Volume 45 Issue 6, June 2013

This review describes the developments of self-assembled photonic crystals (PCs) of chiral liquid crystals (CLCs) and colloidal crystals (CCs) for laser applications. Both CLCs and CCs have intrinsic capabilities to spontaneously assemble 1D-PCs and 3D-PCs, respectively. By combining fluorescence dyes in the structures, the stimulated laser action can be generated by optical excitation. Moreover, the optically excited lasing is controllable by external stimuli due to their self-organization. This review highlights the research backgrounds of CLCs and CCs, as well as the experimental results of soft and tunable laser applications.

Novel 4-phenylethynylphthalic anhydride (PEPA) terminated addition-type imide oligomers derived from 1,2,4,5-benzenetetracarboxylic dianhydride or pyromellitic dianhydride (PMDA), and 2-phenyl-4,4′-diaminodiphenyl ether (p-ODA) showed a high solubility and a very low minimum melt viscosity. These imide oligomers were also converted to crosslinked cured resins with a high glass transition temperature (T_g) (>350 °C) and good mechanical properties after curing. A void-less polyimide/carbon fiber composite with high T_g could also be achieved to fabricate via the imide oligomer solution prepregs.

The synthesis of fac-Ir(ppy)₃ (fac, facial; ppy, 2-phenylpyridyl) end-functionalized poly(4-diphenylaminostyrene) (PDAS) was achieved by the addition reaction of fac-Ir(ppy)₂(vppy) (vppy, 2-(4-vinylphenyl)pyridyl) to poly(4-diphenylaminostyryl)lithium (PDASLi). In this reaction, fac-Ir(ppy)₂(vppy) acts as a fac-Ir(ppy)₃ single-monomer addition reagent for PDASLi; the first fac-Ir(ppy)₂(vppy) molecule readily binds to the carbanion of PDASLi, while the addition of a second fac-Ir(ppy)₂(vppy) molecule to the carbanion on the vinyl group of fac-Ir(ppy)₂(vppy) does not proceed. Thus, fac-Ir(ppy)₃ end-functionalized PDAS consisting of one PDAS molecule and one fac-Ir(ppy)₃ molecule was successfully obtained for the first time.

Radical copolymerization of alkyl 2-norbornene-2-carboxylates 1a–c with alkyl (meth)acrylates to afford copolymers bearing norbornane framework in the main chain is described. γ-Butyrolactone- and hydroxy group-containing norbornene-based monomers 1b and 1c were newly synthesized and their radical copolymerization behavior with n-butyl acrylate was examined. Methyl 2-norbornene-2-carboxylate 1a and the new monomers 1b and 1c were employed as a comonomer for radical terpolymerization with lactone- and adamantane-containing (meth)acrylates to afford copolymers, which could be utilized as new chemically amplified 193-nm photoresist materials.

Hyperbranched poly(ether ether ketone)s with hydroxyl terminal groups were prepared by a one-step synthesis of an AB₂-type monomer 3,5-dihydroxy-4′-(4-fluorobenzoyl)diphenylether through an aromatic nucleophilic substitution reaction. The degree of branching determined by ¹H-NMR analysis was about 52%. The reduced viscosities of the hyperbranched polymers were higher than those of the corresponding dendrimers, the glass transition temperatures of the hyperbranched polymers were higher than those of the dendrimers and the existence of entanglement among the hyperbranched polymer molecules was suggested.

A series of novel photoactive high-performance polyamides bearing different functional group, such as CF₃, substituted imidazole and carbazole rings in their backbone, were prepared in direct polycondensation using ionic liquid media and triphenyl phosphate as an activating agent.

Bulk free-radical polymerization of methyl methacrylate was studied by differential scanning calorimetry (DSC). Dependence of monomer conversion on time was calculated from the experimental DSC data. Proposed model, composed of two contributions to the monomer conversion was found to excellently describe experimental data. First contribution originates from polymerization according to classical theory of radical polymerization and the other from polymerization during the autoacceleration.

