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.     

The thermal properties of polysiloxanes poly(dimethyl siloxane) and poly(diethyl siloxane)

New measurements and literature data on polysiloxanes covering heat capacities, transition parameters, enthalpies, entropies and Gibbs energies are presented and critically reviewed. TheATHAS computation method is used to bring heat capacities into agreement with an approximate frequency spectrum. The various crystal and mesophases are discussed. TheATHAS (1990) recommended data are as follows: For poly(dimethyl siloxane) the glass transition is at 146 K with an increase in heat capacity of 29.24 J/(K mol). The completely crystalline sample melts at about 219 K with a heat of fusion of 2.75 kJ/mol. For poly(diethyl siloxane) the glass transition is at 135 K with an increase in heat capacity of 34.48 J/(K mol). The completely crystalline sample changes to a condis crystal at 206.7 K with a heat of disordering of 2.72 kJ/mol. The transition to a poorly characterized viscous crystal with thermodynamic properties close to the melt occurs at 282.7 K with an enthalpy of transition of 1.84 kJ/mol. Final fusion occurs at 308.5 K and a small endotherm of about 231 J/mol. Tables of heat capacities, enthalpies, entropies and Gibbs energies are given from 0 K to 550 K.

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Zusammenfassung Neue Messungen und Literaturangaben von Polysiloxanen über Wärmekapazität, Umwandlungsparameter, Enthalpien, Entropien und Gibbssche Energien werden vorgestellt und kritisch betrachtet. Das Rechenverfahren ATHAS wurde benutzt, um die Wärmekapazitäten mit einem annähernden Frequenzspektrum in Einklang zu bringen. Es wurden die verschiedenen Kristall- und Mesophasen diskutiert. Die von ATHAS (1990) empfohlenen Werte sind wie folgt: Für Poly(dimethylsiloxan) beträgt der Glasumwandlungspunkt 146 K bei Zunahme der Wärmekapazität um 29.24 J/(K.mol). Die vollständing kristalline Probe schmilzt bei etwa 219 K mit einer Schmelzwärme von 2.75 kJ/mol. Für Poly(diethylsiloxan) beträgt der Glasumwandlungspunkt 135 K bei Zunahme der Wärmekapazität um 34.48 J/(K.mol). Die vollständig kristalline Probe wandelt sich bei 206.7 K um, die Fehlordnungswärme beträgt 2.72 kJ/mol. Die Umwandlung in einen wenig verstandenen viskosen Kristall, dessen thermodynamische Eigenschaften denen der Schmelze gleichen, erfolgt bei 282.7 K mit einer Umwandlungsenthalpie von 1.84 kJ/mol. Letztendlich verläuft das Schmelzen bei 308.5 K mit einem kleinen endothermen Effekt von etwa 231 J/mol. Wärmekapazitäten, Enthalpien, Entropien und Gibbssche Energien sind für den Bereich 0 K–550 K tabellarisch angegeben.

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, , , , . ATHAS , - . . ATHAS (1990) : 146 29,24 / ·. 219 2,75 /. 135 34,48 /·. 206,7 2,72 /. « » 282,7 1,84 /. 308,5 231 /. , , 0–550 .

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This work was supported by the National Science Foundation, Polymers Program, Grant #DMR 83-17097 and early work of J.P.W. was supported by the Am. Chem. Soc. Petroleum Research Found, Grant 12431-AC7. In addition at Oak Ridge National Laboratory the work was sponsored by the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy under contract DE-AC05-84OR21400 with Martin Marietta Energy Systems Inc.     

Light-sensitive chalcone-containing poly(amido imides)

Soluble poly(amido imides) and copoly(amido imides) containing main-and side-chain chromophore chalcone groups have been synthesized. Thermo-and photocrosslinking of polymer chains in films under UV irradiation have been studied. The mechanical properties, dielectric behavior, and photosensitivity and photoconductivity characteristics of the polymers have been investigated.     

Effect of chloroform on the structure and gas-separation properties of poly(ether imides)

The FTIR spectra of poly(ether imide) films prepared from their chloroform solutions were recorded in a wide temperature interval. The cast films were shown to contain residual solvent. This residual solvent existed in films as unbound chloroform that may be removed by heating to 60–70°C and as bound chloroform that is involved in complex formation with polymers and may be removed by heating at temperatures close to their glass transition temperatures (180°C). Quantum-chemical calculations were performed for structures that model fragments and monomer units of poly(ether imides), as well as their complexes with chloroform. Chloroform was shown to be capable of preferential binding with an oxygen atom in a Ph-O-Ph′ fragment via hydrogen bonds. In this case, the conformational set of poly(ether imide) chains is changed. The above evidence is invoked to explain changes in transport characteristics with time for poly(ether imide) films cast from chloroform solutions.     

