Cyclolinear polysiloxanes. II. Crosslinking and characterization

The synthesis and characterization of two groups of novel networks prepared from cyclolinear polysiloxanes are described. The first group of networks from cyclolinear polysiloxanes (N‐CLPSs) was synthesized by the hydrosilation of vinyl‐terminated cyclolinear polyorganosiloxanes [prepared from diacetoxydiethyltetramethylcyclotetrasiloxane (D₄Et₂OAc₂) or diacetoxytriethylpentamethylcyclopentasiloxane (D₅Et₃OAc₂)] with a copolymer of dimethylsiloxane and methylhydrosiloxane as the crosslinking agent. Hydrosilation was effected with a platinum carbonyl catalyst with a cyclovinylsiloxane moderator. The second group of networks (N‐eCLPSs) was prepared similarly with extended cyclolinear polysiloxanes. The mechanical properties of the novel networks were comparable to those of polydimethylsiloxane networks (N‐PDMS). The oxygen permeabilities were similar to or slightly higher than that of N‐PDMS. The glass‐transition temperatures of D₄Et₂OAc₂‐ and D₅Et₃OAc₂‐based N‐CLPSs were ?67.8 and ?90.8 °C, respectively, whereas the incorporation of polydimethylsiloxane spacers into similar N‐eCLPSs lowered their glass‐transition temperatures to ?109.7 and ?115.0 °C. Upon heating to 800 °C in air, N‐CLPSs yielded more residue than N‐eCLPSs, which in turn yielded more residue than N‐PDMS. These results may have been due to the presence of T units in the cyclic siloxane units, which may have inhibited chain degradation or the formation of volatile products. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4053–4062, 2006     

Synthesis of A2B star block copolymers from a heterotrifunctional initiator

We described the obtention of A₂B star block copolymers through the use of a new heterotrifunctional initiator. That way, well‐defined (PCL)₂‐arm‐PtBuMA and (PCL)₂‐arm‐PS star block copolymers have been synthesized from a heterotrifunctional initiator bearing two hydroxyl groups able to initiate ROP of CL (with AlEt₃ or Sn(Oct)₂ as coinitiator) and a bromide function able to initiate ATRP of tBuMA or styrene. Firstly, we have proceeded using a sequential process (two‐steps), leading to an intermediate macroinitiator. Secondly, attempt to polymerize these two monomers in a simultaneous process (one‐step), that is directly from the mixture of monomers, initiator, coinitiators, and solvent, has been realized and has shown that some interferences between the two polymerizations occurred, leading to an inhibition of ATRP when Sn(Oct)₂ was used and an unexpected increase in control when AlEt₃ was used as catalyst for the ROP (obtention of well‐defined (PCL)₂‐arm‐PtBuMA with pdi of 1.18). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1796–1806, 2006     

Synthesis of poly(vinyl chloride)‐b‐poly(n‐butyl acrylate)‐b‐poly(vinyl chloride) by the competitive single‐electron‐transfer/degenerative‐chain‐transfer‐mediated living radical polymerization in water

The synthesis of a block copolymer poly(vinyl chloride)‐b‐poly(n‐butyl acrylate)‐b‐poly(vinyl chloride) is reported. This new material was synthesized by single‐electron‐transfer/degenerative‐chain‐transfer‐mediated living radical polymerization (SET‐DTLRP) in two steps. First, a bifunctional macroinitiator of α,ω‐di(iodo)poly (butyl acrylate) [α,ω‐di(iodo)PBA] was synthesized by SET‐DTLRP in water at 25 °C. The macroinitiator was further reinitiated by SET‐DTLRP, leading to the formation of the desired product. This ABA block copolymer was synthesized with high initiator efficiency. The kinetics of the copolymerization reaction was studied for two PBA macroinitiators with number–average molecular weight of 10 k and 20 k. The relationship between the conversion and the number–average molecular weight was found to be linear. The dynamic mechanical thermal analysis suggests just one phase, indicating that copolymer behaves as a single material with no phase separation. This methodology provides the access to several block copolymers and other complex architectures that result from combinations of thermoplastics (PVC) and elastomers (PBA). From industrial standpoint, this process is attractive, because of easy experimental setup and the environmental friendly reaction medium. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3001–3008, 2006     

Design,synthesis, and characterization of main‐chain,aromatic polyesters based on 3,4‐ethylenedioxythiophene

A series of new thermoplastic polyesters based on 3,4‐ethylenedioxythiophene (EDOT) with flexible aliphatic spacers have been synthesized and characterized for the first time. The thermal properties of these polyesters based on EDOT are comparable to those of conventional polyesters based on the 1,4‐phenyl unit, indicating that EDOT is a viable replacement for the phenyl units. The glass‐transition and melting‐transition temperatures decrease monotonically with an increase in the spacer length. Theoretical calculations have revealed that the core angle for EDOT is comparable to that of unsubstituted thiophene and hence should be compatible with the formation of the mesophase. This has been confirmed experimentally by the synthesis of a main‐chain, thermotropic, liquid‐crystalline polyester based on EDOT that exhibits fluid birefringence. In fact, this is the first report in which a main‐chain, liquid‐crystalline polymer based on 3,4‐disubstituted thiophene has been successfully designed and synthesized. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3479–3486, 2006     

