Chain Tilt and Crystallization of Ethylene Oxide Oligomers with Midchain Defects

Crystallization of Poly(ethylene)s with Regular Phosphoester Defects Studied at the Air-Water Interface

Poly(ethylene) (PE) is a commonly used semi-crystalline polymer which, due to the lack of polar groups in the repeating unit, is not able to form Langmuir or Langmuir-Blodgett (LB) films. This problem can be solved using PEs with hydrophilic groups arranged at regular distances within the polymer backbone. With acyclic diene metathesis (ADMET) polymerization, a tool for precise addition of polar groups after a certain interval of methylene sequence is available. In this study, we demonstrate the formation of Langmuir/LB films from two different PEs with regular phosphoester groups, acting as crystallization defects in the main chain. After spreading the polymers from chloroform solution on the water surface of a Langmuir trough and solvent evaporation, the surface pressure is recorded during compression under isothermal condition. These π-A isotherms, surface pressure π vs. mean area per repeat unit A, show a plateau zone at surface pressures of ~ (6 to 8) mN/m, attributed to the formation of crystalline domains of the PEs as confirmed by Brewster angle and epifluorescence microscopy. PE with ethoxy phosphoester defects (Ethoxy-PPE) forms circular shape domains, whereas Methyl-PPE-co-decadiene with methyl phosphoester defects and two different methylene sequences between the defects exhibits a film-like morphology. The domains/films are examined by atomic force microscopy after transferring them to a solid support. The thickness of the domains/films is found in the range from ~ (2.4 to 3.2) nm depending on the transfer pressure. A necessity of chain tilt in the crystalline domains is also confirmed. Grazing incidence X-ray scattering measurements in LB films show a single Bragg reflection at a scattering vector qxy position of ~ 15.1 nm-1 known from crystalline PE samples.

Theory of statistics of ties, loops, and tails in semicrystalline polymers

Polymer crystals grown from melts consist of alternating lamellar crystalline regions and amorphous regions. We study the statistics of ties: chains which bridge the adjacent lamellae, loops: chains which come out of one lamella and enter back into the same lamella before reaching the other lamellae, and tails: chains which end in an amorphous region. We develop a theory to calculate the probabilities of formation of ties, loops, and tails with consideration of finite chain length and cooperative incorporation of a chain into multiple lamellae. The results of our numerical calculations based on a field-theoretic formalism show that the fraction of ties increases with increasing chain length, and it decreases with increasing interlamellar separation. In the limiting case of an infinite chain confined between only two walls, we recover the classical results of the gambler's ruin model. We show that the density anomaly encountered in previous theories is avoided naturally in the present theory without forcing the majority of stems to form tight loops. The derived results on the probability of tie chains in the amorphous regions are pertinent to the mechanical properties of semicrystalline polymers.

Crystallization of Poly(ethylene oxide) on the Surface of Aqueous Salt Solutions Studied by Grazing Incidence Wide-Angle X-ray Scattering

We report the thin layer crystallization of high-molar mass poly(ethylene oxide) (PEO) on a liquid support using a 4 M K₂CO₃ aqueous solution as a subphase. Because of the Hofmeister effect, PEO does not dissolve and remains at the surface during compression on a Langmuir trough. The transition from the flat pancake conformation upon compression of the spread polymer film to an entangled monolayer results in a plateau region of the Langmuir isotherm. Using grazing incidence wide-angle X-ray scattering, the final crystallization of PEO was observed, and the crystal orientation was determined. The fold surface was (209̅), that is, the helix axis has a tilt angle of 2.9° to the normal vector of the water surface.

Discrete oligodimethylsiloxane–oligomethylene di- and triblock co-oligomers: synthesis, self-assembly and molecular organisation

A new class of discrete-length block co-oligomers comprising oligodimethylsiloxane (oDMS) and oligomethylene (oM) is presented.