Hybrid Polymerization of Ring-Opening Metathesis and Cross-Metathesis for Polyolefins with Tunable Architectures

Low-Loss Dielectric Ink for Printed Radio Frequency and Microwave Devices

Direct write printing is restricted by the lack of dielectric materials that can be printed with high resolution and offer dissipation factors at radio frequency (RF) within the range of commercial RF laminates. Herein, we outline the development of dielectric materials with dielectric loss below 0.006 in X and Ku frequency bands (8.2-18 GHz), the range required for radio frequency and microwave applications. The described materials were designed for printability and processability, specifically a prolonged viscosity below 1000 cps and a robust cure procedure, which requires minimal heat treatment. In the first stage of this work, nonpolar ring-opening metathesis polymerization (ROMP) is demonstrated at room temperature in an open-air environment with a low-viscosity monomer, 5-vinyl-2-norbornene, using the second-generation Grubbs catalyst (G-II). Differential scanning calorimetry (DSC) was used to study how the catalyst activity is increased with heating at various stages in the reaction, which is then used as a strategy to cure the material after printing. The resulting cured poly(5-vinyl-2-norbornene) material is then characterized for dielectric and mechanical performance before and after a secondary heat treatment, which mimics processing procedures to incorporate subsequent printed conductor layers for multilayer applications. After the secondary heat treatment, the material exhibits a 55.0% reduction in the coefficient of thermal expansion (CTE), an increase in glass-transition temperature (T_g) from 32.4 to 46.1 °C, and an increased 25 °C storage modulus from 428 to 1031 MPa while demonstrating a minimal change in dielectric loss. Lastly, samples of the developed dielectric material are printed with silver overtop to demonstrate how the material can be effectively incorporated into fully printed, multilayer RF applications.

Synthesis and Micellization of Bottlebrush Poloxamers

Bottlebrush polymers are characterized by an expansive parameter space, including graft length and spacing along the backbone, and these features impact various structural and physical properties such as molecular diffusion and bulk viscosity. In this work, we report a synthetic strategy for making grafted block polymers with poly(propylene oxide) and poly(ethylene oxide) side chains, bottlebrush analogues of poloxamers. Combined anionic and sequential ring-opening metathesis polymerization yielded low dispersity polymers, at full conversion of the macromonomers, with control over graft length, graft end-groups, and overall molecular weight. A set of bottlebrush poloxamers (BBPs), with identical graft lengths and composition, was synthesized over a range of molecular weights. Dynamic light scattering and transmission electron microscopy were used to characterize micelle formation in aqueous buffer. The critical micelle concentration scales exponentially with overall molecular weight for both linear and bottlebrush poloxamers; however, the bottlebrush architecture shifts micelle formation to a much higher concentration at a comparable molecular weight. Consequently, BBPs can exist in solution as unimers at significantly higher molecular weights and concentrations than the linear analogues.

Synthesis of hyperbranched polyolefins and polyethylenesviaADMET of monomers bearing non-selective olefins

The synthesis of hyperbranched polyolefins and polyethylenesvianon-selective olefin metathesis of monomers with three identical terminal olefins was realized.