The Preparation And Surface Properties Of Polybenzoxazines Anti-adhesive Materials For Nanoimprint Lithography

Nanoimprint lithography (NIL) is a nonconventional lithographic technique for high-throughput patterning of polymer nanostructures at great precision and low costs. One of the most important problems usually encountered with NIL is the tendency for the resist polymer to adhere to the mold surface during the demolding process. The solution to this problem is to apply a low surface free energy coating (anti-adhesive materials) to the hard mould to reduce its surface energy. However, the anti-adhesive agent now commercially available can not fully meets the requirements for the development of NIL. Although the release agents can reduce the attachment of the resist polymer, there still exist some issues such as its expensive price and poor stability. It is very necessary to develop new low-surface-free-energy materials with high anti-adhesion properties for nanoimprint lithography. Therefore, in our study, polybenzoxazine-based low-surface-free-energy anti-adhesive material was prepared and studied. The kinetic curing process was investigated to explain the relationship between the curing degree and the surface free energy of polybenzoxazine. The effect of N-substituent groups on the surface free energy of polybenzoxazine was also investigated to supply experimental and theoretical basis guiding for developing novel low-surface-free-energy materials. The novel fluorinated silane-functional benzoxazine monomer was designed and synthesized. Research results are as follows:Firstly, the film formation property of B-m and B-a benzoxazine monomer and polymer was considered. The effect of curing temperature and curing time on the surface free energy of the polybenzoxazines were investigated. The results indicate that both the monomers and polymers display well film formation property. The lowest surface free energy of the PB-m and PB-a polybenzoxazine is 16.0 mJ/m2 and 16.7 mJ/m2 which are even lower than that of Teflon (22.0 mJ/m2). The thermal stability of PB-a polybenzoxazine is better than that of PB-m polybenzoxazine.The 1%,5% and 10% weight loss temperatures for the PB-a polymer are 290℃,335℃and 356℃发respectively. The 1%,5% and 10% weight loss temperatures for the PB-m polymer are 265℃,279℃and 292℃, respectively.Secondly, the kinetic curing process is investigated to explain the relationship between the curing degree and the surface free energy of PB-a polybenzoxazine. The results show that curing degree of the polymer is larger, the surface free energy of the polymer is lower.The value for beginning curing temperature of the monomer is 149℃. The ring-opening percent conversion of the monomer is close to 100% and the polymer is completely cured when curing above 210℃. The Ea of the curing reaction is around 95.0 KJ/mol. The variation of the surface free energy for the polymer displays the similar tendency. The surface free energy of the polymer is lower when the curing temperature is higher. The lowest surface free energy of the B-a polybenzoxazine is 16.7 mJ/m2 which is obtained by curing at 210℃. The surface free energies of the polymers are around 16.7 mJ/m2 even if we rise the curing temperature.Thirdly, the effect of N-substituent groups on the surface free energy of polybenzoxazine is investigated and the Doppler effect (red shift and blue shift) is used to explain the transition mechanism for the intramolecular and intermolecular hydrogen bonding during the curing for the polybenzoxazines. The results show that the surface free energy of the polybenzoxazine will be lower if the chain length of N-substituent group is longer. The lowest surface free energies of PB-m, PB-e, PB-b and PB-TMOS polybenzoxazines are 16.0 mJ/m2,15.8 mJ/m2, 15.1 mJ/m2 and 14.6 mJ/m2 respectively. The transition degree from the intramolecular hydrogen bonding to intermolecular hydrogen bonding is smaller according to the increase of the chain length. The siloxane group in B-TMOS can not only further lower the surface free energy of the polymer (14.6 mJ/m2) but also keep the stability of the surface free energy in a longer time.Finally, a novel fluorinated silane-functional benzoxazine monomer (TFP-TMOS) is designed and synthesized which not only possess oxazine structure but also have groups which can bond to the mold. As a result, the novel benzoxazine material will possess low surface free energy and high adhesive force with the mold at the same time. The effect of immersion condition to the film formation is investigated and the chemical bonds formation process on the surface of the substrate is investigated. The effect of curing temperature and curing time on the surface free energy of the polybenzoxazines is also investigated. The results indicate that Si-O-Si linkage is produced between the TFP-TMOS benzoxazine molecules and the substrate. The lowest surface free energies of the polybenzoxazines cured at different temperature are 15.6 mJ/m2(160℃,4 h),15.0 mJ/m2(190℃,1 h),15.3 mJ/m2 (220℃,15 min),15.5 mJ/m2 (240℃,5 min), respectively. The polybenzoxazine also possesses well thermal stability and the surface free energy of the polymer can keep stability below 200℃. The novel polybenzoxazine material is the most potential anti-adhesive materials applied in hot-embossing nanoimprint lithography.