Thermal Conductance of Poly(3-methylthiophene) Brushes.

A wide variety of recent work has demonstrated that the thermal conductivity of polymers can be improved dramatically through the alignment of polymer chains in the direction of heat transfer. Most of the polymeric samples exhibit high conductivity in either the axial direction of a fiber or in the in-plane direction of a thin film, while the most useful direction for thermal management is often the cross-plane direction of a film. Here we show poly(3-methylthiophene) brushes grafted from phosphonic acid monolayers using surface initiated polymerization can exhibit through-plane thermal conductivity greater than 2 W/(m K), a 6-fold increase compared to spin-coated poly(3-hexylthiophene) samples. The thickness of these films (10-40 nm) is somewhat less than that required in most applications, but the method demonstrates a route toward higher thermal conductivity in covalently grafted, aligned polymer films.

Degradable Polycaprolactone and Polylactide Homopolymer and Block Copolymer Brushes Prepared by Surface-Initiated Polymerization with Triazabicyclodecene and Zirconium Catalysts.

Surface-initiated ring-opening polymerization (SI-ROP) of polycaprolactone (PCL) and polylactide (PLA) polymer brushes with controlled degradation rates were prepared on oxide substrates. PCL brushes were polymerized from hydroxyl-terminated monolayers utilizing triazabicyclodecene (TBD) as the polymerization catalyst. A consistent brush thickness of 40 nm could be achieved with a reproducible unique crystalline morphology. The organocatalyzed PCL brushes were chain extended using lactide in the presence of zirconium n-butoxide to successfully grow PCL/PLA block copolymer (PCL-b-PLA) brushes with a final thickness of 55 nm. The degradation properties of "grafted from" PCL brush and the PCL-b-PLA brush were compared to "grafted to" PCL brushes, and we observed that the brush density plays a major role in degradation kinetics. Solutions of methanol/water at pH 14 were used to better solvate the brushes and increase the kinetics of degradation. This framework enables a control of degradation that allows for the precise removal of these coatings.

Rapid electrochemical reduction of Ni(II) generates reactive monolayers for conjugated polymer brushes in one step.

This article reports the development of a robust, one-step electrochemical technique to generate surface-bound conjugated polymers. The electrochemical reduction of arene diazonium salts at the surface of a gold electrode is used to generate tethered bromobenzene monolayers quickly. The oxidative addition of reactive Ni(0) across the aryl halide bond is achieved in situ through a concerted electrochemical reduction of Ni(dppp)Cl2. This technique limits the diffusion of Ni(0) species away from the surface and overcomes the need for solution deposition techniques which often require multiple steps that result in a loss of surface coverage. With this electrochemical technique, the formation of the reactive monolayer resulted in a surface coverage of 1.29 × 10(14) molecules/cm(2), which is a 6-fold increase over previously reported results using solution deposition techniques.