Mitsutoshi Jikei

Hyperbranched polymers: a promising new class of materials

Abstract Hyperbranched polymers are highly branched macromolecules that are prepared through a one-step polymerization process. Many kinds of hyperbranched polymers have been investigated as novel dendritic macromolecules. The general concepts, syntheses and the properties of hyperbranched polymers are reviewed in this article. The polymerization reactions are classified into three categories: (1) step-growth polycondensation of AB x monomers; and (2) self-condensing vinyl polymerization of AB ∗ monomers; (3) multibranching ring-opening polymerization of latent AB x monomers. Hyperbranched polymers are generally composed of dendritic, linear and terminal units and a degree of branching (DB) helps to describe their structures. It has been shown that most of the hyperbranched polymers possess some of the unique properties exhibit dendritic macromolecules, such as low viscosity, good solubility, and multi-functionality. Owing to multi-functionality, physical properties such as solubility in solvents and the glass transition temperature can be controlled by the chemical modification of the end functional groups (endcapping reactions). Applications of designed hyperbranched polymers to specific fields are also described.

Synthesis and properties of polyurethane elastomers crosslinked with amine-terminated AB2-type hyperbranched polyamides

Abstract Amine-terminated AB 2 -type hyperbranched polyamides of different molecular weights were prepared from 3,5-bis-(4-aminophenoxy)benzoic acid (AB 2 monomer) by fractional precipitation technique and characterized by FTIR, 1 H-NMR spectroscopies, DSC and GPC techniques. The degree of branching (DB) of hyperbranched polymers (HBP) was determined using 13 C-NMR spectroscopy and it was found that the value increased with decrease in molecular weight of polymer considered. As the molecular weight distribution was narrow, the approximate number of end functional groups of each HBP was conveniently calculated. Three polymers were selected and used as crosslinkers in the preparation of polyurethanes. The incorporation of hyperbranched polyamide into the polyurethane chains was confirmed using FTIR and 1 H-NMR spectroscopic techniques. Among the range studied (1–6%), it was found that high tensile strength is attained with 1% of HBP. It was also found that the tensile strength decreases with increase in number of end functional groups and decrease in DB of HBP. However, glass transition temperatures and thermal stability of polyurethanes crosslinked with up to 6% of HBP, above which gelation occurred, were not affected and similar to the blank polymer prepared without AB 2 polymer.

Synthesis and Characterization of New Polyimides Containing Nitrile Groups

Two new nitrile-containing diamine monomers, 4-[bis(4-aminophenyl)amino]benzonitrile and 4-[4-(1-cyanopropoxy)phenyl]2,6-bis(4-aminophenyl)pyridine were synthesized. The diamine monomers were reacted with various tetracarboxylic dianhydrides, followed by cyclodehydration (imidization) without isolation to produce a series of novel polyimides with pendant nitrile groups on the side chain. The polymers were obtained in quantitative yields with high molecular weight. Among them, polymers derived from ODPA and 6FDA showed good solubility, they could dissolve in polar solvents such as DMF, NMP, DMSO and even pyridine and m-cresol. These tough, transparent and flexible polyimide films had a tensile strength of 80–120 MPa, an elongation at break of 4–12% and a tensile modulus of 1.2–2.3 GPa. The polymers obtained exhibited high glass transition temperatures between 305 and 360 C. Moreover, they were fairly stable up to a temperature around or above 400 C and lost 10% weight in the range of 500–590 C and 470–580 C in nitrogen and air, respectively. Together the dielectric constants of the polyimides were measured to be 3.10–3.73 at 10 GHz. On the other hand, blank polyimides with no – CN groups were also prepared for comparison and the results revealed that the nitrile group affected the thermal property of polyimides as well as the electrical properties. Introduction of the –CN groups would increase the glass transition temperature and also the dielectric constant.

Adhesion behaviour of polyamic acid cured epoxy

The adhesion behaviour or lack thereof, of polyimides is well known. The inherent brittleness of epoxy resins has also led to a search for additives to improve the physical properties of epoxy. In order to improve both of these properties, we utilized a unique strategy to cure a diepoxy (diglycidyl ether of bisphenol A) with a polyamic acid derived from oxydianiline and pyromellitic dianhydride. The polyamic acid synthesis was conducted in a low boiling point solvent consisting of tetrahydrofuran and methanol (80/20) and not traditional high boiling point aprotic solvents such as dimethylacetamide. This resulted in a material that had adhesion superior to both the pure epoxy and the pure polyimide. The state of cure was also seen to have an effect of the adhesion strengths.

New fluorescent polyimides for electroluminescent devices based on 2,5-distyrylpyrazine

Abstract New fluorescent polyimides, having an electroluminescent (EL) active unit, 2,5-distyrylpyrazine (DSP), were synthesized by the poly-condensation of 2,5-bis(4-aminostyryl)pyrazine 4 with various tetracarboxylic dianhydrides 5 . Intense photoluminescence originating from the DSP chromophore units was demonstrated. Furthermore, a light emitting diode (LED) was fabricated based on the polyimide Langmuir-Blodgett film, using indium tin oxide and a Mg-Ag alloy as the anode and the cathode, respectively. Under forward bias, orange-red light emission (λmax = 560 nm) could be observed, which was similar to the emission generated by photoexcitation. Meanwhile the EL intensity linearly depended on the applied current density, which indicated that light emission resulted from recombination of the injected charges in the polyimide layer.