Fibrinolytic poly(dimethyl siloxane) surfaces

PDMS surfaces have been modified to confer both resistance to non-specific protein adsorption and clot lyzing properties. The properties and chemical compositions of the surfaces have been investigated using water contact angle measurements, ATR FT-IR spectroscopy, and XPS. The ability of the PEG component to suppress non-specific protein adsorption was assessed by measurement of radiolabeled fibrinogen uptake from buffer. The adsorption of plasminogen from human plasma to the various surfaces was studied. In vitro experiments demonstrated that lysine-immobilized surfaces with free epsilon-amino groups were able to dissolve fibrin clots, following exposure to plasma and tissue plasminogen activator. [Figure: see text].     

Transitions in poly(diethyl siloxane)

An adiabatic heat capacity study of poly(diethylsiloxane) confirms that it has a single glass transition occurring at 130°K, the lowest glass transition reported to date for a high molecular weight polymer. The two previously reported glass transitions are first-order thermodynamic peaks whose location is dependent upon prior thermal history. Combination of these data with low-temperature x-ray diffraction indicates that the transitions in this temperature range are related to a crystal–crystal transformation. A crystal melting transition is observed near 270°K. In addition an anomalous rise in heat capacity near 60°K suggests a sub-glass transition of unknown origin.     

Molecular structure and photoreaction of poly(methylpropylsilane)

The molecular structure and photoreaction of poly(methylpropylsilane) (PMPrS) are investigated. The ²⁹Si-NMR spectra reveal that PMPrS is a linear polymer with no blanches. Fine multiple splitting of ²⁹Si-NMR is observed at room temperature. This multiple splitting is thought to be due to molecular conformation. The photo-oxidation reaction of the PMPrS film is found to be caused by light irradiation at the UV absorption band, 330 nm. Quantum efficiencies of scission and crosslink related to photodegradation are evaluated. There is little difference in either the molecular structure or photoreactivities between the high and the low molecular weight portions of the bimodal molecular weight distributions of PMPrS.     

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     

Stress relaxation and dynamic viscoelastic properties of end-linked poly(dimethyl siloxane) networks containing unattached poly(dimethyl siloxane)

Stress relaxation in uniaxial extension and dynamic shear moduli G′ and G″ have been studied in networks of vinyl-terminated poly(dimethyl siloxane) (PDMS) of five different molecular weights (M _n from 1800 to 29,200) crosslinked with cis-dichlorobis (diethyl sulfide) platinum (II) and containing 10 and 15 wt % of two samples of high-molecular-weight unattached linear hydroxyl-terminated PDMS (M _w 700,000 and 950,000). The M _w/M _n ratio of both the network prepolymers and the unattached linear species was approximately 2. In stress relaxation the stretch ratio was 1.25 or less and the shear relaxation modulus was calculated from the neo-Hookean stress-strain relation. In the dynamic measurements, the strain amplitude was 15% or less; after conversion to the timedependent shear relaxation modulus G(t) the two sets of measurements were combined and the contribution of the unattached species G₁(t) was calculated by difference. After multiplication by (1 − v)⁻¹G/G_e, where v₂ is the volume fraction of network, G is the plateau modulus of the uncrosslinked polymer, and G_e is the equilibrium modulus of the network containing unattached molecules, G₁(t) was compared with G₁₁(t), the relaxation modulus was essentially the same in both environments. The relaxation was slower in the networks than in the uncrosslinked polymer by 1 to 2 orders of magnitude, and it increased gradually with increasing G_e, which is a measure of total to pological obstacles represented by crosslinks plus trapped entanglements. A similar but less striking difference between relaxation in a network and in the homologous environment of a linear polymer was previously observed in end-linked polybutadiene networks and the butadiene phase of a styrene-butadiene-styrene block copolymer. It appears that, in these systems where the topology of the obstacles is fixed, the reptation is severely restricted or else alternative modes of configurational rearrangement which contribute to relaxation in the uncrosslinked polymer are suppressed.     

Effect of structure and conformational composition on the transport behavior of poly(ether imides)

With the example of two isostructural poly(ether imides), the effects of isopropylidene and hexafluoroisopropylidene groups and hydrogen bonding with chloroform on changes in geometry and energy parameters of polymer chains have been analyzed. The relationship between changes in the geometry characteristics of polymer chains and the gas-separation behavior of films cast from these poly(ether imides) has been established. It has been shown that an increase in permeability is related to a rise in rotation barriers and, consequently, to enhancement of chain rigidity, while the improvement of gas-separation selectivity is associated with a reduction in the amount of isoenergy conformers and an increase in the conformational uniformity of polymer chains. As was detected by FTIR spectroscopy and confirmed by quantum-chemical calculations, the conformational nonuniformity and the small-scale mobility of poly(ether imide) chains are possible only in the Ph-O-Ph′ fragment. The data obtained are applicable for estimation of the role of molecular mobility of polymer chains in the mechanism of gas or penetrant transfer through the polymer film and for predicting the transport behavior of polymers from this family. With the example of two other poly(ether imides), the prediction is confirmed by the experimental data on gas separation.     

