Tuning Epoxy Thermomechanics via Thermal Isomerization: A Route to Negative Coefficient of Thermal Expansion Materials

Abstract

Fine control over the thermal expansion and contraction behavior of polymer materials is challenging. Most polymers have large coefficients of thermal expansion (CTEs), which preclude long performance lifetimes of composite materials. Herein, we report the design and synthesis of epoxy thermosets with low CTE values below their T g and large contraction behavior above T g by incorporating thermally contractile dibenzocyclooctane (DBCO) motifs within the thermoset network. This atypical thermomechanical behavior was rationalized in terms of a twist-boat to chair conformational equilibrium of the DBCO linkages. We anticipate these findings to be generally useful in the preparation of materials with designed CTE values.

Non-Linearity of Thermosetting Polymers’ and GRPs’ Thermal Expanding: Experimental Study and Modeling

“…The main characteristic results are presented in Table 3 . The following analysis of points on the curves specifies the polymers’ thermal expansion: The thermal expanding (TE) has non-linearity from normal to extreme temperature that probably accords to the glassing temperature of polymer Tg, and TE can be characterized by the coefficient of integral non-linear thermal expanding (CNTE) α nl ; After temperature breaking point, the TE achieves the extremum and linearity of expansion with further heating; and can be characterized by coefficient of linear TE (CLTE) α tg ; According to DMA results, the Tg is equal to temperature T nl , finishing the period of polymers’ thermal expanding non-linearity [ 22 ]; Prolonged thermal relaxation (at aging) of epoxy and phenolic glassed polymers (GP) results in some reduction in epoxy CNTE and an increase the phenolic and epoxy-phenolic CNTE, thus increasing all polymers’ CLTE; CNTE changing after thermal relaxation is conditional, because CNTE depends on extreme non-linear relative expansion ε nl-max that accords to temperature of GP: thermal relaxation causes an increase the ε nl-max containing epoxy resin, and a reduction in the ε nl-max containing phenolic resin. …”

“…According to DMA results, the Tg is equal to temperature T nl , finishing the period of polymers’ thermal expanding non-linearity [ 22 ];…”

“…In most cases, it was related with the polymer molecules conformation mechanisms, 3D molecule replacement and the distribution. This alteration causes the change and non-linearity of CTE [ 21 , 22 , 23 ].…”

Hydrocarbon Resin-Based Composites with Low Thermal Expansion Coefficient and Dielectric Loss for High-Frequency Copper Clad Laminates

“…Conversely, materials with CTE close to that of copper foil have excellent dimensional stability. In previous works, three main ways to reduce the CTE of substrate materials were proposed: firstly, the addition of an inorganic filler with low (such as SiO 2, carbon nanotubes) [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ] or negative (such as Hafnium pyrovanadate) CTE [ 28 , 29 ] into the organic matrix; secondly, the addition of a low-CTE organic monomer (such as an alkoxysilyl-functionalized resin) or a negative-CTE organic monomer (such as dibenzocyclooctane) or the use of a resin with a low CTE (such as cyanate ester resin) [ 30 , 31 , 32 , 33 ]; finally, the interpenetration of the network structure by combining a ceramic skeleton with organic matter (such as Al 2 W 3 O 12 ) [ 34 , 35 ]. However, the CTE is not the only factor that should be considered, and other key indicators such as D k and D f should be taken into account either.…”

A study on the viscosity reduction mechanism of high-filled silicone potting adhesive by the formation of Al2O3 clusters

“…Epoxy resin potting adhesive has high hardness, good adhesion, and low CLTE (50-70 ppm/ C), 2 while the repairability of the device is poor. 3,4 Polyurethane potting adhesive has good elasticity and anti-vibration performance, but its thermal resistance is poor (usually lower than 150 C). 5 Silicone has good elasticity, wide working temperature range of minus 60 to 200 C, and excellent repairability of the device.…”