Faculty of Science

The analysis of chemical and physical network heterogeneities has been carried out for synthetic isobutylene-based elastomers using 1 H spin echo NMR imaging. Spatial homogeneity was compared for isobutylene-p-methylstyrene-p-bromomethylstyrene (PIB-PMS/BrPMS) terpolymers cured with inorganic versus organic curatives and unfilled materials versus those filled with carbon black. Surprising differences in the network structure were found for materials cured with an inorganic curative (ZnO) relative to those cured with an organic curative (1,6-hexamethylenediamine). Voids and void distributions were found to be an important performance variable on the basis of comparisons between the NMR imaging data and mechanical testing. Systematic comparison of solvent images and polymer images revealed the optimum experimental conditions for enhancing network density contrast or detecting microvoids. For the first time, direct 1 H images of polymer spins in a fully compounded, commercial polyisobutylene-based elastomer were acquired in the absence of any swelling solvent. Multislice imaging experiments were investigated as a method to construct three-dimensional void densities in elastomer compounds. Chemical-shift selective polymer imaging was used to selectively obtain network density information for either component of a two-phase blend containing the PIB-PMS/BrPMS terpolymer and polybutadiene. The ability of NMR imaging to provide data over statistically relevant sampling areas (hundreds of mm 3 ) for both neat polymers and fully compounded commercial materials (containing carbon black) represents a unique advantage over microscopic imaging methods for material property analyses.

A qualitative and quantitative study of the curing behaviour of a high-ortho novolac resin with paraformaldehyde under different conditions is reported. The extent of cure by means of the formaldehyde/phenol ratio, the degree of conversion, and the characterization of the final structure after curing are determined based on quantitative 13C solid-state nuclear magnetic resonance with cross polarization and magic angle spinning. The T1H relaxation time is measured as a probe to follow the evolution of cure. In conjunction Fourier transform–Raman spectroscopy is proposed as a qualitative tool to follow the degree of crosslinking in this high-ortho novolac.

The 1 H and 13 C NMR chemical shifts of model chloro-alkenes are evaluated at different levels of approximation and compared to experimental data. DFT calculations employing the B3LYP exchange-correlation functional with the 6-311+G(2d,p) basis turned out to be reliable to account for most of the variations of the chemical shifts. Then, after accounting for the linear regression fits, the mean absolute error goes down to 3.8 ppm and 0.05 ppm for the 13 C and 1 H chemical shifts, respectively. Using these linear regression relationships, the NMR chemical shifts are determined for a PVC chain bearing an unsaturated defect inside a meso and a racemic dyad. These simulations, which account for the many conformations of the PVC segment, are used to interpret recent experimental spectra of PVC containing unsaturations.

Different resol phenol-formaldehyde prepolymer resins have been synthesized with different Formaldehyde/Phenol (F/P) ratios or different catalysts and characterized by 13 C NMR spectroscopy in solution. A fast quantitative measuring protocol is proposed based on the use of chromium(III)acetylacetonate as a relaxation agent. APT (attached proton test) and DEPT (distortionless enhancement by polarisation transfer) spectra were acquired to enable proper resonance assignments, especially in the regions with severe signal overlap. Equations are presented in which the methylene bridges (MB), the methylol groups (MG) and the dimethylene ether bridges (DMEB) of resol resins are quantitatively taken into account. Important structural factors determined quantitatively for resol prepolymer resins are the F/P ratio after reaction, the degree of polymerization ðnÞ; the number average molecular weight ðM n Þ and the content of free ortho and para positions. q

Myelin-reactive T cells are responsible for initiating the cascade of autoreactive immune responses leading to the development of multiple sclerosis. For better insights into the disease mechanism, it is of major importance to have knowledge on the sites at which these cells are active during disease progression. Herein, we investigated the feasibility of tracking myelin-reactive T cells, upon labelled with SPIO particles, in the central nervous system (CNS) of experimental autoimmune encephalomyelitis (EAE) animals by MRI. First, we determined the optimal labelling condition leading to a high particle uptake and minimal SPIO–Poly-l-lysine (PLL) aggregate formation using Prussian blue staining and inductively coupled plasma spectroscopy measurements. Results from labelling of myelin reactive T cells with low concentrations of SPIO particles (i.e. 25 µg/ml) combined with different concentrations of PLL (0–1.5 µg/ml) showed that increasing amounts of PLL led to augmented levels of free remnant SPIO-PLL aggregates. In contrast, a low PLL concentration (i.e. 0.5 µg/ml) combined with high concentrations of SPIO (i.e. 400 µg Fe/ml) led to a high labelling efficiency with minimal amounts of aggregates. Second, the labelled myelin-reactive T cells were transferred to control rats to induce EAE. At the occurrence of hindlimb paralysis, the SPIO labelled myelin-reactive T cells were detected in the sacral part of the spinal cord and shown to be highly confined to this region. However, upon transfer in already primed rats, T cells were more widely distributed in the CNS and shown present in the spinal cord as well as in the brain. Our study demonstrates the feasibility of tracking SPIO labelled myelin-reactive T cells in the spinal cord as well as the brain of EAE rats upon systemic administration. Furthermore, we provide data on the optimal labelling conditions for T cells leading to a high particle uptake and minimal aggregate formation. Copyright © 2010 John Wiley & Sons, Ltd.

Azo-linked polymeric prodrugs of 5-aminosalicylic acid (5-ASA) were prepared and evaluated in simulated human intestinal microbial ecosystem. Release of 5-ASA was demonstrated. Polyamides containing azo groups in the backbone were prepared and tested in vitro in a reductive buffer or in the bioreactor medium. It was demonstrated that for the hydrophobic polymer reduction stops at the hydrazine stage whereas for a hydrophilic analogue reduction with formation of amines occurred.

