Structure and physical properties of bacterially synthesized polyesters

NMR and fractal properties of polymeric liquids and gels

In this work we have investigated how the dynamics of poly(vinyl methyl ether), PVME, changes by blending with deuterated polystyrene. The experimental techniques used were dielectric spectroscopy, quasielastic neutron scattering, and 13C nuclear magnetic resonance. By means of these techniques, the dynamics of the poly(vinyl methyl ether) units in the blends can be selectively investigated in a huge time range (101−10-11 s). Two different blend compositions have been investigated. The main relaxation processes observed in this range are the secondary β-process and the segmental α-relaxation. It turns out that the β-relaxation is not affected by blending. The data analysis procedure followed by us in the case of the α-process is based on the assumption that the dynamics of the PVME segments in the blends is a superposition of dynamical processes with the same shape as that in pure PVME, but with the relaxation times distributed due to the presence of concentration fluctuations. From this analysis we found...

Effect of blending on the PVME dynamics. A dielectric, NMR, and QENS investigation

The two‐dimensional (2D) exchange nuclear magnetic resonance (NMR) experiment is applied to study ultraslow as well as faster motions in powdered solids. The theoretical framework required for the simulation of 2D exchange of the faster motions, and for the evaluation of the experimental data, is developed. Calculations are presented for two standard models: two‐site jump and isotropic rotational diffusion. For discrete jump motion, anisotropic spin‐lattice relaxation during the mixing time is also considered. The resulting, simulated 2D line shapes show new characteristics in the intermediate dynamic range. Experimental data are presented for two‐site exchange in the model compound polycrystalline dimethylsulphone. The technique is then applied to study the chain dynamics of linear polystyrene in the glass transition range. Close to Tg the correlation times extracted from 2D exchange NMR exhibit strong non‐Arrhenius behavior. This data together with correlation times obtained at higher temperatures from conventional T1 data follows the WLF equation over 11 orders of magnitude, from 10−6 to 1000 s. It is shown that 2D exchange NMR and spin‐lattice relaxation probe the α and the β process, respectively, of the chain dynamics in the glass transition region.

Two‐dimensional exchange nuclear magnetic resonance of powder samples. III. Transition to motional averaging and application to the glass transition

Polyisobutylene (PIB)-based polymer networks potentially useful as smart coatings for photovoltaic devices have been developed. Low molecular weight coumarin functional triarm star PIB was synthesized via a single step SN2 reaction of bromoallyl functional triarm star PIB with 4-methylumbelliferone or umbelliferone in the presence of sodium hydride. Quantitative end functionality was confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. UVA (λmax = 365 nm) induced reversible photodimerization of the coumarin moieties resulted in cross-linked elastomeric films exhibiting self-healing behavior. The extent of photodimerization/photoscission was monitored by UV–vis spectroscopy. The low oxygen (1.9 × 10–16 mol m m–2 s–1 Pa–1) and moisture (46 × 10–16 mol m m–2 s–1 Pa–1) permeability of the cross-linked polymer films suggest excellent barrier properties of the cross-linked polymer films. The self-healing process was studied by atomic force microscopy (AFM). For this, mechan...

Photoinduced Smart, Self-Healing Polymer Sealant for Photovoltaics

Carbon-13 NMR investigation of local dynamics in bulk polymers at temperatures well above the glass transition temperature. 1. Poly(vinyl methyl ether)

Carbon-13 NMR investigation of local dynamics in bulk polymers at temperatures well above the glass-transition temperature. 3. cis-1,4-Polybutadiene and cis-1,4-polyisoprene

Carbon-13 NMR investigation of local dynamics in bulk polymers at temperatures well above the glass transition temperature. 2. Poly(propylene oxide) and linear and cross-linked poly(ethylene oxides)

F. Laupretre

Papers

Carbon-13 NMR investigation of local dynamics in bulk polymers at temperatures well above the glass transition temperature. 1. Poly(vinyl methyl ether)

Carbon-13 NMR investigation of local dynamics in bulk polymers at temperatures well above the glass-transition temperature. 3. cis-1,4-Polybutadiene and cis-1,4-polyisoprene

Carbon-13 NMR investigation of local dynamics in bulk polymers at temperatures well above the glass transition temperature. 2. Poly(propylene oxide) and linear and cross-linked poly(ethylene oxides)

Spectroscopic Investigation of Local Dynamics in Polybutadienes

Local Motions in Bulk Polymers