三臂星形聚苯乙烯的链缠结及松弛行为

使用差示扫描量热仪和旋转流变仪测定了三臂星形聚苯乙烯(sPS)的玻璃化转变温度、稳态及动态流变性能,并与线型聚苯乙烯(lPS)进行对比分析,研究三臂星形支化结构对聚苯乙烯链缠结及松弛行为的影响。结果表明,当sPS双臂长度与lPS主链长度相当时,sPS的玻璃化转变温度(T_g)、储存模量(G')、零剪切黏度(η_0)、末端松弛时间均大于lPS,而非牛顿指数(n)更小;当sPS与lPS重均相对分子质量相当时,sPS的T_g、n更大,η_0更小,末端松弛时间更短。sPS长支链的存在对链缠结的促进作用小于sPS高线团密度对链缠结的抑制作用,单根支链的引入主要延缓了PS的链段松弛。

Chain Entanglement and Relaxation Behavior of Three-Arm Star-Shaped Polystyrene

The glass transition temperature,steady and dynamic rheological properties of three-arm star-shaped polystyrene (sPS) compared with linear polystyrene (lPS) were measured by DSC and rotational rhcometer.The influence of three-arm star-shaped structure on chain entanglement and relaxation behavior of PS was studied.The results show that when the dual-arm length of sPS is equal to the backbone length of IPS,the glass transition temperature Tg,storage modulus G',zero-shear viscosity η0 and terminal relaxation time for sPS are higher than those for lPS,with smaller non-Newtonian exponent n.When the weight-average molecular weight of sPS is close to that of lPS,the Tg and n for sPS are higher,with lower η0 and terminal relaxation time.The effect of long branch chain of sPS on the improvement of chain entanglement is less than the influence of higher molecular coil density of sPS on the inhibition of chain entanglement.The introduction of one branch chain mainly delays the relaxation of the segments of PS.