STRESS-RELAXATION IN POLY(STYRENE-BUTADIENE-STYRENE) AND POLY(STYRENE-ISOPRENE-STYRENE) TRIBLOCK COPOLYMERS AND THEIR DERIVATIVES

The streSS relaxation properties of poly(styrene-b-butadiene-b-styrene ) (SBS), epoxidized SBS (ESBS), poly(styrene-b-isoprene-b-styrene) (SI S) and 1-vinyliinidazole grafted SIS (SIS-g-VIm) copolymers in air wer e investigated. The stress relaxation of SBS copolymer occurs as a res ult of the physical flow, the physical entanglements and the domains. The stress relaxations for SBS, ESBS, SIS and SIS-g-VIm copolymers are temperature dependent, with a higher relaxation rate at higher temper atures. The stress relaxation activation energies of SBS, ESBS, SIS an d SIS-g-VIm were 83.7, 46.0, 113.0 and 52.2 kJ mol - 1, respectively, indicating that ESBS and SIS-g-VIm had higher stress-relaxation rates than SBS and SIS at constant temperature. The procedure X method, prev iously proposed by Tobolsky and Murakami, was utilized for separation and identification of the three processes causing stress relaxation. A general representative equation, f(t)/f(0)=A exp(-k(A)t)+B exp(-k(B)t ) + C exp(-k(C)t), was obtained for the stress relaxation of the physi cal flow, the physical entanglements and the domain region, respective ly. The relationship k(A) > k(B) > k(C) that was found demonstrates th at the relaxation rates decrease in the order physical flow>physical e ntanglements>the domain.