzed Transesterification of Polyesters to Ester Copolymers

Lipase‐catalyzed intermolecular transesterification between two different polyesters has been carried out using in toluene. The transesterification of poly(ε‐caprolactone) (PCL) and (1,4‐butylene adipate) took place via catalysis of lipase from Candida antarctica to give an ester copolymer. ¹³C NMR analysis showed that the resulting polymer was not a mixture of the starting polyesters, but a copolymer consisting of both units. The reaction temperature and solvent amount greatly affected the microstructure of the ester copolymer. Under appropriate conditions, the random copolymer was formed. The enzymatic transesterification has been monitored by size exclusion chromatography (SEC) and ¹³C NMR. Ester copolymers were enzymatically obtained from PCL and other poly(α,ω‐alkylene dicarboxylate)s and their microstructure depended on the polyester structure.     

Benzylic triflates prepared in‐situ: novel initiators for mono‐, bi‐ and trifunctional living poly(THF)s

Mono‐, bis‐, and tris(trifluoromethanesulfonate ester)s ((triflate ester)s) were prepared by the reaction of benzyl alcohol ( 1 ), 1,4‐bis(hydroxymethyl)benzene ( 2 ) and 1,3,5‐tris(hydroxymethyl)benzene ( 3 ) with trifluoromethanesulfonic anhydride in the presence of 2,6‐di‐tert‐butylpyridine. These benzylic triflate esters were applied in‐situ for the living polymerization of tetrahydrofuran (THF). The subsequent end‐capping reaction with a suitable nucleophile proceeded quantitatively to produce mono, bi‐ and, in particular, novel trifunctional telechelic poly(THF)s, respectively.