Nanoporous Low Dielectric Cyclosiloxane Bearing Polysilsesquioxane Thin Films Templated by Poly(ε‐caprolactone)

Abstract

Summary: Dielectric cyclosiloxane bearing polysilsesquioxanes (CS‐PSSQs) were prepared by acid catalyzed polymerization using 2,4,6,8‐tetramethyl‐2,4,6,8‐tetra(trimethoxysilylethyl)cyclotetrasiloxane. The molecular weight, and content of the functional end‐groups of the CS‐PSSQs were found to be dependent on the process parameters, such as the molar ratio of water and catalyst to the OCH3 group of the silane monomer, the amount of solvent, and the poly(ε‐caprolactone) (PCL) content, etc. Based on these CS‐PSSQ prepolymers, nanoporous organic/inorganic hybrid thin films were fabricated by spin‐coating mixtures of these prepolymers with star‐shaped PCL on the silicon substrate, and subsequently heating them at 150 and 250 °C for 1 minute each and then at 420 °C for 1 hour. A dielectric constant as low as 2.28 was achieved for the nanoporous PCL/CS‐PSSQ (3:7 v/v) film, along with low moisture absorption in ambient and water conditions, primarily due to the presence of hydrophobic moieties such as ethylene and methyl groups of the polymer and nano‐sized hydrophobic pores inside the matrix, resulting in the film having stable dielectric properties. Moreover, the PCL/CS‐PSSQ (3:7 v/v) nanohybrid film revealed a nanoporous structure containing ca. 1.52 nm of average‐sized mesopores, as measured by the N2 adsorption method. The CS‐PSSQ‐only film showed high mechanical strengths having an elastic modulus and hardness of 6.64 and 0.88 GPa, respectively, for the 7 500 Å thick film and 2.41 and 0.38 GPa, respectively, for the PCL/CS‐PSSQ (3:7 v/v) film. In addition, the crack velocity of the CS‐PSSQ‐only film was found to be ca. 10−11 m · s−1 in ambient conditions and an aqueous environment, probably due to the enhanced hydrophobicity and mechanical toughness of the incorporated methyl group, siloxane unit and ethylene moieties in the polymer matrix. magnified image

Slick Synthetic Approach to Various Fluoroalkyl Silsesquioxanes—Assessment of their Dielectric Properties

“…Interestingly, the SQs-based materials, in most cases, exhibited lower dielectric constants than the host polymers, and what is more, the dielectric constants can be tuned by adjusting the content of SQs. In general, there is a tendency for the dielectric constant value to decrease with the increasing content of SQs [42,[48][49][50][51]. The fluorinated silsesquioxanes, mainly based on octasubstituted-T 8, but also DDSQs systems, are groups of compounds being building blocks of low-κ hybrid materials [42,44].…”

Thermally curable polymers consisting of alcohol-functionalized cyclotetrasiloxane and melamine derivatives for use as insulators in OTFTs

“…Cyclotetrasiloxane (CTS) derivative was used as the inorganic part and hexamethoxymethylmelamine (HMMM) as the organic cross-linking agent to yield thermally curable polymers at low temperatures. CTS is a well-known siloxane derivative with excellent thermal and electrical properties and low tendency to adsorb moisture [18,19]. In order to allow for cross-linking, CTS was functionalized with four propyl alcohol groups (CTS-OH), which were introduced by hydrosilylation reaction catalyzed by Pt(0).…”

Nanoporous Thin Films Based on Polylactide-Grafted Norbornene Copolymers

“…An established method consists of blending porogens (or pore-generating materials) with organosilicate materials that can then be applied as intermetallic dielectric (IMD) materials. − The miscibility of two components is the key factor that governs the size and dispersion of pores in the matrix. However, the main drawback of organosilicate-based materials is their brittleness, particularly for film thickness above 1 μm.…”