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Zhu, Y. ; Burgaz, E. ; Gido, S.P. ; Weidisch, R. ; Staudinger, U. ; Uhrig, D. ; Mays, J.W.
Morphology and Tensile Properties of Multigraft Copolymers with Regularly Spaced Tri-, Tetra- and Hexa-functional Janction Points

The effect of chain architecture on the morphological and tensile properties of series of multigraftcopolymers, with regularly spaced tri-, tetra-, and hexafunctional junction points, was investigated using transmissionelectron microscopy (TEM), small-angle X-ray scattering (SAXS), and tensile testing. The materials weresynthesized by coupling difunctional polyisoprene (PI) spacers and living polystyrene (PS) branches, made byanionic polymerization, with chlorosilanes of different functionalities. Since the coupling process is a step-growthpolymerization, yielding polydisperse products, fractionation was utilized to separate each material into threefractions (high, middle, and low molecular weight), each of low polydispersity. All three fractions have the samechain architecture on a per junction point basis but differ in the number of junction point units per molecule. Byapplying the constituting block copolymer concept, the physical behavior of these molecules was compared withcurrent theories. It was found that morphological behavior of these graft copolymers can be predicted usingtheoretical approaches and is independent on the number of junction points. The number of the junction points,however, greatly influences the
long-range order of microphase separation. Additionally, two new parameters foradjusting mechanical properties of multigraft copolymers were found in this investigation: (1) functionality ofthe graft copolymer-tri-, tetra-, or hexafunctional-and (2) number of junction points per molecule. An increasein functionality causes a change in morphology, resulting in a high level of tensile strength for tetrafunctional(cylindrical) and hexafunctional (lamellae) multigraft copolymers, leading to about the twice the strength of thespherical trifunctional multigrafts of similar overall composition. Tetrafunctional multigraft copolymers show asurprisingly high strain at break, far exceeding that of commercial block copolymer thermoplastic elastomers(TPEs). Strain at break and tensile strength increase linearly with the number of junction points per molecule.Hysteresis experiments at about 300-900% deformation demonstrate that multifunctional multigraft copolymershave improved high elasticity as compared to commercial TPEs like Kraton or Styroflex.

Macromolecules 39



Erschienen am
July 2006

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