2.1.2. The Grafting-onto method
For the grafting-onto method, rod and coil blocks have been polymerized individually and then the two blocks having specific functional end groups were coupled together by further condensation reactions (Scheme 5). Aldehyde end-functionalized PPV was used as the quencher for the living chain end poly(styrene), poly(4-vinylpyridine), or poly(isoprene), to obtain rod–coil diblock copolymers [37], [38] and [39]. Similarly, Mullen and coworkers used the convergent anionic polymerization to produce PPP-b-PS copolymers ( Scheme 5(a)) [42]. Besides, poly(p-phenylenevinylene)-b-poly(methyl methacrylate) (PPV-b-PMMA) copolymers were synthesized using the Siegrist polycondensation and anionic polymerizations followed by the click reaction. Alkylene-terminated PPV and azido-terminated PMMA were synthesized separately, and then two functionalized polymers were underwent 1,3-cycloaddition reaction to obtain copolymers ( Scheme 5(b)) [40]. Yu and coworkers prepared oligo(phenylene vinylene)-b-poly(ethylene oxide) or -poly(propylene oxide) (OPV-b-PEO or OPV-b-PPO) copolymers through an ester linkage between a carboxyl group of the rod end and a hydroxyl group of the coil end ( Scheme 5(c)) [82], [83] and [84]. Another successful example was presented by Mori et al., in which they successfully linked aldehyde-terminated OPV with an amino-terminated PEO by an azomethine linkage [41]. Mullen and coworkers also synthesized poly(p-phenylene)-b-PEO in a similar way [42]. In addition, they successfully prepared poly(p-phenyleneethynylene)-b-PEO [43] or polyfluorene-b-PEO (PF-b-PEO) [20] through the esterification of the rod block with the carboxyl acid end group and the hydroxyl-terminated coil block ( Scheme 5(c)).