Synthesis and characterization of Poly(vinylphosphonic acid) for proton exchange membranes in fuel cells

Vinylphosphonic acid (VPA) was polymerized at 80 ºC by free radical polymerization to give polymers (PVPA) of different molecular weight depending on the initiator concentration. The highest molecular weight, Mw, achieved was 6.2 x 104 g/mol as determined by static light scattering. High resolution nuclear magnetic resonance (NMR) spectroscopy was used to gain microstructure information about the polymer chain. Information based on tetrad probabilities was utilized to deduce an almost atactic configuration. In addition, 13C-NMR gave evidence for the presence of head-head and tail-tail links. Refined analysis of the 1H NMR spectra allowed for the quantitative determination of the fraction of these links (23.5 percent of all links). Experimental evidence suggested that the polymerization proceeded via cyclopolymerization of the vinylphosphonic acid anhydride as an intermediate. Titration curves indicated that high molecular weight poly(vinylphosphonic acid) PVPA behaved as a monoprotic acid. Proton conductors with phosphonic acid moieties as protogenic groups are promising due to their high charge carrier concentration, thermal stability, and oxidation resistivity. Blends and copolymers of PVPA have already been reported, but PVPA has not been characterized sufficiently with respect to its polymer properties. Therefore, we also studied the proton conductivity behaviour of a well-characterized PVPA. PVPA is a conductor; however, the conductivity depends strongly on the water content of the material. The phosphonic acid functionality in the resulting polymer, PVPA, undergoes condensation leading to the formation of phosphonic anhydride groups at elevated temperature. Anhydride formation was found to be temperature dependent by solid state NMR. Anhydride formation affects the proton conductivity to a large extent because not only the number of charge carriers but also the mobility of the charge carriers seems to change.

Core-shell microspheres with surface grafted poly(vinyl alcohol) as drug carriers for the treatment of hepatocellular carcinoma

Core(polyvinyl neodecanoate-ethylene glycol dimethacrylate)-shell(polyvinyl alcohol) (core (P(VND-EGDMA))-shell(PVA)) microspheres were developed by seeded polymerization with the use of conventional free radical and RAFT/MADIX mediated polymerization. Poly(vinyl pivalate) PVPi was grafted onto microspheres prepared via suspension polymerization of vinylneodecanoate and ethylene glycol dimethacrylate. The amount of grafted polymer was found to be independent from the technique used with conventional free radical polymerization and MADIX polymerization resulting into similar shell thicknesses. Both systems—grafting via free radical polymerization or the MADIX process—were found to follow slightly different kinetics. While the free radical polymerization resulted in a weight gain linear with the monomer consumption in solution the growth in the MADIX controlled system experienced a delay. The core-shell microspheres were obtained by hydrolysis of the poly(vinyl pivalate) surface grafted brushes to form poly(vinyl alcohol). During hydrolysis the microspheres lost a significant amount of weight, consistent with the hydrolysis of 40–70% of all VPi units. Drug loading was found to be independent of the shell layer thickness, suggesting that the drug loading is governed by the amount of bulk material. The shell layer does not appear to represent an obstacle to the drug ingress. Cell testing using colorectal cancer cell lines HT 29 confirm the biocompatibility of the empty microspheres whereas the clofazimine loaded particles lead to 50% cell death, confirming the release of the drug.

Surface Initiated Polymerization from Substrates of Low Initiator Density and Its Applications in Biosensors

Surface initiated polymerization (SIP) has become an attractive method for tailoring physical and chemical properties of surfaces for a broad range of applications. Most of those application relied on the merit of a high density coating. In this study we explored a long overlooked field of SIP. SIP from substrates of low initiator density. We combined ellipsometry with AFM to investigate the effect of initiatior density and polymerization time on the morphology of polymer coatings. In addition, we carefully adjusted the nanoscale separation of polymer chains to achieve a balance between nonfouling and immobilization capacities. We further tested the performance of those coating on various biosensors, such as quartz crystal microbalance, surface plasmon resonance, and protein microarrays. The optimized matrices enhanced the performance of those biosensors. This report shall encourage researches to explore new frontiers in SIP that go beyond polymer brushes.

