Perfectly Controlled Lamella Thickness and Thickness Distribution: A Morphological Study on ADMET Polyolefins

High Morphological Order in a Nearly Precise Acid-Containing Polymer and Ionomer

Linear polyethylenes with functional groups at precise intervals along the backbone possess a number of remarkable properties, but the current synthetic methods that produce these precise polymers are difficult to scale up beyond the laboratory setting. When evaluating alternative synthetic routes, a critical question is how precise must the polymer microstructure be to achieve the properties of interest? As a first step in answering this question, we present morphological characterization of a nearly precise polymer-that is, an acid-containing polymer wherein the acid groups are separated by either n or n + 1 methylene groups. We find that the size scale and uniformity of the amorphous morphologies of the nearly precise acid-containing polymer and its sodium-neutralized ionomer are essentially indistinguishable from the precise polymers based on X-ray scattering. Meanwhile, the nearly precise polymer is strikingly distinct from a pseudorandom copolymer with similar average composition. This result suggests that the properties of nearly precise polymers could likewise be quite similar to truly precise polymers and beckons future work to explore their properties.

Spectroscopic examinations of hydrogen bonding in hydroxy-functionalized ADMET chemistry

Wide-angle X-ray scattering (WAXS) and temperature-dependent Fourier transform infrared spectroscopy (FTIR) spectroscopy are used to study hydrogen bonding interactions of a hydroxyl-functionalized polyethylene (PE) prepared by acyclic diene metathesis (ADMET) chemistry. The hydroxyl polymer exhibits an orthorhombic unit cell structure with characteristic reflection planes at (110) and (200), comparable to pure crystalline PE. These data unequivocally demonstrate that the OH branch is excluded from the PE lamellae. Furthermore, the polymer melts 100 °C higher than all previous analogous polymers possessing precision placed long aliphatic branches that also are excluded from PE lamellae. Temperature-dependent FTIR spectroscopy from ambient to 150 °C, followed by cooling to 125 °C supports exclusion of the hydroxyl group from the crystalline lattice. It is concluded that these hydroxyl groups form stable physical networks in the amorphous region via hydrogen bonding and are important for the overall morphology of such polymers.

Cross Nucleation in Polyethylene with Precisely Spaced Ethyl Branches

In cross nucleation, an early nucleating crystalline polymorph (A) nucleates another crystalline polymorph (B) of higher or lower thermodynamic stability without undergoing a polymorphic transformation. Although this phenomenon was recently observed in the crystallization process of several small molecules, there has been insufficient evidence for cross nucleation in a crystalline polymer. In this paper, we report cross nucleation behavior during an isothermal crystallization of a crystalline polymer with precisely spaced branches. Polyethylene with ethyl branches on every 21st carbon exhibited growth of new spherulites at the growth front of an initially formed spherulite. The radial growth rate of the initially formed spherulite and the newly grown spherulite calculated from polarized optical microscope data were 0.76 μm/min and 1.01 μm/min, respectively. The growth rate of the newly grown spherulite is faster than that of the initially formed spherulite, which meets a required condition for cross nucleation. Scanning microbeam wide-angle X-ray scattering (WAXS) confirmed that the crystalline polymorphs of the two kinds of spherulites are not the same.