Syntheses of poly(siloxane)-supported zirconocene catalysts and application to olefin polymerizations

Poly(siloxane)s with bisindenyl, bisfluorenyl, bis(1,2,3,4-tetramethylcyclopentadienyl), bis(2,4,7-trimethylindenyl) and monoindenylmethyl side groups were synthesized by condensation of the corresponding dichlorosilanes and water. For reference, diphenylsilanediol or hydroquinone was also employed in place of water. A series of poly(siloxane)-supported zirconocene catalysts were then prepared from these precursors and applied to ethene and propene polymerizations as well as to the copolymerization of ethene with 1-octene in the presence of methylalumoxane. The polymerization activity of the new supported metallocenes depends drastically upon the substituents in the siloxane backbone. The zirconocene catalysts supported on poly(bisindenylsiloxane) and poly(bisfluorenylsiloxane) give the highest activities for ethene and propene polymerizations, respectively. The weight-average molecular weights of the polymers are also markedly dependent upon the substituents. On the other hand, the molecular mass distributions (MMD) are generally not so sharp, suggesting that the active species formed in these supported catalysts are not uniform. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 : 421–428, 1998     

Solution properties of poly(dimethyl siloxane)

The solution properties of poly(dimethyl siloxane) (PDMS) were studied with light scattering (LS), gel permeation chromatography/light scattering (GPC/LS), and viscometry methods. PDMS samples were fractionated, and the weight‐average molecular weights, second virial coefficient, and the z‐average radius of gyration of each fraction were found according to the Zimm method with the LS technique. In this work, the molecular weight range studied was 7.5 × 10⁴ to 8.0 × 10⁵. Molecular weights and molecular weight distributions were determined by GPC/LS. The intrinsic viscosities of these fractions were studied in toluene at 30 °C, in methyl ethyl ketone (MEK) at 20 °C, and in bromocyclohexane (BCH) at 26 °C and 28 °C. The Mark–Houwink–Sakurada relationship showed that toluene was a good solvent, and MEK at 20 °C and BCH at 28 °C were θ solvents for PDMS. The unperturbed dimensions were calculated with LS and intrinsic viscosity data. The unperturbed dimensions, expressed in terms of the characteristic ratio, were found to be 6.66 with different extrapolation methods in toluene at 30 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2678–2686, 2000     

Fluoroalkylation of poly(cyclopentadienyl)siloxane and the surface properties of poly(fluorocyclopentenyl)siloxane films

In this work, poly(fluorocyclopentenyl)siloxane (FPCS) was obtained via a single electron transfer addition reaction of poly(cyclopentadienyl)siloxane (PCS) and perfluoroalkyl iodides, and reduction reaction of the intermediates. PCS was prepared by substitution and hydrolysis reactions using methyltrichlorosilane and sodium cyclopentadienide (NaCp) as raw materials. Fourier transform infrared (FTIR), ¹H NMR, and ¹⁹F NMR indicated the structures of the target polymers. The XPS results showed that the thin films prepared by dip-coating were fluorine enriched at the surface. Atomic force microscopy (AFM) image showed that on the rough surface of films, there were many pinnacles which were generated through the migration of side chain fluoroalkyl groups. The relative static contact angles of water and n-hexadecane on FPCS and PCS indicated that sodium dithionite initiated the reaction of perfluoroalkyl iodides and PCS so that FPCS was successfully synthesized. The measured surface energy of PCS was 2.57 × 10^?2 N/m; while FPCS was 2.14 × 10^?2 N/m, which represented better liquid repellent property compared to PCS.     

Ion conductive poly(ethylene oxide-dimethyl siloxane) copolymers

A series of poly(ethylene oxide-dimethyl siloxane) copolymers, — [SiMe₂O(CH₂CH₂O)_n]_m — (n = 2, 3, 4, 5, 6.4, 8.7, 13.3), were synthesised by the reaction of polyethylene glycol with dimethyl dimethoxy/diethoxysilane. Corresponding ion-conductive polymers were prepared by complexing these copolymers with salts (sodium tetrafluoroborate or ammonium adipate). The highest conductivity of these systems at room temperature was 3 × 10⁻⁴ S cm⁻¹ and 6 × 10⁻⁵ S cm⁻¹, respectively. The glass transition temperature of these copolymers is reported and is seen to be dependent on the length of the ether units. The effects of siloxane content, salt concentration, and temperature on the conductivity are discussed. © 1996 John Wiley & Sons, Inc.     