Synthesis and Characterization of Hyperbranched Poly(ether amide)s with Thermoresponsive Property and Unexpected Strong Blue Photoluminescence

A facile and efficient strategy for the syntheses of novel hyperbranched poly(ether amide)s (HPEA) from multihydroxyl primary amines and (meth)acryloyl chloride has been developed. The chemical structures of the HPEAs were confirmed by IR and NMR spectra. Analyses of SEC (size exclusion chromatography) and viscosity characterizations revealed the highly branched structures of the polymers obtained. The resultant hyperbranched polymers contain abundant hydroxyl groups. The thermoresponsive property was obtained from in situ surface modification of abundant OH end groups with N-isopropylacrylamide (NIPAAm). The study oil temperature-dependent characteristics has revealed that NIPAAm-g-HPEA exhibits an adjustable lower critical solution temperature (LCST) of about 34-42 degrees C depending on the grafting degree. More interestingly, the work provided an interesting phenomenon where the HPEA backbones exhibited strong blue photoluminescence.

Effect of swelling response of the support particles on ethylene polymerization

Macroporous and modified macroporous poly(styrene-co-methyl methacrylate-co-divinylbenzene) particles (m-PS and mm-PS) supported Cp2ZrCl2 were prepared and applied to ethylene polymerization using methylaluminoxane (MAO) as cocatalyst. The influences of the swelling response of the support particles on the catalyst loading capabilities of the supports as well as on the activities of the supported catalysts were studied. It was shown that the Zr loadings of the supports and the activities of the supported catalysts increased with the swelling extent of the support particles. The m-PS or mm-PS supported catalysts exhibited very high activities when the support particles were well swollen, whereas those catalysts devoid of swelling treatment gave much lower activities. Investigation on the distribution of the supports in the polyethylene by TEM indicated that the swelling of the support particles allowed the fragmentation of the catalyst particles. In contrast, the fragmentation of the support particles with poor swelling was hindered during ethylene polymerization.

Composition dependence of the crystallization behavior and morphology of the poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer

The crystallization behavior and morphology of the crystalline-crystalline poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer (PEO-b-PCL) was studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), small-angle X-ray scattering (SAXS), and hot-stage polarized optical microscope (POM). The mutual effects between the PEO and PCL blocks were significant, leading to the obvious composition dependence of the crystallization behavior and morphology of PEO-b-PCL. In this study, the PEO block length was fixed (M-n = 5000) and the weight ratio of PCL/PEO was tailored by changing the PCL block length. Both blocks could crystallize in PEO-b-PCL with the PCL weight fraction (WFPCL) of 0.23-0.87. For the sample with the WFPCL of 0.36 or less, the PEO block crystallized first, resulting in the obvious confinement of the PCL block and vice versa for the sample with WFPCL of 0.43 or more. With increasing WFPCL, the crystallinity of PEO reduced continuously while the variation of the PCL crystallinity exhibited a maximum. The long period of PEO-b-PCL increased with increasing WFPCL from 0.16 to 0.50 but then decreased with the further increase of WFPCL due to the interaction of the respective variation of the thicknesses of the PEO and PCL crystalline lamellae.

Synthesis and characterization of maleated poly(3-hydroxybutyrate)

Graft copolymerization of maleic anhydride (MA) onto poly(3-hydroxybutyrate) (PHB) was carried out by use of benzoyl peroxide as initiator. The effects of various polymerization conditions on graft degree were investigated, including solvents, monomer and initiator concentrations, reaction temperature, and time. The monomer and initiator concentrations played an important role in graft copolymerization, and graft degree could be controlled in the range from 0.2 to 0.85% by changing the reaction conditions. The crystallization behavior and the thermal stability of PHB and maleated PHB were studied by DSC, WAXD, optical microscopy, and TGA. The results showed that, after grafting MA, the crystallization behavior of PHB was obviously changed. The cold crystallization temperature from the glass state increased, the crystallization temperature from the melted state decreased, and the growth rate of spherulite decreased. With the increase in graft degree, the banding texture of spherulites became more distinct and orderly. Moreover, the thermal stability of maleated PHB was obviously improved, compared with that of pure PHB.

