Controlled grafting of cationic poly[(ar-vinylbenzyl)trimethylammonium chloride] on hydrogen-terminated silicon substrate by surface-initiated RAFT polymerization

Controlled grafting of well-defined cationic poly[(ar-vinylbenzyl)trimethylammonium chloride] [poly(VBTAC)] brushes on a hydrogen-terminated silicon substrate (SiH) was performed via surface-initiated RAFT polymerization. The azo-initiator was immobilized on the SiH surface via a three step process involving (i) coupling of the t-butyloxycarbonyl (t-BOC) protected allylamine to the SiH surface under UV irradiation, (ii) conversion of the t-BOC protected allylamine groups into the free amine groups by trifluoroacetic acid, and (iii) the amide reaction of allylamine with the 4,4′-azobis(4-cyanopentanoyl chloride) initiator. The living polymerization produced silicon substrate coated with well-defined cationic poly(VBTAC) with a target molecular weight and a grafting density as high as 0.93 chains/nm².     

UV-light assisted single step route to functional PEEK surfaces

Polyether ether ketone (PEEK) is a thermoplastic polymer of high technological relevance and is composed of repeating phenyl ether and benzophenone units. In the present work we will demonstrate the potential of UV irradiation assisted generation of free radicals on the surface benzophenone units to graft a variety of polymer chains on the PEEK surface. Both “grafting-to” and “grafting-from” approaches were explored by using different monomers and polymers. Styrene, butyl acrylate (BA), vinyl phosphonic acid (VPA), acrylic acid (AA), polyacrylic acid (PAA) and monomethoxy terminated oligo (ethylene glycol) methacrylate (MeOEGMA) were successfully utilized for this purpose. The functionalized membranes were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier-transformed Infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM), and contact angle (CA) goniometry. PAA and PVPA functionalized PEEK surfaces exhibited pH responsive wettability behavior. PAA functionalized PEEK surfaces were further modified with lysine, which led to the controlled surface wettability over a broader pH range as compared to the simple PAA functionalized surface. The grafting with polyMeOEGMA rendered PEEK surface with nonfouling properties against bacterial growth. Employing this highly economical and simple method, the surface properties of PEEK can be modulated and tuned according to a specific application.     

Trans-Cinnamic Acid Increases Adiponectin and the Phosphorylation of AMP-Activated Protein Kinase through G-Protein-Coupled Receptor Signaling in 3T3-L1 Adipocytes

Adiponectin and intracellular 5′adenosine monophosphate-activated protein kinase (AMPK) are important modulators of glucose and fat metabolism. Cinnamon exerts beneficial effects by improving insulin sensitivity and blood lipids, e.g., through increasing adiponectin concentrations and AMPK activation. The underlying mechanism is unknown. The G_i/G_o-protein-coupled receptor (GPR) 109A stimulates adiponectin secretion after binding its ligand niacin. Trans-cinnamic acid (tCA), a compound of cinnamon is another ligand. We hypothesize whether AMPK activation and adiponectin secretion by tCA is transmitted by GPR signaling. Differentiated 3T3-L1 cells were incubated with pertussis toxin (PTX), an inhibitor of G_i/G_o-protein-coupling, and treated with different tCA concentrations. Treatment with tCA increased adiponectin and the pAMPK/AMPK ratio (p ≤ 0.001). PTX incubation abolished the increased pAMPK/AMPK ratio and adiponectin secretion. The latter remained increased compared to controls (p ≤ 0.002). tCA treatment stimulated adiponectin secretion and AMPK activation; the inhibitory effect of PTX suggests GPR is involved in tCA stimulated signaling.     

Double-responsive core-shell-corona micelles from self-assembly of diblock copolymer of poly(t-butyl acrylate-co-acrylic acid)-b-poly(N-isopropylacrylamide)

Self-assembly of poly(t-butyl acrylate-co-acrylic acid)-b-poly(N-isopropylacrylamide) [P(tBA-co-AA)-b-PNIPAM], which was obtained from part hydrolysis of PtBA-b-PNIPAM synthesized by sequential atom transfer radical polymerization (ATRP) was studied. Thermo- and pH-responsive core-shell-corona (CSC) micelles with different structures were formed from (PtBA-co-PAA)-b-PNIPAM in aqueous solution. At pH 5.8 and 25 °C, the block copolymer self-assembled into spherical core-shell micelles with hydrophobic PtBA segments as the core, hydrophilic PAA/PNIPAM segments as the mixed shell. Increasing temperatures, core-shell micelles converted into CSC micelles with PtBA as the core, collapsed PNIPAM as the shell and soluble PAA as the corona. Moreover, decreasing pH at 25 °C, PAA chains collapsed onto the core resulting in CSC micelles with PtBA as the core, PAA as the shell and PNIPAM as the corona.     

