Articles in 2014

Cascading energy landscapes through funneling has been postulated as a mechanistic route for achieving lowest energy configuration of a macromolecular system (such as, proteins and polymers). In particular, understanding molecular mechanism of melting and crystallization of polymers is a challenging fundamental question. The structural modifications that lead to melting of PEG are investigated here. Specific Raman bands corresponding to different configurations of the PEG chain have been identified and the molecular structural dynamics of PEG melting has been addressed using Raman spectroscopy, two-dimensional Raman correlation and DFT calculations.

It was found that the γ-ray-induced grafting of AAm on PET film is considerably facilitated by hot DMSO pretreatment. The DMSO pretreated PET films exhibit noticeable surface morphological changes including micropore creation, which is hypothesized to promote the AAm grafting.

UV-cured polyurethanes and linear polyurethanes are investigated for the potential use of thermo-optic waveguide materials. The thermo-optic effects of these polymer films are improved with higher contents of urethane backbones. The urethane polymers exhibit high light transmission in NIR region after deuterium-exchange reaction.

The electro-optical properties of the low-molecular-weight liquid crystal (LC) blue phase and the polymer-stabilized blue phase are investigated using the cyanobiphenyl homologue chiral nematic LC mixtures. It was found that the driving voltage and the switching hysteresis of blue phase were increased by polymer stabilization. Also, it was confirmed that the electro-optical rising time of blue phase was varied with the molecular parity of the n-CB homologue chiral nematic LC mixtures.

Poly(m-phenylene diethynylene)s tethering a pendant rotaxane switch were synthesized. The reversible switching behavior of rotaxane in a polymer side chain matched that of the monomer. The dynamic foldamer behavior of these polymers was controlled by solvent and rotaxane moiety. The amine-type polyrotaxanes were confirmed to favor a folded conformation in a CH₂Cl₂/CH₃CN mixed solvent. In contrast, the ammonium salt-type polyrotaxanes exhibited only a random-coil conformation because of the ionic character in the same mixed solvent.

Drug can be loaded into the silica nanoparticle-crosslinked thermosensitive hydrogels while preparing the hydrogels by mixing the silica nanoparticle suspension and copolymer solution at room temperature. These hydrogels can then be used for release study without any other processing like washing, purification, etc., as the copolymer and other chemicals were purified in advance. The simplicity of this preparation method allows a great control of drug loading. Because of the high swelling ratios of these hydrogels, cumulative release is high (more than 90%) in both higher and lower temperature than lower critical solution temperature.

A hydrophilically modified poly(dimethylsiloxane) (HPM-PDMS) bearing quaternized amino groups on the side chains was dissolved in mixtures of methanol (MeOH) and water, and studied by light scattering and small-angle x-ray scattering. According to the ternary phase diagram of polymer + solvent + non-solvent, MeOH-rich and water-rich solutions are in the one-phase and biphasic regions, respectively. In the latter solutions, the concentrated phase exists as colloidal droplets, which coagulate gradually. The multiplet structure in the melt HPM-PDMS sample may be responsible for the tentative dispersion of HPM-PDMS even in the biphasic region.

A novel plant oil-based green composite was developed using a porous bacterial polyester, poly(3-hydroxybutyrate) (PHB). The porous PHB prepared by thermally induced phase separation was impregnated via immersion with epoxidized soybean oil (ESO), and the subsequent acid-catalyzed curing of ESO afforded a full bio-based composite. The resulting composites exhibited relatively good transparency due to the nanoscale fibrous structure of PHB. The mechanical properties of the composites improved without sacrificing toughness.

Dynamic viscoelasticity and dynamic birefringence of phenolic resins having different cross-linking density were examined to clarify the relationship between structure and viscoelastic properties. Dynamic modulus was found to be insensitive to cross-linking density at a high cross-linking density, where molar mass between the cross-linking points was smaller than the viscoelastic segment size of phenolic resin, whereas the complex strain-optical coefficient reflects more sensitively the cross-linking density.