Biodegradable amphiphilic block copolymers bearing protected hydroxyl groups: Synthesis and characterization

A new biodegradable amphiphilic block copolymer, poly(ethylene glycol)-b-poly(L-factide-co-9-phenyl-2,4,8, 10-tetraoxaspiro[5,5]undecan-3-one) [PEG-b-P(LA-co-PTO)], was successfully prepared by ring-opening polymerization (ROP) Of L-lactide (LA) and functionalized carbonate monomer 9-phenyl-2,4,8,10-tetraozaspiro[5,5]undecan-3-one (PTO) in the presence of monohydroxyl poly(ethylene glycol) as macroinitiator using Sn(Oct)(2) as catalyst. NMR, FT-IR, and GPC studies confirmed the copolymer structure.

Novel pH- and temperature-responsive block copolymers with tunable pH-responsive range

A series of novel pH- and temperature-responsive diblock copolymers composed of poly(N-isopropylacrylamide) (PNIPAM) and poly[(L-glutamic acid)-co-(gamma-benzyl L-glutamate)] [P(GA-co-BLG)] were prepared. The influence of hydrophobic benzyl groups on the phase transition of the copolymers was studied for the first time. With increasing BLG content in P(GA-co-BLG) block, the thermal phase transition of the diblock copolymer became sharper at a designated pH and the critical curve of phase diagram of the diblock copolymer shifted to a higher pH region.

Branched polystyrene with abundant pendant vinyl functional groups from asymmetric divinyl monomer

Branched polystyrenes with abundant pendant vinyl functional groups were prepared via radical polymerization of an asymmetric divinyl monomer, which possesses a higher reactive styryl and a lower reactive butenyl. Employing a fast reversible addition fragmentation chain transfer (RAFT) equilibrium, the concentration of active propagation chains remained at a low value and thus crosslinking did not occur until a high level of monomer conversion. The combination of a higher reaction temperature (120 degrees C) and RAFT agent cumyl dithiobenzoate was demonstrated to be optimal for providing both a more highly branched architecture and a higher polymer yield.

Enantiomeric PLA-PEG block copolymers and their stereocomplex micelles used as rifampin delivery

A novelty approach to self-assembling stereocomplex micelles by enantiomeric PLA-PEG block copolymers as a drug delivery carrier was described. The particles were encapsulated by enantiomeric PLA-PEG stereocomplex to form nanoscale micelles different from the microspheres or the single micelles by PLLA or PDLA in the reported literatures. First, the block copolymers of enantiomeric poly(L-lactide)-poly(ethylene-glycol) (PLLA-PEG) and poly(D-lactide)-poly(ethylene-glycol) (PDLA-PEG) were synthesized by the ring-opening polymerization of L-lactide and D-lactide in the presence of monomethoxy PEG, respectively. Second, the stereocomplex block copolymer micelles were obtained by the self-assembly of the equimolar mixtures of enantiomeric PLA-PEG copolymers in water. These micelles possessed partially the crystallized hydrophobic cores with the critical micelle concentrations (cmc) in the range of 0.8-4.8 mg/l and the mean hydrodynamic diameters ranging from 40 to 120 nm. The micelle sizes and cmc values obviously depended on the hydrophobic block PLA content in the copolymer.Compared with the single PLLA-PEG or PDLA PEG micelles, the cmc values of the stereocomplex micelles became lower and the sizes of the stereocomplex micelles formed smaller. And lastly, the stereocomplex micelles encapsulated with rifampin were tested for the controlled release application.

Synthesis and morphology of polyethylene chains grafted onto the surface of crosslinked polystyrene microspheres

The bifunctional comonomer 4-(3-butenyl) styrene was used to synthesize crosslinked polystyrene microspheres (c-PS) with pendant butenyl groups on their surface via suspension copolymerization. Polyethylene chains were grafted onto the surface of c-PS microspheres (PS-g-PE) via ethylene copolymerizing with the pendant butenyl group on the surface of the c-PS microspheres under the catalysis of metallocene catalyst. The composition and morphology of the PS-g-PE microspheres were characterized by means of Fourier transform infrared spectroscopy, Fourier transform Raman spectroscopy, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. It is possible to control the content of PE grafted onto the surface of c-PS microspheres by varying the polymerization time or the initial quantity of pendant butenyl group on the surface of c-PS microspheres. Investigation on the morphology and crystallization behavior of grafted PE chains showed that different surface patterns could be formed under various crystallization conditions. Moreover, the crystallization temperature of PE chains grafted on the surface of c-PS microspheres was 6 degrees C higher than that of pure PE. The c-PS microspheres decorated by PE chains had a better compatibility with PE matrix.

