Research articles

Changes in the crystalline phase structures and molecular mobility of a semi-crystalline P(VDF₇₅/TrFE₂₅) have been analyzed using solid-state ¹⁹F MAS and ¹H→¹⁹F CP/MAS NMR spectroscopy. The conformational exchange motion at the head-to-tail linkage has a key role for the ferroelectric→paraelectric phase transition. The anomalous decrease in the signal intensity of the amorphous peaks and its T_1ρ^F value similar to the crystalline domain at 122 °C indicate the existence of cooperative motion occurring in both phases just above the transition temperature (T_c).

Proton spin diffusion (SD) experiments performed on low-field NMR spectrometers are a valuable means for the estimation of domain sizes in phase-separated polymers. We here investigate the interplay of the SD effect and fast T₁ relaxation by means of fits of data taken for two different polystyrene-polybutadiene di- and multiblock copolymers to numerical simulations. We demonstrate the necessity to explicitly include an interphase of intermediate mobility, and further show that a previously published, popular calibration of the SD coefficient for mobile polymer phases based on the transverse relaxation time T₂ should be revised.

The quaternary carbons linking to sulfur as cross-linking junction was assigned to the molecular singularity, which had an important role in the outstanding mechanical properties of natural rubber.

Infrared spectroscopy is used to probe the melting point depression and crystallization of polycaprolactone in the presence of supercritical CO₂. Comparison of the amorphous and crystalline peaks at 41 °C shows a melting point at 100 bar CO₂. Increasing this temperature further reduces the pressure required to melt polycaprolactone. Infrared spectroscopy is also used to probe the crystallization of polycaprolactone during CO₂ venting.

Number of aggregations is very small when THF was used compared with methanol and methanol–water. Aggregation of copolymers was difficult in THF due to back-folding and looping of PDMS block. This was unfavorable as it increases free energy of system. This probably resulted in higher CMC of pHEMA-b-PDMS-b-pHEMA copolymers in THF than in methanol. Micellar size of most of triblock copolymers in THF was smaller than in methanol.

Two topics concerning the utilization of internal and external magnetic field gradients are discussed. The first topic concerns the transport of conformons in the quasi-ordered phase of a regioregular, π-conjugated polymer, poly(4-methylthiazole-2,5-diyl), using a combination of longitudinal and transverse relaxation dispersion measurements. The effects of conformon diffusion on the relaxation exponent were successfully estimated via a numerical approach that used the Fourier spectrum solution of the one-dimensional Bloch-Torrey equation. The second topic demonstrates a low-cost magnetic resonance imaging method using a magnetic field gradient from a neodymium ferromagnet. Spin echo experiments are shown for three-layered thin films of PDMS/PTFE/PDMS under a large magnetic field.

The images of ¹H spin density, ¹H T₂ and diffusion coefficient (D) of water molecules in the layer of silk-based vascular grafts (VG) coated by different materials that are silk fibroin or polyurethane were non-destructively observed in water using ¹H MR imaging. The inner and outer coating materials affect significantly the amount and mobility of water molecules in the VG.

Iodine transfer dispersion polymerization (dispersion ITP) with CHI₃ and reversible chain transfer-catalyzed dispersion polymerization (dispersion RTCP) with N-iodosuccimide (NIS) of methyl methacrylate (MMA) were successfully applied to supercritical carbon dioxide (scCO₂) medium. Both polymerizations proceeded smoothly and yielded the polymeric product as a powder. In both systems, the number-average molecular weights increased with increasing conversion and polydispersity (M_w/M_n) was maintained at low values throughout the polymerizations. A chain extension test indicated that PMMA prepared by dispersion ITP and dispersion RTCP in scCO₂ had high degrees of livingness.

Mono- and bis-stannylation at the chain ends of regioregular poly(3-hexylthiophene) (P3HT) were conducted by post-functionalization of P3HT synthesized through Ni-catalyzed Grignard metathesis polymerization. Lithiation of P3HT with s-BuLi and subsequent stannylation with Me₃SnCl led to the formation of bis-stannylated P3HT. The highest conversion of 81% was achieved with the additive N,N,N′,N′-tetramethylethylenediamine (TMEDA), which could enhance the stability of the lithiated compound. On the other hand, mono-stannylated P3HT was synthesized without contamination by bis-stannylated P3HT through successive reactions with a Grignard reagent and Me₃SnCl.

The endo-structure tetracarboxylic dianhydride was a crystal and could be divided into meso and racemic isomers. However, the exo-structure tetracarboxylic dianhydride was a highly viscous liquid. Polyimides derived from these tetracarboxylic dianhydrides and 4,4′-oxydianiline were colorless and organosoluble. The exo-structure polyimides had better mechanical properties and higher glass transition temperatures than the endo-structure polyimides.