One-pot synthesis of molecular glass photoresists based on β-cyclodextrin containing a <Emphasis Type="Italic">t</Emphasis>-butyloxy carbonyl group for i-line lithography

Positive chemically amplified molecular glass with pendant t-butyloxy carbonyl (t-BOC) groups based on β-cyclodextrin (β-CD) was prepared. The β-CD derivatives were obtained from the reaction of β-CD and di-tert-butyl dicarbonate (DBDC) in the presence of 4-dimethylaminopyridine, and the protecting ratio was controlled using various feed amounts of DBDC. Fourier-transform infrared spectroscopy and proton nuclear magnetic resonance were employed to characterize the chemical structure, indicating that the synthesis was successful. Thermal behavior was characterized by thermogravimetric analysis; the results showed that the initial thermal decomposition temperature occurred at approximately 160 °C, which could satisfy the lithography process. Ultraviolet–visible spectrophotometer indicated that the t-BOC-protected β-CD derivatives had low absorbance at 365 nm wavelength. Additionally, X-ray diffraction analysis results showed that the β-CD derivatives had amorphous form, and exhibited excellent film-forming property. The photoresists consisting of different t-BOC protecting groups showed high sensitivity when exposed to 365 nm light and post-baked at 105 °C for 90 s, followed by developing in 2.38 wt% aqueous tetramethylammonium hydroxide solution at room temperature. An enhanced line and space positive patterns with 1 μm resolution were delineated according to digital microscope.     

Synthesis of well‐defined responsive membranes with fixable solvent responsiveness

A versatile method is described to synthesize a new family of solvent‐responsive membranes whose response states can be not only tunable but also fixable via ultraviolet (UV) irradiation induced crosslinking. The atom transfer radical polymerization (ATRP) initiator 2‐bromoisobutyryl bromide was first immobilized on the poly(ethylene terephthalate) (PET) track‐etched membrane followed by room‐temperature ATRP grafting of poly(2‐hydroxyethyl methacrylate) (PHEMA) and poly(2‐hydroxyethyl methacrylate‐co‐2‐(dimethylamino)ethyl methacrylate) (P(HEMA‐co‐DMAEMA)) respectively. The hydroxyl groups of PHEMA were further reacted with cinnamoyl chloride (a photosensitive monomer) to obtain photo‐crosslinkable PET‐g‐PHEMA/CA membrane and PET‐g‐P(HEMA/CA‐co‐DMAEMA) membrane. The length of grafted polymer chains was controllable by varying the polymerization time. X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy in attenuated total reflection and thermogravimetric analysis were employed to characterize the resulting membranes. The various membrane surface morphologies resulting from different states of the grafted chains in water and dimethylformamide were characterized by scanning electron microscopy. It was demonstrated that the grafted P(HEMA/CA‐co‐DMAEMA) chains had more pronounced solvent responsivity than the grafted PHEMA/CA chains. The surface morphologies of the grafted membranes could be adjusted using different solvents and fixed by UV irradiation crosslinking. © 2014 Society of Chemical Industry     

Grafting of end-functionalized poly(tert-butyl acrylate) to poly(ethylene-co-acrylic acid) film

Poly(tert-butyl acrylate) (PtBA) was grafted to the surface of poly(ethylene-co-acrylic acid) (EAA) film and the pendant groups of the tethered PtBA were modified to create chemically tailored surface modifying layers. The carboxylic acid groups in the copolymer film served as the grafting sites for the covalent tethering of end-functionalized PtBA. The progression of these reactions was monitored using attenuated total reflectance (ATR)-FTIR and X-ray photoelectron (XPS) spectroscopies along with static contact angle measurements. By controlling the reaction conditions, the chemical functionality of the grafted layer ranged from tert-butyl ester (EAA-g-PtBA) to carboxylic acid (EAA-g-PAA) and was demonstrated by corresponding changes in wettability. The choice of PtBA as the tethered polymer allows for the subsequent substitution of the tert-butyl ester groups. To demonstrate, a novel procedure was used to replace the tert-butyl ester with N,N-dimethylethylenediamine (DMEDA) to form EAA-g-PDMEDA. These reaction schemes can be used to create tunable surface-grafted layers with various pendant group chemistries.     

