Characterization of poly(ethylene oxide) modified with different phenyl hepta isobutyl polyhedral oligomeric silsesquioxanes

Journal of Thermal Analysis and Calorimetry - Poly(ethylene oxide)/polyhedral oligomeric silsesquioxanes (PEO/POSSs) composites were prepared by the melting method. The investigation of their...     

Synthesis and characterization of heptaphenyl polyhedral oligomeric silsesquioxane-capped poly(N-isopropylacrylamide)s

In this work, a novel initiator bearing heptaphenyl polyhedral oligomeric silsesquioxane (POSS) was synthesized via the copper-catalyzed Huisgen 1,3-cycloaddition (i.e., click chemistry). With this initiator, the atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAAm) was carried out to afford the POSS-capped PNIPAAm. The organic–inorganic amphiphiles were characterized by means of nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). Atomic force microscopy (AFM) showed that the POSS-capped PNIPAAm amphiphiles in bulk displayed microphase-separated morphologies. In aqueous solutions, the POSS-capped PNIPAAm amphiphiles were self-assembled into micelle-like aggregates as evidenced by dynamic light scattering (DLS) and transmission election microscopy (TEM). It was found that the sizes of the self-organized nanoobjects decreased with increasing the lengths of PNIPAAm chains. By means of UV–vis spectroscopy, the lower critical solution temperature (LCST) behavior of the organic–inorganic amphiphiles in aqueous solution was investigated and the LCSTs of the organic–inorganic amphiphiles decreased with increasing the percentage of POSS termini. It is noted that the self-assembly behavior of the POSS-capped PNIPAAm in aqueous solutions exerted the significant restriction on the macromolecular conformation alteration of PNIPAAm chains while the coil-to-globule collapse occurred.     

Nanostructures and thermal‐mechanical properties of cyanate ester/epoxy thermosets modified with poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) triblock copolymer

Phase structures and mechanical properties of epoxy/acryl triblock copolymer alloys using several curing agents were studied. The nanostructured thermosets were obtained at the compositions investigated for every blends studied. The dependence of the morphological structures on block copolymer content and dicyanate ester, 2,2′‐bis(4‐cyanatophenyl) isopropylidene (BCE)/epoxy (EP) ratio for thermosetting blends was interpreted on the basis of the difference in hydrogen bonding interactions and reaction resulting from the cross‐linked network structures of matrixes. Moreover, the effect of F68 (poly(ethylene oxide)‐co‐poly(propylene oxide)‐co‐poly(ethylene oxide) block copolymer) on the curing characteristics and performance of BCE/EP resin was discussed. Results show that the incorporation of F68 cannot only effectively promote the curing reaction of BCE/EP but can also significantly improve the toughness of the cured BCE/EP resin. In addition, the toughening effect of F68/EP is greater than single EP resin. For example, the notched impact strength of systems with BE‐80/20 (B and E being the overall contents of BCE and EP, respectively) modified with 10 wt% F68 showed 55% increase compared with neat BCE/EP resin and even is more than three times of that value for pure BCE resin, 5.9 kJ/cm². Copyright © 2015 John Wiley & Sons, Ltd.     

Microphase separation in polybenzoxazine thermosets containing benzoxazine-terminated poly(ethylene oxide) telechelics

Benzoxazine-terminated poly(ethylene oxide) telechelics (Ba-terminated PEO) was synthesized and incorporated into polybenzoxazine to obtain the nanostructured thermosets. The morphology of the thermosets was investigated by means of atomic force microscopy (AFM), small angle X-ray scattering (SAXS) and dynamic mechanical analysis (DMA). The formation of the nanophase structures in the thermosetting composites was addressed on the basis of the mechanism of reaction-induced microphase separation (RIMPS), which was in marked contrast to the case of the binary thermosetting blends of polybenzoxazine with hydroxyl-terminated poly(ethylene oxide). The occurrence of RIMPS resulted from the copolymerization reaction of the end groups of Ba-terminated PEO telechelics with the precursor of thermosetting matrix (i.e., benzoxazine), which suppressed the occurrence of the macroscopic phase separation. It was found that the formation of the nanostructures has a significant effect on the melting behavior of PEO in the thermosets, thermal transition properties of the PBZ thermosets.     