Thermogravimetric analysis of poly(alkyl methacrylates) and poly(methylmethacrylate-g-dimethyl siloxane) graft copolymers

The thermal stabilities of various poly(alkyl methacrylate) homopolymers and poly(methyl methacrylate-g-dimethyl siloxane) (PMMA-g-PSX) graft copolymers have been determined by thermogravimetric analysis (TGA). As expected, the thermal stabilities of poly(alkyl methacrylates) were a function of the ester alkyl group, and polymerization mechanism. In particular, thermally labile linkages, which result from termination during free radical or nonliving polymerization mechanisms, decrease the ultimate thermal stabilities of the polymers. However, graft copolymers, which were prepared by the macromonomer technique with free radical initiators, exhibited enhanced thermal stability compared to homopolymer controls. A more complex free radical polymerization mechanism for the macromonomer modified polymerization may account for this result. © 1994 John Wiley & Sons, Inc.     

Morphology and properties of polycaprolactone-poly(dimethyl siloxane)-polycaprolactone triblock copolymers

The molecular structure, crystallization, solid-state morphology, thermal properties, and phase behavior of two copolymers consisting of a poly(dimethylsiloxane) (PDMS) mid-block coupled to polycaprolactone (PCL) end-blocks were investigated. Both copolymers (which differ only in the molecular lengths of the PCL end-blocks) were found to be lamellar systems, whose core consists of PCL chains having the same crystal structure as PCL homopolymer, and whose amorphous interlayers contain the PDMS blocks and the PCL noncrystalline segments. From x-ray and electron-microscopy results, it is expected that the PCL blocks may be folded once in the longer copolymer and not at all in the shorter. As a result of their differing PCL lengths, the former crystallizes as regular PCL spherulites (at a growth rate reduced with respect to PCL homopolymer), whereas the latter yields only defective, immature axialites of low overall crystallinity. Electron diffraction showed that these spherulites grow preferentially along b crystallographic axis and that the PCL crystalline stems are arranged perpendicularly to their lamellae. © 1993 John Wiley & Sons, Inc.     

Siloxane/silane‐crosslinked systems from supercritical carbon dioxide: II. Pendant phenyl poly(carbosilane/siloxane)s

New silicone‐containing polymers with crosslinkable units have been synthesized by hydrosilation polymerization in both toluene and supercritical carbon dioxide (70°C, 3000 psi) catalyzed by platinum‐divinyltetramethyldisiloxane (Pt‐DVTMS). It was found that high molecular polymers were obtained in both toluene and supercritical carbon dioxide. The polymers were characterized by FTIR, NMR, GPC, TGA, and DSC. The molecular weights of these polymers ranged from 9000 to 39,000. With further hydrolysis and thermal curing, the molecular weight can be increased significantly. Comparison of the properties between reactions in toluene versus supercritical carbon dioxide indicated that the green solvent is a usable alternative for hydrosilation polymerization. The new polymers synthesized in either toluene or supercritical carbon dioxide are thermally stable, ranged from 350 to 488°C. Copyright © 2008 John Wiley & Sons, Ltd.     

The absorption of organic liquids in poly(aryl-ether-ether-ketone) [PEEK]

The absorption and subsequent desorption of benzene, toluene, carbon disulfide, and chloroform in amorphous and 27% crystalline poly (aryl-ether-ether-ketone) (PEEK) were determined. At 35°C, the equilibrium weight gain (solubility) of benzene, toluene, chloroform, and CS₂ are 23.5, 19.8, 51.2, and 21.2 wt%, respectively. The initial weight gain is linear with root-time and pseudodiffusion constants for absorption into amorphous PEEK ranging from 0.35 to 9.85 x 10^-12m²/s were calculated. The desorption processes are two-step and are controlled by the T_g of the penetrant-resin mixture. The rate of diffussion into the crystalline material is extremely slow; crystalline PEEK reaches saturation (12.5 wt%) after immersion in CS₂ (35°C) for several hundred hours but, even after 1300 h immersion, the other fluids do not reach saturation.     

Morphology of a Poly(imide siloxane) Segmented Copolymer/Silica Hybrid Composite

The role of polydimethylsiloxane (PDMS) as a compatibilizer of polyimide/silica hybrid composites was investigated. Introduction of PDMS into a polyimide matrix retards the phase separation of hybrid composites and also prevents the formation of high‐molecular‐weight silicate. PDMS interacts with silica because of the similarity of its structure with the sol‐gel glass matrix of the silica precursor, indicating that poly(imide siloxane)/silica might be a good candidate material for organic/inorganic hybrid composites.     

