Novel tricontinuous hydrophilic–lipophilic–oxyphilic membranes: Synthesis and characterization

Novel tricontinuous membranes consisting of well‐defined hydrophilic poly(ethylene glycol) (PEG) and lipophilic polyisobutylene (PIB) segments crosslinked by oxyphilic poly(pentamethylcyclopentasiloxane) (PD₅) domains have been synthesized and characterized. Tricontinuity arises because the three membrane constituents—PEG, PIB, and PD₅—are mutually incompatible and give rise to three independent cocontinuous phases (channels). The continuous PEG segments impart swelling in water (hydrogel character), the rubbery PIB moieties provide strength, and the PD₅ domains provide crosslinking and enhanced O₂ permeability. The synthesis involves the random cohydrosilation of various lengths (number‐average molecular weights) of α,ω‐diallyl‐PEG and α,ω‐diallyl‐PIB segments by pentamethylcyclopentasiloxane (D₅H) followed by water‐mediated oxidation of the SiH groups of the D₅H to SiOH groups, which immediately polycondense to PD₅ domains. Membranes containing about equal amounts of PEG, PIB, and PD₅ give rise to tricontinuous morphologies that allow the simultaneous permeation of water, heptane, and oxygen via three cocontinuous channels. The number‐average molecular weight of the PEG segment, that is, the number‐average molecular weight of the hydrophilic segment between two PD₅ crosslink sites, determines the dimensions (pore sizes) of the channels through which water can permeate. A method has been developed for studying the oxygen permeability of membranes. The microarchitecture of the membranes has been investigated with selective swelling experiments and Fourier transform infrared spectroscopy, their mechanical properties have been examined in the water‐swollen state with Instron measurements, and their bulk morphologies and thermal degradation have been determined with differential scanning calorimetry and thermogravimetric analysis, respectively. The findings have been interpreted in terms of phase‐separated PEG, PIB, and PD₅ microdomains. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1209–1217, 2002     

Poly(pentamethylcyclopentasiloxane). I. Synthesis and characterization

We have discovered that pentamethylcyclopentasiloxane (D₅H) can be readily polymerized into poly(pentmethylcyclopentasiloxane) (PD₅) with a Pt (Karstedt) catalyst in the presence of water in bulk or in solution at 100 °C and that the product is a solid with extraordinary properties. The polymerization starts with the oxidation of the SiH groups by water into an intermediate containing SiOH groups (SiH + H₂O → SiOH + H₂), which is followed immediately by the condensation (2SiO → Si? O? Si) of D₅H rings into complex aggregates of cyclosiloxane moieties. According to Raman spectroscopy, an average of three of the five SiH functionalities are converted, and the final product contains only a negligible number of SiOH groups. The melting and glass‐transition temperatures of the monomer are exceptionally low: T_m,D5H = ?137.6 ± 1 and T_g,D5H = ?152 ± 2 °C. The polymer exhibits an unprecedented combination of properties: it is a stiff and brittle solid, is insoluble in common solvents, does not exhibit a melting endotherm but has an extremely low glass transition (T_g,PD5 = ?151 ± 0.5 °C), and is thermally stable up to at least 700 °C. Brillouin scattering indicates very slow variation of the relaxation time with temperature, a property characteristic of strong glass‐forming systems such as silica glass. This characteristic may account for the unique combination of properties of the new polymer: an extremely low glass‐transition temperature combined with solidlike properties even at ambient temperature (more than twice its glass‐transition temperature). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1285–1292, 2002     

Influence of interfaces on the rates of crosslinking in poly(dimethyl siloxane) coatings

