Nafion®/(organically modified silicate) nanocomposites via polymer in situ sol–gel reactions: Mechanical tensile properties

A series of Nafion®/[organically modified silicate (ORMOSIL)] hybrid materials have been created by in situ sol–gel copolymerizations of tetraethylorthosilicate and semiorganic silicon alkoxide monomers. The trends in the mechanical tensile properties of these hybrid materials were largely rationalized in terms of the entrapment of the long sulfonic acid side chains in silicate or ORMOSIL structures. There is a significant increase in the mechanical strength relative to that of unfilled Nafion®, except in one case. Young's modulus is enhanced relative to that of unfilled acid form Nafion® in a number of cases, although the degree of ductility is reduced relative to that of unfilled Nafion®. The filler fractions are beneath a critical value that would reflect percolation of a glassy, direct load‐bearing silicate phase. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2237–2247, 2002     

Dependence of silica particle sizes on network chain lengths,silica contents,and catalyst concentrations in in situ‐reinforced polysiloxane elastomers

Poly(dimethylsiloxane) networks were prepared by tetrafunctionally end‐linking hydroxyl‐terminated chains with tetraethoxysilane (TEOS). Molecular composites were then prepared by in situ sol–gel reactions on additional TEOS swelled into the networks, resulting in the formation of reinforcing silica fillers within the host elastomers. The amount of filler generated generally increased linearly with an increase in the TEOS swelling ratio, as expected. The silica particles formed were examined by small‐angle X‐ray scattering. Of particular interest were the relationships between particle size and molecular weight M_c of the network chains (mesh sizes), amount of filler introduced, and catalyst concentration. Particle sizes were smallest for the smallest values of M_c, possibly demonstrating constraining effects from the very short network chains. At fixed M_c and filler concentrations, higher catalyst concentrations gave larger particles. Increase in filler concentration generally had little effect on particle size at low and high loadings, but markedly increased sizes at intermediate levels (10–20 wt %), presumably caused by coalescence of the scattering entities into considerably larger aggregates. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1421–1427, 1999     

Novel Nafion®/ORMOSIL hybrids via in situ sol-gel reactions: 2. Probe of ORMOSIL phase nanostructure by 29Si solid state NMR spectroscopy

Perfluorosulfonic Acid (PFSA)]/[Organically-Modified Silicon Oxide (ORMOSIL)] hybrids were formulated via sol-gel reactions of mixtures of tetraethoxysilane (TEOS) and diethoxydimethylsilane (DEDMS) in the nanophase-separated morphology of a PFSA membrane (Nafion^®). The molecular structures of the ORMOSIL phases were investigated by ²⁹Si solid state NMR spectroscopy and the spectra compared with those of corresponding bulk ORMOSILs. PFSA-in situ ORMOSIL composition can be tailored by manipulating TEOS/DEDMS source solution composition and quantified by ²⁹Si solid state NMR spectroscopy. Copolymerization of TEOS and DEDMS monomers, rather than block formation, occurs within the PFSA as well as in the bulk. As DEDMS feed concentration increases, ORMOSIL nanostructures are more hydrophobic and more flexible. Dimethylsiloxane rings are dominant in PFSAs in which hydrolysis + condensation of pure DEDMS occurs.     

Synthesis of poly(vinylidene fluoride) (PVdF)/silica hybrids having interpenetrating polymer network structure by using crystallization between PVdF chains

High transparent and homogeneous poly(vinylidene fluoride) (PVdF)/silica hybrids were obtained by using an in‐situ interpenetrating polymer network (IPN) method. The simultaneous formation of PVdF gel resulting from the physical cross‐linking and silica gel from sol–gel process prevented the aggregation of PVdF in silica gel matrix. To form the physical cross‐linking between PVdF chains, the cosolvent system of dimethylformaide (DMF) and γ‐butyrolactone was used. The obtained PVdF/silica hybrids had an entangled combination of physical PVdF gel and silica gel, which was called a “complete‐ IPN” structure. The physical cross‐linking between PVdF chains in silica gel matrix was confirmed by differential scanning calorimetry (DSC) measurements. The miscibility between PVdF and silica phase was examined by scanning electron microscopy (SEM) and tapping mode atomic force microscopy (TM‐AFM) measurements. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3543–3550, 2005     

Temperature induced structural evolution of a fluorene‐thiophene copolymer on rubbed surfaces

