Fluorescently labeled polystyrene (PS) tracer molecules are enclosed in a semidilute, entangled solution of PS matrix polymers. The latter carry photo-cross-linkable groups such that the matrix can be successively cross-linked by UV-irradiation. The diffusion coefficient of the labeled tracer chains is measured via FRAP at every stage of the cross-linking process during the transition from sol to gel. In the sol state, significant deviations from the reptation predictions appear unless the matrix chains are considerably longer than the tracer chains. Cross-linking of the matrix chains results in a more or less pronounced decrease of the tracer diffusion coefficient, occurring gradually with rising conversion of the cross-linking reaction, while the observed dependencies of the tracer diffusion coefficient on tracer molecular weight and on matrix concentration converge to what is predicted by reptation theory.

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The rodlike ionogenic polymers poly(p-pyridylene-phenylene) and poly(p-pyridylene/phenylene-ethynylene) form polyelectrolytes when protonated with toluene sulfonic acid or ethane sulfonic acid in chloroform solution. This molecular modification, clearly indicated by a marked red shift of the UV absorption band, induces the formation of prolate, bundlelike aggregates, whose size and shape are obtained from their rotational dynamics as revealed by electric birefringence relaxation and their translational dynamics as measured by dynamic light scattering. The aggregates have a length of 400-600 nm and a high aspect ratio >15. In general, the polyelectrolyte molecules are arranged with their long axes parallel to the long axis of the aggregates. They probably attract each other through the electrostatic interaction with counterions. The counterions are not bound to specific sites but may be shifted under the action of an external electric field to account for the highly anisotropic electric polarizability. When inert salt or excess sulfonic acid is added, these compounds seem to accumulate within the aggregates and influence the attractive forces. This is generally leading to an elongation of the aggregates and, in the case of added salts, even to a marked reduction of birefringence.

The coloration of plastics is an important quality feature of medical devices, and it is most frequently done by using masterbatches. This study investigates the influence of masterbatches with different carrier resins on the impact resistance and the morphology of an acrylonitrile-butadiene-styrene (ABS)/styreneacrylonitrile (SAN) blend. The experimental results were compared with thermodynamical models based on Hansen and Flory-Huggins theory. The models, as well as notched impact testing, indicated strong immiscibility and incompatibility when using a masterbatch carrier based on polystyrene (PS). Immiscibility was confirmed by morphology studies that revealed the formation of PS-droplets with increasing masterbatch content. Masterbatches based on ABS and SAN showed no significant impact and theoretical calculations were in good accordance with mechanics and morphology. The proposed theoretical calculation of solubility between blend partners potentially allows a prediction for selecting a suitable masterbatch carrier.

Ethylene-propylene-diene rubber (EPDM) scrap was devulcanized in an internal mixer with varying amounts of dibenzamido diphenyl disulfide (DBD) at temperatures below 200 C. The devulcanization effect and sol-gel analyses of the devulcanizates, and the mechanical properties of the sulfur-cured revulcanizates were studied. Residual DBD was still present in the sol at 160 C and degraded DBD at 200 C. DBD affects the curing leading to poor properties. So, the temperature must be adjusted according to the DBD concentration to obtain a superior recyclate for sealing systems. At 0.4 wt% DBD, the degradation reaction was already complete at 120 C, but only 52% and 61% of the tensile strength σ and strain at break ε of the virgin material were achieved. At 160 C and 2 wt%, the degradation reaction was complete, and the DBD effect on properties was small; 65% and 86% of σ and ε were recovered, respectively. To prevent property degradation, 200 C was required at 3.9 wt% DBD, resulting in 97% and 95% of σ and ε, but only 70% of hardness.

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Summary: Linear polystyrene chains that were labeled with a fluorescent dye were enclosed in a semidilute matrix of polystyrene in toluene. The matrix polymers used were suitably functionalized such that they could be photocross-linked in a stepwise and controlled manner without attachment of the tracer chains. The diffusion coefficient of the tracer chains was determined by fluorescence recovery after photobleaching while the state of the matrix was changing from a semidilute solution to a covalently cross-linked gel. The progress of the photocross-linking reaction was macroscopically monitored by rheology. The tracer chains were polystyrenes with molecular weights ranging from 50 000 to 2 000 000 g mol À1 and low polydispersity.They were labeled via polymer analogous reactions with the fluorescent dye 6-(7-nitrobenzfurazan-4-ylamino) hexanoic acid. The matrix polymers covered a similar molecular weight range. The results of these measurements show that the dependence of the diffusion coefficient on the tracer molecular weight in the gel can be described by a scaling law in the sense of the reptation theory whereas distinct deviations of this scaling behavior appear in the sol state. The ratio of the matrix molecular weight and tracer molecular weight in the initial sol state significantly influences the change of the probe dynamics during the sol-gel transition.

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