We have determined with infrared spectroscopic ellipsometry how the nature of the interface between a thin poly(dimethyl siloxane) (PDMS) coating and its substrate affects the rate of PDMS crosslinking reactions. Reactions between vinyl (? CH?CH₂) end groups on PDMS and silyl (SiH) groups in a crosslinker (hydrosilylation) and between SiH groups and silanol (SiOH) groups, during the so‐called postcure crosslinking stage, have been probed in situ. The overall consumption of SiH follows first‐order reaction kinetics. The first‐order reaction coefficient (k₁) for the hydrosilylation crosslinking reaction is the same for coatings on three different substrates: native oxide on silicon (SiO₂/Si), polystyrene (PS), and poly(ethylene terephthalate). For the slower postcure reactions, however, the rate of SiH consumption depends on the substrate. In 2.5‐μm PDMS coatings on PS, k₁ is about seven times greater than k₁ in the same coating on SiO₂/Si. In PDMS coatings on a PDMS substrate, when the effect of the interface is thus minimal, k₁ is 16 times higher than on SiO₂/Si. The dependence of k₁ on the type of interface is probably the result of the interfacial segregation and complexation of the Pt catalyst for the postcure reactions. We propose that polar surfaces more strongly attract Pt and form complexes that inhibit the postcure reactions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1421–1431, 2004     

Positron annihilation and differential scanning calorimetry studies of polyacrylamide and poly(dimethylacrylamide)/poly(ethylene glycol) blends

Positron annihilation lifetime spectroscopy and differential scanning calorimetry (DSC) measurements were performed for blends of polyacrylamide (PAM) and poly(ethylene glycol) (PEG) and blends of poly(dimethylacrylamide) (PDMAM) and PEG. The samples were prepared by codissolution in a concentration range of 0–100 wt % PEG. The thermal behavior, characterized by DSC measurements, showed similar variations of the glass‐transition temperatures (T_g's) with the PEG concentration for the two systems. Pure PAM and PDMAM presented T_g's of 188 and 111 °C, respectively. A relatively small and nearly linearly decreasing T_g was observed for the two systems in the range of 20–80 wt % PEG. PEG crystals were present in all blend compositions, and no melting point depression was observed. The thermal results pointed to the partial miscibility of the blends. The degree of crystallinity of PEG increased with increasing PEG concentration for the PDMAM/PEG systems. The ortho‐positronium lifetime (τ₃) increased with increasing PEG concentration for both blends. However, the parameter of the ortho‐positronium formation probability (I₃) decreased with the PEG concentration. The product τI₃, which was proportional to the total free volume fraction, was approximately constant with the PEG concentration for PDMAM blends and increased with the PEG concentration for PAM systems. This result may be interpreted as a consequence of a more heterogeneous structure in PAM blends. Scanning electron microscopy micrographs of blends with 40 and 80 wt % PEG provided evidence of the regions associated with PEG crystallites. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1493–1500, 2003     

Synthesis, characterization and thermoreversible behaviours of poly(dimethyl siloxane)/poly(N-isopropyl acrylamide) semi-interpenetrating networks

Simultaneous and sequential poly(N-isopropyl acrylamide) (PNIPAAm)/poly(dimethyl siloxane) (PDMS) semi-interpenetrating polymer networks (IPNs) with different linear PDMS contents were prepared by free radical polymerization method. Their phase morphologies have been characterized by FTIR, DSC and SEM. The simultaneous semi-IPNs exhibited phase transition temperatures (T_pt) shifted higher temperature from glass transition temperatures (T_g) of their respective homopolymers, suggesting a heterophase morphology and only physical entanglement between the PNIPAAm network and linear PDMS with high molecular weight (Mn≈9000 g/mol). For sequential semi-IPNs, the shift of T_pts towards lower temperature suggested that the chemical interaction between the constituents of the IPNs increased with increasing PDMS content in the network. In addition, these semi-IPNs were characterized for their thermo-sensitive behaviour by equilibrium swelling studies. The results showed that incorporation of hydrophobic PDMS polymer into the thermo- and pH-sensitive PNIPAAm and P(NIPAAm-co-IA) (itaconic acid) hydrogels by semi-IPN formation decreased swelling degrees of IPNs without affecting their LCSTs whereas addition of acrylated PDMS (Tegomer V-Si 2250) as crosslinker instead of N,N^′-methylenebisacrylamide (BIS) into the structures of these hydrogels changed their LCSTs along with their swelling degrees.     

