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

Synthesis and crystal structure of 2,9-di-amino-5,6,11,12-tetra-hydro-dibenzo[a,e]cyclo-octene

The cis- form of di-amino-dibenzo-cyclo-octane (DADBCO, C16H18N2) is of inter-est as a negative coefficient of thermal expansion (CTE) material. The crystal structure was determined through single-crystal X-ray diffraction at 100 K and is presented herein.

Relaxation Model of the Relations between the Elastic Modulus and Thermal Expansivity of Thermosetting Polymers and FRPs

This research was completed in the development of studies devoted to relations between the elastic modulus (MoE) and thermal expansivity (CTe) of different materials. This study, based on experimental data, confirmed the models of the relations between MoE and CTe under normal and heating temperatures for thermosetting epoxy polymers and glass-fiber FRPs in two variants (unfilled and filled by mineral additives), after the usual glassing and prolonged thermal conditioning (thermo-relaxation). The experiment was based on dilatometric and elastic deformation testing. Two models of MoE/CTe were tested: Barker's model and our authors relaxation model (MoE = f(CTe)), which is based on previous modelling of the non-linearity of the physical properties of polymers' supramolecular structures. The result show that the models' constants depend on composition; Barker's model is applicable only to polymers with satisfying agreement degrees in the range 10-20%; our model is applicable to polymers and FRPs with satisfying agreement degrees in the range of 6-18%.

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

The rapid development of the 5G communication technology requires the improvement of the thermal stability and dielectric performance of high-frequency copper clad laminates (CCL). A cyclic olefin copolymer (COC) resin was added to the original 1,2-polybutadienes (PB)/styrene ethylene butylene styrene (SEBS) binary resin system to construct a PB/SEBS/COC ternary polyolefin system with optimized dielectric properties, mechanical properties, and water absorption. Glass fiber cloths (GFCs) and SiO₂ were used to fill the resin matrix so to reduce the thermal expansion coefficient (CTE) and enhance the mechanical strength of the composites. It was found that the CTE of polyolefin/GFCs/SiO₂ composite laminates decreased with the increase of SiO₂ loading at first, which was attributed to the strong interfacial interaction restricting the segmental motion of polymer chains between filler and matrix. It was obvious that the addition of COC and SiO₂ had an effect on the porosity, as shown in the SEM graph, which influenced the dielectric loss (D_f) of the composites directly. When the weight of SiO₂ accounted for 40% of the total mass of the composites, the laminates exhibited the best comprehensive performance. Their CTE and D_f were reduced by 63.3% and 22.0%, respectively, and their bending strength increased by 2136.1% compared with that of the substrates without COC and SiO₂. These substrates have a great application prospect in the field of hydrocarbon resin-based CCL.

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

Heat dissipation has become a key problem for highly integrated and miniaturized electronic components. High thermal conductivity, good flowability and low coefficient of linear thermal expansion (CLTE) are indispensable performance parameters in the field of electronic potting composite materials. In this study, spherical alumina (Al₂O₃) was surface modified by γ-(2,3-epoxypropoxy) propyltrimethoxy silane (KH560) and γ-aminopropyltriethoxy silane (KH550) and labelled as Al₂O₃-epoxy and Al₂O₃–NH₂, respectively. Al₂O₃-epoxy and Al₂O₃–NH₂ powders were equally filled in vinyl silicone oil to prepare a high Al₂O₃ loading (89 wt%) precursor of silicone potting adhesive. The viscosity of the precursor rapidly decreased with increasing reaction time of Al₂O₃-epoxy and Al₂O₃–NH₂ at 140 °C. The viscosity reduction mechanism may be due to the formation of some Al₂O₃ clusters by the reaction of Al₂O₃-epoxy with Al₂O₃–NH₂, which results in some vinyl silicone oil segments being held in the channel of particles through capillary phenomenon, leading to the friction among Al₂O₃ clusters decreasing considerably. Laser particle size analysis and scanning electron microscopy (SEM) results confirmed the existence of Al₂O₃ clusters. Energy dispersive spectroscopy (EDS) and dynamic viscoelasticity experiments revealed that some segments of vinyl silicone oils were held by Al₂O₃ clusters. When Al₂O₃-epoxy and Al₂O₃–NH₂ reacted for 4 h, the thermal conductivity, CLTE and volume electrical resistivity of the silicone potting adhesive reached 2.73 W m⁻¹ k⁻¹, 75.8 ppm/°C and 4.6 × 10¹³ Ω cm, respectively. A new strategy for preparing electronic potting materials with high thermal conductivity, good flowability and low CLTE is presented.

Surface-modified Al₂O₃-epoxy reacts with Al₂O₃–NH₂ to form clusters that reduce the viscosity of electronic potting composites.