System constants of synthesized poly(methyl-3,3,3-trifluoropropyl) siloxanes

The method of solvation model has been applied to five poly (methyl-trifluoropropyl) siloxanes (TFPSXX) prepared in our laboratories, at five trifluoropropyl (TFP) group contents, XX = 0, 11.5, 26.3, 35.5 and 50.0%, at 80, 100, 120 and 140 degrees C. Previously, specific retention volumes of 60-odd solutes of varied polarities were measured upon each of these stationary phases within the above temperature range. Constant s prevails over all other constants, TFPSXX stationary phases showing strong dipole/induced dipole forces with the solutes, moderate acidity and no basicity at all. Constant e is zero in the stationary phase without TFP groups, but has negative low-medium values for the other fluorine contents, XX from 11.5 to 50.0%, hinting at repulsive forces, as expected. Normal values for constant l, decreasing from the less cohesive TFPS00 to the more cohesive TFPS50, were found. For each TFP content constants s, a and l show a negative temperature dependence, while constant e increases as temperature increases. Constant c also decreases with increasing temperature. At each temperature, constants s and a increase with increasing %TFP (or increasing stationary phase polarity), whereas constants e and l show the opposite trend, diminishing with increasing polarity of the stationary phase. Principal component analysis shows that the five stationary phases presented in this work conform a group with other earlier synthesized trifluoropropyl siloxanes and other fluorinated stationary phases taken from literature: VB-210, QF-1, DB-200, DB-210 and PFS6, showing the same selectivity which only the fluorine atom confers. A dendrogram of 38 stationary phases supports these results.     

Poly(ethylene imine) hybrids containing polyhedral oligomeric silsesquioxanes: Preparation, structure and properties

Both octaglycidyletherpropyl polyhedral oligomeric silsesquioxane and hepta(3,3,3-trifluoropropyl)glycidyletherpropyl polyhedral oligomeric silsesquioxane were synthesized via the hydrosilylation reactions between octahydrosilsesquioxane [and/or hepta(3,3,3-trifluoropropyl)hydrosilsesquioxane] and allyl glycidyl ether. The polyhedral oligomeric silsesquioxane (POSS) macromers were characterized by means of Fourier transform infrared and nuclear magnetic resonance spectroscopy. The inter-component macromolecular reactions between the POSS macromers and poly(ethylene imine) (PEI) were employed to prepare the POSS-containing organic-inorganic PEI hybrids. The inclusion of octaglycidyletherpropyl POSS into PEI results in the formation of the organic-inorganic hybrid networks whereas the introducing hepta(3,3,3-trifluoropropyl)glycidyletherpropyl POSS to PEI affords the linear POSS-grafted PEI copolymers. Differential scanning calorimetry and thermogravimetric analysis show that the POSS-containing PEI hybrids displayed increased glass transition temperatures (T_g’s) and enhanced thermal stability compared to the plain PEI. These PEI hybrid composites can be significantly swollen with water without dissolving, suggesting the formation of hydrogels. The PEI hydrogels containing octaglycidyletherpropyl POSS is in reality the chemically-crosslinked hydrogels whereas the those containing hepta(3,3,3-trifluoropropyl)glycidyletherpropyl POSS displayed the behavior of physical hydrogels. The formation of physical hydrogels is ascribed to the microphase-separated morphology in the hybrids. In addition, the hybrids containing hepta(3,3,3-trifluoropropyl)glycidyletherpropyl POSS exhibited the typical amphiphilicity as evidenced by the increase in surface hydrophobilicity.     

Synthesis, characterization and in vitro oxidative stability of poly(3,3,3-trifluoropropyl)methylsiloxane modified polyurethaneurea

A series of α,ω-bis(3-hydroxypropyl)-poly[(3,3,3-trifluoropropyl)methylsiloxane] (FPS) with different molecular weights were synthesized and characterized, then the FPS modified polyurethaneurea (FSPUU) elastomers were further synthesized with poly(tetramethylene glycol)/FPS as soft segments and 4,4′-diphenylmethane diisocyanate/ethylene diamine as hard segments. The surface properties of the FSPUU films were measured. It was found that the surface hydrophobicity of these FSPUU films was enhanced with increasing the molecular weight of FPS, due to the enrichment of FPS segments at the surface region. Oxidative stability of the FSPUU films was examined in vitro by immersing the films with 200 μm thickness in oxidative solution (H₂O₂/CoCl₂) for 21 days. The experimental results showed that the degree of degradation of all FSPUU films was lower than that of polydimethylsiloxane modified polyurethaneurea (MSPUU), and the oxidative stability of these FSPUU films was fair enhanced with increasing the molecular weight of FPS, which could be attributed to the lowering of swelling ratios in H₂O and 20% H₂O₂, as well as the permeation rate of H₂O in FSPUU films. Furthermore, the tensile strength of all FSPUU films is higher than that of MSPUU film.     

