Diffusion of Methanol in Polydimethylsiloxane

The permeation and sorption of methanol in polydimethylsiloxane at 10 and 30°C. has been measured and the results analyzed to determine the concentration dependence of the steady-state diffusion coefficient D which is found to decrease as the total concentration C is increased. An analysis of the isotherms indicates that clustering of the methanol occurs in the polymer, becoming more predominant as the concentration is increased. A polymerization model used to describe the shape of the D versus C curve for water in polydimethylsiloxane has been modified and applied with some success to describe the shape of the isotherm and the D versus C curve for methanol. The linearity of the permeation rate with relative pressure in this and a number of water—polymer systems is briefly commented on.     

Direct Stereoconvergent Allylation of Chiral Alkylcopper Nucleophiles with Racemic Allylic Phosphates

Copper-catalyzed stereoconvergent allylation of chiral sp³-hybridized carbon nucleophiles with a racemic mixture of acyclic secondary allylic phosphates is reported. In the presence of a copper-catalyst complexed with chiral BenzP* ligand, tandem coupling reaction of vinyl arenes, bis(pinacolato)diboron, and racemic allylic phosphates provided β-chiral alkylboronates possessing (E)-alkenyl moiety through a direct stereoconvergent allylic coupling with concomitant generation of a C(sp³)-stereogenic center. A range of vinyl (hetero)arenes and secondary allylic phosphates bearing 1°, 2°, 3° alkyl and phenyl α-substituents were suitable for the reaction, forming products with high enantioselectivities up to 95 % ee. Density functional theory calculations were conducted in detail to elucidate the origin of the observed regioselectivity of borylcupration and stereoconvergent (E)-olefin formation from racemic allylic phosphates.     

Synthesis and Photopolymerization of Silicon-Containing Multifunctional Oxetane Monomers

Abstract

A series of silicon-containing multifunctional oxetane monomers has been prepared and characterized. These monomers were compared among themselves and with other oxetane monomers with respect to their reactivity in photoinitiated cationic polymerization.     

Polysiloxanes having aromatic heterocyclic units. I. Polydimethylsiloxane benzimidazole polymer

A polymer containing dimethylsiloxane units (35) and benzimidazole units (1) has been prepared by the condensation of 3,3′-diaminobenzidine and an α,ω-bis-(γ-carboxy-n-propyl) polydimethylsiloxane. The new polymer has some rubbery properties, but it decomposes catastrophically at 400°C.     

Donor-Acceptor Complexes in Copolymerization. XXXVI. Alternating Diene-Dienophile Copolymers. 4. Copolymerization of Furan and 2-Methylfuran with Maleic Anhydride

Abstract

The copolymerization of furan and 2-methylfuran with maleic anhydride in the presence of a radical catalyst yields equimolar, alternating copolymers in which the furan units have a 2,5-linkage (NMR and IR). The copolymerization appears to have a floor temperature of about 40°C. The furan-maleic anhydride Diels-Alder adduct polymerizes in solution in the presence of a radical catalyst at temperatures above 60°C to yield the identical copolymer as is obtained from the monomers. The adduct undergoes a retrograde reaction above 60°C to regenerate the monomers which then copolymerize through excitation of the ground state comonomer charge transfer complex.     

The Synthesis,Characterization, and Photoinitiated Cationic Polymerizaton of Difunctional Oxetanes

Abstract

Seven novel difunctional oxetane monomers have been prepared and characterized using standard spectroscopic techniques. The photoinitiated cationic polymerization of these seven monomers was carried out and their reactivity compared to a typical diepoxide monomer. In these studies the reactivities of the various oxetane monomers were evaluated and compared by three different techniques: gel time measurements, differential scanning photocalorimetry, and real time infrared spectroscopy. It was observed that the difunctional oxetanes are generally more reactive than their structurally similar epoxide counterparts in photoinitiated cationic polymerization.     