Preparation of high molecular weight polybenzoxazine prepolymers containing siloxane unites and properties of their thermosets

High‐molecular‐weight polybenzoxazine prepolymers containing polydimethylsiloane unit in the main‐chain have been synthesized from α,ω‐bis(aminopropyl)polydimethylsiloxane (PDMS) (molecular weight = 248, 850, and 1622) and bisphenol‐A with formaldehyde. Moreover, another type of prepolymers was prepared using methylenedianiline (MDA) as codiamine with PDMS. The weight average molecular weight of the obtained prepolymers was estimated from size exclusion chromatography to be in the range of 8000–11,000. The chemical structures of the prepolymers were investigated by ¹H NMR and IR analyses. The prepolymers gave transparent free standing films by casting their dioxane solution. The prepolymer films after thermally cured up to 240 °C gave brown colored transparent and flexible polybenzoxazine films. Tensile test of the films revealed that the elongation at break increased with increasing the molecular weight of PDMS unit. Dynamic mechanical analysis of the thermosets showed that the T_gs were as high as 238–270 °C. The thermosets also revealed high thermal stability as evidenced by the 5% weight loss temperatures in the range of 324–384 °C from thermogravimetic analysis. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Mechanical properties and morphology of epoxy/poly(vinyl acetate)/poly(4-vinyl phenol) brominated system

Diglycidyl ether of bisfenol-A (DGEBA)/poly(vinyl acetate) (PVAc)/poly(4-vinyl phenol) brominated (PVPhBr) ternary blends cured with 4,4’-diaminodiphenylmethane (DDM) were investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM). Homogeneous (DGEBA+DDM)/PVPhBr networks with a unique T _g are generated. Ternary blends (DGEBA+DDM)/PVAc/PVPhBr are initially miscible and phase separate upon curing arising two T _gs that correspond to a PVAc-rich phase and to epoxy network phase. Increasing the PVPhBr content the T _gof the PVAc phase move to higher temperatures as a consequence of the PVAc-PVPhBr interactions. Different morphologies are generated as a function of the blend composition.     

Synthesis and thermal crosslinking of benzophenone‐modified poly(dimethylsiloxane)s

Dihydridocarbonyltris(triphenylphosphine)ruthenium catalyzes the regiospecific anti‐Markovnikov addition of an ortho C? H bond of benzophenone across the C? C double bonds of α,ω‐bis(trimethylsilyloxy)copoly(dimethylsiloxane/vinylmethylsiloxane) (99:1), α,ω‐bis(vinyldimethylsilyloxy)poly(dimethylsiloxane), and 1,3‐divinyltetramethyldisiloxane to yield α,ω‐bis(trimethylsilyloxy)copoly[dimethylsiloxane/2‐(2′‐benzophenonyl)ethylmethylsiloxane]), α,ω‐bis[2‐(2′‐benzophenonyl)ethyldimethylsilyloxy]poly(dimethylsiloxane), and 1,3‐bis[2‐(2′‐benzophenonyl)ethyl]tetramethyldisiloxane, respectively. These materials have been characterized with ¹H, ¹³C, and ²⁹Si NMR and IR spectroscopy. Their molecular weight distributions have been determined by gel permeation chromatography. The thermal stability of the polymers has been measured by thermogravimetric analysis, and their glass‐transition temperatures (T_g's) have been determined by differential scanning calorimetry. The molecular weight distribution, thermal stability, and T_g's of the modified polysiloxanes are similar to those of the precursor polymers. The molecular weights of these materials can be significantly increased via heating to 300 °C for 1 h. This may be due to crosslinking, by pyrocondensation, of pendant anthracene groups, which are produced by the pyrolysis of the attached ortho‐alkyl benzophenones. UV spectroscopy of the pyrolysate of 1,3‐bis[2‐(2′‐benzophenonyl)ethyl]tetramethyldisiloxane has confirmed the presence of pendant anthracene groups. Thermal crosslinking by the pyrocondensation of pendant anthracene groups has been verified by the pyrolysis of α,ω‐bis(trimethylsilyloxy)copoly[dimethylsiloxane/2‐(9′‐anthracenyl)ethylmethylsiloxane] (97:3). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5514–5522, 2004     