Controllable surface modifications of polyamide by photo‐induced graft polymerization using immobilized photo‐initiators

A novel two‐step UV initiated grafting method has been developed and applied on surface modification of polyamide. Anthraquinone‐2‐sulfonate sodium, an acid dye, was chosen as the photo‐initiator. In the first step, photo‐initiators were ionically bonded onto polyamide through a normal acid dye dyeing process. Vinyl monomers such as acrylic acid were then grafted onto polyamide surface in the following step. During UVA irradiation, not only monomers were grafted onto polymer surface, photo‐initiator itself was also covalently bonded onto polymer. The grafted polymers were characterized by Fourier transform infrared spectrometer (FTIR), X‐ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM).The degree of photo‐grafting can be controlled by adjusting concentrations of photo‐initiator and monomer, as well as UVA exposure time. This process demonstrated the feasibility of efficiently modifying polymer surface under low UV intensity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Analysis of inner structure in high-strength biodegradable fibers by X-ray microtomography using synchrotron radiation

The observation of the inner structure of materials without pretreatment or damage is a very useful analytical method in the field of materials science as well as in medicine and biology. We have carried out a three-dimensional (3D) analysis of biodegradable polyester bacterial-poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] (P(3HB-co-3HV)) fibers with high tensile strength (1.07 GPa) using X-ray microtomography with synchrotron radiation. The inner structure of the fibers was visualized at a spatial resolution of 1 μm. There are many fine voids for one-step-drawn P(3HB-co-3HV) fibers after isothermal crystallization from the result of X-ray microtomography. This revealed that the clear streak reflection along the equator in small-angle X-ray scattering is caused by these fine voids. The recalculated tensile strength of one-step-drawn P(3HB-co-3HV) fibers after isothermal crystallization is suggested to be 2.02 GPa, taking the cross-section area with 52.7% (polymer region) into consideration. These fine voids in fibers seemed to be generated by the volume changes due to the contraction of polymer chains during isothermal crystallization.     

Synthesis and characterization of photo‐crosslinkable polyfluorene with acrylate side‐chains

A photo‐crosslinkable polymer, poly[2,7‐(9,9‐dioctylfluorene)‐co‐2,7‐(9‐hexyl‐9‐(2‐acrylate ethyl)‐9H‐fluorene)] (P3), was synthesized and the photo‐crosslinkable acrylate groups were introduced into the side‐chains of the polyfluorene derivative after its polymerization. This method avoids the possible crosslinkage of the crosslinkable groups on the monomers during polymerization in the traditional synthesis route by the polymerization of the monomers with the crosslinkable side‐chains. The soluble and processable polymer P3 could be crosslinked via the acrylate groups in its side‐chains upon exposure to UV light in nitrogen atmosphere. The crosslinking was confirmed by IR spectroscopy: the IR peak of C?C bond at 1635 cm^?1 decreased and that of the vinyl C? H bond at 742 cm^?1 disappeared after the UV exposure. The absorption spectra of P3 remain unchanged after crosslinking, but a longer wavelength emission at 517 nm appeared in the photoluminescent and electroluminescent spectra of the crosslinked P3, which could be attributed to the formation of keto defects during the photo crosslinking. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2336–2342, 2006     

Monitoring pH-dependent conformational changes in aqueous solutions of poly(methacrylic acid)-b-polydimethylsiloxane copolymer based on fluorescence spectra of pyrene and 1,3-bis(1-pyrenyl)propane

Aqueous solutions of poly(methacrylic acid)-b-polydimethylsiloxane copolymer (PMA-b-PDMS), and reference solutions of PMA homopolymer, were studied as a function of pH using fluorescent probes: pyrene (P) and 1,3-bis(1-pyrenyl)propane (P3P). In both polymers the conformational transition of PMA chains at pH>5 was reflected in the sharp increase of the intensity ratio of the first to the third vibronic band in emission spectra of P; an excimer emission appeared for P3P, as well as for P if the probe concentration was higher than its solubility limit in water. The excimer to monomer intensity ratio of both probes is a sensitive indicator of the conformational transitions of polymer chains, but P3P is significantly more sensitive compared to pyrene. The data clearly indicated that the presence of PDMS blocks markedly facilitated the transition, even though the ratio of dimethylsiloxane to methacrylic acid units in the copolymer was low, 1:34. The absence of the P3P excimer emission at pH≈3 was rationalized by assuming that clustering of sections of PMA chains around pyrene moieties imposes an extended conformation of the probe molecule.     