Molecular dynamics simulations of a poly(ethylene oxide) surface

Potentials developed earlier for crystalline and amorphous bulk PEO systems have been used for the MD simulation of a PEO surface model. The surface comprises the outer region of a 122 Å-thick sheet of PEO in which the PEO, -(CH₂-CH₂-O)_n- chains run obliquely across the cell, and are terminated by C₂H₅ ethyl groups. The atoms on one side of the sheet are tethered to facilitate a satisfactory Ewald summation. The sheet expands from its ‘crystalline’ width of 122 Å to 128 Å in the simulated model. Simulations were performed at three temperatures: 300 K, 400 K and 500 K. Different behaviour in the surface layer was found compared to that in the bulk. The structural and dynamical properties of the surface were analyzed at each temperature.     

Conventional free-radical and RAFT copolymerization of poly(ethylene oxide) containing macromonomers

Conventional free-radical and RAFT copolymerization of poly(ethylene oxide) substituent containing methacrylate macromonomers, PEO₅MEMA and PEO₄₅MEMA, was studied by the use of ¹H NMR spectroscopy for an analysis of residual monomers. From the monomer consumption curves, several parameters including monomer conversion, instantaneous copolymer composition and reactivity ratios of the monomers were evaluated. Reactivity ratios of PEO₅MEMA and MAA estimated by non-linear approach of error-in-variables model and presented as joint confidence regions were constant during conventional free-radical and RAFT copolymerizations of the above monomers but were slightly affected by the RAFT process. Reactivity ratio of PEO₄₅MEMA was found to be lower than that of PEO₅MEMA and varied during copolymerization: increased with conversion in conventional free-radical copolymerization and slightly (without confidence) decreased in the RAFT process. RAFT copolymerization of PEO₄₅MEMA and MAA enabled to synthesize comb copolymers with low composition distribution and more homogeneous distribution of PEO side chains along the mainchain. Under copolymerization with MAA, PEO₄₅MEMA behaved like typical macromonomer with appropriate steric hindrance while the behavior of PEO₅MEMA was similar to that of a low-molecular methacrylate.     

Thermodynamic and transport properties of polyhedral oligomeric sislesquioxanes in poly(dimethylsiloxane)

Polyhedral oligomeric silsesquioxane (POSS) molecules when functionalized appropriately and dispersed in polymers show promise as monodisperse organic-inorganic hybrid nanocomposite materials characterized by superior mechanical properties. We report here molecular-simulation results for POSS-POSS radial distribution functions, potentials of mean force, and self-diffusion coefficients for POSS monomers dissolved in poly(dimethylsiloxane) in the temperature range of 300-1000 K. Our results demonstrate that it is possible to modulate the effective POSS-POSS interaction by increasing the temperature or by substituting the hydrogen atoms in the POSS monomer with methyl groups. In addition, our results indicate that the motion of POSS monomers dissolved in poly(dimethylsiloxane) follows a hopping mechanism.     

Restricted self-diffusion in an aqueous solution of poly(ethylene oxide) poly(propylene oxide) poly(ethylene oxide) triblock copolymer

 The self-diffusion behavior of a triblock copolymer (PEO–b– PPO–b–PEO) in an aqueous solution of 20% (m/m) was investigated during a temperature-induced phase transition from liquid to gel state using pulsed field gradient NMR and static light scattering. The measured self-diffusivity shows a strong dependence on the observation time in the gel phase indicating the existence of diffusion barriers in the size range of about 0.6 μm. Additional static light-scattering measurements show a structure in the same size range of several hundred nanometers, which is far above molecular or micellar sizes and thus, has to be caused by larger clusters. The similarity in the space scales suggests that the restriction of molecular propagation is correlated with the grain boundaries between the domains of the poly-crystalline structure formed by the arranged micelles. Received: 28 October 1996 Accepted: 21 March 1997     

Rheology and gelation kinetics in laponite dispersions containing poly(ethylene oxide)

We report results on the rheology of a model polymer/clay system, laponite clay particles with added poly(ethylene oxide) (PEO), focusing on the kinetics of gel formation and on molecular weight effects. We examined solutions at both pH = 7, where interparticle attractions are present and a networked gel is formed; and at pH = 10, where repulsive forces dominate and laponite forms a colloidal glass. We found that PEO of low to moderate molecular weight significantly slows down gelation and decreases the complex viscosity and elastic modulus of the dispersion by several orders of magnitude for both pH = 7 and 10. In the former case, adsorbed PEO likely forms a steric barrier to the formation of an attractive gel. In the latter case, we propose that free PEO chains in solution induce a depletion attraction between particles, preventing or slowing the formation of a colloidal glass. At higher molecular weights, PEO chains are long enough to bridge between particles and form an associative network, enhancing the viscosity and elastic modulus for both pH = 7 and 10. Finally, we have shown the critical molecular weight for transitioning between these two types of behavior scales with the interparticle distance. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 233–240, 2005     

