High-Performance Photocurable Resins Derived from Small-Molecule Naphthalene-Type Epoxides: Enabled by Biphenyl Main and Side-Chain Editing

With the booming of the electronics industry, solder resist (SR) inks used in printed circuit boards (PCBs) face increasingly stringent performance requirements, including storage modulus, heat resistance, dielectric properties, and alkaline developability, posing more challenges for the rational design of molecular structures. Herein, through the reaction of biphenyldicarboxylic acid (BPDA) with naphthalene-type epoxy (NDE), a series of epoxy resins bearing biphenyl structures in the main chain were synthesized, while 4-aminobiphenyl (ABP) was introduced to obtain epoxy resins with biphenyl structures in the side chain. Subsequently, main-chain (NM x AT) and side-chain (NS x AT) photocurable resins were prepared through sequential reactions with acrylic acid and tetrahydrophthalic anhydride. The effect of the introduction amount of biphenyl on the properties of the resin and its cured film was systematically investigated. Meanwhile, detailed comparisons were conducted to examine the property differences between biphenyl structures in the main chain and side chains, respectively. The contention that large spatial structures can effectively increase molecular free volume ratio was verified by using molecular dynamics simulations and a molecular model of a double-bonded cross-linked network. As a conclusion, chain extension needs to be controlled at a low molecular weight (≈1100 g mol -1 ) to inhibit the chain movement, thereby effectively improving the modulus of the resin. Additionally, large spatial structures mitigate the decrease of heat resistance caused by chain extension and effectively lower the dielectric constant. Ultimately, the preferred photocurable resins (NM 10 AT) were developed as SR inks for PCB applications, providing a strategy to enhance the performance of photocurable resins and constructing molecular models of double-bonded crosslinked networks.