The thermal alignment of the liquid crystalline fluorene‐thiophene copolymer (F8T2) on rubbed polyimide surfaces is investigated by ex‐situ and in‐situ X‐ray scattering experiments. The ex‐situ characterization allows an assignment of the observed diffraction peaks to distances between polymer backbones (1.6 nm), distances between the flexible side groups of the polymer chains (0.43 nm), and intramolecular distances of adjacent ring units (0.5 nm). The in‐situ characterization allows a temperature dependent observation of the polymer chain alignment. A gradual alignment process of the polymer backbones is observed for temperatures up to 563 K. Decreasing temperature after the polymer chain alignment is accompanied by a glass transition of the side chains at 380 K. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47:1599–1604, 2009     

Influence of reaction parameters on the structure of in situ rubber/silica compounds synthesized via sol–gel reaction

In situ silica was synthesized in three non‐vulcanized rubber matrices, namely natural rubber, styrene‐butadiene rubber, and EPDM (ethylene‐propylene diene ter‐polymer), using the sol–gel method with tetra‐ethoxysilane (TEOS) as silica precursor and hexylamine as catalyst. The effect of the reaction parameters such as the amount of TEOS, the reaction time (15–120 min), and the type of rubber was explored. Transmission electron microscopy was used to study the gradient in silica content and particle size over the sample thickness. The diffusion gradient of TEOS and catalyst solution in the rubber matrix responsible for the gradient was studied with Fick's law. An excellent dispersion of silica was obtained for all rubbers, even for the very non‐polar EPDM, without the use of any additives to improve the dispersion. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 967–978     

Preparation of poly(methyl acrylate‐co‐itaconic anhydride)/SiO2 hybrid materials via the sol–gel process—The effect of the coupling agent,inorganic content,and nature of the catalyst

Transparent poly(methyl acrylate‐co‐itaconic anhydride)/SiO₂ hybrid materials were prepared from methyl acrylate‐itaconic anhydride copolymer and tetraethoxysilane (TEOS) with the coupling agent (3‐aminopropyl)triethoxysilane (APTES) via a sol–gel process. The covalent bonds between the organic and inorganic phases were introduced by the in situ aminolysis of the itaconic anhydride units with APTES forming a copolymer bearing a triethoxysilyl group. These groups subsequently were hydrolyzed with TEOS and allowed to form a network. These reactions were monitored by Fourier transform infrared analysis. The amount of APTES had a dramatic influence on the gel time and sol fraction. The effect of APTES, the inorganic content, and the nature of the catalyst on the thermal properties and morphology of the hybrid materials were studied by differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and atomic force microscopy. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 321–328, 2000     

Synthesis,structure, and morphology of polymer–silica hybrid nanocomposites based on hydroxyethyl methacrylate

Two types of polymer–silica nanocomposites have been prepared by undergoing free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) either in the presence of HEMA-functionalized SiO₂ nanoparticles (Type 1) or during the simultaneous in situ growing of the silica phase through the acid-catalyzed sol–gel polymerization of tetraethoxysilane (TEOS) (Type 2). Relationships between synthesis conditions, chemical structure, and resulting morphology have been studied. Type 1 systems exhibit a classical particle-matrix morphology, but where particles tend to form aggregates. Type 2 systems possess a finer morphology characterized by a very open mass-fractal silicate structure, which is believed to be bicontinuous with the organic phase at a molecular level. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3172–3187, 1999     

Ethylene/1‐heptene copolymers as interesting alternatives to 1‐octene‐based LLDPE: Molecular structure and physical properties

Classical linear low density polyethylenes (LLDPEs) are copolymers of ethylene and 1‐octene or 1‐hexene, respectively. In the past, other 1‐olefins have been tested as comonomers but the resulting LLDPEs were never commercialized as large scale products. The present study focuses on the use of 1‐heptene as an interesting comonomer for the synthesis of LLDPE. For a comparison of the molecular structure and the physical properties of 1‐heptene‐ and 1‐octene‐based LLDPEs, five Ziegler–Natta LLDPEs of varying comonomer contents based on 1‐heptene and 1‐octene, respectively, were acquired and analysed using advanced methods. The comonomer contents of the resins were between 0.35 and 6.4 mol %. Crystallization‐based techniques revealed similar bimodal distributions that are due to the formation of copolymer and polyethylene homopolymer fractions. The compositional distribution of the copolymers was studied by high‐temperature (HT) HPLC and HT‐2D‐LC. The analytical results indicate similar chemical heterogeneities and molar mass distributions of the two sets of LLDPE up to a comonomer content of 3 mol %. Similar to the molecular structure, the physical properties of the materials are quite similar. At comonomer contents of ≥3 mol % differences between the two sets of samples are seen that are attributed to differences in the abilities of 1‐heptene and 1‐octene in disrupting the crystal arrangements of the polymer chains in solid state. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 962–975     