Various nonspherical polystyrene (PS) particles were prepared by slow evaporation of toluene from homogeneous PS/hexadecane (HD)/toluene droplets dispersed in surfactant aqueous solutions at room temperature, followed by rapid removal of HD from PS/HD particles with various phase-separated morphologies. The morphology of PS/HD particles could be controlled by tuning each interfacial tension employing various types of surfactants. Consequently, hemispherical PS particles with flat surface were obtained from phase-separated PS/HD/toluene droplets having Janus structure, when Emulgen 931 was used as the surfactant.

Our study explored layered microstructures and the resistivity of injection stainless steel fiber-filled polymer composite. Figure 2 in this paper shows the microstructures at different layers of the molding, which was used to discuss the distribution and mass fraction of the fibers in the matrix at different layers. Based on the results of Figure 2, we discussed the effects of injection parameters on the resisitivity of each layer of the molding.

Fluorescence emission spectra of PCL-co-P4HCA50 with UV irradiation at λ=302 nm for various times, and the inset shows the fluorescent intensity changes with UV irradiation time.

Poly(3,4-ethylenedioxythiophene) is electropolymerized on a single-walled carbon nanotube film to reduce sheet resistance without causing loss in transparency.

The polysilsesquioxane (PSQ) containing ethylxanthate groups was used for the graft polymerization of several acrylamide monomers by MADIX process. The controlled graft polymerization gave the PSQs containing the polymeric components as the graft chains. The introduction of the polymers provided an amphiphilic property to the polysilsesquioxaneane. In addition, the grafted PSQ containing poly(acryloyl morpholine) showed a thermoresponsive property in an aqueous solution. The reversible hydrophobic aggregation of the polysilsesquioanes was observed at ca. 80°C.

π-Conjugated polymers are synthesized by C–H and C–X polycondensation of 2-(4-haloaryl)thiophene monomers with a nickel catalyst and Knochel–Hauser base (TMPMgCl·LiCl (chloromagnesium 2,2,6,6-tetramethylpiperidide lithium chloride salt)). The C–H functionalization polycondensation reaction of a monobrominated monomer undergoes dehydrobrominative polymerization with an equimolar amount of TMPMgCl·LiCl and a catalytic amount of NiCl₂dppp to afford poly(2,5-thienylene-1,4-phenylene) and poly(2,5-thienylenepyridine-2,5-diyl) in reasonable yields. Polycondensation with triflate as a leaving group proceeds under similar conditions to afford poly(thienylenephenylene) with excellent yield. Poly(benzodithiophene) is also found to be obtained by the reaction of the corresponding monobrominated benzodithiophene in the presence of a nickel-catalyst-bearing N-heterocyclic carbene as a ligand.

An isotope-labeled hornet (Vespa) cocoon in which the Ala carbons of silk proteins were substituted with ¹³C was successfully obtained by feeding a mixture of larval saliva with [¹³C₃]Ala to mature larvae. The Ala fraction in the α-helix conformation of hornet silk was estimated by obtaining high-resolution ¹³C solid-state NMR spectra of the labeled cocoon, which also helped in understanding the molecular structure of hornet silk.

Monodispersed spherical silver nanoparticles with 35±5 nm diameter were prepared by microwave irradiation of an AgNO₃ aqueous solution in poly(ethylene glycol) (PEG). Thanks to the hydroxyl groups at the chain-ends of the PEG, the matrix of the Ag nanoparticles suspension was well incorporated into a polyurethane backbone, allowing a good distribution of the metal particles inside the final nanocomposite without aggregation. An optimal antibacterial activity was observed for a 35 p.p.m. Ag concentration against P. aeruginosa and E. faecalis without significant variation of the intrinsic physicochemical properties of polyurethane material.

m-Terphenyl-based random copolymers of chiral and achiral amidines and its complementary homopolymer of achiral carboxylic acids self-assembled to form complementary double helices with a preferred-handed helical sense via interstrand amidinium–carboxylate salt bridges, thus showing induced cotton effects in the π-conjugated main-chain chromophore regions. A unique amplification of the helical chirality (‘the sergeants and soldiers effect’) was, for the first time, observed during the double-helix formation.

The crystalline structure and molecular mobility of PVDF blended with PMMA at various fractions were investigated by solid-state ¹⁹F MAS NMR spectroscopy. The origin of the characteristic peaks observed for typical polymorphs of PVDF (α-, β- and γ-forms) are explained based on DFT calculations. The dominant crystalline form in the blends of [PVDF/PMMA]=[80/20], [70/20] and [50/50] is α-form containing a small portion of β-form, whereas that of [65/35], [60/40] and [55/45] consists of β-form and γ-form. In contrast, no crystalline structure is found in [45/55], [40/60] and [20/80], indicating that PVDF and PMMA chains are miscible at the molecular level.