Gradient copolymer, its production and application thereof

A gradient copolymer comprising or consisting of n polymer components, wherein the n polymer components each independently represents an addition polymer (particularly a radical addition polymer) of a monomer of the formula (I),

• and/or a mixture thereof, or
• the n polymer components each independently comprises or consists essentially of one or more structural units represented by the formula (I-1),
• and the symbol n represents an integer within the closed interval [5, ∞], preferably an integer within the closed interval [8, ∞], preferably the upper limit of the integer represented by the symbol n is 20000, 10000, 5000, 1000, 500, 200, 100 or 50, and
• in the formula (I) or formula (I-1),
• the group R1 represents H or
• preferably H,
• the group R2 represents H or a C1-4 linear or branched alkyl, preferably H or methyl,
• the symbol a represents 0 or 1, preferably 1,
• the group R′ represents H or a group R3, preferably the group R3,
• the group R3 represents a C1-C30 linear or branched alkyl group, preferably a C6-C24 linear or branched alkyl group, more preferably a C6-C20 linear alkyl group, and
• where the average number of carbon atoms in side chain of the i-th polymer component as determined according to the nuclear magnetic resonance method is expressed as Xi, with the symbol i representing an arbitrary integer from 1 to n, the following relationship holds,
• X1<X2< . . . <Xn−1<Xn (II),
• and there is preferably a gradual increase from X1 to Xn, and more preferably a linear increase from X1 to Xn.