No abstract

Placing artificial folding elements into precision polymers is an important strategy to systematically study structure formation in self‐assembly, particularly in the semicrystalline state. To this purpose, a series of precision polymers bearing either a N‐protected or N‐unprotected diaminopyridine (DAP) unit after every 16th, 18th, and 20th carbon as well as a urea unit after every 20th carbon along a polyethylene‐like polymer were synthesized via acyclic diene metathesis polymerization and subsequent hydrogenation. The polymers thus contain either H‐bonds (urea/DAP), π–π‐elements (DAP), or no H‐bonds (respective Nprotected urea/DAP‐units) in their main chain, able to consequently study the crystallization behavior under influence of such supramolecular moieties. Therefore, the thermal properties and crystallization behavior were analyzed via differential scanning calorimetry (DSC) as well as wide angle X‐ray diffraction. The obtained crystalline polymer is influenced by the different supramolecular interactions existing between adjacent polymer chains and the varying defect size exerted by the incorporated functional groups. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3736–3748

Front Cover: Ordering phenomena in polymers are core principles in biological and synthetic macromolecules. A precision poly(olefin) containing a beta‐turn mimic as a repetitive folding‐constraint after every 16 methylene units is designed, which enables the constrained crystallization of the methylene units to be studied within the obtained polymer. Further details can be found in the article by S. Reimann, U. Baumeister, and W. H. Binder* on page 1963.

The synthesis and thermal properties of a new type of precision polyethylene containing perfectly placed conformationally constraining elements after every 16 methylene units are presented. The precise placement of a 2,6-diaminopyridine moiety (DAP) is accomplished via acyclic diene metathesis (ADMET) polymerization of specially designed monomers, where the DAP serves as the conformational constraint. Polymerization of the diene-mono mer ( N,N′ -pyridin-2,6-diyl-bis-dec-9-enamide) displaying free-amide hydrogen bonds leads to largely insoluble polymers due to self-aggregation via the hydrogen bonds and π-π stacking. However, when using the N -methyl-protected monomer N,N ′-pyridin-2,6-diylbis( Nmethyldec-9-enamide), the polymerization furnishes soluble polymers with molecular weights ranging from 1500 up to 60 000 g mol −1 using different Grubbs or Umicore catalysts. Matrix-assisted laser desorption/ionization (MALDI) measurements prove the structure of linear and cyclic polymers, all containing the precisely placed DAP units within the polymer. Subsequent hydrogenation with p -toluenesulfonhydrazide yields the fi nal semicrystalline polymers, displaying an ordered lamellar crystal phase as characterized via differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements.

An approach to influence and control layered superstructures by varying the methylene sequence length between two consecutive functional groups in linear precision polymers containing 2,6-diaminopyridine (DAP) groups is presented. Layered superstructures with repeating units involving three monomeric units along the chain direction with very high coherence lengths upto 110 nm are observed in case of shorter alkyl segments, (16 and 18 CH 2 units), while more conventional layer superstructures incorporating only one monomer are found for related polymers with 20 CH 2 units per methylene sequence. A building block model explaining the unusually large periodicity of three monomeric units is proposed wherein layers containing crystalline or amorphous methylene sequences occur in different combinations. Occurrence of different layered structures depending on crystallization conditions, methylene sequence length as well as functional group type is explained by a competition of H-interactions between the DAP groups and the van der Waal forces between the hydrophobic methylene groups.