Abstract
The semilocal structure (space scale: ≈50 A) of a styrene−butadiene−styrene triblock copolymer (SBS) was investigated by observing residual dipole−dipole interactions that govern the transverse relaxation of protons attached to the polymer. The molar masses were 104 and 5 × 104 g/mol for polystyrene (PS) and polybutadiene (PB), respectively. It is shown that, above the glass transition of PB, there exists a network structure; the comparison made with NMR properties of long PB chains, in the melt, suggests this structure is a network formed by entanglements. These chain coupling junctions are trapped by the presence of PS glassy domains where the interface plays the role of embedding points for PB block ends. The mean segmental spacing between chain coupling junctions was found to vary as c-1 where c is the concentration of PB in heptane, a selective solvent of PB. A probability distribution function of end-to-end vectors joining two consecutive coupling junctions, along a PB chain, is proposed to analyze ...
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