Low Dielectric Cross-linked Styrene Resins Based On Coordination Bonds

Cross-linked polystyrene resin is one of the most excellent low-k resins.However,the crosslinked polystyrene resin possessed poor mechanical properties.Meanwhile,the crosslinked polystyrene resin cannot be degraded and recycled because of its covalent crosslinked network structure,thus causing environmental pollution and waste of resources.In contrast to covalent bond networks,reversible dynamic bond cross-linking networks can build reprocessable cross-linked polymers via the reversibility of dynamic bond,which provides a new idea for the recycling of low-dielectric resins.At the same time,reversible dynamic bonds can also be used as sacrificial bonds to improve the mechanical properties of crosslinked polymers.Metal-coordination bonds possess reversibility,have high bond energy and can be uncrosslinked/recrosslinke in mild conditions,so it has an advantage to prepare low dielectric resins via metal-coordination.Based on the above ideas,metal-coordination cross-linked polystyrene resins were prepared in this paper.On the one hand,the construction methods and properties of reprocessable resins are studied in detail.On the other hand,effect of metal coordination bonds on covalent crosslinking system were investigated.This paper provides a reference for preparation of reprocessable and high-performance low-dielectric resins via metal coordination bond.In this paper,low dielectric styrene resins were prepared by using styrene（St）and 4-vinylpyridine（VP）as monomers and benzoyl peroxide（BPO）as initiator,via the bulk polymerization.Then,metal-crosslinked low-dielectric styrene resin was prepared via the Zn²⁺coordination interactions with the ligand of styrene resin.The research show that the crosslinked polymer has excellent properties.This crosslingked polymer possessed outstanding thermal stability（T_d=387℃,T_g=117℃）and mechanical properties（the tensile strength up to 40MPa）,and excellent dielectric properties（2.73 at 10MHz）.More significantly,the crosslingked polymer was recycle via conveniently dissolving in THF and then hot-pressed.The cross-linking polymer also exhibited good recyclability as it preserved the original mechanical strength（the tensile strength up to 30MPa）and low dielectric constant（2.94 at 10MHz）after third cycling.Furthermore,a series of cross-linked polystyrene resins with different metal ion coordination were prepared.The effects of different metal ions on their dielectric and mechanical properties were also compared.It was found that styrene resins with Cu and Ni centers（PSVP-Cu and PSVP-Ni）possess higher mechanical strength and lower dielectric constant as compared with that with Zn centers（PSVP-Zn）.The tensile strength of PSVP-Cu and PSVP-Ni are 23MPa and 28MPa.The dielectric constants of PSVP-Cu and PSVP-Ni are 2.60 and 2.69.In addition,it found that the interaction force between Ni²⁺and Cu²⁺with PSVP is stronger than that of Zn²⁺,which makes it more difficult to recyclability.After 3rd cycling,the cycling ability of PSVP-Cu and PSVP-Ni will be worse.The mechanical properties of PSVP-Cu and PSVP-Ni were restored to the previous 60%and 78%,respectively.In addition,PSVP-Cu and PSVP-Ni will be difficult to disassembly by tetrahydrofuran at room temperature.PSVP-Cu and PSVP-Ni can be quickly disassembled by pyridine with strong coordination ability.Finally,the influence of metal coordination bonds introduced into covalently cross-linked polystyrene as sacrificial bonds on the properties of the resin was explored.The copolymerization method of styrene（St）,4-vinylpyridine（VP）and divinylbenzene（DVB）was introduced.At the same time,2%Zn²⁺was introduced in situ in the polymerization system to prepare metal coordination and covalent double-crosslinking low-dielectric polystyrene resin.It shown that the metal coordination cross-linked low-dielectric polystyrene resins possessed good thermal stability（T_d=380℃）and tensile strength（the tensile strength up to 55MPa）.It shows that the introduction of metal coordination as sacrificial bonds can effectively enhance the mechanical properties of the resin.Meanwhile,with the increase of VP content,the dielectric constant of the crosslinked polystyrene resin gradually decreases.