Autori: 1. Emil Buzdugan, 2. Norbert Stribeck, 3. Paul Ghioca, 4. Eric J. Beckman, 5. Sever Serban

Editorial: Wiley-VCH, Macromolecular Materials and Engineering, 286 (8), p.497-505, 2001.

Rezumat:

Block copolymers containing epsilon-caprolactone were synthesized. Mechanical properties as a function of
chemical composition and domain structure as a function of elongation were studied. Based on previous optimal
conditions determination by factorial design of experiments of e-caprolactone anionic polymerization, polystyrene-block-poly(e-caprolactone), polyisoprene-block-poly(e-caprolactone), polystyrene-block-polybutadiene-block-poly(e-caprolactone) (SBCL), and polystyrene-
block-polyisoprene-block-poly(e-caprolactone) (SICL)with different compositions where synthesized, and char
acterized by GPC and DSC. Both the SICL and SBCL materials are thermoplastic elastomers, from which spin cast films were prepared. Their mechanical properties were determined, small angle X-ray scattering (SAXS) measurements were carried out during straining, and
dynamic mechanical analysis (DMA) was performed. All diblock polymers separate into a two-phase structure, but
the melting point of crystalline poly(e-caprolactone)domains in the block polymer is higher than in the case of
the homopolymer. According to DMA data, some of the SICL and SBCL materials are three-phase systems, but others are only two-phase systems. The two-phase materials show a considerable depression of the composite hard
domain glass transition and, consequently, turn out to be very soft. It appears peculiar that the transition from three-phase to two-phase material is accomplished by decreasing the soft block length. For the soft material
SAXS exhibits a lamellar stack nanoscale structure and several reflections of colloidal crystals. As a function of increasing elongation, the crystal reflections broaden, whereas lamellar stacks rotate as a whole.

Cuvinte cheie: block polymers, styrene, isoprene, butadiene, caprolactone, anionic polymerization, DMA, glass transition temperature, small angle x-ray scattering