Infrared thermographic analysis on copolymerization of spiroorthoester with oxetane

Infrared (IR) thermography was employed to monitor temperature changes during the copolymerization of a spiroorthoester monomer with an oxetane monomer initiated with a benzyl sulfonium salt. The temperature changes in the polymerizations decreased with the increase of the initial feed ratios of the spiroorthocarbonate monomer. For instance, the temperature in the copolymerization of the equimolar mixture of both of the monomers increased only ～1 °C, whereas that in the homopolymerization of the oxetane monomer increased more than 20 °C. This result indicates that the copolymerization employing spiroorthocarbonate monomers effectively suppress temperature increase, which are responsible to shrinkage during cooling. The suppression of polymerization shrinkage by spiroorthocarbonate was also confirmed by density measurement of the polymers using a gas pycnometer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1388–1393, 2007.     

Polymerization of diethylene glycol bis(allyl carbonate) by means of di-sec-butyl peroxydicarbonate

The initial stages of the free radical polymerization of diethylene glycol bis(allyl carbonate) at temperatures of 35–65°C have been studied. The polymer is unsaturated and cyclization to give a 16-membered ring occurs only to a small extent. The kinetic order with respect to the initiator, di-sec-butyl peroxydicarbonate, has an average value of 0.79; the order increases slightly with peroxydicarbonate concentration over the range 0.018–0.22M. The molecular weight of the polymer isolated after 3% polymerization is close to 19,000. It shows no significant dependence on initiator concentration or on temperature. The dominant feature of the bulk polymerization, as in free radical polymerization of the other allyl and diallyl monomers, is degradative chain transfer in which the growing polymer radical abstracts a hydrogen atom from a monomer unit to give a relatively unreactive allylic radical. The dependence of rate on initiator concentration is rationalized if some of these allylic radicals are able to reinitiate polymerization. The transfer constant to monomer is 0.014 at 50°C, assuming that the main termination step involves mutual termination of allylic radicals. Carbon tetrachloride is an active transfer agent with a transfer constant of 0.20 ± 0.04 at 50°C. Toluene, which is less active, has a transfer constant of 0.0064 at 50°C and also retards the polymerization. Some kinetic studies have been made with other initiators, including di-2-methyl-pentanoyl peroxide which initiates polymerization at temperatures as low as 13°C.     

Thermoelastic and dielectric studies of poly(3,3-dimethyl oxetane) chains

Poly(3,3-dimethyl oxetane) was synthesized by ring opening polymerization of 3,3-dimethyl oxetane. Elongation experiments were performed on unswollen elastomeric networks prepared from this polymer over the temperature range 30–90°C. The changes in the tensile stress while the networks crystallized were examined at various elongations. From thermoelastic data which were free from the effects of network crystallization, the temperature coefficient of the chain dimensions was found to be 1.1 × 10^?3 K^?1 in the vicinity of 60°C. The dipole moment ratio and its temperature coefficient were also measured; the average values of these parameters at 30°C were 0.20₆ and 2.5 × 10^?3 K^?1, respectively. All of these experimental-configuration-dependent properties were critically interpreted in terms of the rotational isomeric-state model. In comparing theory and experiment, conclusions were obtained which confirm earlier results according to which gauche states about C—C skeletal bonds in poly(3,3-dimethyl oxetane) are strongly favored over the alternative trans states.     

Synthesis and properties of mesogenic laterally fluorinated compounds containing benzoxazole unit

