Yoshio Kasashima

Preparation and properties of polyamides and polyimides from 4,4″-diamino-o-terphenyl

Abstract Polyamides and polyimides having 4,4″- o -terphenyldiyl units in the main chain were synthesized. The polyamides were prepared from 4,4″-diamino- o -terphenyl and aromatic dicarboxylic acids or aromatic dicarbonyl dichlorides. The polyimides were prepared from 4,4″-diamino- o -terphenyl and aromatic tetracarboxylic dianhydrides. Copolyamides and copolyimides were also prepared using 4,4″-diamino- o - and other diamines. The T g values of the polyamides were high (283–298°C). The polyamides were soluble in cyclohexanone and pyridine. The polyimides also possessed high T g values (298–372°C). The solubilities of the polyimides, on the other hand, were poor. The introduction of o -terphenyl units into the main chain of the polyamides led to high thermal stability as well as good solubility.

Synthesis and properties of novel aromatic polyamides containing 2-methyl-4,5-oxazolediyl structure

Abstract Novel aromatic polyamides having 2-methyl-4,5-oxazolediyl units in the main chains were synthesized. The polyamides were prepared from 4,5-di(4-aminophenyl)-2-methyloxazole (DAPMO) and/or 4,4′-[4,5-(2-methyl) oxazole]dibenzoic acid (MODBA) by the direct polycondensation method. The polyamides, the inherent viscosities of which ranged from 0.64 to 1.95 dl g −1 , were obtained almost quantitatively. The polyamides indicated high thermal properties: glass transition temperatures were found in the range between 280 and 354°C, and thermal decomposition temperatures ranged from 376 to 421°C. The polyamides exhibited good solubility in many organic solvents such as m -cresol, N,N -dimethylacetamide, 1-methyl-2-pyrrolidone, N,N -dimethyl formamide and conc. H 2 SO 4 at 2.0% (w/v). All the polyamides showed amorphous nature. The introduction of the zigzag, rigid and polar 2-methyl-4,5-oxazolediyl structure into the main chains of polyamides was effective in improving the solubility without lowering the high thermal properties.

Exclusive Photodimerization Reactions of Chromone-2-carboxylic Esters Depending on Reaction Media

The irradiation of chromone-2-carboxylic esters resulted in the stereo- and regioselective formation of C(2) chiral anti-HH dimers from the triplet excited state. On the contrary, photolysis in the solid-state gave anti-HT dimers exclusively controlled by molecular arrangement in the crystal.

Photochemical asymmetric synthesis of phenyl-bearing quaternary chiral carbons using chiral-memory effect on β-hydrogen abstraction by thiocarbonyl group

Quaternary chiral carbons were effectively generated from tertiary chiral carbons via photochemical intramolecular beta-hydrogen abstraction reaction of thioimides involving the highly-controlled chiral-memory effect.

CURING BEHAVIOR AND PROPERTIES OF EPOXY RESINS CURED WITH THE DIAMINE HAVING HETEROCYCLIC RING

ABSTRACT Diamines having heterocyclic ring, 4,5-bis (4-aminophenyl)-2-phenyl-imidazole (BAPI), 4,5-bis(4-aminophenyl)-2-methyloxazole (BAPO) and novel diamine, 2,3-bis(4-aminophenyl)benzo[g]quinoxaline (BABQ) were prepared as curing agents for epoxy resin. Epoxy resins were obtained by curing diglycidyl ether of bisphenol A (DGEBA) with the above diamines. Properties of these DGEBA-diamine systems were studied and compared to that of DGEBA cured with commercially available diamine, 4,4′-diaminodiphenyl sulfone (DDS). On differential scanning calorimetry (DSC), the peaks of exotherms of the mixtures of DGEBA with these diamines having heterocyclic rings were observed at lower temperature and these reactions were completed in shorter time than that of DGEBA with DDS. The epoxy resins cured with these diamines containing heterocyclic ring showed excellent bonding strength even at high temperature and thermal resistance, e.g., DGEBA-BABQ gives greater bonding strengths as 35.1, 30.0, and 26.2 MPa when tested at 20, 120, and 180°C, respectively and residual weight at 600°C was 44% after being cured at 160°C for 2 hours. In the curing of DEGBA-BAPI, the reaction was accelerated and completed in a shorter time, but the bonding strength lowered somewhat, since the tertiary amine in the imidazole ring acts as catalytic curing agent which leads to epoxy homopolymerization.