Preparation and properties of polybenzoxazine/poly(imide‐siloxane) alloys: In situ ring‐opening polymerization of benzoxazine in the presence of soluble poly(imide‐siloxane)s

Benzoxazine monomer (Ba) was blended with soluble poly(imide‐siloxane)s in various weight ratios. The soluble poly(imide‐siloxane)s with and without pendent phenolic groups were prepared from the reaction of 2,2′‐bis(3,4‐dicarboxylphenyl)hexafluoropropane dianhydride with α,ω‐bis(aminopropyl)dimethylsiloxane oligomer (PDMS; molecular weight = 5000) and 3,3′‐dihydroxybenzidine (with OH group) or 4,4′‐diaminodiphenyl ether (without OH group). The onset and maximum of the exotherm due to the ring‐opening polymerization for the pristine Ba appeared on differential scanning calorimetry curves around 200 and 240 °C, respectively. In the presence of poly(imide‐siloxane)s, the exothermic temperatures were lowered: the onset to 130–140 °C and the maximum to 210–220 °C. The exotherm due to the benzoxazine polymerization disappeared after curing at 240 °C for 1 h. Viscoelastic measurements of the cured blends containing poly(imide‐siloxane) with OH functionality showed two glass‐transition temperatures (T_g's), at a low temperature around ?55 °C and at a high temperature around 250–300 °C, displaying phase separation between PDMS and the combined phase consisting of polyimide and polybenzoxazine (PBa) components due to the formation of AB‐crosslinked polymer. For the blends containing poly(imide‐siloxane) without OH functionalities, however, in addition to the T_g due to PDMS, two T_g's were observed in high‐temperature ranges, 230–260 and 300–350 °C, indicating further phase separation between the polyimide and PBa components due to the formation of semi‐interpenetrating networks. In both cases, T_g increased with increasing poly(imide‐siloxane) content. Tensile measurements showed that the toughness of PBa was enhanced by the addition of poly(imide‐siloxane). Thermogravimetric analysis showed that the thermal stability of PBa also was enhanced by the addition of poly(imide‐siloxane). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2633–2641, 2001     

Novel polyisobutylene/poly(dimethylsiloxane) bicomponent networks. I. Synthesis and characterization

The synthesis of novel polyisobutylene (PIB)/poly(dimethylsiloxane) (PDMS) bicomponent networks is described. The synthesis strategy (see Figure 1) was to prepare well-defined and -characterized allyl-tritelechelic polyisobutylenes [ϕ(PIB—C—C=C)₃] and SiH-ditelechelic poly(dimethylsiloxanes) (HSi–PDMS–SiH) and then crosslink these moieties by hydrosilation. The ϕ(PIB—C—C=C)₃ was prepared by living isobutylene polymerization followed by end-quenching with allyltrimethylsilane, whereas the HSi–PDMS–SiH was obtained by equilibrium polymerization of octamethylcyclotetrasiloxane and tetramethyldisiloxane. The detailed structures of the starting polymers were characterized by GPC and ¹H-NMR spectroscopy. A series of PIB/PDMS bicomponent networks of varying compositions and average molecular weights between crosslinks (M _c) of ∼ 20,000 g/mol were assembled. Optimum crosslinking conditions were defined in terms of H₂PtCl₆ catalyst concentration, nature of solvent, time, temperature, and stoichiometry of ∼ CH₂CH=CH₂/∼SiH groups, allowing for the convenient synthesis of well-defined model bicomponent networks. Swelling studies and elemental analysis confirm the correctness of the synthetic strategy. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1891–1899, 1998     

Miscibility in crystalline/amorphous blends of poly(3-hydroxybutyrate)/DGEBA

A differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) study of miscibility in blends of the semicrystalline polyester poly(3-hydroxybutyrate) (PHB) and amorphous monomer epoxy DGEBA (diglycidyl ether of bisphenol A) was performed. Evidence of the miscibility of PHB/DGEBA in the molten state was found from a DSC study of the dependence of glass transition temperature (T_g) as a function of the blend composition and isothermal crystallization, analyzing the melting point (T_m) as a function of blend composition. A negative value of Flory–Huggins interaction parameter χ_PD was obtained. Furthermore, the lamellar crystallinity in the blend was studied by SAXS as a function of the PHB content. Evidence of the segregation of the amorphous material out of the lamellar structure was obtained. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Complex phase behavior and state of miscibility in Poly(ethylene glycol)/Poly(l‐lactide‐co‐ε‐caprolactone) Blends