A nanocomposite of polyurethane (PU) containing 8.78 vol% chemically bonded copper phthalocyanine oligomers (CuPc) was developed. At 100 Hz, the nanocomposite film exhibits a dielectric constant of 391. Under an electric field of 10 V μm⁻¹, a strain of 17.7% and an elastic energy density of 0.927 J cm⁻³ can be achieved. CuPc particle size had a very important role in the enhancement of the electric properties.

A Z type sexiphenyltetracarboxylic dianhydride, 3,3′′′′′,4,4′′′′′-1,1′:2′,1′′:4′′,1′′′:4′′′,1′′′′:2′′′′,1′′′′′-sexiphenyltetracarboxylic dianhydride (1), was synthesized in seven steps from diethyl 4-bromophthalate. Aromatic polyimides (PI1x) were synthesized from 1 and various aromatic diamines (x) by both a conventional two-step procedure and a one-step procedure, and the properties were compared with those of the polyimides (PI2x) previously prepared from rigid 3,3′′′′′, 4,4′′′′′-p-sexiphenyltetracarboxylic dianhydride (2), the isomer of 1. The values of glass transition (T_g) temperatures are much higher (270–345 °C) than those of the corresponding PI2x, and the decrease in the storage modulus at T_g is larger than that of the corresponding PI2x.

This study demonstrates a low amount of halloysite nanotubes modified by a CVA process remarkably improve the thermal stability of PC nanocomposites. The n-octadecyltrimethoxysilane modifier bearing a longer alkyl tails shows stronger affinity with the matrix than the N-(2-aminoethyl)-3-aminopropyltrimethoxysilane modifier bearing shorter alkyl tails with amino group.

A bis(tert-butyl) isophthalate (B-IP) was utilized as a dissolution inhibitor in chemically amplified three-components resist. In extreme ultraviolet (EUV) exposed area, tert-butyl groups of B-IP were decomposed by the effect of protons generated from photo-acid generator, and B-IP was converted to a carboxylic acid, being played a role of dissolution promoter. Furthermore, B-IP was acted as a plasticizer in the resist and the protons were diffused through the resist easily. The resist containing B-IP was improved its sensitivity and dissolution contrast, although the properties are a relation of trade-off.

We obtained a flexible nano-alloy with a continuous soft, lacy SEB matrix after blending a high-styrene-content styrene-b-styrene-co-butadiene-b-styrene triblock copolymer (S-SEB-S) with a modified poly(2,6-dimethyl-l,4-phenylene ether) (PPE). The simultaneous stress and birefringence measurements revealed that the orientation of the glassy domain is suppressed, and only the soft SEB segments are oriented from the lower strain region in the nano-alloy when compared with those in the S-SEB-S material. Consequently, the S-SEB-S/PPE nano-alloy is flexible despite its blending of the high-styrene-content S-SEB-S with a high-strength PPE.

Conventional preformed particle gels (PPGs) of homo-polyacrylamide have been improved by incorporating an optimized ratio of functional groups, AMPS and NVP. The improved PPG shows acceptable viscoelastic properties, thermal and ionic strength stability when they are exposed and aged under high-temperature (130 °C) and high-salinity (225 000 p.p.m. of TDS) conditions. According to the experimental results obtained, these improved PPG can be used for water control purposes under harsh reservoir conditions.

Temperature dependence of electric current for fully aromatic and semi-aliphatic polyimide films (PIs) having different chemical structures was investigated. The current densities of PIs having a triphenylamine (TPA) structure (pyromellitic dianhydride/DATPA and 3,4,3′,4′-biphenyltetracarboxylic dianhydride/DATPA) significantly increased above 120 °C, which is mainly due to the exponential increase in thermally excited electronic carriers. In contrast, the current density of PIs without TPA structure exhibited smaller temperature dependence, which suggests that ionic current is dominant because of the limited numbers of thermally excited carriers because of their large band gaps (E_g).

The structures and electronic states in polymorphs (Forms I–IV) of PVDF were calculated by the density functional theory at PBE0/cc-pVTZ level. The calculated lattice constants agreed well with experimental values. Derived electronic and vibrational frequencies corresponded closely with the experimental vXPS and IR/Raman spectra, respectively. The amounts of spontaneous polarization in the polar crystal forms (I, III, and IV) were calculated. Those for Forms III and IV were determined for the first time.