Structure–property co‐relationship of fluorinated poly(imide‐siloxane)s

Eight poly(imide‐siloxane)s co‐polymers have been prepared by one pot solution imidization method. The polymers are synthesized by the reaction of bisphenol‐A‐dianhydride (BPADA) with fluorinated diamine 4,4′‐bis(3″‐trifluoromethyl‐p‐aminobiphenyl ether) biphenyl, and aminopropyl‐terminated polydimethylsiloxane (APPS). The polymers are synthesized by varying the siloxane loading to 5, 10, 15, 20, 25, 30, 35, and 40 wt%, respectively. Thermal, mechanical, rheological, and dielectric properties of these polymers have been evaluated with respect to siloxane loading. The polymers showed glass transition temperature of 107–203°C and tensile strength at break of 24–75 MPa depending on siloxane loading. The elongation break of the polymers ranges from 24 to 144% depending on siloxane loading. The amounts of char residue in the polymers have been correlated with incorporated siloxane in the polymer by NMR techniques. The polymers showed very low water absorption and dielectric constant as low as 2.43 when the siloxane loading is 40 wt%. Copyright © 2008 John Wiley & Sons, Ltd.     

SiO2–poly(amidoamine) dendrimer inorganic/organic hybrids

SiO₂–poly(amidoamine) (PAMAM) dendrimer hybrids were synthesized via (1) a Michael addition reaction between the dendrimer and 3‐(trimethoxysilyl) propyl acrylate, (2) the dissolution of the formed compound in methanol, and (3) the mixing of the latter solution with a methanol solution of partly hydrolyzed tetraethylorthosilicate (TEOS) and its casting on a glass substrate. ¹H NMR indicated that in the first step, 77% of the secondary amines were converted into tertiary amines when the fourth‐generation dendrimer was employed and 46% were converted when the second‐generation dendrimer was used. The final SiO₂–PAMAM dendrimer hybrids were obtained via the hydrolysis and condensation of the compound obtained via the Michael addition and the methanol solution of partly hydrolyzed TEOS. The compartmentalized structure of the hybrids due to the compartments of the dendrimers could be controlled by changing the dendrimer and the amount of TEOS. Scanning electron microscopy and transmission electron microscopy micrographs provided information about the structure of the hybrids. Like the PAMAM dendrimer, the SiO₂–PAMAM dendrimer hybrids exhibited a high metal ion complexing capacity because of the presence of the compartments of the dendrimer; they can be, however, much more easily handled, and, as demonstrated by thermogravimetric experiments, have much higher thermal resistance. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1443–1449, 2000     

Monodisperse polystyrene particles crosslinked with poly(dimethyl siloxane) diacrylate using dispersion polymerization and their monomer swelling capability

A flexible poly(dimethyl siloxane) diacrylate (PDMSDA) crosslinker was synthesized using different molecular weights of poly(dimethyl siloxane) (PDMS, M _n =550, 1,700, 4,000 g/mol). The monodisperse polystyrene (PS) particles crosslinked with various contents of PDMSDA were prepared by dispersion polymerization, and applied as seed particles in the seeded polymerization. The crosslinking density of the PS particles was determined from the rate of transport of the monomer molecules to the crosslinked seed particles. It was confirmed that the monomer swelling capacity of seed particles and final morphological changes of polymer beads were determined significantly by the crosslinking density of the seed particles. In addition, the morphological change was not observed without the oligomer swelling step in the seeded polymerization due to the hydrophobic property of PDMS. When highly crosslinked seed particles were used in the seeded polymerization, peculiar morphology (doublet structure) of polymer beads appeared.     

Atmospheric aging of poly[methyl(phenyl)silanediyl] monitored by FTIR spectroscopy

Poly[methyl(phenyl)silanediyl] films were irradiated in ATLAS Weather-O-Meter Ci 3000+ for ca 3 h. Changes in the region of siloxane, carbonyl, hydroxyl, and C-H (aromatic) bands were monitored by FTIR. Main attention was paid to changes in siloxane formation, which could be reduced in the presence of phenolic UV absorber 1 and oxalanilide 3 .     

Adsorption of stereoregular poly(methyl methacrylates) on γ-alumina: Spectroscopic analysis

ABSTRACTS: Three poly(methyl methacrylates) (PMMA) with a racemic fraction ranging from 0.25 to 0.91 have been adsorbed from a chloroform solution on γ-alumina and studied by diffuse reflectance infrared spectroscopy (DRIFT) and solid-state ¹³C NMR spectroscopy. From DRIFT spectra, it is seen that the fraction of carbonyl groups bonded to the surface goes from 0.29 for s-PMMA to 0.41 for i-PMMA, but there is a larger amount of s-PMMA retained on the surface (at any given solution concentration). NMR spectroscopy indicates, from shifts of the methylene and α-methyl carbon peaks (due to the γ-gauche effect), that the adsorption is accompanied by changes in conformation, with an increase in the number of trans conformers, particularly with i-PMMA. These results indicate that s-PMMA adsorbs on γ-alumina in a brush-like configuration, with a relatively small number of groups attached to the surface, and tails and loops sticking out of the surface, whereas i-PMMA adsorbs in a sheet-like configuration, with a greater number of interacting groups. In both cases, the adsorption is accompanied with an increase in the number of trans conformers as compared to the bulk conformation. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2985–2995, 1999     