Dynamic elasticity of triblock copolymer of poly(ethylene oxide) and poly(propylene oxide) on a water surface

Dilatational viscoelasticity of adsorbed and spread films of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer at the air-water interface is studied by the capillary waves and oscillating barrier techniques. At the surface pressure below 10 mN/m, dynamic surface properties of these films coincide with those of poly(ethylene oxide). At higher surface pressures, the results obtained indicate the desorption of poly(propylene oxide) segments from the monolayer and their interaction with poly(ethylene oxide) segments in an aqueous phase. At a surface pressure close to 19 mN/m, the behavior of adsorbed and spread poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) films becomes different. The real part of dynamic surface elasticity of spread films tends toward its maximum value (20 mN/m) and, upon further compression, films begin to dissolve. At the same time, the surface elasticity of adsorbed films decreases nearly twofold upon the achievement of the maximum value that testifies the formation of looser structure of the surface layer.     

Dipole moments of poly(ethylene oxide) and poly(hexamethylene oxide) chains

The mean-square dipole moments of poly(ethylene oxide) and poly(hexamethylene oxide) chains have been determined from dielectric constant measurements on dilute solutions of the polymers in benzene. The values obtained are in good agreement with those predccted using the rotational isomeric state models for these chains. In addition, the unperturbed dimensions of poly(hexamethylene oxide) have been calculated as a function of molecular weight, using the isomeric state theory.     

Synthesis and characterization of anionic graft copolymers containing poly(ethylene oxide) grafts

Anionic graft copolymers were synthesized through grafting of poly(ethylene glycol) monomethyl ether (MPEG) onto terpolymers containing succicinic anhydride groups. The backbone polymers were prepared through radical terpolymerization of maleic anhydride, styrene, and one of the following monomers: methyl methacrylate, ethylhexyl methacrylate, and diethyl fumarate. MPEG of different molecular weights were grafted onto the backbone through reactions with the cyclic anhydride groups. In this reaction one carboxylic acid group is formed together with each ester bond. The molecular weights of MPEG were found to influence the rate of the grafting reaction and the final degree of conversion. The graft copolymers were characterized by IR, GPC, and ¹H-NMR. Thermal properties were examined by DSC. Graft copolymers containing 50% w/w of MPEG 2000 grafts were found to be almost completely amorphous, presumably because of crosslinking, and hydrogen bonding between carboxylic acid groups in the backbone and the ether oxygens in MPEG grafts. © 1995 John Wiley & Sons, Inc.     

Effect of poly(ethylene oxide) on the release behaviors of poly(epsilon-caprolactone) microcapsules containing erythromycin

The biodegradable poly(epsilon-caprolactone) (PCL)/poly(ethylene oxide) (PEO) microcapsules and the analyzing of form and features for the manufacturing conditions were investigated in a prospective drug delivery systems (DDS) through drug release. The effects of emulsifier, emulsifier concentration, and stirring rate on the diameter and form of the microcapsules were examined using image analyzer (IA) and scanning electron microscope (SEM). The role of interfacial adhesion between PCL/PEO and drug was determined by contact angle measurements, and the drug release rate of the microcapsules was characterized by UV-vis spectroscopy. As a result, the microcapsules were made in spherical forms with a mean particle size of 170 nm approximately 68 microm. And the work of adhesion between water and PCL/PEO was increased with increasing the PEO content, which is due to higher hydrophilicity of PEO. The drug release rate of the microcapsules was significantly increased as the PEO content increased, which could be attributed to the increasing of the hydrophilic groups or the degree of adhesion at the interfaces.     

Synthesis and characterization of poly(ethylene oxide)/polylactide/poly(ethylene oxide) triblock copolymer

Poly(ethylene oxide/polylactide/poly(ethylene oxide) (PEO/PL/PEO) triblock copolymers, in which each block is connected by an ester bond, were synthesized by a coupling reaction between PL and PEO. Hydroxyl‐terminated PLs with various molecular weights were synthesized and used as hard segments. Hydroxyl‐terminated PEOs were converted to the corresponding acid halides via their acid group and used as a soft segment. Triblock copolymers were identified by Fourier transform infrared spectroscopy, ¹H NMR, and gel permeation chromatography. Differential scanning calorimetry (DSC) and X‐ray diffractometry of PEO/PL/PEO triblock copolymers suggested that PL and PEO blocks were phase‐separated and that the crystallization behavior of the PL block was markedly affected by the presence of the PEO block. PEO/PL/PEO triblock copolymers with PEO 0.75k had two exothermic peaks (by DSC), and both peaks were related to the crystallization of PL. According to thermogravimetric analysis, PEO/PL/PEO triblock copolymer showed a higher thermal stability than PL or PEO. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2545–2555, 2002