Thermal polymerizations of alkali and alkaline earth 4-vinylbenzoates in bulk

Thermal polymerizations of alkali and alkaline earth 4-vinylbenzoates (4-VBAs) in bulk were investigated. The relative reactivity of the alkali salts decreases in the following order: K > Na > Li, which is in reverse order to that of alkali methacrylates. In the polymerization of K-4-VBA at 240°C, the number-average molecular weight decreases with increasing reaction time, although the yield of polymer increases. The polymerization of the K salt proceeds as long as the crystallinity of the monomeric salt is maintained, and is terminated when there is no crystalline compound in the reaction mixture left. The relative reactivity of the alkaline earth salts decreases in the following order: Mg > Ca > Sr >> Ba. The polymerization of Mg-4-VBA proceeds rapidly at 240°C in the initial stage (30 min) and then levels off, however, the appearance of the reaction mixture still remains crystalline.

Asymmetric Synthesis of an Amino Acid Derivative from Achiral Aroyl Acrylamide by Reversible Michael Addition and Preferential Crystallization

Single-handed α-amino acid derivatives were generated from achiral precursors without an external chiral source. Conjugate addition of phenethylamine to an achiral aroyl acrylamide under homogeneous conditions gave the α-amino amides in quantitative yields, which crystallized as a conglomerate of a P21 crystal system. Dynamic preferential crystallization or attrition-enhanced deracemization resulted in the formation of enantiomorphic crystals of 99 % ee.

Diastereoselective photocycloaddition using memory effect of molecular chirality controlled by crystallization

Naphthamides derived from L-proline, which exist as a mixture of several diastereomers in solution, converged to single diastereomer by crystallization, and the conformational transformation was controlled after the crystals were dissolved in the solvent at low temperature, where the frozen conformation was retained long enough for subsequent asymmetric reaction.

Metal adhesive properties of polyamides having the 2,3‐bis(1,4‐phenylene)quinoxalinediyl structure

Polyamides were synthesized by interfacial polycondensation of 2,3-bis(4-chloroformylphenyl)quinoxaline (BCFPQ) and several aliphatic diamines using a phase transfer catalyst, and their adhesive property for stainless steel was investigated. The inherent viscosity of the obtained polyamides ranged from 0.37 to 1.24 dL g−1. The glass transition temperatures of the polyamides ranged between 154 and 201°C, and their thermal decomposition temperatures were above 450°C. The polyamides were soluble in several organic solvents, including m-cresol, N-methyl-2-pyrrolidone (NMP), and formic acid. The adhesive property for stainless steel was examined by a standard tensile test. One member of the series, polyamide P8, derived from BCFPQ and 1,8-octanediamine, displayed high tensile strength with values of 232 kgf cm−2 at 20°C, 173 kgf cm−2 at 120°C, and 137 kgf cm−2 at 180°C. Thus, the tensile strength of P8 decreased at 180°C, but the decrease was much smaller than that of an epoxy resin in wide use as a metal adhesive. Heat distortion temperature, measured by thermal mechanical analysis, of P8 was 191°C. This suggested that P8 possessed high thermal resistance in metal adhesives.

Asymmetric Synthesis by Using Natural Sunlight under Absolute Achiral Conditions

Irradiation of prochiral (E)-aroylacrylamide with sunlight gave single-handed pyrrolinone quantitatively and with an enantiomeric excess (ee) of over 99 % under absolutely achiral conditions. The phenomenon was explained by photoisomerization and reversible cyclization followed by dynamic crystallization involving deracemization.