The effect of unidirectional shear on the structure of triblock copolymers. I. Polystyrene-polybutadiene-polystyrene

Flow severely affects the morphological and rheological properties of microphase-separated block copolymers as shown with a polystyrene--polybutadiene--polystyrene triblock copolymer. Small-angle X-ray scattering (SAXS) and form birefringence show that cylindrical polystyrene domains orient in the f...

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Bibliographic Details
Published in:Macromolecules 1989-09, Vol.22 (9), p.3533-3540
Main Authors: Morrison, Faith A, Winter, H. Henning
Format: Article
Language:English
Subjects:
Applied sciences
Exact sciences and technology
Organic polymers
Physicochemistry of polymers
Properties and characterization
Rheology and viscoelasticity
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Summary:Flow severely affects the morphological and rheological properties of microphase-separated block copolymers as shown with a polystyrene--polybutadiene--polystyrene triblock copolymer. Small-angle X-ray scattering (SAXS) and form birefringence show that cylindrical polystyrene domains orient in the flow direction reaching a saturated orientation after approx 30 shear units in a constant-stress experiment. The size and shape of the domains are unaffected by the flow as measured by SAXS and transmission electron microscopy (TEM). Shift factors a sub T used to obtain master curves from small-strain dynamic measurements also do not change with shear. The master curves of samples sheared at 160 deg C first drop at all frequencies, omega , with increasing strain and then recover at high omega for the highest strains. Samples sheared at 180 deg C behave similarly but recover completely to the initial rheological state even though the domains in the samples are highly oriented. A flow mechanism is proposed to describe these results. Graphs. 18 ref.--AA
ISSN:0024-9297
1520-5835
DOI:10.1021/ma00199a006