Metallocene/methylaluminoxane‐catalyzed copolymerizations of oxygen‐functionalized long‐chain olefins with ethylene

Copolymerizations of ethylene with 10‐undecen‐1‐ol, 10‐undecenyl methyl ether, 10‐undecenyl trimethyl silyl ether, and 1‐undecene were performed with rac‐ethylene‐bis(1‐indenyl)zirconium dichloride as a catalyst and methylaluminoxane as a cocatalyst. All three oxygen‐functional comonomers copolymerized with ethylene, although the activity of the catalyst decreased considerably compared with the homopolymerization of ethylene. The conversions of the comonomers varied from 17 to 40%, depending on the amount of comonomer in the feed. Under the same conditions, the conversion of 1‐undecene was 50–75%. The incorporation (0.7–3.6 mol %, depending on the feed) and the effect on the activity of the catalyst were on the same level for all the functional comonomers, which indicates that trimethylsilyl or methyl groups do not act as effective protecting groups for oxygen atoms. According to NMR and Fourier transform infrared analyses, the final functional group in the copolymers of the trimethylsilyl ether comonomer was hydroxyl. In contrast, the methyl ether group remained untouched in the copolymer, which suggests that the formation of aluminum alkoxides via a reaction with a cocatalyst is not a prerequisite for comonomer incorporation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1966–1971, 2000     

Thermal and mechanical analysis of metallocene‐catalyzed ethene–α‐olefin copolymers: The influence of the length and number of the crystallizing side chains

Copolymers of ethene and 1‐octene, 1‐dodecene, 1‐octadecene, and 1‐hexacosene were carried out with [Ph₂C(2,7‐di‐^tertBuFlu)(Cp)]ZrCl₂/methylalumoxane as a catalyst to obtain short‐chain branched polyethylenes with branch lengths of 6–26 carbon atoms. This catalyst provided high activity and a very good comonomer and hydrogen response. In this study, the influence of the length and number of the side chains on the mechanical properties of the materials was investigated. The crystalline methylene sequence lengths of the copolymers and lamellar thicknesses were calculated after the application of a differential scanning calorimetry/successive self‐annealing separation technique. By dynamic mechanical analysis, the storage modulus as an indicator of the stiffness and the loss modulus as a measure of the effect of branching on the α and β relaxations were studied. The results were related to the measurements of the polymer density and tensile strength to determine the effect of longer side chains on the material properties. The hexacosene copolymers had side chains of 24 carbons and remarkable material properties very different from those of conventional linear low‐density polyethylenes. The side chains of these copolymers crystallized with one another and not only parallel to the backbone lamellar layer, depending on the hexacosene concentration in the copolymer. The side chains crystallized even at low hexacosene concentrations in the copolymer. A transfer of these results to 16 carbons side chains in ethene–octadecene copolymers was also possible. © 2006 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1600–1612, 2006     

The role of TEOS‐TIP within a pentablock ionomer: Morphology,physical properties,and ion transport

Inorganic–organic nanocomposites were created using tetraethylorthosilicate (TEOS), titanium isopropoxide (TIP), and poly(t‐butylstyrene‐b‐hydrogenated isoprene‐b‐sulfonated styrene‐b‐hydrogenated isoprene‐b‐t‐butylstyrene) or pentablock copolymer (PBC). A TEOS–TIP–H₂O ternary phase diagram was generated to create homogenous sol solutions with designable condensation reactions that led to controllable materials. An inorganic TEOS–TIP network was synthesized using sol–gel chemistry within the organic PBC domain. All TEOS–TIP–PBC films exhibited higher water sorption than unmodified PBC ionomer that was attributed to a change in morphology. Proton conductivity increased up to 80% due to TEOS–TIP within the nanocomposite film. This can be attributed to ion domain redistribution and partial charge transfer from the titanate's inorganic domains to sulfonate groups that promote acid dissociation. PBC had a microphase‐separated morphology that changed with increasing TIP concentration, which was observed from atomic force microscopy and small‐angle X‐ray scattering results. Finally, thermal gravimetric analysis revealed a decrease in degradation temperature, and dynamic mechanical analysis results demonstrated reduced polymer chain mobility caused by inorganic–organic interactions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 575–586     