Molecular mobility of ultrasonically devulcanized silica‐filled poly(dimethyl siloxane)

We used NMR relaxation and pulsed‐gradient diffusion measurements at 70 °C in precipitated silica‐filled poly(dimethylsiloxane) (PDMS; silicone rubber) after crosslinking, after subsequent devulcanization by intense ultrasound, and after subsequent revulcanization. As in unfilled PDMS, transverse relaxation displays three distinct rate components attributed to an entangled and crosslinked network (similar in T₂), light sol plus dangling network fragments, and unreactive trace oligomers. Ultrasound produces copious amounts of extractable sol. The T₂ relaxation times decreased modestly with increasing filler content, but they and the components' proportions correlated mainly with the sol fraction, that is, the network degradation. In rupturing the network, devulcanization produces large diffusing fragments and dangling ends; revulcanization largely reverses these effects. The rates and amplitudes of the bimodal diffusivity distribution confirmed this conclusion. The weakness of the effects of filler suggests that ultrasound devulcanization is easily adaptable to the recycling of the preponderantly particulate‐filled industrial rubbers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 454–465, 2003     

An efficient synthesis of benzyl bromides from aromatic aldehydes using polymethylhydrosiloxane and (bromodimethyl)sulfonium bromide or N-bromosuccinimide

Polymethylhydrosiloxane (PMHS) in combination with (bromodimethyl)sulfonium bromide or NBS has been utilized for the first time for reductive bromination of aromatic aldehydes at room temperature to afford the corresponding benzyl bromides in excellent yields.     

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     

A Transparent,Highly Stretchable,Autonomous Self‐Healing Poly(dimethyl siloxane) Elastomer

An innovative self‐healing polydimethylsiloxane (PDMS) elastomer, namely, PDMS‐TFB, is reported by incorporating the reversibly dynamic imine bond as the self‐healing points into the PDMS networks. The PDMS‐TFB elastomer features good optical transmittance (80%) in full visible light region, high stretchability (≈700%), and excellent autonomous self‐healing ability at room temperature. Surprisingly, the self‐healing behavior can take place in water and even at a temperature as low as −20 °C in air, showing a promising outlook for broader applications. As a proof‐of‐concept, this study demonstrates the use of the PDMS‐TFB elastomer for preparing anticorrosion coating and adhesive layer, and also the use of such an elastomer to be the platform for fabricating the flexible interconnector and chemical sensor. Remarkably, no significant difference is observed between the pristine and healed samples. Taking full advantage of these unique properties, it is anticipated that such a PDMS‐TFB elastomer shows wide applications in the fields of materials science, electronics, biology, optics, etc.

     

Preparation and characterization of polyurethan‐block‐poly(trifluoro‐ propylmethyl)siloxane elastomers

A series of polyurethane‐block‐poly(trifluoropropylmethyl)siloxane (PUFS) elastomers were prepared via a two‐step process from toluenediisocyanate (TDI), α ω‐bis(3‐aminopropyldiethoxylsilane) poly(trifluoropropylmethyl)siloxane (APFS), and poly(tetramethylene oxide) (PTMO). The PUFS films were formed through moisture curing and characterized by DSC, DMTA, TGA, mechanical testing, and water contact angle. It was found that the extent of microphase separation of the PUFS system would increase with the increase in APFS content, and result in the decrease in the tensile strength and the thermal stability. On the other hand, the crosslink density of the PUFS system would apparently increase with the increase in the TDI content, which reduced the microphase separation and improved the tensile properties and the thermal stability of the PUFS elastomers. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal oxidation of poly(1-trimethylsilylprop-1-yne) studied by IR spectroscopy

Thermal oxidation of poly(1-trimethylsilylprop-1-yne) was studied by IR spectroscopy in the 20—245 °C temperature interval. In the 20—160 °C temperature range, the reaction proceeds predominantly at the C—Me group as revealed by the decrease in the intensity of the bands of the methyl group bound to the C atom and the appearance of the bands of the hydroperoxide and methylene groups. The decomposition of hydroperoxides produces aldehydes and ethers. At 160—200 °C, oxidation occurs via two routes: at the C—Me and C=C groups, while the Me₃Si group remains unchanged. At 230—240 °C, the rate of the reaction occurring at the C=C bond is higher than the rates of the processes involving the MeC and Me₃Si groups. The relative content of the structural units was calculated for the samples oxidized at different temperatures. Plausible mechanisms of thermal oxidation of poly(1-trimethylsilylprop-1-yne) were considered on the basis of the data obtained.