Ekaterini Siakali-Kioulafa

Block copolymers with crystalline/amorphous, crystalline/polyelectrolyte and amorphous/polyelectrolyte blocks

Diblock and triblock copolymers containing polybutadiene (PB) with high 1,4-butadiene content and poly(tert-butyl methacrylate) (PtBMA) blocks were synthesized by anionic polymerization using high vacuum techniques. These polymers were transformed by homogeneous hydrogenation, using the Wilkinson catalyst, into block copolymers containing a semicrystalline polyethylene (PE) block and an amorphous semiflexible PtBMA block. Subsequent hydrolysis resulted in block copolymers with semi- crystalline (PE) and polyelectrolyte (poly(methacrylic acid), PMAA) blocks. The PB/PtBMA copolymer precursors were also converted by direct hydrolysis to PB/PMAA copolymers, and subsequently to PB/poly(sodium methacrylate) amorphous/polyelectrolyte block copolymers by neutralization with NaOH. The extent of the transformation reactions was determined by solution and solid-state NMR spectroscopy. The materials containing a semicrystalline block were also characterized by differential scanning calorimetry (DSC). Some preliminary results from DSC on the phase behavior (mixing of phases and interplay between organization in the amorphous and semicrystalline phases) of these new materials are also presented.

Characteristic ratio of poly(tetrahydrofurfuryl acrylate) and poly(2‐ethylbutyl acrylate)

The synthesis, characteristic ratio C∞ and glass transition temperature (Tg) of poly(tetrahydrofurfuryl acrylate) (PTHFA) and of poly(2-ethylbutyl acrylate) (P2EBA) are reported. P2EBA has slightly lower flexibility (C∞ = 9.2) than PTHFA (C∞ = 8.6), mainly because of the higher bulkiness of its side group and the closer proximity to the main chain. The C∞ results compared with the corresponding polymethacrylates show an increase in flexibility due to the absence of the α-methyl group. Comparison with poly(methyl acrylate) clearly shows the influence of the bulkiness of the side group on the chain flexibility. The lower Tg of P2EBA than that of PTHFA may be explained by the higher flexibility of the 2-ethylbutyl side group.

Association behavior of linear ω‐functionalized polybutadienes in cyclohexane

The dilute solution properties of linear polybutadienes with dimethylamine and zwitterionic end groups were studied by membrane osmometry (MO), low-angle laser light scattering (LALLS), viscometry, and dynamic light scattering (DLS) in cyclohexane. The polymers were prepared by anionic polymerization, under high vacuum conditions using [3-(dimethylamino)propyl]lithium as initiator. The dimethylamine groups were converted to zwitterions by reaction with cyclopropane sultone. No evidence of association was found for the amine-capped polymers, whereas the zwitterionic samples exhibited strong association in cyclohexane. The degrees of association increase by decreasing molecular weight of the base polymer due to the excluded volume repulsions. These aggregation numbers are of the same order as those found for ω-functionalized polyisoprenes, with the same polar groups in the same solvent. The hydrodynamic properties, measured by viscometry and dynamic light scattering, supported the conclusions drawn by LALLS and provide strong evidence that the aggregates behave hydrodynamically as star polymers. Comparison with theoretical models shows that the association behavior is best described by the linear head packing model.

Use of Synchrotron Radiation in Plastics Analysis

We demonstrate the application of synchrotron small angle X-ray scattering (SAXS) in measuring the thermodynamic properties of polymer blends. The polymers under investigation consist of poly(cyclohexyl acrylate) (PCHA) blended with the ortho and meta isomer of poly(bromostyrene) (P2BrS, P3BrS). Measurements of the absolute scattered intensity enable the determination of the second derivative of the Gibbs free energy of mixing with respect to the concentration, the location of the spinodal temperature, and the Flory-Huggins X-parameter.