Mechanical Property Enhancement of ABA Block Copolymer-Based Elastomers by Incorporating Transient Cross-Links into Soft Middle Block

详细信息    查看全文

• 作者：Mikihiro Hayashi ; Satoru Matsushima ; Atsushi Noro ; Yushu Matsushita
• 刊名：Macromolecules
• 出版年：2015
• 出版时间：January 27, 2015
• 年：2015
• 卷：48
• 期：2
• 页码：421-431
• 全文大小：498K
• ISSN：1520-5835

文摘

We propose a new strategy to enhance mechanical properties of ABA triblock copolymer-based elastomers by incorporating transient cross-links into the soft middle block. An ABA triblock-type copolymer, poly(4-vinylpyridine)-b-[(poly(butyl acrylate)-co-polyacrylamide]-b-poly(4-vinylpyridine) (P鈥揃a鈥揚), was synthesized via RAFT polymerization. In the molecular design, the poly(4-vinylpyridine) (P) end blocks with a high T_g formed pseudo-cross-link domains due to segregation against the soft Ba middle block, while acrylamide units on the middle block formed self-complementary hydrogen bonding, serving as transient cross-links. According to tensile tests, the Young鈥檚 modulus, elongation at break, maximum stress, and material toughness were 1.9 MPa, 200%, 2.6 MPa, and 2.8 MJ/m³, respectively. Comparison between mechanical properties of P鈥揃a鈥揚 and those of another triblock copolymer, poly(4-vinylpyridine)-b-poly(butyl acrylate)-b-poly(4-vinylpyridine) (P鈥揃鈥揚), revealed that P鈥揃a鈥揚 showed larger Young鈥檚 modulus, longer elongation at break, and larger maximum tensile stress than P鈥揃鈥揚. Particularly, the material toughness of P鈥揃a鈥揚 (2.8 MJ/m³) was more than 100 times larger than that of P鈥揃鈥揚 (0.02 MJ/m³). Rheological analysis on the basis of sticky Rouse relaxation of Ba middle block of P鈥揃a鈥揚 suggested that the hydrogen bonds on the middle block serve as dynamic stickers in elastic strands of elastomers under stress. Such dynamic behavior of the hydrogen bonds could prevent local concentration of applied stress for activating break/failure of the materials during elongation, leading to mechanical property enhancement of the materials. In addition, zinc chloride was blended with P鈥揃a鈥揚 to form metal鈥搇igand coordination in the P end block domains, which also affected the mechanical properties of the elastomers.