Macromolecular Research

Utilization of small-molecule based organic photovoltaic (OPV) devices has received strong attention due to their easy preparation, purification, and batch-to-batch resemblance in properties. In this work, a series of simple benzothiadiazole and triphenylamine-containing molecules were synthesized, and their application to organic photovoltaic devices was investigated. The absorption spectra demonstrated that the absorption wavelength of the small molecules could be tuned dramatically by extension of molecular structure from donor-acceptor-acceptor (D-A-A’) to A’-A-D-D-A-A’ sequences. Due to the intramolecular energy transfer from the acceptor to donor and vice versa in D-A-A’ structures in prepared molecules, the maximum emission wavelengths were red-shifted gradually with the increase of chain length. Bulk heterojunction (BHJ) type solar cell devices were fabricated by using the small molecules as donors and (6,6)-phenyl C61-butyric acid methyl ester (PC61BM) as acceptor (2:1), gave maximal open circuit voltage of the photovoltaic cells of 0.59 V and the power conversion efficiencies of the devices were measured 0.83% under AM 1.5G irradiation (100 mWcm-2).

Clay platelets have been used to make clay polymer nanocomposite (CPN) in order to enhance the barrier properties of plastic substrates and sputtered barrier films. Clay platelets tend to be randomly dispersed and should be oriented in the film direction to achieve effective barrier properties. In this work, well-oriented nanocomposites were prepared on substrates by adopting a dry lamination process between two heated rubber rolls during the curing step. Dry lamination enabled the clay platelets to be oriented upon application before the sample was completely cured, and the final curing step froze the structure to maintain the orientation. The dry lamination time was optimized at a maximum peak of isothermal curing reaction using DSC. Through characterization via XRD and TEM, it was confirmed that clay platelets are well dispersed and exfoliated in the CPN. The CPN with highly oriented clay platelets enhanced the barrier properties to reach a water vapor transmittance rate of 5.5×10-4 g/m2/day, while maintaining optical properties.

In the petroleum industry, water-soluble polymers can be used as oil displacement agents. However, the use of water-soluble polymers is limited because of poor temperature and salt resistance. To improve temperature and salt resistance, a weakly cationic polymer with large side groups (PAM/AMPS/VI) was prepared by copolymerizing acrylamide (AM) with 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and 1-vinylimidazole (VI). The viscosity of PAM/AMPS/VI water solutions can be increased more than 20 mPa·s compared with PAM/AMPS. In addition, the viscosity of the solution increased continuously after aging at 80 °C, showing good temperature and salt stability. The protonated tertiary amine in the imidazole ring electrostatically interacts with the sulfonic group, increasing the viscosity and salt resistance of the polymer. The five-membered ring of imidazole also enhances the rigidity of the polymer chain and improves the temperature tolerance. As a confirm of the result, a complete spatial network of PAM/AMPS/VI was observed in scanning electron microscopy (SEM) micrographs. Using weak cationic polymers with large side groups can provide a reference for the design of new temperature tolerance and salt resistant polymer.

Regulation of cell-material interactions is an important factor for modulating the cell function in many tissue engineering applications. A more attractive strategy for enhancing the cell-material interactions is to mimic the physical and chemical features of the native extracellular matrix (ECM). The main goal of this study was to develop ECM-like substrates that can control the cell-material interactions including adhesion, spreading, proliferation and differentiation. Poly(L-lactide-co-ɛ-caprolactone) (PLCL) fibrous meshes were fabricated using electrospinning. The meshes were functionalized with acrylic acid (AAc) using γ-ray irradiation, and Arg-Gly-Asp (RGD)-containing peptide was immobilized on the resulting mesh as a cell adhesive ligand. The adhesion and proliferation of the MC3T3-E1 pre-osteoblastic cells grown on the RGD-AAc-PLCL fibrous meshes were greater than those of the cells grown on the other fibrous meshes for up to 7 days. In addition, mature formation of F-actin stress fibers and focal adhesion (co-localized with vinculin) was only observed on the RGD-AAc-PLCL meshes. Moreover, the ALP activity and calcium content on the RGD-AAc-PLCL meshes were approximately 7.5 and 6.7 times higher than those on the other meshes, respectively. In addition, the expression of selected osteogenic genes, Cbfa1, ALP, and OCN, was significantly up-regulated (at least 5 to 9.7 times greater) on the RGD-AAc-PLCL meshes. This suggests that peptide-modified fibrous meshes eliciting desirable cellular responses may provide a useful tool for many tissue engineering applications.

The photostabilization and cure kinetics of UV-curable, optical resins containing various formulations of photostabilizers were investigated to determine the system with the highest cure conversion and durability. Photo-DSC analysis revealed that increasing the concentration of a UV absorber (UVA) decreased both the cross-link density and the cure rate due to competition for the incident photons between the photoinitiator and the UVA, whereas including a hindered amine light stabilizer (HALS) hardly affected either the cure conversion or the cure rate due to its very low absorption of 365 nm. This result was confirmed by FTIR-ATR spectroscopy and UV-visible spectroscopy analyses. QUV ageing experiments showed that the cure conversion and durability were the highest for the UVA/ HALS formulation at a ratio of 1 : 2, which is due to their synergistic action.