Series of mesogenic laterally fluorinated compounds, 2-(2′,3′-difluoro-4′-alkoxybiphenyl-4-yl)-benzoxazole derivatives (nB-Fx) bearing different substituents (H, CH₃, Cl, NO₂, coded as nB-FH, nB-FM, nB-FC and nB-FN, respectively) at 5-position, were prepared and characterised. Their phase transition behaviour was investigated by differential scanning calorimetry and polarising optical microscopy. nB-Fx with alkoxy chain lengths of 2 to 10 carbons exhibited enantiotropic mesophases, for which the mesophase ranges were 0°C–58°C and 0°C–71°C on heating and cooling for nB-FH, 41°C–93°C and 66°C–140°C for nB-FM, 44°C–133°C and 87°C–155°C for nB-FC, and 0°C–76°C and 0°C–95°C for nB-FN, respectively. Compared to non-fluorinated analogues, with the exception of nB-FC, fluorinated nB-Fx mainly exhibited nematic mesophase both in heating and cooling, which were attributed to the disruption of the side-to-side intermolecular packing caused by the two ortho-lateral fluoro substituents. For nB-Fx series, nB-FM, nB-FC and nB-FN exhibited a much wider mesophase range than the corresponding nB-FH series, which indicated that the substituent at benzoxazole moiety was helpful in increasing the mesophase stability. With the exception of nB-FN, the nB-Fx series displayed intense photoluminescence emission at 379–383 nm in methylene chloride solution, when it was excited at its absorption maxima.     

A study of helix formation in polydimethysiloxane by Raman scattering

Depolarization ratios ρ of the Raman bands due to CH₃ stretching at 2907 cm^?1 and the Si? O skeletal mode at 491 cm^?1 have been measured in polydimethylsiloxane gum as a function of temperature from 100°C to ?45°C. Below 0°C the changes in p have been interpreted in terms of the formation of helical regions in the gum. The enthalpy of helix formation ΔH has been determined as 3200 ± 600 cal/mole. An upper limit on the entropy change, ΔS, of 16 ± 3 e.u./mole and minimum values of helix content at different temperatures have been found. The Raman spectrum of crystalline polydimethylsiloxane is presented.     

Structure of Liquids. VIII. An X-Ray Diffraction Study of Liquid Mercury-Gallium Systems

Abstract

X-ray diffraction measurements were made at 0°, 30°, and 50°C on pure mercury and on two mercury-gallium systems of composition 0.9658 and 0.0197 mole fraction of mercury. Peak positions of the radial distribution functions for all samples show no significant change with temperature; the average position of the first and second peaks of the mercury curves are 3.01 Å and 5.80 Å, respectively. Coordination numbers for mercury as determined by the symmetrical curve method are 7.5, 7.3, and 7.0 atoms for 0°, 30°, and 50°C. The scattering function and the features of the structure obtained for the Ga-in-Hg solution are not significantly different from those of pure mercury; for the Hg-in-Ga solution, however, the coordination numbers are smaller than those for pure gallium, and the scattering functions are significantly different.     

Chain transfer for vinyl monomers polymerized in N-allylstearamide

Apparent transfer constants have been determined for styrene, methyl methacrylate vinyl acetate, and diethyl maleate polymerized in N-allylstearamide at 90°C. Regression coefficients for transfer were: methyl methacrylate, 0.301 × 10^?3; styrene, with no added initiator, 0.582 × 10^?3; styrene, initiated with benzoyl peroxide, 0.830 × 10^?3; vinyl acetate, 62.01 × 10^?3; and diethyl maleate, 2.24 × 10^?3. Rates of polymerization were retarded for both styrene and methyl methacrylate. Vinyl monomer and comonomer disappearance followed an increasing exponential dependence on both initiator and monomer concentration. Although degradative chain transfer probably caused most of the retardation, the cross-termination effect was not eliminated as a contribution factor. Rates for the vinyl acetate copolymerization were somewhat retarded, even though initiator consumption was large because of induced decomposition. The kinetic and transfer data indicated that the reactive monomers added radicals readily, but that rates were lowered by degradative chain transfer. Growing chains were terminated at only moderate rates of transfer. Unreactive monomers added radicals less easily, producing reactive radicals, which transferred rapidly, so that molecular weights were lowered precipitously. Although induced initiator decomposition occurred, rates were still retarded by degradative chain transfer. A simple empirical relation was found between the reciprocal number-average degree of polymerization, 1/X?_n1 and the mole fraction of allylic comonomer entering the copolymer F₂, which permitted estimation of the molecular weight of copolymers of vinyl monomers with allylic comonomers. This equation should be applicable when monomer transfer constants for each homopolymer are known and when osmometric molecular weights of one or two copolymers of low allylic content have been determined.     