Single electron transfer–degenerative chain transfer living radical polymerization of N‐butyl acrylate catalyzed by Na2S2O4 in water media

Living radical polymerization of n‐butyl acrylate was achieved by single electron transfer/degenerative‐chain transfer mediated living radical polymerization in water catalyzed by sodium dithionate. The plots of number–average molecular weight versus conversion and ln[M]₀/[M] versus time are linear, indicating a controlled polymerization. This methodology leads to the preparation of α,ω‐di(iodo) poly (butyl acrylate) (α,ω‐di(iodo)PBA) macroinitiators. The influence of polymerization degree ([monomer]/[initiator]), amount of catalyst, concentration of suspending agents and temperature were studied. The molecular weight distributions were determined using a combination of three detectors (TriSEC): right‐angle light scattering (RALLS), a differential viscometer (DV), and refractive index (RI). The methodology studied in this work represents a possible route to prepare well‐tailored macromolecules made of butyl acrylate in an environmental friendly reaction medium. Moreover, such materials can be subsequently functionalized leading to the formation of different block copolymers of composition ABA. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2809–2825, 2006     

Sulfonated poly(aryl ether ether ketone ketone)s containing fluorinated moieties as proton exchange membrane materials

A series of sulfonated poly(aryl ether ether ketone ketone)s statistical copolymers with high molecular weights were synthesized via an aromatic nucleophilic substitution polymerization. The sulfonation content (SC), defined as the number of sulfonic acid groups contained in an average repeat unit, could be controlled by the feed ratios of monomers. Flexible and strong membranes in sodium sulfonate form could be prepared by the solution casting method, and readily transformed to their proton forms by treating them in 2 N sulfuric acid. The polymers showed high T_gs, which increased with an increase in SC. Membranes prepared from the present sulfonated poly(ether ether ketone ketone) copolymers containing the hexafluoroisopropylidene moiety (SPEEKK‐6F) and copolymers containing the pendant 3,5‐ditrifluoromethylphenyl moiety (SPEEKK‐6FP) had lower water uptakes and lower swelling ratios in comparison with previously prepared copolymers containing 6F units. All of the polymers possessed proton conductivities higher than 1 × 10^?2 S/cm at room temperature, and proton conductivity values of several polymers were comparable to that of Nafion at high relative humidity. Their thermal stability, oxidative stability, and mechanical properties were also evaluated. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2299–2310, 2006     

Mathematical modeling of crystallization analysis fractionation (Crystaf) of polyethylene

Four polyethylene samples (PE) with different molecular weight distributions (MWD) were analyzed by crystallization analysis fractionation (Crystaf) at several cooling rates to investigate the effect of MWD and cooling rate on their Crystaf profiles. Using these results, we developed a mathematical model for Crystaf that considers crystallization kinetic effects, which are ignored in all previous Crystaf models. The Crystaf model we proposed can fit the experimental Crystaf profiles of the 4 polyethylene resins very well. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2749–2759, 2006     

Magneto-volume effects in Fe–Cu solid solutions

The magnetic properties of Fe–Cu metastable solid solutions have been investigated by means of neutron diffraction and magnetisation measurements. These compounds exhibit ferromagnetic order with Curie temperatures above room temperature for concentrations beyond 40 at% in Fe. The magnetic moment at 5 K can reach values over 2 μ_B, while the high field susceptibility is similar to that found in FCC–FeNi Invar alloys. These features together with the low values for the linear coefficient for thermal expansion in the ferromagnetic region suggest that magneto-volume anomalies, including Invar behaviour, play a major role in the magnetic properties of this system when the crystal structure is face centred cubic. Such behaviour could be explained using theoretical total-band energy calculations.     

0+ analogue state in 118Sb from 117Sn(p,nγ) reaction

The analogue of the 0⁺ ground state in ¹¹⁸Sn has been observed in the compound nucleus ¹¹⁸Sb through ¹¹⁷Sn(p,n γ) ¹¹⁷Sb reaction. The neutron decays of this analogue resonance have been studied from the deexciting γ-rays of the residual nucleus ¹¹⁷Sb. From off resonance excitation functions, spin assignments have been made to states in ¹¹⁷Sb, on the basis of Hauser-Feshbach formalism. The resonance parameters of the isobaric analogue resonance have been determined, including the total, proton and neutron decay widths.     

Radiative corrections to the Lagrangian of the electromagnetic field

The single-loop corrections to the Lagrangian of a uniform, constant electromagnetic field are found which include the anomalous magnetic moment and electric dipole moment of the electron. The imaginary part of the effective Lagrangian, which determines the probability of electron-positron pair production is found. The asymptotic behavior of the effective action is studied for supercritical magnetic fields H » H₀ = m²/e with the dependence of the anomalous magnetic moment on H taken into account.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 37–42, March, 1987.