Synthesis and crystallization of precision ADMET polyolefins containing halogens

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 H-1 NMR, solution and solid state C-13 NMR, solid state F-19 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 angstrom. 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.