Abstract
Fully saturated, aliphatic polymers containing adamantane moieties evenly distributed along the polymer backbone are of great interest due to their exceptional thermal stability, yet more synthetic strategies toward these polymers would be desirable. Herein, we report for the first time the synthesis of poly(1,3-adamantylene alkylene)s based on α,ω-dienes containing bulky 1,3-adamantylene defects precisely located on every 11th, 17th, 19th, and 21st chain carbon via acyclic diene metathesis polycondensation. All saturated polymers revealed excellent thermal stabilities (452–456 °C) that were significantly higher compared to those of structurally similar polyolefins with aliphatic or aromatic ring systems in the backbone of polyethylene (PE). Their crystallinity increases successively from shorter to longer CH2 chains between the adamantane defects. The adamantanes were located in the PE crystals distorting the PE unit cell by the incorporation of the adamantane defect at the kinks of a terrace arrangement. Precise positioning of structural defects within the polymeric backbone provides various opportunities to customize material properties by “defect engineering” in soft polymeric materials.
Highlights
Adamantane consists of three fused cyclohexyl rings, making it superimposable to the lattice of diamond.1,2 Adamantane is commonly functionalized at the tertiary bridgehead positions affording mono- up to tetrafunctionalized derivatives
We report for the first time the synthesis of poly(1,3-adamantylene alkylene)s based on α,ωdienes containing bulky 1,3-adamantylene defects precisely located on every 11th, 17th, 19th, and 21st chain carbon via acyclic diene metathesis polycondensation
A synthesis procedure for symmetrical alkyl branched acyclic diene metathesis (ADMET) monomers was described based on the two-step double alkenylation of primary nitriles with two equivalents of α,ωalkenylbromides subsequently followed by reductive decyanation
Summary
Adamantane (tricyclo[3.3.1.13,7]decane) consists of three fused cyclohexyl rings, making it superimposable to the lattice of diamond. Adamantane is commonly functionalized at the tertiary bridgehead positions affording mono- up to tetrafunctionalized derivatives. The model is supported by the observation we made for the copolymer cP-1,3-Ad-16/18/20, which consists of randomly distributed methylene chain lengths of 16, 18, and 20 units, causing a lower melting point and ΔHm value compared to the precision polymers P-1,3-Ad-18 and P-1,3-Ad-20, indicating a lower crystallinity. Based on the measured heat of fusion and long period of ΔHm = 35 J/g and L = 13 nm, as well as an approximate model that assumes volume-weighted contributions from the adamantly and n-alkyl regions in the crystal structure (see Supporting Information), we observed a lower limit for the lamellar thickness in P-1,3-Ad-20 of 2.6 < l < 3.2 nm, roughly corresponding to effectively 1.1−1.4 kinked monomer units.
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