Chain conformations of syndiotactic poly(m-methylstyrene) in the crystalline state

A conformational energy analysis of the isolated chain of syndiotactic poly(m-methylstyrene) under the constraint of a crystalline field is reported. Two different minimum energy conformations having similar energy have been found; the trans-planar conformation with tcm symmetry and the two-fold helical conformation with s(2/1)2 symmetry, according with the observed polymorphic behavior of this polymer. The calculated chain axes are in agreement with the experimental axes of 5.1 and 7.9 Å found for the different polymorphic forms of syndiotactic poly(m-methylstyrene). However, only a metastable disordered modification (form III) having chains in trans-planar conformation has been described. This indicates that, even though the trans-planar conformation is, in the isolated chain as stable as the helical conformation, the packing of the chains in helical conformation is probably more efficient than that of the trans-planar chains.     

Amphiphilic cylindrical brushes with poly(acrylic acid) core and poly(n-butyl acrylate) shell and narrow length distribution

Core-shell cylindrical polymer brushes with poly(t-butyl acrylate)-b-poly(n-butyl acrylate) (PtBA-b-PnBA) diblock copolymer side chains were synthesized via ‘grafting from’ technique using atom transfer radical polymerization (ATRP). The formation of well-defined brushes was confirmed by GPC and ¹H NMR. Multi-angle light scattering (MALS) measurements on brushes with 240 arms show that the radius of gyration scales with the degree of polymerization of the side chains with an exponent of 0.57±0.05. The hydrolysis of the PtBA block of the side chains resulted amphiphilic cylindrical core-shell nanoparticles. In order to obtain a narrow length distribution of the brushes, the backbone, poly(2-hydroxyethyl methacrylate), was synthesized by anionic polymerization in addition to ATRP. The characteristic core-shell cylindrical structure of the brush was directly visualized on mica by scanning force microscopy (SFM). Brushes with 1500 block copolymer side chains and a length distribution of l_w/l_n=1.04 at a total length l_n=179 nm were obtained. By choosing the proper solvent in the dip-coating process on mica, the core and the shell can be visualized independently by SFM.     

Fluorescent photoimaging with polymers having protected quinizarin dye precursors by a dry process based on chemical amplification

Styrene monomers, possessing three kinds of protected quinizarin (Qz) dye precursors such as tBOC, acetyl and tosyl groups, have been prepared and copolymerized with MMA in high yields to obtain protected-Qz precursor polymers (pr-QzP). Thermal and photoinduced acidolytic deprotection behaviors were investigated to confirm the regeneration of the Qz moieties in the polymer films by thermal and spectral analyses. Lithographic fluorescent photoimaging on spin-cast films of pr-QzP containing a photoacid generator resulted in high resolution and sensitivity by a dry process based on chemical amplification. In the dry lithography process, finely resolved sub-0.4-micrometer fluorescent patterns were delineated on the thin precursor polymer films without using a developer.     

Association behavior of poly(methyl methacrylate-b-methacrylic acid-b-methyl methacrylate) in aqueous medium

ABA type triblock amphiphilic polyelectrolyte consisting of poly(methyl methacrylate-block-methacrylic acid-block-methyl methacrylate) (P(MMA-b-MAA-b-MMA)) was synthesized by atom transfer radical polymerization technique and the self-assembly behavior of the polymers in aqueous solution was studied over the course of neutralization. Combination of potentiometric and conductometric titrations along with dynamic light scattering techniques were used to investigate the size and shape of aggregates at various degrees of neutralization. The effect of hydrophobic-hydrophilic (MMA-MAA) ratio and polymer chain length on the aggregation behavior during neutralization was studied. P(MMA-b-MAA-b-MMA) with longer MMA segment self-assembles via the closed association mechanism through stronger self-entanglement of MMA chains, whereas P(MMA-b-MAA-b-MMA) with shorter MMA chain self-assembles via the open association mechanism, as confirmed by transmission electron microscopy. Conductometric titration was used to determine the counterion condensation during the course of neutralization. When the charge density of micelle approaches a critical value as neutralization progresses, counterion condensation of Na⁺ ions on the polymer chains occurs. The effect of counterion condensation on the aggregation behavior during neutralization was elucidated.     

The use of 2,6-bis (N-pyrazolyl) pyridine as an efficient dopant in conjugation with poly(ethylene oxide) for nanocrystalline dye-sensitized solar cells

Poly(ethylene oxide) (PEO)/2,6-bis (N-pyrazolyl) pyridine (BNPP) polymer electrolyte based photoelectrochemical cells have been fabricated with [cis-dithiocyanato-N, N-bis (2,2′ bipyridyl-4, 4′ dicarboxylic acid)ruthenium(II)] dihydrate (N3 dye) dye complex as the sensitizer and nanoporous TiO₂ film as photo anode. The introduction of 2,6-bis (N-pyrazolyl) pyridine into the poly (ethylene oxide) matrix reduces the crystallinity of the polymer and enhances the mobility of I⁻/I₃⁻ redox couple resulting in an improved performance with a higher conversion efficiency of 8.8% in terms of light energy to electric energy when compared to that of the corresponding dye-sensitized nanocrystalline TiO₂ solar cell.     

