No abstract

The polyaddition reactions of alicyclic diamines such as 1,4‐diaminocyclohexane (1,4‐CHDA) or 4,4′‐diaminodicyclohexylmethane (DCHM) and configurational isomers of 1,4‐CHDA or DCHM with tetracarboxylic aromatic anhydrides in aprotic solvents were carried out to prepare high molecular weight poly(amic acid)s. Through the thermal imidization of poly(amic acid)s, several flexible polyimide films were prepared. Because of the stiffness of the alicyclic moieties in diamines, the resulting polyimides exhibit high glass transition temperatures (220–340°C) almost similar to those for corresponding aromatic polyimides which have phenylene groups in place of cyclohexyl groups, and show good thermal stability. The partial crystallization was observed for polyimides with trans‐cyclohexyl moiety during the heating in differential scanning calorimetry and ascertained by wide‐angle x‐ray diffraction. Thus, the inhibition of the occurrence of charge transfer in polyimides is accomplished by introducing alicyclic diamines in place of aromatic diamines without reducing their thermal stability. © 1993 John Wiley & Sons, Inc.

Constructing s-tetrazine-embedded HCP photocatalysts for the green synthesis of benzimidazoles.

Alternate partial root-zone irrigation has profound impacts on the crop uptake of residual nitrogen originated from the previous season.

SYNOPSISPhotosensitive polyimides with alicyclic diamines and benzophenone moiety were prepared by reactions of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) with diamines in aprotic solvents, followed by thermal or chemical imidizations. Among them the polyimide from BTDA and bis (4-amino-3-methylcyclohexyl) methane (DMDHM) can be dissolved in several organic solvents such as dichloromethane, tetrachloroethane, and N-methyl-2pyrrolidone ( N M P ) . In order to compare properties of the polyimides with alicyclic diamines with those of corresponding aromatic polyimides, the UV absorption spectra and fluorescence spectra of these polyimides and their model compounds were investigated. No occurrence of charge transfer at photoexcited states was ascertained for the polyimides with alicyclic diamines. The hydrogen abstraction and crosslinking during photoirradiation have been studied to learn the influence of the elimination of charge transfer process in these photosensitive polyimides. The quantum yield of hydrogen abstraction for the model compound of alicyclic polyimides is 0.56 in T H F measured with HPLC. The quantum yield for the photocrosslinking reaction of the solvent-soluble polyimide with alicyclic diamine, PI (BTDA/DMDHM) , was determined to be 0.004 in air from gel permeation chromatography (GPC) measurement, which is four times higher than that for photosensitive polyimides with aromatic diamines.