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Low dielectric constant (k) polymers with excellent comprehensive properties are useful materials in the microelectronics industry as matrix resins or encapsulation layers. With the inherent low polarization, high reactivity, good processability, and low cost, poly(dicyclopentadiene) (PDCPD) has received considerable attention as low‐k materials. However, its practical application is limited by the relatively high thermal expansion and k value. Herein, three norbornene‐functionalized polyhedral oligomeric silsesquioxanes (POSSs) with T8, T10, and T12 polyhedral cores are synthesized and employed for enhancing the dielectric and comprehensive properties of PDCPD via reactive blending. The results show that these POSSs have good compatibility with PDCPD matrix and nano‐dispersed POSSs particles could be obtained. As a result, the materials' properties can be largely enhanced by varying the POSS content and POSS size. Especially, PT12N12‐40 (40 wt% of T12N12) shows the lowest k value (2.1) and coefficient of thermal expansion (63.4 ppm°C−1), highest glass transition temperature (202.5 °C), yield strength (78.0 MPa), and elastic modulus (2.36 GPa), along with excellent hydrophobicity. This study highlights a useful strategy to fabricate high‐performance low‐k polymer nanocomposites by using larger POSS and reactive blending, which provides useful materials for the future microelectronic industry and high frequency communication. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two novel POSS bearing norbornene groups (i.e., T 7 N 3 and T 8 N 4) are synthesized. • The addition of T 7 N 3 and T 8 N 4 significantly reduces the k value of PDCPD. • The low- k materials can be rapidly prepared through with low energy consumption approach. Low dielectric constant (low -k, k < 2.5) thermoset polymers play a crucial role in high-frequency communication technology and the microelectronic industry. However, existing low- k materials often suffer from time- and energy-consuming preparation procedures and have k values greater than 2.5. Herein, we present the frontal ring opening metathesis polymerization (FROMP) of dicyclopentadiene and phenyl-functionalized POSS bearing three and four norbornene groups (i.e., T 7 N 3 and T 8 N 4), enabling the rapid formation of high-performance low- k nanocomposites through a low energy consumption approach. The results reveal that T 7 N 3 and T 8 N 4 exhibit excellent compatibility with poly(dicyclopentadiene) (PDCPD) without adversely affecting the materials' FROMP behaviors. Consequently, by increasing IC-POSS content, both the dielectric and comprehensive properties of PDCPD can be significantly enhanced while the influence of IC-POSS type remains limited. In particular, both PT 7 -40 (40 wt% of T 7 N 3 , k = 2.1) and PT 8 -40 (40 wt% of T 8 N 4 , k = 2.12) demonstrate the lowest k values; moreover, PT 8 -40 exhibits the highest dimensional stability (with a coefficient of thermal expansion of 79.3 ppm oC−1), glass transition temperature (188 °C), elastic modulus (2.32 GPa), yield strength (70.4 MPa), and hydrophobicity among all samples. By programming the front velocity, these materials can be processed into complex structures through a combination of FROMP and three-dimensional printing techniques. This work offers a facile and energy-efficient approach for preparing low- k materials with on-demand structures and properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • Larger POSS was introduced into PDCPD to develop low- k materials. • Uniform dispersion of POSS nanoparticles was achieved. • Both POSS size and POSS content can strongly affect the materials' properties. • T 12 V 12 based materials showed the lowest k value and best other properties. Low dielectric constant (low- k) polymer nanocomposites with good comprehensive properties are essential for microelectronics and wireless communication industry. Although extensive studies show that incorporation of polyhedral oligomeric silsesquioxane (POSS) is an effective strategy to realize this purpose, nearly all of them are based on T 8 POSS and the influence of larger POSSs (i.e., T 10 and T 12 POSS) on polymer's properties remains unclear. Herein three vinyl POSSs (T 8 V 8 , T 10 V 10 , and T 12 V 12) with increased sizes were introduced into poly(dicyclopentadiene) (PDCPD) for preparation of high-performance low- k nanocomposites. Because these three POSSs are soluble in dicyclopentadiene monomer, a series of nanocomposites with molecular scale POSS dispersion were achieved after thermo-crosslinking. The results show that the k value of PDCPD can be decreased not only by increasing the content of these three POSSs but also by altering the POSS size. Consequently, the k value of PDCPD at 1 kHz was found to be reduced from 2.54 to 2.10 by adding high content of larger POSS (i.e., 7 wt% of T 12 V 12) without damaging its inherent low dielectric loss. This result highlights the rule of POSS size and POSS content on the dielectric properties and could be used to predicate ultralow- k polymer nanocomposites by extrapolating to larger POSS and higher POSS content. Meanwhile, the comprehensive properties of PDCPD such as glass transition temperature, dimensional stability, mechanical properties, and hydrophobicity, are able to be enhanced by altering the POSS size and increasing the POSS content, making these resulting nanocomposites become useful materials for future microelectronic industry. [ABSTRACT FROM AUTHOR]