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     

Molecular motions in poly(diethyl siloxane) studied by solid-state29Si NMR

Molecular motions in poly(diethyl siloxane) were studied by solid-state²⁹Si-NMR in the temperature range 180–350 K. In this temperature range two solid phases ₁ and ₂, a mesophase _m, and an amorphous isotropic phase exist. The nature of the chain mobility in the different phases was deduced from the resulting changes in the NMR line-shape governed by anisotropic chemical shift. In the intermediate solid phase ₂ its anisotropy is reduced by 25% compared with the low temperature phase ₁ due to the onset of oscillations around the chain axis and conformational transitions. In the mesophase _m the polymer chain rotates about its long axis yielding an axially symmetric chemical shift tensor opposite in sign to that in the ₁, ₂ phases. The broad transition of the mesophase into the isotropic phase is accompanied by an increase in a narrow Lorentzian line arising from the amorphous phase. The results are compared with previous¹H NMR, Raman-spectroscopy and x-ray measurements.After completion of this work we learnt that PDES has recently also been studied through¹³C-MAS and²⁹Si-NMR by Möller et al. [13].     

Steric structure of N-(halomethyl) imides

Conclusions N-(Chloromethyl)- and N-(bromomethyl)imides of phthalic and succinic acids exist in a conformation with arrangement of the C-Hal bond in the plane of the imide ring.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2487–2490, November, 1980.     

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.     

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.     

New poly(amide-imide) siloxane copolymers by polycondensation

Some new poly(amide-imide) siloxane copolymers have been synthesized by solution polycondensation of some aromatic diamines with siloxanic diacids having preformed imide rings. Two polycondensation techniques were used: polycondensation of aromatic diamines with diacid chlorides and direct polycondensation of aromatic diamines with diacids in the presence of organic phosphites, following the Yamazaki-Higashi phosphorylation technique. In all cases the reactions were carried out using equimolecular amounts of the two monomers, in polar aprotic solvents and inert atmosphere.The obtained compounds were characterized by elemental C, H and Si analysis, solubility tests, IR and ¹H-NMR spectrometry. Thermogravimetric curves were also recorded. All data agree with the proposed structures.     

Molecular structure and dynamics of poly(methacrylic acid) and poly(acrylic acid) complexes with dodecyl-substituted poly(ethylene glycol)

The molecular dynamics and the structure of molecular complexes formed by micelles of dodecyl-substituted poly(ethylene glycol) with poly(methacrylic acid) and poly(acrylic acid) in aqueous solutions were studied by viscosimetry, pH measurement, and electron spin resonance spin-probe techniques. At low surfactant concentrations, the conformation of the complex is a compact globule. The local mobility of surfactant molecules in such a complex is much slower than that in the free micelle. At high surfactant concentration, the nonionic micelles and polyacids form hydrophilic associates. The associates have the conformation of extended coils. In an associate, a major part of the micellar poly(ethylene glycol) groups is free. The local mobility of the micellar phase depends on the number of micelles involved in an associate. The mobility of surfactant molecules is slower in the complexes of poly(methacrylic acid) than in the complexes of poly(acrylic acid).     

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.     

Synthesis and characterization of new poly[phenylquinoxaline(ether)imides]

A series of new aromatic poly[phenylquinoxaline(ether)imides] were synthesized by solution polycondensation of aromatic diamines containing preformed phenylquinoxaline groups with dianhydrides having ether linkages and isopropylidene or hexafluoroisopropylidene units. All polymers are readily soluble in polar organic solvents (N-methylpyrrolidinone, DMF, dimethylacetamide) and in less polar liquids such as chloroform. Very thin coatings were deposited onto silicon wafers. According to atomic force microscopy, they had a smooth, pinhole-free surface. The polymers showed high thermal stability with decomposition temperatures above 470 °C and glass transition temperatures in the range of 210–238 °C, being thus characterized by a large gap between the glass transition and decomposition temperatures.Based on the report presented at the International Conference Modern Trends in Organoelement and Polymer Chemistry dedicated to the 50th year anniversary of the A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences (Moscow, May 30–June 4, 2004).Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1952–1957, September, 2004.