Takashi Iizawa

Synthesis of rigid polyimides containing pendant norbornadiene moieties and their valence isomerization between norbornadiene and quadricyclane

Abstract Polymers having pendant norbornadiene (NBD) moieties and rigid main chains were prepared from reactions in DMF of pendant bromomethyl groups present in polyimides with a potassium carboxylate or phenolate derivatives of NBD using a phase transfer catalyst. The substitution was quantitative using tetrabutylammonium bromide at room temperature. The photochemical valence isomerization of pendant NBD to quadricyclane (QC) moieties occurred in films upon irradiation with 365 nm light. NBD polyimide (P-1a) prepared from hex afluoroisopropylidene-2-bis(phthalic anhydride) and 2,2-bis(3-amino-4-methylphenyl)hexafluoropropane showed a higher photochemical reactivity than the other NBD polyimides when the polymers were irradiated with 365 nm light. While usual polyimides have absorptions around 365 nm that hinder the photo-isomerization of NBD and also cause the polymer to decompose because of the irradiation, the P-1a matrix has no absorption at wavelengths above 340 nm and irradiation hardly affected the rate of isomerization. When the irradiated NBD polymers were heated, the reversion isomerization of the QC moieties to the original NBD moieties occurred easily concurrent with their decomposition. The rigid polyimide structure stabilizes the QC moieties and protects them from degradation during cyclic isomerization between NBD and QC. For example, the half-life of a pendant QC moiety in a polyimide is estimated to be 6 years at 25°C.

Novel synthesis of polyimide with pendant 1‐phenylethyl ester using DBU and its thermal acid‐catalyzed deesterification

A model reaction of o-(N-phenylcarbamoyl)benzoic acid (amic acid) with threefold amounts of 1-phenylethyl bromide (PEB) and 1,8-diazabicyclo-[5,4,0]-7-undecene (DBU) was carried out in NMP. The reaction gave N-[m-(1-phenylethoxycarbonyl)phenyl]phthalimide in almost quantitative yield at room temperature for 2 h. Polyimide containing pendant 1-phenylethyl ester (P-1a) was also prepared from polyamic acid with PEB using DBU according to the model reaction. The obtained polymer was exactly consistent with P-1a synthesized stepwise from the esterification of the corresponding polyimide containing pendant carboxylic acid with PEB. Therefore, the reaction of polyamic acid bearing pendant carboxylic acid with alkyl bromide proceeded quantitatively to give polyimide containing pendant ester in the presence of DBU. Also, this method was applied to the synthesis of polyimide containing 1-phenylethyl ether. However, the polyimide with quantitative etherification was not synthesized. The acid-catalyzed deesterification of P-la film was carried out by heating the irradiated polymer film containing 10 wt % of p-nitrobenzyl 9,10-diethoxyanthracene-2-sulfonate, which produced sulfonic acid by irradiation, at various temperatures. Although thermal deesterification of P-1a started at 220°C without any acid catalyst, the deesterification occurred when the irradiated film was heated at the lower temperature. The degree of esterification can be determined from the disappearance of absorption at 700 cm -1 . The deesterification obeyed first-order kinetics.

Novel synthesis of polymeric phase transfer catalysts containing N,N-dialkylacrylamide unit and their catalytic activity

Soluble polymeric phase transfer catalysts (PTCs) containing benzyltributylphosphonium chloride moieties and polar N,N-dialkyl-acrylamide with long alkyl groups such as N,N-dipropylacrylamide, N,N-dibutylacrylamide, N,N-dihexylacrylamide, and N,N-dioctylacrylamide were prepared via two-step reactions from p-chloromethylstyrene and the corresponding N,N-dialkylacrylamide. When the obtained polymers were added, the phase transfer catalyzed reaction of benzylchloride with solid potassium acetate to proceed smoothly. The catalytic activity was strongly affected by the content of phosphonium chloride and the varieties of comonomer unit in the polymeric PTC. The polymeric PTC containing the N,N-dihexylacrylamide unit showed excellent high catalytic activity in a low polar solvent such as the mixed solvent of toluene with 70 vol % n-tridecane. Therefore, the polymer containing lipophilic long chains such as the hexyl group is desirable for polymeric PTC.

Preparation of Asymmetric Thermosensitive Double-layer Gel

Heterogeneous amidation of poly(acrylic acid) gel-1,8-diazabicyclo-[5,4,0]-7-undecene salt ( DAA ) in N -methyl-2-pyrrolidone containing an excess of alkylamine and triphenylphosphite occurred from the surface to give the corresponding DAA -poly( N -alkylacrylamide) ( PNAA ) core-shell type gel, consisting of an unreacted DAA core and a quantitatively amidated shell layer. Further amidation of the DAA-PNAA core-shell type gel with a second alkylamine afforded a novel core-shell type gel consisting of two PNAA layers: PNAA(2) and PNAA(1) . The resulting cylindrical PNAA(2)-PNAA(1) core-shell type gels were resistant to marked deformation caused by swelling/de-swelling because of their axial symmetry. This paper proposes a new approach to the preparation of asymmetric thermosensitive PNAA(2)-PNAA(1) double-layer gels by several procedures using the synthetic method of the core-shell type gels containing of poly(N-isopropylacrylamide) and poly( N -n-propylacrylamide) layers. Among the obtained asymmetric double-layer gels the model I type gel (cylindrical grooved PNNPA-PNIPA core-shell type gel) was markedly bent in water at temperatures between the lower critical solution temperatures of both layers.