A miscibility and phase behavior study was conducted on poly(ethylene glycol) (PEG)/poly(l ‐lactide‐ε‐caprolactone) (PLA‐co‐CL) blends. A single glass transition evolution was determined by differential scanning calorimetry initially suggesting a miscible system; however, the unusual T_g bias and subsequent morphological study conducted by polarized light optical microscopy (PLOM) and atomic force microscopy (AFM) evidenced a phase separated system for the whole range of blend compositions. PEG spherulites were found in all blends except for the PEG/PLA‐co‐CL 20/80 composition, with no interference of the comonomer in the melting point of PEG (T_m = 64 °C) and only a small one in crystallinity fraction (X_c = 80% vs. 70%). However, a clear continuous decrease in PEG spherulites growth rate (G) with increasing PLA‐co‐CL content was determined in the blends isothermally crystallized at 37 °C, G being 37 µm/min for the neat PEG and 12 µm/min for the 20 wt % PLA‐co‐CL blend. The kinetics interference in crystal growth rate of PEG suggests a diluting effect of the PLA‐co‐CL in the blends; further, PLOM and AFM provided unequivocal evidence of the interfering effect of PLA‐co‐CL on PEG crystal morphology, demonstrating imperfect crystallization in blends with interfibrillar location of the diluting amorphous component. Significantly, AFM images provided also evidence of amorphous phase separation between PEG and PLA‐co‐CL. A true T_g vs. composition diagram is proposed on the basis of the AFM analysis for phase separated PEG/PLA‐co‐CL blends revealing the existence of a second PLA‐co‐CL rich phase. According to the partial miscibility established by AFM analysis, PEG and PLA‐co‐CL rich phases, depending on blend composition, contain respectively an amount of the minority component leading to a system presenting, for every composition, two T_g's that are different of those of pure components. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014 , 52, 111–121     

Effect of the graft ratio on the properties of polythiophene‐g‐poly(ethylene glycol)

Graft copolymers formed by anchoring poly(ethylene glycol) (PEG) chains to conjugated polythiophene have been prepared by copolymerizing two compounds: unsubstituted α‐terthiophene (Th₃) and a thiophene‐derived macromonomer having an α‐terthiophene conjugated sequence and one Th₃ bearing a PEG chain with molecular weight of 2000 as substitute at the 3‐position of the central heterocycle (Th₃‐PEG₂₀₀₀). The grafting ratio of the resulting copolymers (PTh₃^*‐g‐PEG), which were obtained using 75:25 and 50:50 Th₃‐PEG₂₀₀₀:Th₃ weight ratios, is significantly smaller than that of copolymers derived from polymerization of macromonomers consisting of a α‐pentathiophene sequence in which the central ring bears a PEG chain of M_w = 2000 (PTh₅‐g‐PEG). The electroactivity and electrochemical stability of PTh₃^*‐g‐PEG is not only higher than that of PTh₅‐g‐PEG but also higher than that of PTh₃, the latter presenting a very compact structure that makes difficult the access and escape of dopant ions into the polymeric matrix during the redox processes. Furthermore, the optical π‐π^* lowest transition energy of PTh₃^*‐g‐PEG is lower than that of both PTh₅‐g‐PEG and PTh₃. These properties, combined with suitable wettability and roughness, result in an excellent behavior as bioactive platform of PTh₃^*‐g‐PEG copolymers, which are more biocompatible, in terms of cellular adhesion and proliferation, and electro‐compatible than PTh₅‐g‐PEG. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 239–252     

Synthesis,micelle formation,and bulk properties of poly(ethylene glycol)‐b‐poly(pentafluorostyrene)‐g‐polyhedral oligomeric silsesquioxane amphiphilic hybrid copolymers