Anticancer and antiangiogenic activity of surfactant-free nanoparticles based on self-assembled polymeric derivatives of vitamin e: Structure-activity relationship

α-Tocopheryl succinate (α-TOS) is a well-known mitochondrially targeted anticancer compound, however, it is highly hydrophobic and toxic. In order to improve its activity and reduce its toxicity, new surfactant-free biologically active nanoparticles (NP) were synthesized. A methacrylic derivative of α-TOS (MTOS) was prepared and incorporated in amphiphilic pseudoblock copolymers when copolymerized with N-vinylpyrrolidone (VP) by free radical polymerization (poly(VP-co-MTOS)). The selected poly(VP-co-MTOS) copolymers formed surfactant-free NP by nanoprecipitation with sizes between 96 and 220 nm and narrow size distribution, and the in vitro biological activity was tested. In order to understand the structure-activity relationship three other methacrylic monomers were synthesized and characterized: MVE did not have the succinate group, SPHY did not have the chromanol ring, and MPHY did not have both the succinate group and the chromanol ring.

Modification d'acides biliaires à l'aide de polymères pour en moduler les propriétés d'agrégation

Les polymères amphiphiles sont largement utilisés pour les applications biomédicales et pharmaceutiques. Afin d’améliorer les chances de biocompatibilité des nouveaux polymères que nous voulons développer, nous avons utilisé des composés naturels, les acides biliaires, comme produits de départ dans la synthèse de ces polymères. De nouveaux polymères anioniques amphiphiles dérivés de l’acide cholique ont été préparés par polymérisation radicalaire par transfert d’atomes. Par un contrôle rigoureux des conditions de polymérisation, des bras de poly(acide acrylique) de différentes longueurs ont été greffés sur le squelette de l’acide cholique. L’architecture moléculaire des polymères a été étudiée par spectroscopie 1H RMN et par spectrométrie de masse. Ces polymères en étoile formés par l’acide biliaire modifié sont capables de s’agréger dans l’eau même si les groupements hydroxyles ont été remplacés par des segments plus volumineux. Il a été observé que les liaisons ester entre le polymère et le cœur d’acide cholique sont sensibles à l’hydrolyse en solution aqueuse. Pour remédier au problème de stabilité en solution aqueuse et pour avoir, en même temps, des bras hydrophiles non ioniques et biocompatibles, de l’oxyde d’éthylène a été polymérisé sur l’acide cholique par polymérisation anionique. Les liaisons éther formées entre le polymère et les groupements hydroxyles de l’acide biliaire sont plus stables que les liaisons ester sur le polymère de poly(acide acrylique). Les conditions de réaction de la polymérisation anionique ont été optimisées et ont donné des polymères aux architectures et aux masses molaires contrôlées. Les nouveaux polymères forment des agrégats sphériques tel qu’observé par microscopie électronique à transmission avec des échantillons préparés par la méthode de fracture à froid. Leur morphologie est différente de celle des agrégats cylindriques formés par les acides biliaires. Avec la méthode optimisée pour la polymérisation anionique, l’éther d’allyle et glycidyle a été polymérisé sur un dérivé d’acide cholique, suivi par une thiolation des liaisons doubles pour introduire l’amine ou l’acide sur la chaîne polymère. Cette addition radicalaire est efficace à plus de 90%. Les polymères qui en résultent sont solubles dans l’eau et s’agrègent à une certaine concentration critique. Il est particulièrement intéressant d’observer la thermosensibilité des polymères ayant des groupements amine, laquelle peut être modulée en acétylant partiellement les amines, donnant des points nuages entre 15 et 48°C.