Synthesis of amphiphilic ethyl cellulose grafting poly(acrylic acid) copolymers and their self-assembly morphologies in water

Amphiphilic ethyl cellulose (EC)-g-poly(acrylic acid) (PAA) copolymers were synthesized by atom transfer radical polymerization (ATRP). Firstly, ethyl cellulose macro-initiators with the degree of the 2-bromoisobutyryl substitution of 0.04 and 0.25 synthesized by the esterification of the hydroxyl groups remained in EC macromolecular chains and the 2-bromoisobutyryl bromides. Secondly, tert-butyl acrylate was polymerized by ATRP with the ethyl cellulose macro-initiator and EC-g-PtBA copolymers were prepared. Finally, the EC-g-PAA copolymers were prepared by hydrolyzing tert-butyl group of the EC-g-PtBA copolymers. The grafting copolymers were characterized by means of GPC, ¹H NMR and FTIR spectroscopies. The molecular weight of graft copolymers increased during the polymerization and the polydispersity was low. A kinetic study showed that the polymerization was first-order. Meanwhile, EC-g-PAA copolymers were self-assembled to micelles or particles with diameters of 5 nm and 100 nm in water (pH = 10) when the concentration was 1.0 mg/ml.     

Two-step formation of entanglement from disentangled polymer melt detected by using nucleation rate

“How do chain molecules spontaneously entangle from completely disentangled polymer melt?” remains the most interesting unsolved problem. In order to solve this problem, we used the concept that the melt of “nascent” polymer crystallized during polymerization just after melting does not include any entanglements. We succeeded in detecting the increase of entanglement density ν_e with the increase of annealing time Δt above the equilibrium melting temperature before isothermal crystallization. The increase of ν_e was detected by observing the decrease of nucleation rate I from the melt of nascent polymer with different Δts. I is a very sensitive detector of entanglements because the nucleation is a rearrangement process of chains to the crystalline lattice through the disentanglement. Therefore, I is significantly suppressed with the increase of ν_e. We found a two-step decrease of I with an increase of Δt for the first time. This should correspond to a two-step increase of ν_e with an increase of Δt. This indicates that simple entanglements such as twist or knot with lower order (one time knot) were formed within short time and then the complicated ones such as knot with higher order (two or three times knots) or loops (entanglements by loop conformation) were formed.     

Upper critical solution temperature—type cononsolvency of poly(N,N-dimethylacrylamide) in water—organic solvent mixtures

The behaviour of linear poly(N,N-dimethylacrylamide) (PDMAM) chains was studied by turbidimetry and viscometry in mixtures of water with the polar organic solvents methanol, dioxane and acetone. The swelling-deswelling behaviour of PDMAM gels in the same solvent mixtures was also investigated. Contrary to the behaviour in water-methanol mixtures, in water-dioxane and water-acetone mixtures a significant shrinkage of polymer chains and deswelling of polymer gels, followed by phase separation, was observed for high organic solvent fractions. Cononsolvency phenomena were found to be temperature-dependent, as demixing occurred upon decreasing temperature. This upper critical solution temperature (UCST) phase separation behaviour in mixed solvents was studied by turbidimetry and compared to the well-known lower critical solution temperature (LCST) behaviour of poly(N-isopropylacrylamide) (PNIPAM) in similar solvents mixtures.     

Binding of chrysophenine G by methyl cellulose and poly(vinyl alcohol)

Equilibrium constants (nK) for the binding of Chrysophenine G by methyl cellulose (MC) and poly(vinyl alcohol) (PVA) were determined spectrophotometrically in the temperature range 15–40°C. The polymer chains of PVA extended by the dye binding but those of MC shrank slightly. The enthalpy change and the entropy change for the binding by MC were negative and positive, respectively, whereas those for the binding by PVA were both negative. When the dye was bound to the extended polymer chains, the contribution of the entropy term to the binding increased. The rate of the dye bindings was studied by means of the temperature jump method. For the dye binding to PVA, the whole relaxation process finished in a very rapid step. On the other hand, for dye binding to MC, the initial rapid step was followed by two successive slower steps; the relaxation times for the slower steps were independent of the polymer concentration. The results were interpreted in terms of the stiffness of polymer chain of MC; the conformational change of the stiff chains to accommodate the dye in stable states seems to be the rate determining step in each slow relaxation.