A Fluorinated Thermocrosslinkable Organosiloxane: A New Low-k Material at High Frequency with Low Water Uptake

Bio-based Low-k Polymers at High Frequency Derived from Anethole: Synthesis and the Relationship between the Structures and the Properties

Bio-based polymers have been widely investigated as sustainable low dielectric (low-k) materials in past decades. Nevertheless, a few of the polymers with excellent comprehensive properties have been achieved to satisfy the requirements of high-frequency communication application. In this paper, two fluorinated monomers (BCB-F and 2BCB-F) have been designed and successfully prepared from biomass anethole. The thermal-cross-linkable benzocyclobutene and polyfluorobenzene groups were introduced in order to obtain low-k polymers with good comprehensive properties. A control monomer C1 was prepared from the estragole, the isomer of anethole, to study intensively the effect of structures on properties. Among the thermally cured polymers, cured BCB-F with higher fluoride content shows a comparable dielectric constant (Dk) of 2.62 and lower dielectric loss (Df) of 1.31 × 10-3 at a frequency of 10 GHz, as well as better hydrophobic properties with a water uptake of 0.18%. Such good hydrophobic properties enable it to maintain the good dielectric properties even after being soaked in boiling water for 96 h. Cured 2BCB-F with bifunctional benzocyclobutene groups displays excellent heat resistance with a high glass transition temperature (Tg) of 408 °C and a low coefficient of thermal expansion (CTE) of 52 ppm/°C in the temperature range 30-300 °C. Cured 2BCB-F also shows good dielectric properties with a Dk of 2.61 and a Df of 2.60 × 10-3 at a frequency of 10 GHz. The good comprehensive properties reveal that the anethole-based polymers are suitable candidates as matrix or encapsulation resins for application in electronics and microelectric fields.

Comb Polybutadiene with Long Polystyrene Side Chains: A Solution for Tunable Flowability and Enhancing Dielectric Properties in High-Frequency Printed Board Adhesive Films

Liquid high-vinyl polybutadiene (PB) possessed excellent dielectric properties, rendering them suitable candidates for adhesive films of high-frequency printed boards. However, their inherent low molecular weights resulted in chain slippage and overflow during processing, thereby diminishing the performance of the adhesive films. To address this challenge, we synthesized comb PB with long polystyrene side chains via reversible addition-fragmentation chain transfer (RAFT) polymerization, effectively immobilizing the PB backbone and restricting relative chain slippage. Controlling the length and number of "comb teeth" (styrene side chains) efficiently regulated the flowability of comb PB, achieving distinct flow states. Simultaneously, molecular dynamics simulations revealed that the elongated and inflexible polystyrene side chains of comb PB could create minuscule cavities, which impeded close packing of molecules and led to low dielectric constants (2.39/2.01, 1 MHz/10 GHz) and ultralow dielectric losses (0.0071/0.0016, 1 MHz/10 GHz). Furthermore, a series of printed circuit boards were fabricated using a comb PB adhesive film, and the signal loss was significantly reduced to 48.8% (19 GHz) in comparison with a commercial epoxy adhesive. This study demonstrated the potential of comb PB with polystyrene side chains to achieve desirable flow and dielectric properties by introducing tangles, large volume potential resistance, and microporosity compared with block structures.

Tris(pentafluorophenyl)borane-catalyzed Hydride Transfer Reactions in Polysiloxane Chemistry-Piers-Rubinsztajn Reaction and Related Processes

Tris(pentafluorophenyl)borane (TPFPB) is a unique Lewis acid that catalyzes the condensation between hydrosilanes (Si-H) and alkoxysilanes (Si-OR), leading to the formation of siloxane bonds (Si-OSi) with the release of hydrocarbon (R-H) as a byproduct-the so-called Piers-Rubinsztajn reaction. The analogous reactions of hydrosilanes with silanols (Si-OH), alcohols (R-OH), ethers (R-OR') or water in the presence of TPFPB leads to the formation of a siloxane bond, alkoxysilane (Si-OR or Si-OR') or silanol (Si-OH), respectively. The above processes, often referred to as Piers-Rubinsztajn reactions, provide new synthetic tools for the controlled synthesis of siloxane materials under mild conditions with high yields. The common feature of these reactions is the TPFPB-mediated hydride transfer from silicon to carbon or hydrogen. This review presents a summary of 20 years of research efforts related to this field, with a focus on new synthetic methodologies leading to numerous previously difficult to synthesize well-defined siloxane oligomers, polymers and copolymers of a complex structure and potential applications of these new materials. In addition, the mechanistic aspects of the recently discovered reactions involving hydride transfer from silicon to silicon are discussed in more detail.

The ultimate Lewis acid catalyst: using tris(pentafluorophenyl) borane to create bespoke siloxane architectures

The breadth of utility of a commercially available and stable strong Lewis acid catalyst, tris(pentafluorophenyl)borane, has been explored, highlighting its use towards a wide range of unique siloxane products and their corresponding applications. This article focuses on the variety of different outcomes that this impressive borane offers in controlled and selective manners by the variation of reaction conditions, precursor functionalities, reagent or catalyst loading, and the mechanistic considerations that contribute. With a predominant focus on the Piers-Rubinsztajn reaction and its modifications, tris(pentaflurophenyl)borane's utility is highlighted in the synthesis of linear, cyclic and macrocyclic siloxanes, aryl-/alkoxysiloxanes, and other bespoke products. The significance of the catalytic transformation within the field of siloxane chemistry is discussed alongside some of the challenges that arise from using the borane catalyst.

Thermo-curable and photo-patternable polysiloxanes and polycarbosiloxanes by a facile Piers–Rubinsztajn polycondensation and post-modification

A series of BCB-functionalized organosilicon materials were prepared by a facile Piers–Rubinsztajn polycondensation and Heck coupling post-modification method, rendering a simple and efficient option for advanced packaging dielectric materials.

Low dielectric resins derived from hyperbranched carbosilane oligmers functionalized by benzocyclobutene groups

Polycarbosilanes have been considered as potential materials used in electronic packaging and circuit boards owing to their excellent low-dielectric performance. In this work, we prepared new hyperbranched carbosilane oligomers (HCBOs) which were functionalized by benzocyclobutene (BCB) groups. HCBOs can be thermally cured to produce transparent (HCBRs) with low dielectric constant and high thermostability.

All-carbocycle hydrocarbon thermosets with high thermal stability and robust mechanical strength for low-k interlayer dielectrics

Two kinds of hydrocarbon precursors were synthesized and cured at elevated temperatures to give cross-linked all-aliphatic/aromatic-ring polymers with a low dielectric constant for next-generation interlayer dielectrics.