High field magnetic resonance imaging (MRI) has been increasingly used to assess experimental spinal cord injury (SCI). In the present investigation, after partial spinal cord injury and excision of the whole spine, pathological changes of the spinal cord were studied in spinal cord-spine blocks, from the acute to the chronic state (24 h to 5 months). Using proton density (PD) weighted imaging parameters at a magnetic field strength of 9.4 tesla (T), acquisition times ranging from <1 to 10 h per specimen were used. High in-plane pixel resolution (68 and 38 m, respectively) was obtained, as well as high signalto-noise ratio (SNR), which is important for optimal contrast settings. The quality of the resulting MR images was demonstrated by comparison with histology. The cord and the lesion were shown in their anatomical surroundings, detecting cord swelling in the acute phase (24 h to 1 week) and cord atrophy at the chronic stage. Haemorrhage was detected as hypo-intense signal. Oedema, necrosis and scarring were hyper-intense but could not be distinguished. Histology confirmed that the anatomical delimitation of the lesion extent by MRI was precise, both with high and moderate resolution. The present investigation thus demonstrates the precision of spinal cord MRI at different survival delays after compressive partial SCI and establishes efficient imaging parameters for postmortem PD MRI.

The transport kinetics of methanol in PMMA have been studied over the temperature range 25-60°C, using magnetic resonance imaging. It is shown that transport behavior changes from being relaxation controlled (Case II) at the lowest temperature to approaching Fickian behavior at the higher temperatures. It is also shown that the change of the exponent of time, n, describing the methanol uptake, with the swelling temperature can be compared with a change of the mechanical behavior of the polymer matrix in the presence of the penetrant. From DSC and DMA measurements, it can be concluded that the transition from Case II toward Fickian diffusion takes place at a temperature around the effective Tg of the imbibed material.

Efficient fibre formation for all regioregular poly(3-alkylthiophene)s (P3ATs) with alkyl chain lengths (A) between 3 and 9 carbon atoms has been accomplished in several solvents. It was observed that for the aliphatic and (chlorinated) aromatic hydrocarbon solvents used, the solvent refractive index offers some rationale to predict the feasibility of a solvent for fibre formation. The fibres were separated from remaining non-organised polymer by centrifugation. This enabled the characterisation of the isolated fibres in function of alkyl chain length (A) with TEM, AFM, XRD and UV-Vis spectroscopy. The fibres are 20 +/− 5 nm wide and 0.5 to >4 µm long and mainly crystallize in the common type I crystal phase. The order within the fibres was probed with XRD, SAED, and UV-Vis and was found to strongly improve with increasing alkyl chain length in going from P33T to P35T, resulting in a longer conjugation length. For P35T to P39T the improvement in order is only marginal.

The analysis of chemical and physical network heterogeneities has been carried out for synthetic isobutylene-based elastomers using 1 H spin echo NMR imaging. Spatial homogeneity was compared for isobutylene-p-methylstyrene-p-bromomethylstyrene (PIB-PMS/BrPMS) terpolymers cured with inorganic versus organic curatives and unfilled materials versus those filled with carbon black. Surprising differences in the network structure were found for materials cured with an inorganic curative (ZnO) relative to those cured with an organic curative (1,6-hexamethylenediamine). Voids and void distributions were found to be an important performance variable on the basis of comparisons between the NMR imaging data and mechanical testing. Systematic comparison of solvent images and polymer images revealed the optimum experimental conditions for enhancing network density contrast or detecting microvoids. For the first time, direct 1 H images of polymer spins in a fully compounded, commercial polyisobutylene-based elastomer were acquired in the absence of any swelling solvent. Multislice imaging experiments were investigated as a method to construct three-dimensional void densities in elastomer compounds. Chemical-shift selective polymer imaging was used to selectively obtain network density information for either component of a two-phase blend containing the PIB-PMS/BrPMS terpolymer and polybutadiene. The ability of NMR imaging to provide data over statistically relevant sampling areas (hundreds of mm 3 ) for both neat polymers and fully compounded commercial materials (containing carbon black) represents a unique advantage over microscopic imaging methods for material property analyses.

The analysis of chemical and physical network heterogeneities has been carried out for synthetic isobutylene-based elastomers using 1 H spin echo NMR imaging. Spatial homogeneity was compared for isobutylene-p-methylstyrene-p-bromomethylstyrene (PIB-PMS/BrPMS) terpolymers cured with inorganic versus organic curatives and unfilled materials versus those filled with carbon black. Surprising differences in the network structure were found for materials cured with an inorganic curative (ZnO) relative to those cured with an organic curative (1,6-hexamethylenediamine). Voids and void distributions were found to be an important performance variable on the basis of comparisons between the NMR imaging data and mechanical testing. Systematic comparison of solvent images and polymer images revealed the optimum experimental conditions for enhancing network density contrast or detecting microvoids. For the first time, direct 1 H images of polymer spins in a fully compounded, commercial polyisobutylene-based elastomer were acquired in the absence of any swelling solvent. Multislice imaging experiments were investigated as a method to construct three-dimensional void densities in elastomer compounds. Chemical-shift selective polymer imaging was used to selectively obtain network density information for either component of a two-phase blend containing the PIB-PMS/BrPMS terpolymer and polybutadiene. The ability of NMR imaging to provide data over statistically relevant sampling areas (hundreds of mm 3 ) for both neat polymers and fully compounded commercial materials (containing carbon black) represents a unique advantage over microscopic imaging methods for material property analyses.