Effect of Temperature and Annealing on the Phase Composition, Molecular Mobility, and the Thickness of Domains in Isotactic Polypropylene Studied by Proton Solid-State NMR, SAXS, and DSC

A Numerical simulation method for analyzing 1H spin diffusion NMR for Multicomponent and multiphase polymer systems

A numerical simulation method, namely, SDNMR-WEBFIT, is reported for simulating proton spin diffusion NMR based on the Levenberg-Marquardt algorithm and a pseudo-2D diffusion model. This method is used for the precise quantification of dynamics heterogeneity of the interphase within multiphase polymer systems. The numerical simulation method provides measurements of spin-lattice relaxation time (T1), proton density (ρH), lamellar thickness (d), and spin diffusion coefficient (D) for each component. The pseudo-2D diffusion model is employed to simulate the proton spin diffusion build-up/decay curves, simultaneously calculating the lateral fraction of island-like structures (x-ratio). Such approach was successfully applied to various polymer systems, such as semi-crystalline polymer (Poly(ε-caprolactone), PCL), block copolymers (Styrene-butadiene-styrene triblock copolymer, SBS), and plasticized semi-polymers (Polvinyl alcohol, PVA).

Evidence for complexation-induced micro-extension of poly(vinyl alcohol) chains in interphase and amorphous domains from solid-state NMR

The three-phase structure of poly(vinyl alcohol) (PVA)-iodine complexes was elucidated by solid-state NMR (SSNMR), of which the micro-extension of the PVA segment in the interphase and amorphous domains was directly confirmed. The three-phase structure of the PVA-iodine complex was decomposed by the inverse ¹³C T₁-filter, where ¹³C NMR resonance lines of a C(H) triplet were observed in all three phases. The chain axis of ∼26% extended chains in the interphase deviates 35°-50° relative to the stretching direction, while there is only a 1° deviation for the extended chains in the crystalline domain. The increasing iodine concentration results in the increment of hydrogen-bonded C(H) fractions in both the amorphous and interphase domains, while the distribution of different C(H) fractions remains almost constant in the crystalline domain. Such an increment results from the locally extended PVA chains induced by polyiodine species (I₃^-/I₅^-), since the hydrogen bond(s) (HBs) required a specific direction. Direct evidence for this comes from the similar ¹³C CP/MAS spectra of C(H) in the three phases between unoriented iodine-doped PVA and highly oriented pure PVA. This supports the aggregation model for the formation mechanism of PVA-iodine complexes, where the PVA chain takes an extended zig-zag conformation.

Crystallinity of polyolefins with large side groups by low-field 1H NMR T2 relaxometry: Isotactic Polybutene-1 with form II and I crystals

Phase composition and molecular mobility were studied using ¹H NMR T₂ 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.

Toughening mechanism in impact polypropylene copolymer containing a β-nucleating agent

The voids in β-nucleated IPC could help to ease craze formation and multiply shear yielding while extensive stress whitening phenomenon appears in neat IPC.

Effects of annealing stress field on the structure and properties of polypropylene hollow fiber membranes made by stretching

By adopting three types of annealing stress fields, this work focused on investigating their effects on the microstructural evolution of polypropylene (PP) hollow fiber precursors obtained by the melt spinning process.

In situ study of the annealing process of a polyethylene cast film with a row-nucleated crystalline structure by SAXS

The secondary crystallization has more effect on polyethylene crystal thickening than melt recrystallization during the annealing process.