Block copolymer is a special type of copolymer that comprises two or more chemically distinct polymer blocks covalently linked together.This special structure endows the block copolymer a variety of unique properties unpossessed by the homopolymers.However,it is still a challenge to separate and characterize the block copolymers because they not only have molecular weight distribution of the overall chain but also have molecular weight distribution for the individual blocks.It has been reported that liquid chromatography at the critical condition(LCCC)is an effective method for the characterization of individual blocks in block copolymers.1 This method is based on the assumption that a block can be made chromatographically “invisible” at the critical condition of its corresponding homopolymer and then the retention of the block copolymer is dominated solely by the other block(i.e.the “visible” block)in the block copolymer.2-4 However,Chang and coworkers also observed some dependence of retention on “invisible” block length in the LCCC analysis of block copolymer.5-6 In the current study,we re-examined the validity of the LCCC technique for AB,BAB and ABA block copolymers by the lattice Monte Carlo simulation method with using random walk(RW)and self-avoiding walk chain(SAW)models.In our simulations,the A block is in the size-exclusion mode(chromatography “visible”),whereas the interaction between the B type monomer and the column surface are varied to identify the critical condition of B block in the block copolymer.The simulation results show that the B block has its own critical condition,which is different from the critical condition of B homopolymer,as shown as Figure 1a-1c.For the AB diblock copolymer(Figure 1a),it is clear that B blocks critical condition shifts to a weaker adsorptive point compared to the critical condition of B homopolymer.Similar deviation of B blocks critical condition from B homopolymers critical condition is also observed for the BAB triblock copolymer,as shown in Figure 1b.For the ABA triblock copolymer,however,the critical condition of B block shits to stronger adsorptive point compared to the critical condition of B homopolymer,as shown in Figure 1c.The current study further confirms the dependence of retention on the “invisible” block length in the LCCC characterization of block copolymer is a real phenomenon.