The synthesis, micelle formation, and bulk properties of semifluorinated amphiphilic poly(ethylene glycol)‐b‐poly(pentafluorostyrene)‐g‐cubic polyhedral oligomeric silsesquioxane (PEG‐b‐PPFS‐g‐POSS) hybrid copolymers is reported. The synthesis of amphiphilic PEG‐b‐PPFS block copolymers are achieved using atom transfer radical polymerization (ATRP) at 100 °C in trifluorotoluene using modified poly(ethylene glycol) as a macroinitiator. Subsequently, a proportion of the reactive para‐F functionality on the pentafluorostyrene units was replaced with aminopropylisobutyl POSS through aromatic nucleophilic substitution reactions. The products were fully characterized by ¹H‐NMR and GPC. The products, PEG‐b‐PPFS and PEG‐b‐PPFS‐g‐POSS, were subsequently self‐assembled in aqueous solutions to form micellar structures. The critical micelle concentrations (cmc) were estimated using two different techniques: fluorescence spectroscopy and dynamic light scattering (DLS). The cmc was found to decrease concomitantly with the number of POSS particles grafted per copolymer chain. The hydrodynamic particle sizes (R_h) of the micelles, calculated from DLS data, increase as the number of POSS molecules grafted per copolymer chain increases. For example, R_h increased from ～60 nm for PEG‐b‐PPFS to ～80 nm for PEG‐b‐PPFS‐g‐POSS25 (25 is the average number of POSS particles grafted copolymer chain). Static light scattering (SLS) data confirm that the formation of larger micelles by higher POSS containing copolymers results from higher aggregation numbers (N_agg), caused by increased hydrophobicity. The R_g/R_h values, where R_g is the radius of gyration calculated from SLS data, are consistent with a spherical particle model having a core‐shell structure. Thermal characterization by differential scanning calorimetry (DSC) reveals that the grafted POSS acts as a plasticizer; the glass transition temperature (T_g) of the PPFS block in the copolymer decreases significantly with increasing POSS content. Finally, the rhombohedral crystal structure of POSS in PEG‐b‐PPFS‐g‐POSS was verified by wide angle X‐ray diffraction measurements. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 152–163, 2010     

Synthesis and properties of poly(sulfone‐arylate) copolymers

Poly(sulfone‐arylate) was synthesized in a reaction between dihydroxy polysulfone prepolymers and either diphenyl terephthalate or terephthaloyl chloride. The dihydroxy polysulfone prepolymers had molecular weights of 2000 and 4000 g/mol. The polymerization with diphenyl terephthalate was carried out at high temperature (280 °C) in the presence of a catalyst, whereas the polymerization with terephthalic chloride was conducted in solution at low temperature in the presence of an acid acceptor. High‐molecular weight copolymers (η_inh ～ 0.60 dL/g) could be obtained through both methods. The copolymers were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, DMA, and differential scanning calorimetry measurements and were found to exhibit high T_g values. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3904–3913, 2009     

Amphiphilic membranes crosslinked and reinforced by POSS

This article concerns the synthesis and characterization of novel tricomponent amphiphilic membranes consisting of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic polydimethylsiloxane (PDMS) segments cocrosslinked and reinforced by octasilane polyhedral oligomeric silsesquioxane (octasilane‐POSS) cages. Rapid and efficient network synthesis was effected by cocrosslinking diallyl‐telechelic PEG (A‐PEG‐A) and divinyl‐telechelic PDMS (V‐PDMS‐V) with pentamethylpentacyclosiloxane (D₅H), using Karstedt's catalyst in conjunction with Et₃N cocatalyst and water. Films were prepared by pouring charges in molds and crosslinking by heating at 60 °C for several hours. The films were characterized by sol fractions and equilibrium swelling both in hexane and water, extent of crosslinking, contact angle hysteresis, oxygen permeability, thermogravimetric analysis, and mechanical properties. The crosslinking of octasilane‐POSS achieved by the same catalyst system was studied in separate experiments. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4337–4352, 2004     

Miscible blends containing a crystallizable component: poly(vinyl alcohol)/poly(ethyleneimine)

