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, /s c S o10 À7 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 (/s c S 410 s). In addition, lamellar thickness, /lS of iPB1 and a low isotacticity iPB1 (low_iPB1) with /mmmmS¼78%, respectively, were investigated by small-angle X-ray scattering. The low_iPB1 sample shows very week supercooling dependence of /lS (B5 nm), whereas iPB1 shows strong supercooling dependence of /lS (10-28 nm). On the basis of molecular dynamics and /lS results, molecular dynamics effects on structures and unique mechanical property of iPB1 are discussed.

Morphology of Form I′ crystals of polybutene-1 formed on melt-crystallization

“…Though crystallization is non-spherulitic, the small, irregularly oriented stacks of birefringent lamellae are then also detected by polarizing optical microscopy. In a wider view, the experimental observations reported here are in agreement with independently performed small-angle X-ray scattering measurements which suggested presence of Form I 0 lamellae with a thickness of about 5 nm in melt-crystallized stereo-defective polybutene-1 [23]. …”

“…It may be emphasized again that formation of Form I 0 crystals from the melt has only been observed in butene-1 based polymers containing highly defective chains. Such Form I 0 crystals were characterized in the past as being either disordered [11,12] or very small/thin [23], based on X-ray and thermal analyses, however, direct observation of Form I 0 crystals using imaging techniques is not reported yet.…”

“…Together with the observation of distinctly broadened X-ray diffraction peaks, the low melting temperature was initially interpreted being caused by structural disorder [11]. Such interpretation of the low melting temperature of the Form I 0 phase was contrasted by analysis of the chain dynamics, being indifferent in Form I and Form I 0 crystals [23]. Rather than it has been suggested that the low melting temperature of the Form I 0 crystals is due to the formation of very thin lamellae with an average thickness of only 4e5 nm, being almost independent on the degree of supercooling of the melt prior crystallization [23].…”

Influence of Tacticity on Structural Ordering of Isotactic Polypropylene under Annealing

“…Average lamellae thickness was calculated by examining the SAXS patterns taken at room temperature using correlation function described earlier [15]. All  1 rich samples and annealed at different temperatures the average lamellae thicknesses are plotted against annealing temperatures (Figure 7).…”

“…C spin-lattice relaxation time in the laboratory frame (T 1C ) and T 1ρH measurements were used for selective observation of the pure crystalline signals of iPP [15]. In this study, a T 1ρH filter under a spin-locking (SL) field strength of 55 kHz was used for a selective observation of the pure crystalline signals.…”