Provided is a mixture which can be subjected to a Diels-Alder reaction, comprising polymer (I) and polymer (II), wherein the structures of the polymer (I) and the polymer (II) are as shown in (I), wherein x1, y1, x2, y2, z1 and z2 are percentage molar contents; said x1 is >0, x2 is >0, y1 is >0, y2 is >0, z1 is ≥0, and z2 is ≥0; x1+y1+z1=1, and x2+y2+z2=1; Ar1, Ar2, Ar2-1, Ar3, Ar4 and Ar4-1 are each independently selected from: an aryl, or heteroaryl group containing 5-40 ring atoms; R1 and R2 are each independently a linking group; D is a conjugated diene functional group, and A is a dienophilic functional group; and n1 is greater than 0, and n2 is greater than 0. The mixture for a Diels-Alder reaction has a very good optical performance.