The liquid-phase oxidation of 2,4-dimethylpentane

The initiated oxidation of 2, 4-dimethylpentane in the neat liquid phase at 100°C with 760 torr O₂ gives more than 90% of a mixture of 2,4-dihydroperoxy-2,4-dimethylpentane and 2-hydroperoxy-2, 4-dimethylpentane in a ratio of 7:1. The rate of oxidation depends closely on the [initiator]^1/2, consistent with a mechanism in which chain termination occurs mostly by interactions of two 2-hydroperoxy-2, 4-dimethyl-4-pentylperoxy radicals. 2, 4-Dimethylpentane oxidizes only one sixth as fast as isobutane at the same rate of initiation at 100°C. In cooxidations of the same hydrocarbons, it is 0.71 as reactive as isobutane toward any of the peroxy radicals involved. 2, 4-Dimethylpentane oxidizes 7.5 times as fast at 1.25°C as at 50°C for the same rate of initiation, but the ratio of dihydroperoxide to monohydroperoxide increases only from 5 to 7, corresponding to a difference in activation energy between intramolecular and intermolecular abstraction of 1 kcal/mole. The overall activation energy (E_p – E_t/2) is 10.7 kcal/mole, close to the value of 12 kcal/mole found for isobutane. Absolute values for E_p, E_t, k_p, k_r, and k_t were derived. Ring closure of 2-hydroperoxy-2, 4-methyl-4-pentyl radicals to oxetane, not detected during oxidation, was observed when this radical was generated at 100°C in the near-absence of oxygen. The ratio of rate constants for oxetane formation and addition of oxygen to the 2, 4dimethyl-2-hydroperoxy-4-pentyl radical is about 5.4 × 10^?5 M at 100°C. Thus, ring closure to oxetane is too slow to compete with addition of oxygen above ?200 torr. At 100°C, 2, 3-dimethylbutane gave no evidence of any intramolecular abstraction. However, 2, 3-dimethylpentane did give at least 12% 2, 4-glycol or hydroxyketone.     

Poly[3,3-bis(hydroxymethyl) oxetane]—an analog of cellulose: Synthesis,characterization, and properties

Poly[3,3-bis(hydroxymethyl)oxetane], PBHMO, was prepared in high molecular weight (η_inh up to 5.2) by polymerizing the trimethylsilylether of 3,3-bis(hydroxymethyl)oxetane with the i-Bu₃Al–0.7 H₂O cationic catalyst at low temperature, followed by hydrolysis. PBHMO is crystalline, very high melting (314°C) and highly insoluble, much like its analog, cellulose. It is soluble in 75% H₂SO₄ at 30°C, being 65% converted to the acid sulfate ester; these conditions are useful for viscosity measurement, since the degradation rate is low and at least an order of magnitude less than for cellulose in this solvent. PBHMO can be prepared as oriented films and fibers using the lower melting diacetate (184°C) which can be melt or solution (CHCl₃) fabricated and then the oriented forms saponified to oriented PBHMO. BHMO can be directly polymerized to low molecular weight, perhaps somewhat branched, PBHMO (η_inh 0.1) with trifluoromethanesulfonic acid catalyst at room temperature. Poly(3-methyl-3-hydroxymethyloxetane), (PMHMO), prepared in high molecular weight (η_inh up to 3.8) by the same method used for PBHMO, is more soluble and lower melting (165°C) than PBHMO, appears to be atactic and can be compression molded at 195°C to a tough, clear film which is readily oriented. Copolymers of BHMO with MHMO are crystalline over the entire composition range with a linear variation of T_m with composition, a new example of isomorphism in the polymer area.     

