Critical roles of molecular dynamics in the superior mechanical properties of isotactic-poly(1-butene) elucidated by solid-state NMR

Abstract

Isotactic-poly(1-butene) (iPB1) shows superior mechanical properties after crystal–crystal transitions. Recently, Miyoshi et al. found that crystalline stems in metastable tetragonal crystal perform uniaxial rotational diffusions accompanying side-chain conformational transitions in the fast motional limit (correlation time, 〈τc〉 <10−7 s; Macromolecules 2010, 43, 3986–3989.). In this study, molecular dynamics in stable trigonal crystal is investigated by solid-state nuclear magnetic resonance, which indicates that crystalline stems and side-chain conformations are completely fixed up to melting points (〈τc〉 >10 s). In addition, lamellar thickness, 〈l〉 of iPB1 and a low isotacticity iPB1 (low_iPB1) with 〈mmmm〉=78%, respectively, were investigated by small-angle X-ray scattering. The low_iPB1 sample shows very week supercooling dependence of 〈l〉 (∼5 nm), whereas iPB1 shows strong supercooling dependence of 〈l〉 (10–28 nm). On the basis of molecular dynamics and 〈l〉 results, molecular dynamics effects on structures and unique mechanical property of iPB1 are discussed. Isotactic-poly(1-butene) shows superior mechanical property after crystal–crystal transitions. Very recently, Miyoshi. revealed molecular dynamics of the crystalline stems in metastable tetragonal form. In this study, molecular dynamics in stable trigonal crystal is investigated by 13C center bands only detection of exchange nuclear magnetic resonance. The experimental results indicate that overall motions and side-chain dynamics in slow dynamic range are frozen up to melting temperatures. On the basis of molecular dynamics, roles of (i) unique crystallization and (ii) solid–solid transitions for superior mechanical property are discussed.