The possibility of phase separation of benzoxazine (BZ)/epoxy resin (ER) blends were investigated via model components. The experiment result indicated that if the molecular weight of ER can increase to a higher extent (for example, ⩾4370 g mol⁻¹) before the polymerization of BZ resin occurs, phase separation of BZ/ER blends can take place in-situ. By varying the ER content in the system, sea-island structure, ribbon weave-like bi- continuous structure and inverted-phase structure can be obtained.

Stereocomplex poly (lactic acid) films were prepared by casting chloroform, acetonitrile or tetrahydrofuran solution of a mixture, mix-poly(lactic acid) (PLA), of poly (L-lactic acid) and poly (D-lactic acid). Time dependence of cloud point (Figure 1), as well as the morphology of the cast films (Figure 2) was markedly different in these three cast-solvents. The cast-solvent dependence of the morphology was studied by assuming that structure of stereocomplex is constructed through two processes.

The Δs′ value (s′_max−s′_min) represents the cross-linking efficiency of peroxide, which is defined as the number of moles of chemical cross-links formed per mole of peroxide. Efficiency of peroxide is higher for EOCs with lower-octene content. The reason might be difficulty of peroxide-free radicals to attack the main chains due to increased hindrance by octene side groups.

Assembly of poly(acrylic acid) (PAAc) gel particles with DNA–ethidium bromide (EtBr) complexes was synthesized and the pH-sensitivity was evaluated for application in optical-sensor devices. The swelling ratio of the assembly was regularly changed with pH and the response speed of the assembly was approximately the same as the gel particles. The great increase in pH-sensitivity of the assembly was assumed to be induced by the porous structure. The fluorescence intensity was changed corresponding to the volume alteration of the assembly. The assembly could quickly detect the pH in the surrounding as an optical-signal.

We present the optimization of poly(N-vinylcarbazole) (PVCz)-based photorefractive composite films for use in a dynamic holographic imaging system. The compositions of the composite films used in this study included PVCz/4-azacycloheptylbenzylidenemalononitrile (7-DCST)/carbazoylethylpropionate (CzEPA), N-ethylcarbazole (ECz), benzyl n-butyl phthalate (BBP)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM), or 2,4,7-trinitro-9-fluorenone (TNF) (44/35/20/1 wt%). PVCz with molecular weights of 23 000, 100 000, 290 000, 370 000, and 810 000 gmol⁻¹ were used. The PPC film (PVCz with Mw: 370000/7-DCST/CzEPA/TNF, 44/35/20/1 wt%) was observed to be the most well-balanced for photorefractive performance. To demonstrate the practical application of these films, dynamic holographic images were reflected from a spatial light modulator (SLM). The optimized PPC film was used in the dynamic holographic imaging system, and well-balanced dynamic holographic images were obtained.

To investigate the electroactive shape-memory property of the hydro-epoxy composites, a sample with 1.9 wt% carbon black powder is investigated. The figure shows that the recovery of the original shape occurred after only a few minutes. Moreover, the shape recovery ratio (Rr) of the electroactive shape-memory hydro-epoxy composite is almost 100%. This finding indicates good electroactive shape-memory performance.

A highly bulky methacrylate, tris(trimethylsilyl)silyl or supersilyl methacrylate, was polymerized quantitatively with 9-fluorenyllithium in the presence of (−)-sparteine as a chiral ligand in toluene at −78 °C to give insoluble polymers. The obtained polymers exhibited high isotacticity (mm>99%) and chirality, which was confirmed by diffuse reflectance circular dichroism spectroscopy. Thus, the bulky silyl methacrylate undergoes asymmetric anionic polymerization with the chiral initiating systems via formation of a prevailing one-handed helical conformation.

The cloud point was determined for aqueous solutions of two poly(N-isopropylacrylamide) samples, one having a hydrophobic nonionic chain-end group (M sample) and the other having a hydrophilic anionic chain-end group (R sample), with an addition of two kinds of surfactants, anionic sodium n-dodecyl sulfate (SDS) or cationic n-dodecyltrimethylammonium chloride (DTAC). It is found that behavior of the cloud point as a function of the concentration c_s of the surfactants largely depends on the kinds of chain-end group and surfactant.