Blends of poly(vinyl alcohol) (PVAI) with poly(ethyleneimine) (PEI) were prepared by casting from a common solvent. All blends show a single, composition dependent glass transition temperature (T_g), indicating that the blends are miscible in the amorphous state and in the melt. The overall crystallization rate of PVAI in the blend decreases with increasing PEI content. The crystallinity index of PVAI in the blend does not decrease greatly with PEI content up to a composition of 70/30 PVAI/PEI, since the T_g of the crystallizable component PVAI is larger than that of the non-crystallizable component PEI. The T_g of the system PVAI/PEI decreases with increasing PEI content. The interaction parameter B of the two polymers in the melt was found to be −24 J/cm³.     

Synthesis of trans‐4‐hydroxy‐L‐proline‐based telechelic prepolymers and poly(ester‐urethane)

The synthesis of hydroxyproline‐based telechelic prepolymers by the condensation polymerization of trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L ‐proline methyl ester was investigated. All the polymerizations were carried out in the melt with stannous octoate as the catalyst and with different diols. The products were characterized by differential scanning calorimetry, proton nuclear magnetic resonance, infrared spectrophotometry, and inherent viscosity (η_inh). According to the analytic results, the η_inh value of the prepolymers depended on the kind and amount of diols that were added. With an increase in the 1,6‐hexanediol feed from 2 to 10 mol %, there was a decrease in η_inh from 0.78 to 0.41 along with a decrease in the glass‐transition temperature (T_g ) from 63 to 42 °C. When 2 mol % of different kinds of diols were used, η_inh ranged from 0.78 to 0.21, and T_g varied from 70 to 43 °C. These new prepolymers could be linked to poly(ester‐urethane) by the chain extender 1,6‐hexamethylene diisocyanate. The poly(ester‐urethane) was amorphous, and the T_g was 76 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2449–2455, 2000     

Synthesis of high glass transition temperature copolymers based on poly(vinyl chloride) via single electron transfer—Degenerative chain transfer mediated living radical polymerization (SET‐DTLRP) of vinyl chloride in water

α,ω‐di(iodo) poly(isobornyl acrylate) macroiniators (α,ω‐di(iodo)PIA) with number average molecular weight from M _n,TriSEC = 11,456 to M _n,TriSEC = 94,361 were synthesized by single electron transfer‐degenerative chain transfer mediated living radical polymerization (SET‐DTLRP) of isobornyl acrylate (IA) initiated with iodoform (CHI₃) and catalyzed by sodium dithionite (Na₂S₂O₄) in water at 35 °C. The plots of number average molecular weight vs conversion and ln{[M]₀/[M]} vs time are linear, indicating a controlled polymerization. α,ω‐di(iodo) poly(isobornyl acrylate) have been used as a macroinitiator for the SET‐DTLRP of vinyl chloride (VCM) leading to high T_g block copolymers PVC‐b‐PIA‐b‐PVC. The dynamic mechanical thermal analysis of the block copolymers suggests just one phase indicating that copolymer behaves as a single material. This technology provides the possibility of synthesizing materials based on PVC with higher T_g in aqueous medium. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Fractal character of the SAXS correlation volume in poly(ethylene glycol)/silica hybrid wet gels

Small-angle X-ray scattering (SAXS) was employed to study the nanostructural properties of poly(ethylene glycol)(PEG)/silica hybrid wet gels prepared from hydrolysis of tetraethoxysilane (TEOS) in mixtures with PEG/(PEG + TEOS) molar ratio in the nominal range between 0 and 0.8. The SAXS pattern was found to be well fitted by the scattering from a polymeric particle of radius of gyration R _g with an internal structure of primary silica particles described by a polymeric constraint of a mass-fractal of dimension D. R _g increases with the PEG quantity while D first increases from 2.24 for the pure TEOS-derived gel to reach values between 2.46 and 2.40 with the additions of PEG. The correlation volume V _c as determined by SAXS for such a polymeric structure behaves as a volume-fractal and accordingly scales with R _g as V _c ~ R _g ^D . An overall mean value of about 1 nm could be estimated as an upper limit for the radius of the primary silica particle building up the structure of all the wet gels, independent of the PEG addition.