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Polybutene-1 with form I crystals exhibits excellent creep resistance and environmental stress crack resistance. The filaments of polybutene-1 and its random copolymer with 4 mol% ethylene co-units were produced via extrusion melt spinning, which are expected to be in form I states and show outstanding mechanical properties. The variances in microstructure, crystallization–melting behavior, and mechanical properties between homopolymer and copolymer filaments were analyzed using SEM, SAXS/WAXD, DSC, and tensile tests. The crystallization of form II and subsequent phase transition into form I finished after the melt-spinning process in the copolymer sample while small amounts of form II crystals remained in homopolymer filaments. Surprisingly, copolymer filaments exhibited higher tensile strength and Young's modulus than homopolymer filaments, while the homopolymer films showed better mechanical properties than copolymer films. The high degree of orientation and long fibrous crystals play a critical role in the superior properties of copolymer filaments. The results indicate that the existence of ethylene increases the chain flexibility and benefits the formation of intercrystalline links during spinning, which contributes to an enhancement of mechanical properties. The structure–property correlation of melt-spun PB-1 filaments provides a reference for the development of polymer fibers with excellent creep resistance. [ABSTRACT FROM AUTHOR]

Polybutene-1 (PB-1) exhibits excellent mechanical properties, while an unavoidable polymorphic transition from a metastable form II to the stable form I occurs after solidification from the molten state. This transition goes along with a deformation of the crystal lattice corresponding to a lateral shrinkage and normal elongation of about 20% and 12%, respectively. Here we study the semicrystalline morphology before and after the transition using small-angle X-ray scattering (SAXS) and differential scanning calorimeter (DSC). Scattering curves of samples with form II crystals could be well described by a model of layer-like stacked lamellar crystals. However, the scattering signal of form I samples showed additional scattering contributions at higher scattering vectors, indicating the generation of fine structures during the transition, much smaller than lamellar long spacing. The lamellar thickness increased less than the factor of 1.12, expected from the elongation of the lattice. The results indicate that the large lamellar crystals split up into blocks during the transition creating new interstitial spaces within the lamellae. This process is caused by the fact that the laterally extended lamella of form II cannot shrink as a whole due to the connectivity of the chains emanating from the crystals and due to possible overcrowding of the chain segments at the crystalline/amorphous interfaces. Image 1 • The semicrystalline morphology before and after the form II to I transition in PB-1 was studied using SAXS techniques. • Fine structures much smaller than lamellar long spacing were formed after form II to I transition in PB-1. • Lamellar thickness increases a bit after phase transition, but not to full extent of the elongation of the crystal lattice. [ABSTRACT FROM AUTHOR]

Phase composition and molecular mobility were studied using 1H NMR T 2 relaxometry in isotactic polybutene-1 (iPB-1) with two polymorphs - form I and II crystals. Several types of NMR relaxation methods and data analysis were evaluated for determining the most reliable way for studying physical phases in iPB-1. Three-phase model provided the most appropriate description of the phase composition in iPB-1, i.e., a crystal-amorphous interface separates the crystalline and the amorphous phases. Due to complex molecular mobility in iPB-1, the amount of rigid fraction should be considered as NMR crystallinity number. Two types of chain segments are present in the amorphous phase: (1) chain segments with anisotropic mobility due to chain anchoring to crystals and chain entanglements; and (2) highly mobile chain end segments. The polymorphic phase II to I transition causes significant immobilization of polymer chains in the crystalline and the amorphous phases. Molecular weight of iPB-1 largely influences phase composition and molecular mobility in crystalline and amorphous phases. Image 1 • Phase composition and molecular mobility in isotactic polybutene-1 are studied using 1H NMR T 2 relaxometry. • The three-phase model provides the best description of the phase composition. • Advantages and disadvantages of different types of T 2 relaxation experiments are discussed. • The polymorphic phase II to I transition causes decrease in chain mobility in the crystalline and the amorphous phases. • Molecular weight of iPB-1 largely influences phase composition and molecular mobility in crystalline and amorphous phases. [ABSTRACT FROM AUTHOR]