Block copolymer has been used to reduce the domain size of immiscible polymer blends in order to improve the mechanical properties. This method, however, is not as effective, if a high percentage of the polymeric surfactant does NOT stay at the interface. In fact, theoretical as well as experimental work have shown that a large amount of block copolymers form micelles in the bulk of one or both of the component polymers. These micelles may serve as weak spots initiating crack propagation. Many efforts have been focused on the design of molecular architecture and synthesis of new block copolymers to address this problem. In this presentation, a simple mixing strategy is applied to make each and every block copolymer molecules stay at the interface. As one example, when this strategy is used to mix natural rubber (NR) with butadiene rubber (BR), a small amount of low molecular weight block copolymer (LIR) improves not only the crack resistance, but also, by surprise, the melt viscosity. AFM micrographs (Fig. 1) show the much smaller domain size; and an original real-time monitoring system reveals the lowest crack growth rate at both low and high load, and a finest crack surface morphology.Figure 1. Tapping mode AFM phase images of NR/BR/LIR unvulcanizated blend samples : M1: without LIR block copolymer; M2: with LIR using a general mixing method; M3: with LIR using the proposed mixing strategy; and M4: with LIR using another general mixing method.

How to make each and every block copolymer molecules stay at the interface of a polymer blend

248th National Meeting (2014)

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