Electromechanical Responses of a Crosslinked Polydimethylsiloxane

A high molecular weight polydimethylsiloxane, PDMS, gel was prepared and investigated as an electroactive polymer actuator. Electromechanical properties of the PDMS gels were measured under an oscillatory shear mode at the temperature of 27 °C to determine the effects of crosslink ratio and electric field strength. The storage modulus, G′, of PDMS gel increases linearly with crosslink density but nonlinearly with electric field. The increase in the storage modulus with crosslink density is due to the increase in the number of junction points and strands. With increasing electric field strength, the storage modulus increases as the electric field induces dipole moments generating the electrostatic forces within the matrices. The gel with the crosslink ratio of 0.01 possesses the highest G′ sensitivity of 41% at 2 kV/mm. The temporal response of PDMS gels upon repeated applications of electric field strength of 2 kV/mm was investigated. For the crosslink PDMS (N_c/N_m = 0.01) system, at the electric field of 2 kV/mm, G′ immediately increases and rapidly reaches a steady-state value. With electric field off, G′ decreases and nearly recovers its original value. The crosslinked PDMS (N_c/N_m = 0.01) is nearly a reversible system. Finally, we investigated the bending response of the PDMS films, suspended in silicone oil between copper electrodes. From the deformation data, we estimated the dielectrophoresis force, F_D, to be a linear function of electric field strength.     

Preparation of Allylstannanes and Distannanes Using Zinc in Liquid Ammonia

Abstract

Barbier-type reductive coupling of allylic bromides and organotin compounds can be carried out in liquid ammonia (?33°C) using commercial zinc powder. This procedure provide a new simple and environment-friendly method for the synthesis of allylstannanes and distannanes.     

Acid‐promoted double ring‐opening reaction of bicyclobis (γ‐butyrolactone) with alcohol and its application to polyester synthesis

Bicyclobis(γ‐butyrolactone) (BBL) bearing methyl group 1a reacted with benzyl alcohol (BnOH) in the presence of p‐toluenesulfonic acid (p‐TsOH) through the double ring‐opening of the bislactone structure to afford the corresponding adduct 2a bearing carboxyl group. The resulting carboxyl group underwent condensation with BnOH to afford the corresponding diester 3a . The second step was quite slow at ambient temperature; however, it was efficiently accelerated by elevating temperature to 120 °C or performing under reduced pressure at 80 °C to afford 3a in an excellent yield. Based on these results, the reaction of 1a with xylene‐α,α‐diol (XyD) was carried out in chlorobenzene at 120 °C to obtain the corresponding polyester bearing ketone group in the side chain. The condensation reaction in the second step was effectively promoted by simultaneous removal of water under reduced pressure. BBLs 1b and 1c bearing reactive groups, isopropenyl and chloromethyl, respectively, were also employed as monomers efficiently. Their reactions with XyD gave the corresponding reactive polyesters bearing methacryloyl and chloroacetyl moieties, respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Terpolymerization of Cyclic Ethers with Cyclic Anhydride

Abstract

A unique solution polymerization and polymer family have been discovered in the ring-opening terpolymerization of three heterocyclic monomers initiated by organometallic compounds, particularly trialkylaluminum. The products have repeating ether-ester-ester linkages along the chain and are alternating terpolymers, … ABCABCABC…, of three different monomers A, B, and C. Monomer A is a four- or five-membered cyclic oxide, such as tetrahydro-furan or oxocylobutane (oxetane). Monomer B is an epox-ide, and Monomer C is a cyclic acid anhydride. Many epoxides and anhydrides participate in the polymerization which enables the preparation of alternating terpolymers containing various substituents and unsaturatlons at regu-lar intervals along the chain. The alternating sequence can be near-perfect or less so depending on the initial monomer charge ratio. Evidence of the alternating struc-ture was obtained by chemical and NMR analyses of polymer sampled at intermediate and final conversions, and by glass transition temperatures.