Synthesis of supramolecular precision polymers: Crystallization under conformational constraints

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

Crystallization of Long-Spaced Precision Polyacetals II: Effect of Polymorphism on Isothermal Crystallization Kinetics

“…Melting-recrystallization-melting events are commonly found in the melting thermograms of precision polyethylene-like systems, often indicating the transformation, on heating, from one crystal form to another with higher thermal stability. − Moreover, upon analysis of isothermal crystallization rates over a wide range of temperatures covering polymorphic transitions in other semicrystalline polymers, minima or discontinuities in the negative coefficient of the crystallization rates are often observed at temperatures within the transition between polymorphs. − Rate discontinuities found in PLA and other polyesters are explained as a competition between primary nucleation and radial growth of the two crystal modifications. ,, Similarly, fast scanning calorimetric measurements of the overall crystallization rates of different polyamides display two maxima with increasing temperature overlapping at the intersection between two polymorphic forms. Coupled with morphological studies, the maxima were interpreted as a combined change in crystal structure and nucleation mechanisms. − Recently, a deep minimum in the variation of the growth rate with temperature was found in precision polyethylenes with halogens .…”

Efficient, Solvent-Free Aminolysis of Monoesters Catalyzed by Sodium

“…[5] Ester aminolysis is the classical method for making amides, regardless of the lower level activation of esters than acyl halides, anhydrides acyl azides and acylimidazoles, as esters produce fewer side reactions. [6] For example, acyl chlorides [7] were prone to be hydrolyzed in the reaction with ammonia, the same holds true for the reaction of trifluoroacetic anhydride [8] with ammonia in methanol. Carboxylic acid ammoniolysis is also a common method for making amides.…”

Tuning layered superstructures in precision polymers

“…The detailed synthesis route is described in Refs. 35,36 . The molecular weights of the sample are in the range 5-20 kg/mol as taken from secondary information and related systems 35,37 .…”

“…35,36 . The molecular weights of the sample are in the range 5-20 kg/mol as taken from secondary information and related systems 35,37 . Direct information from GPC is inaccessible since no suitable solvent is found for the investigated samples.…”