Orientation Relaxation of Triblock Copolymer with Cylindrical Microdomain by in situ Stress-Birefringence Measurements

Abstract

The orientation relaxation behavior of polystyrene-block-hydrogenated polyisoprene-block-polystyrene (SEPS) with cylindrical microdomains of polystyrene (PS) dispersed in the rubbery segments was investigated by simultaneous measurements of stress and birefringence, and small angel X-ray scattering (SAXS) measurements. At short relaxation time, the stress ' and the birefringence Án decreased at almost constant rate with time and temperature. At long relaxation time, however, the ' and Án decreased steeply with time, and the decrease became larger with increasing time and temperature. The decrease of the Án stopped and large Án remained at high temperature, while the ' was close to zero. Such characteristic relaxation behavior is ascribed to the form birefringence induced by the orientation of the parallel arranged cylindrical microdomains and the conformational change of the phenyl ring side group associating with the orientation relaxation of PS. The analysis of these results suggest that the orientation relaxation of the rubbery segments occurs at short relaxation time during the stress relaxation after the uniaxial stretching, and then the orientation relaxation of the PS segments in the cylindrical PS microdomains occurs associating with the conformational change of the phenyl side group at long relaxation time at high temperature while the orientation of the cylindrical domain is not changed.KEY WORDS: Tribrock Copolymer / Cylindrical Microdomain / Birefringence / Stress / Orientation Relaxation / Triblock copolymers consisting of glassy end blocks and rubbery midblock such as polystyrene-block-polybutadieneblock-polystyrene (SBS) are typical thermoplastic elastomers.1,2 Since the elastomeric deformation properties are directly related to the molecular and phase structures, the deformation properties such as stress-strain 3-21 and stress relaxation behavior [22][23][24][25][26][27][28][29][30][31][32][33][34][35] have been widely studied. Especially, the stress relaxation behavior is closely related to the practical important properties for elastomers, such as tension and compression permanent set.The birefringence method is often used in combination of the deformation studies. 8,15,[19][20][21][29][30][31][32]36,37 It has shown a great advantage to estimate the physical property and molecular structure because 1) birefringence is sensitive to the change of orientation at small deformation, 2) in situ measurement of high-speed deformation processes is possible by fast measurement, and 3) the orientations of microdomain segments and matrix ones can be evaluated separately by using the additive rule for each segment.Recently, we found that the birefringence of polystyreneblock-hydrogenated polyisoprene-block-polystyrene (SEPS) with cylindrical microdomains of glassy polystyrene (PS) dispersed in the rubbery ethylene-propylene matrix changed little below a yield strain, increased sharply with strain above a yield strain up to a strain of 0.5, and then increased gradually during uniaxial stretching, while the s...

A Physical and Mechanical Study of Prestressed Competitive Double Network Thermoplastic Elastomers

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Stress Relaxation and Underlying Structure Evolution in Tough and Self-Healing Hydrogels

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Flexible and flame‐retardant S‐SEB‐S triblock copolymer/PPE nano‐alloy

“…Overcoming the trade‐off between flexibility and flame retardancy is attributed to the two‐phase structure at the nanometer scale, which consists of flame‐retardant styrene/PPE domains in a continuous soft, lacy SEB matrix. Our recent results for simultaneous measurements of stress and birefringence revealed that the S‐SEB‐S/modified PPE nano‐alloy orients in a two‐step process, that is, both the rubbery SEB matrix and the glassy domains are oriented at low strains, and then only the rubbery SEB matrix is oriented at high strains . Such characteristic deformation behavior might be the origin of the flexibility of the S‐SEB‐S/modified PPE nano‐alloy.…”