Authors Zhu, Y. ; Weidisch, R. ; Gido, S.P. ; Velis, G. ; Hadjichristidis, N.
Title Morphologies and Mechanical Properties of a Series of Block-Double-Graft Copolymers and Terpolymers
Date 23.07.2002
Number 10785
Abstract Morphological characteristics and mechanical properties of a series of block-double-graft(BDG) copolymers and terpolymers polystyrene-[1,2-polybutadiene-<I>g</I>-X<SUB>2</SUB>] (X = 1,4-polybutadiene, polyisoprene, polystyrene, and polystyrene-<I>b</I>-polyisoprene diblocks) were investigated by transmission electronmicroscopy (TEM), small-angle X-ray scattering (SAXS), and tensile testing. All BDG materials havelinear polystyrene-1,2-polybutadiene (PS-<I>b</I>-1,2-PBD) diblock copolymer backbones. Two identical branchesare grafted at every randomly distributed tetrafunctional junction point on the 1,2-PBD part of thebackbone. Standard microstructures, such as body-center-cubic spheres, hexagonally packed cylinders,and lamellae, are obtained at different total PS volume fractions. It is found that when the branches arepolydienes, the BDG molecules form the same morphologies as their linear diblock counterparts. In suchcases, phase separation occurs between the polystyrene domain and a combined diene microdomain formedby the backbone 1,2-PBD part and the polydiene branches. In BDG materials in which the branches arepolystyrene-polyisoprene diblock copolymers, lamellae are obtained at a total PS volume fraction closeto 0.50. It is found that the domain spacings of these materials are predominately determined by themolecular weights of the diblock branches instead of the backbones. A lamellae-forming BDG terpolymerwith an average of three tetrafunctional junction points per molecule exhibited characteristic thermoplasticelastomer properties with a stress at break of 32 MPa and strain at break of 1000%. It is proposed thatthe high strength of this BDG terpolymer is attributed to the chain<br /> conformation in the microphase-separated state. The elastic PBD blocks of the backbone bridge adjacent PS domains through multiplejunction points, resulting in the enhanced elastomeric properties. Several parameters are found to influencethe mechanical properties of these BDG materials: (1) the existence of backbone PS, (2) the molecularweight of the branches, and (3) the number and functionality of branch points on the 1,2-PBD part of thebackbone.
Publisher Macromolecules
Citation Macromolecules 35 (2002) 5903-5909

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