Charge transport in amorphous organic semiconductors is governed by carriers hopping between localized states with small spin diffusion length. Furthermore, the interfacial resistance of organic spin valves (OSVs) is poorly controlled resulting in controversial reports of the magnetoresistance (MR) response. Here, surface‐initiated Kumada transfer polycondensation is used to covalently graft π‐conjugated poly(3‐methylthiophene) brushes from the La0.67Sr0.33MnO3 (LSMO) bottom electrode. The covalent attachment along with the brush morphology allows control over the LSMO/brush interfacial resistance and large spacer mobility. Remarkably, with 15 nm brush spacer layer, an optimum MR effect of 70% at cryogenic temperatures and a MR of 2.7% at 280 K are observed. The temperature dependence of the MR is nearly an order of magnitude weaker than that found in control OSVs made from spin‐coated poly(3‐hexylthiophene). Using a variety of different brush layer thicknesses, the thickness‐dependent MR at 20 K is investigated. A spin diffusion length of 17 nm at −5 mV junction voltage rapidly increased to 48.4 nm at −260 mV.

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.

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.

Summary: Surface-initiated Kumada-catalyst transfer polycondensation (SI-KCTP) has become the preferred method for fabricating surface-bound conjugated polymer thin films. Here, the chain-growth character of SI-KCTP is exploited to allow for re-initiation of surface-bound films. Additionally, surface enhanced Raman spectroscopy (SERS) is shown to be a powerful tool in the analysis of surface-bound intermediates.