Copolymerization of propylene with higher α‐olefins in the presence of the syndiospecific catalyst i‐Pr(Cp)(9‐Flu)ZrCl2/MAO

The catalyst system i‐Pr(Cp)(9‐Flu)ZrCl₂/methylaluminoxane was used for the synthesis of random syndiotactic copolymers of propylene with 1‐hexene, 1‐dodecene, and 1‐octadecene as comonomers. An investigation of the microstructure by ¹³C NMR spectroscopy revealed that the stereoregularity of the copolymers decreased because of an increase in skipped insertions in the presence of the higher 1‐olefin. The melting temperature of the copolymers, as measured by differential scanning calorimetry (DSC), decreased linearly with increasing comonomer content independently of the comonomer nature. During the DSC heating cycle, an exothermic peak indicating a crystallization process was observed. The decrease in the crystallization temperature with higher 1‐olefin content, measured by crystallization analysis fractionation, indicated a small but significant dependence on the nature of the comonomer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 128–140, 2002     

Synthesis,rheology, and morphology of nylon‐11/layered silicate nanocomposite

Exfoliated nylon‐11/layered silicate nanocomposites were prepared via in situ polymerization by dispersing organoclay in 11‐aminoundecanoic acid monomer. The original clay was modified by a novel method with 11‐aminoundecanoic acid. In situ Fourier transform infrared spectroscopy results show that stronger hydrogen bonds exist between nylon‐11 and organoclay than that of between nylon‐11 and original clay. The linear dynamic viscoelasticity of organoclay nanocomposites was investigated. Before taking rheological measurements, the exfoliated and intercalating structures and the thermal properties were characterized using X‐ray diffraction, transmission electron microscopy, differential scanning calorimetry, and thermogravimetric analysis. The results show that the clay was uniformly distributed in nylon‐11 matrix during in situ polymerization of clay with 4 wt % or less. The presence of clay in nylon‐11 matrix increased the crystallization temperature and the thermal stability of nanocomposites prepared. Rheological properties such as storage modulus, loss modulus, and relative viscosity have close relationship with the dispersion favorably compatible with the organically modified clay. Comparing with neat nylon‐11, the nanocomposites show much higher dynamic modulus and stronger shear thinning behavior. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2161–2172, 2006     

Nanostructure and properties of polysiloxane‐layered silicate nanocomposites

The relationship between nanostructure and properties in polysiloxane layered silicate nanocomposites is presented. Solvent uptake (swelling) in dispersed nanocomposites was dramatically decreased as compared to conventional composites, though intercalated nanocomposites and immiscible hybrids exhibited more conventional behavior. The swelling behavior is correlated to the amount of bound polymer (bound rubber) in the nanocomposites. Thermal analysis of the bound polymer chains showed an increase and broadening of the glass‐transition temperature and loss of the crystallization transition. Both modulus and solvent uptake could be related to the amount of bound polymer formed in the system. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1595–1604, 2000     

Precision PEGylated Polymers Obtained by Sequence‐Controlled Copolymerization and Postpolymerization Modification

Copolymers containing water‐soluble poly(ethylene glycol) (PEG) side chains and precisely controlled functional microstructures were synthesized by sequence‐controlled copolymerization of donor and acceptor comonomers, that is, styrene derivatives and N‐substituted maleimides. Two routes were compared for the preparation of these structures: a) the direct use of a PEG–styrene macromonomer as a donor comonomer, and b) the use of an alkyne‐functionalized styrenic comonomer, which was PEGylated by copper‐catalyzed alkyne–azide cycloaddition after polymerization. The latter method was found to be the most versatile and enabled the synthesis of high‐precision copolymers. For example, PEGylated copolymers containing precisely positioned fluorescent (e.g. pyrene), switchable (e.g. azobenzene), and reactive functionalities (e.g. an activated ester) were prepared.     

