| Adhesive plays a very important role in the industrial products and daily life.Compared with the thermoplastic adhesive,thermosetting adhesive has excellent mechanical properties and heat resistance.However,due to the traditional thermosetting adhesive form crosslinked network after curing,it’s difficult to achieve de-bonding and reuse.This will cause some expensive base materials to be difficult to recycle and increase greatly the cost.At the same time,the non-degradability of the three-dimensional cross-linked network will also cause serious waste and environmental pollution.Reversible thermosetting adhesive,mainly including heat-induced reversible adhesive and photo-induced reversible adhesive,which can solve the above problems caused permanent crosslinking network,is able to respond to the external stimulus.Compared to the heat-induced reversible adhesive,photo-induced reversible adhesive has some feature,including directional reaction,long distance induced reaction,mild reaction conditions and fast curing rate,etc.In this paper,anthracene group[4+4]reversible cycloaddition was selected to construct reversible crosslinking networks which were applied to photo-induced reversible adhesive.The main research contents and obtained results of this paper are as follows:First,a reversible three-dimensional cross-linking network of epoxy resin containing anthracene group was designed and synthesized,and its photoinduced reversible bonding behaviors were investigated.In this paper,Using 9anthraxyl methanol(AM)as raw material,after epoxidation and epoxy-amine ring-opening reaction,tetra-anthraxene functional pre-polymers(preAER/D230,pre-AER/D400 and pre-AER/D2000)was obtained.Among them,pre-AER/D2000 exhibits a solid-liquid phase transition at room temperature after being subjected to 365 nm and 254 nm UV light.DSC proved that the film(AER/D2000)has a low Tg(-35℃),so it has sufficient chain movement ability to complete the curing and de-crosslinking reaction.After the 254 nm UVinduced de-polymerization reaction,the film de-polymerizes transform from the crosslinked network into a tetra-functional pre-polymer,namely re-liquefaction.The ability of de-polymerization and repeated crosslinking were demonstrated by UV-vis absorption spectra.Taking quartz glass as the bonding substrate,the lap shear test shows that the bonding strength reaches about 2.4 MPa,and the recovery rate of the bonding strength reaches 92%after re-bonding.Secondly,to ensure that non-heated light curing reaction has a high degree,the lower Tg which needs lower than the room temperature is necessary.But it usually leads to lower bonding strength and creepocity.In order to solve this contradiction,this paper designs a crystallizable polyurethane molecular structure containing anthracene pendent side groups to realize the unification of low Tg and high mechanical performance.The ε-polycaprolactone diol(PCL20H,Mn≈2000)was reacted with the 4,4’-dicyclohexyl methane diisocyanate(HMDI)for polyurethane pre-polymer(PCL/HMDI).Then,the epoxide of 9anthracyl methanol(AER)and 2-mercaptoethanol were subjected to the epoxymercaptoethanol ring-opening reaction to obtain the diol containing anthracyl side chain(AERMT),which was mixed with 1,4-butanediol(BDO)as the chain extender of PCL/HMDI.Linear polyurethanes(APU-1/APU-0.8/APU0.5/APU-0.2/APU-0)containing different number of anthracene side groups were prepared by adjusting the ratio between BDO and AERMT.The crosslinked amorphous chain segments ensure the curing reaction and reverse reaction due to its low Tg,while the crystalline segments connected by BDO can improve the mechanical property of the gule film with low Tg.The result of XRD showed that these products were amorphous and crystallized.These curing.reaction processes were characterized by UV-vis absorption spectroscopy.The time required for crystallization after complete melting is significantly longer than the curing reaction time,which is fully proved by DSC test,which makes the product have sufficient curing time.Using quartz glass as the bonding substrate,the lap shear test shows that the bonding strength is as high as 7.48 MPa. |
