Harold W. Boone

Perfluorocyclobutane (PFCB) polyaryl ethers: versatile coatings materials

Abstract The cyclopolymerization of aromatic trifluorovinyl ether (TFVE) monomers offers a versatile route to a unique class of linear and network fluoropolymers containing the perfluorocyclobutyl (PFCB) linkage. Polymerization proceeds by a thermal — radical mediated — step-growth mechanism and provides well-defined polymers containing known fluoroolefin end groups. PFCB polymers combine the engineering thermoplastic nature of polyaryl ethers with fluorocarbon segments and exhibit excellent processability, optical transparency, high temperature performance, and low dielectric constants. An intermediate strategy utilizing Grignard and aryllithium reagents has been developed which offers access to a wide variety of hybrid materials amenable to coatings applications. Liquid crystalline examples have recently been achieved in addition to tailoring optical properties by co-polymerization.

Intra- and intermolecular NMR studies on the activation of arylcyclometallated hafnium pyridyl-amido olefin polymerization precatalysts.

Pyridyl-amido catalysts have emerged recently with great promise for olefin polymerization. Insights into the activation chemistry are presented in an initial attempt to understand the polymerization mechanisms of these important catalysts. The activation of C1-symmetric arylcyclometallated hafnium pyridyl-amido precatalysts, denoted Me2Hf{N(-),N,C(-)} (1, aryl = naphthyl; 2, aryl = phenyl), with both Lewis (B(C6F5)3 and [CPh3][B(C6F5)4]) and Brønsted ([HNR3][B(C6F5)4]) acids is investigated. Reactions of 1 with B(C6F5)3 lead to abstraction of a methyl group and formation of a single inner-sphere diastereoisomeric ion pair [MeHf{N(-),N,C(-)}][MeB(C6F5)3] (3). A 1:1 mixture of the two possible outer-sphere diastereoisomeric ion pairs [MeHf{N(-),N,C(-)}][B(C6F5)4] (4) is obtained when [CPh3][B(C6F5)4] is used. [HNR3][B(C6F5)4] selectively protonates the aryl arm of the tridentate ligand in both precatalysts 1 and 2. A remarkably stable [Me2Hf{N(-),N,C2}][B(C6F5)4] (5) outer-sphere ion pair is formed when the naphthyl substituent is present. The stability is attributed to a hafnium/eta(2)-naphthyl interaction and the release of an eclipsing H-H interaction between naphthyl and pyridine moieties, as evidenced through extensive NMR studies, X-ray single crystal investigation and DFT calculations. When the aryl substituent is phenyl, [Me2Hf{N(-),N,C2}][B(C6F5)4] (10) is originally obtained from protonation of 2, but this species rapidly undergoes remetalation, methane evolution, and amine coordination, giving a diastereomeric mixture of [MeHf{N(-),N,C(-)}NR3][B(C6F5)4] (11). This species transforms over time into the trianionic-ligated [Hf{N(-),C(-),N,C(-)}NR3][B(C6F5)4] (12) through activation of a C-H bond of an amido-isopropyl group. In contrast, ion pair 5 does not spontaneously undergo remetalation of the naphthyl moiety; it reacts with NMe2Ph leading to [MeHf{N(-),N}NMe2C6H4][B(C6F5)4] (7) through ortho-metalation of the aniline. Ion pair 7 successively undergoes a complex transformation ultimately leading to [Hf{N(-),C(-),N,C(-)}NMe2Ph][B(C6F5)4] (8), strictly analogous to 12. The reaction of 5 with aliphatic amines leads to the formation of a single diastereomeric ion pair [MeHf{N(-),N,C(-)}NR3][B(C6F5)4] (9). These differences in activation chemistry are manifested in the polymerization characteristics of these different precatalyst/cocatalyst combinations. Relatively long induction times are observed for propene polymerizations with the naphthyl precatalyst 1 activated with [HNMe3Ph][B(C6F5)4]. However, no induction time is present when 1 is activated with Lewis acids. Similarly, precatalyst 2 shows no induction period with either Lewis or Brønsted acids. Correlation of the solution behavior of these ion pairs and the polymerization characteristics of these various species provides a basis for an initial picture of the polymerization mechanism of these important catalyst systems.

Perfluorocyclobutane aromatic ether polymers. III. Synthesis and thermal stability of a thermoset polymer containing triphenylphosphine oxide

The preparation of a novel triaryl phosphine oxide thermoset polymer con- taining the perfluorocyclobutane linkage is described. The synthetic methodology in- volves the formation of a Grignard reagent from 4-bromotrifluorovinyloxybenzene and reaction with phosphorous trichloride to form the triaryl phosphine trifluorovinyl ether monomer. Oxidation of the phosphine monomer with hydrogen peroxide in ethanol provides quantitative conversion of the phosphine to the phosphine oxide. Analysis of the thermal decomposition of the resulting polymer in both nitrogen and air indicates improvement in thermal and thermal/oxidative stability with respect to the previously reported polymer prepared from 1,1,1-tris(4-trifluorovinyloxy)phenyl ethane. Differ- ences in thermal and thermal/oxidative performance still exist, indicating that oxida- tive processes contribute to the polymer decomposition in air. q 1998 John Wiley & Sons,