Synthesis and Crystallization of Precision ADMET Polyolefins Containing Halogens

Abstract

We report the synthesis and characterization of a series of precision polyethylene (PE) structures containing either a fluorine, chlorine, or bromine on each and every 19th carbon. The use of ADMET polymerization chemistry allows unprecedented control in the synthesis of these halogen containing PE derivatives, and results in the first bromine containing polyolefin with a precisely defined primary structure. Polymerization with Grubbs' first generation catalyst followed by hydrogenation by diimide reduction or Wilkinson's catalyst leads to these precise structures, which have been characterized by 1H NMR, solution and solid state 13C NMR, solid state 19F NMR, IR, elemental analysis, TGA, DSC, AFM, and WAXD. The TGA data, coupled with elemental analysis, supply definitive proof of the structural composition through the observed thermal decomposition and release of exact masses of HX (X = F, Cl, or Br). In reference to analogous random copolymers, these precisely substituted polymers display sharper WAXD diffraction patterns, higher crystallinities and much narrower melting peaks, typical of a homopolymer-like crystallization. This crystallization behavior is supported by solid-state NMR based on the observed equivalence in the relative distribution of halogens between crystalline and noncrystalline regions. Extensive experimental data provide evidence for a crystalline state built on the basis of substitutional solid solutions. Lattice distortions caused by the accommodation of the substituent in the lattice render a change from orthorhombic to triclinic structures at a van der Waals atomic radius of the solute >1.6 Å. The observed melting temperatures and enthalpies of fusion decrease dramatically with increasing volume of the substituent and scale proportionally to the van der Waals atomic radius in the halogenated series.

Tailored Polymer Microstructures Prepared by Atom Transfer Radical Copolymerization of Styrene and N‐substituted Maleimides

“…[1][2][3][4][5][6][7][8][9] The core idea of this new trend is to progress beyond the current state of the art in polymer synthesis and, in particular, beyond the control of macromolecular architecture. For instance, one of the primary goals of the field of precision macromolecular chemistry is to control monomer sequence distribution in synthetic polymer chains.…”

“…For example, in stepgrowth polymerizations, precise periodic primary structures can be synthesized if appropriate monomers and linking chemistries are used. [5,16,17] In chain-growth polymerizations, fascinating regular microstructures such as alternating AB, [18,19] AAB, [18,20] or ABC [21] can be also obtained. Still, these interesting examples remain exceptions rather than the norm.…”

“…[5,13,15,20,[22][23][24][25][26][27][28][29][30][31][32] In particular, a few research groups investigated sequence-regulation in chaingrowths polymerizations. For instance, the innovative approaches recently reported by the research groups of Sawamoto, [26,29,32,33] Thomas, [10,27] and Kamigaito [20,30] have to be mentioned.…”

Crystallization of Polyethylenes Containing Chlorines: Precise vs Random Placement

“…15 Despite the lack of control in tacticity, the crystallization is driven by the accommodation of the substituent in a close-packing arrangement of chain segments in a symmetric lattice. 15 Each precision system, distinguished by the substitution type, is a unique polyolefin with crystalline properties characterized by the level of strain induced by the incorporation of the substituent in the lattice. A quantitative correlation was found between the halogen's van der Waals radius and the degree to which the orthorhombic lattice of the linear PE chain can tolerate atomic hydrogen substitution at a level of 5.3 mol %.…”

Synthesis of well-defined complex polymer architectures by iterative growth

“…Sequence-control has been reported to influence crystallization properties, polyolefinic macromolecules with precisely positioned branches indicated uniform crystal sizes and narrow transitions in comparison to their random counterparts 3,121 . The solubility of macromolecule in a specific solvent can be tuned by altering the monomersequence 122 .…”