The dispersion of starch as a filler in hydrophobic ethylene-co-vinyl acetate (EVA) rubber is an issue. To obtain a fine dispersion of starch in EVA rubber, EVA/starch blends were prepared by reactive extrusion in the presence of maleic anhydride (MA), benzoyl peroxide (BPO), and glycerol. MA, BPO, and glycerol play the role of coupling agent, free-radical initiator, and plasticizer, respectively. Molau experiment and Fourier transform infrared spectroscopy (FTIR) results showed that EVA chains were grafted onto the surface of starch particles during reactive extrusion via a free-radical grafting mechanism. As a result, EVA-g-starch copolymers acted as a compatibilizer, leading to fine dispersion of starch and strong interfacial adhesion between the starch and the EVA matrix. Scanning electron microscope (SEM) images showed that the starch particle size reduced from hundreds micrometers in the case of physical blending to approximately 1 micrometer in the case of reactive blending, and consequently, the EVA rubber was effectively reinforced by the incorporation of starch and the reactive compatibilization (e.g., the tensile strength of the EVA/starch (50/50, wt/wt) was increased by a factor of 6 after the addition of 0.9–1.8 wt% MA). The property stability of starch compounds is usually an issue, while the mechanical properties of the (compatibilized) EVA/starch blends reported in this article were stable during storage.

While biodegradable polyesters or their copolymers have been used widely as scaffolding materials in tissue engineering, these polymers intrinsically lack the cell-binding motifs on the surface. In this study, a GL-PEG, which is a poly(ethylene glycol) monoacrylate combined with glycerol (G)-lactide (L) triols, was synthesized and fabricated into a porous three dimensional (3D) structure. In addition, peptide ligands, Arg-Gly-Asp (RGD) or Arg-Glu-Asp-Val (REDV) were grafted directly onto the GL-PEG, producing GL-PEG-GRGD and GL-PEG-GREDV scaffolds to improve the specific cell adhesion. Both GL-PEG and GL-PEG-GRDG scaffolds were also prepared as a control. The ESCA spectra showed that peptide-grafted GL-PEG carried a nitrogen peak, which is indicative of the amine group in the peptide sequence. The nitrogen content in the GL-PEG-peptides was significantly higher than that on the the GL-PEG. When the peptide-grafted GL-PEG scaffolds were seeded with fibroblasts and endothelial cells (ECs) and cultured for up to 4 days, specific cell interactions were identified by scanning electron microscopy (SEM). More fibroblasts were found on the GL-PEG-GRGD scaffold but more ECs were found attached to GL-PEGGREDV. The total protein assay also supported the same trend that the fibroblasts/GL-PEG-GRGD or EC/GL-PEGGREDV constructs had the highest protein content with the specific cells, compared with the other groups. This data suggests that cell adhesion could be specific and dependent on the type of peptide ligands. Such 3D porous and crosslinked peptide-grafted GL-PEG scaffolds can be very useful for harboring specific cell populations for tissue engineering and vascular stents.

In the present paper, the temperature and salt-dependent dielectric properties of poly(ethylene oxide) (PEO) and poly(vinyl pyrrolidone) (PVP) blend matrix complexed with LiBOB are investigated in the frequency range 1 Hz to 1 MHz and temperature range 40 °C to 100 °C (@10 °C). The real and imaginary part of the complex permittivity, complex conductivity have been simulated in the whole frequency window and the various fitted parameters were evaluated respectively. The estimated value of the dielectric constant and the ac conductivity increases with the increase of temperature. The lowering of relaxation time and hopping length is observed with the salt addition that is in correlation with the complex conductivity results. The modulus formalism was used to analyze the recorded dielectric data. The dc conductivity, hopping frequency, and segmental motion are strongly coupled with each other as evidenced by the Debye-Stoke-Einstein (DSE) plot. An interaction mechanism has also been proposed to explore the effect of temperature on the hopping length, relaxation time, hopping potential barrier and the segmental motion of the polymer chain.

Heteroleptic ruthenium-complexed ladder-like structured polysilsesquioxane (LPSQ-Ru) was synthesized by post coordination reaction of bidentate ligand side chains in LPSQ with reactive Ru(II) complexes, which was well characterized by 1H and 29Si NMR, FT-IR, and spectroscopic techniques. The photophysical properties of LPSQ-Ru were examined by UV and PL analyses in both solution and solid states, comparing to analogous polymers of ruthenium-complexed polystyrene (PS-Ru). Obtained absorptions of LPSQ-Ru and PS-Ru were broadened ranging from 390-490 nm regardless of the states. However, LPSQ-Ru exhibited higher and shaper PL emission spectrum in comparison to that of PS-Ru, particularly in the solid state, because Ru-complexes in LPSQ were much effectively isolated, preventing their aggregations due to the rigid double strained siloxane backbone. This extinguished photophysical property in LPSQ-Ru kept after intensive thermal treatment at 250 °C for 90 min, which was not achieved in PS-Ru (~5-fold decrease). These differences originated from the backbone structures were also appeared in electrochemical properties in the solid states.