Synthesis of polypropylene graft copolymers by the combination of a polypropylene copolymer containing pendant vinylbenzene groups and atom transfer radical polymerization

This article discusses a facile and inexpensive reaction process for preparing polypropylene‐based graft copolymers containing an isotactic polypropylene (i‐PP) main chain and several functional polymer side chains. The chemistry involves an i‐PP polymer precursor containing several pendant vinylbenzene groups, which is prepared through the Ziegler–Natta copolymerization of propylene and 1,4‐divinylbenzene mediated by an isospecific MgCl₂‐supported TiCl₄ catalyst. The selective monoenchainment of 1,4‐divinylbenzene comonomers results in pendant vinylbenzene groups quantitatively transformed into benzyl halides by hydrochlorination. In the presence of CuCl/pentamethyldiethylenetriamine, the in situ formed, multifunctional, polymeric atom transfer radical polymerization initiators carry out graft‐from polymerization through controlled radical polymerization. Some i‐PP‐based graft copolymers, including poly(propylene‐g‐methyl methacrylate) and poly(propylene‐g‐styrene), have been prepared with controlled compositions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 429–437, 2005     

Inorganic–organic hybrids involving poly(ε‐caprolactone) and silica network: Hydrogen‐bonding interactions and isothermal crystallization kinetics

Inorganic–organic hybrids mediated by hydrogen‐bonding interactions involving silicon oxide network and poly(ε‐caprolactone) (PCL) were prepared via an in situ sol–gel process of tetraethoxysilane in the presence of PCL. Fourier transform infrared spectroscopy indicated that there were hydrogen‐bonding interactions between carbonyls of PCL and silanol hydroxyls that were formed by incomplete polycondensation in the sol–gel process. In terms of the frequency shift of the hydroxyl stretching vibration bands, it is concluded that the strength of the interassociation between PCL and silicon oxide networks is weaker than that of the self‐association in the control silica network. The phenomenon of equilibrium melting point depression was observed for the PCL/silica system. The hybridization of PCL with silica network causes a considerable increase in the overall crystallization rate and dramatically influences the mechanism of nucleation and growth of the PCL crystallization. The analysis of isothermal crystallization kinetic data according to the Hoffman‐Lauritzen theory shows that with increasing silica content in the hybrids, the surface energy of extremity surfaces increases dramatically for the hybrids. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2594–2603, 2005     

Preparation of gradient copolymers via ATRP in miniemulsion. II. Forced gradient

A series of forced gradient copolymers with different controlled distribution of monomer units along the copolymer backbone were successfully prepared by atom transfer radical polymerization in miniemulsion. The newly developed initiation technique, known as activators generated by electron transfer, was beneficial for forced gradient copolymers preparation because all polymer chains were initiated within the miniemulsion droplets and the miniemulsion remained stable throughout the entire polymerization. Various monomer pairs with different reactivity ratios were examined in this study, including n‐butyl acrylate/t‐butyl acrylate, n‐butyl methacrylate/methyl methacrylate, and n‐butyl acrylate/styrene. In each case, the added monomer diffused across the aqueous suspending medium and gradient copolymers with different forced distributions of comonomer units along the polymer backbone were obtained. The shape of the gradient along the backbone of the copolymers was influenced by the molar ratio of the monomers, the reactivity ratio of the comonomers as well as the feeding rate. The shape of the gradient was also affected by the relative hydrophobicities of the comonomers. Copolymerizations exhibited good control for all feeding rates and comonomer feeding ratios, as evidenced by narrow molecular weight distribution (M_w/M_n = 1.20–1.40) and molecular weight increasing smoothly with polymer yield, indicating high initiation efficiency. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1413–1423, 2007     

Surlyn®/silicate nanocomposite materials via a polymer in situ sol–gel process: Morphology

Surlyn®/silicate hybrid materials were produced via diffusion‐controlled polymer in situ sol–gel reactions for tetraethylorthosilicate. The heterogeneous morphologies of these materials were inspected with transmission electron (TEM), atomic force (AFM), and environmental scanning electron microscopic methods. The silicate uptake was highly dependent on the water affinity of the particular Surlyn® form (acid or ionic) rather than on the affinity of the solvent. The morphology consisted of silicate particles with diameters that were on the order of tens of nanometers. Hence, these materials can be classified as nanocomposites. The particle size distributions in both the TEM and AFM images for all composites appeared to be narrow, with un‐neutralized Surlyn® exhibiting a broader distribution. Larger particles were found near the film surfaces, and the silicon elemental distribution across the film thickness indicated higher concentrations near the surfaces, which is most likely due to the fact that the sol–gel reaction is diffusion controlled in these polymeric media. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1563–1571, 2003