Hyperbranched aromatic polyamides prepared by direct polycondensation

Hyperbranched aromatic polyamides and copolymers were prepared by direct polycondensation in the presence of condensation agents. Three strategies were described: (1) self-polycondensation of AB x -type monomers, (2) copolymerization of AB2 and AB monomers and (3) polymerization of A2 and B3 monomers. The self-polycondensation of AB x monomers proceeded without gelation to form soluble powdery polymers. The degree of branching of the hyperbranched polyamides was greatly influenced by the structure of the monomers. Copolymerization of AB2 and AB monomers allowed control of the branching density of the resulting polymers. Spectroscopic measurements revealed that the copolymers were composed of five kinds of repeating units. The good solubility and adequate solution viscosity of the copolymers allowed the preparation of transparent yellow films by casting the copolymer solution onto a glass plate. The polymerization of A2 and B3 monomers was also investigated as a novel route to prepare hyperbranched polyamides without using AB x -type monomers. Gelation during the polymerization could be avoided by the optimization of the reaction conditions. The structure and properties of the resulting polymers were compared with the hyperbranched polyamide prepared from the corresponding AB2 monomer.

Preparation and Properties of Novel Aromatic Polyimides from 4,4′-Diamino-4″ -Hydroxytriphenylamine and Aromatic Tetracarboxylic Dianhydrides

Novel aromatic polyimides containing hydroxytriphenylamine units were prepared from 4,4′-diamino-4″-hydroxytriphenylamine 1 and various aromatic tetracarboxylic dianhydrides 2. The glass transition temperatures (Tg s) of these polyimides were in the range of 274–388 °C and the 10% weight loss temperatures (T d10s) were above 462 and 511 °C in air and nitrogen respectively. Polyimide 4f prepared from diamine 1 and 4,4′-hexafluoroisopropylidenebis(phthalic anhydride) (6FDA) was soluble not only in organic solvents such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, 1, 3-dimethyl-2-imidazolidone and dimethyl sulfoxide but also in tetramethylammonium hydroxide aqueous solution. Other resulting polyimides were not soluble in organic solvents. The resulting polyimides 4 possessed Tg s about 20–70 °C higher and poorer solubilities than the previously reported polyimides prepared from 4,4′-diaminotriphenylamine and various aromatic tetracarboxylic dianhydrides. These results indicated that polymer properties such as thermal behaviour and solubilities were influenced by the intermolecular interaction of hydrogen bonding due to hydroxy units.

Polyimide Containing an Acetal Structure with a Photoacid Generator: A Novel Positive Polyimide Photoresist:

A main-chain degradable photosensitive polyimide containing an acetal structure which degrades by the action of acid coming from a photoacid generator has been developed. Polyimides 4 were prepared by the reaction of bis(4-aminophenoxy)methane 1 and various tetracarboxylic anhydrides 2, followed by thermal treatment. In the resulting polyimides 4, 4f filmderivedfrom 4,4′-hexafluoroisopropylidenebis(phthalicanhydride)(6FDA)and 1 showedgood solubility in organic solvents and transparency to UV light. The acid-catalysed degradation reaction was confirmed by the model imide compound in the presence of p-toluenesulfonic acid. The system of the polyimide 4f containing 30 wt% of diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate (DIAS), which is a photoacid generator (PAG) showed a sensitivity of 150 mJ cm−2 with 436 nm light, when it was post-exposure baked at 140°C for 30 min, followed by development with 5% tetramethylammonium hydroxide solution at 45°C.

Electrical properties and electroluminescence of poly(p-phenylene vinylene) Langmuir-Blodgett film

Abstract The electrical and electroluminescent (EL) properties of poly(p-phenylene vinylene) (PPV) Langmuir-Blodgett (LB) film based light emitting diodes, i.e. ITO/PPV/A1 and ITO/HTL/PPV/A1 devices, were investigated, and found to depend strongly on the thickness of the PPV LB film. The electrical conductivity of the PPV LB film was in the range of 10 −12 to 10 −15 S cm −1 . Under a forward bias, the light emission reached more than 100 cd m −2 in an ITO/PPV(80L) /Al device. Since the EL spectrum was similar to the photoluminescent (PL) spectrum, it was concluded that EL resulted from the recombination of injected charges in the PPV layer.

Heterostructural Electroluminescent Devices Based on Poly (P-Phenylenevinylene) and Polyimide LB Films

Abstract Several polymeric electroluminescent (EL) devices, possessing the poly(p-phenylenevinylene) (PPV) and polyimide LB films used as the light emitting layer and the hole transporting layer respectively, were fabricated by the LB technique. In these heterostructural EL devices, the luminance over 100 cd/m2 was achieved, which was more than 10 times higher than that of the single layer (PPV LB film only) device. Furthermore, by incorporation of the hole transporting layer to the EL devices, remarkable improvements in charge injection and EL efficiency were observed. These improvements could be controlled by varying the thickness of the hole transporting layer.