Living Polymerization via Anionic Initiation for the Synthesis of Well‐Defined PPV Materials

Abstract

The anionic polymerization of PPV via the sulfinyl precursor route is further investigated. When LHMDS is employed as the base to form the actively propagating quinodimethane system and THF as the solvent, anionic polymerizations can be observed. With the use of tert- butyl-substituted anionic initiators, specific functional groups can be built in the polymer chain and the chain length can be efficiently controlled, which is demonstrated here for the first time. With introduction of branched side chains on the aromatic core, soluble conjugated PPV material can be obtained with molecular weights in the range of 5000-16,000 g mol(-1).

Anionic PPV polymerization from the sulfinyl precursor route: Block copolymer formation from sequential addition of monomers

“…In our previous studies we demonstrated that a pure anionic PPV polymerization can be achieved [20,21]. As mentioned above, however, deviations from ideal polymerization were still observed before and doubts remained about the initiation efficiency of the employed initiator.…”

“…With such component 1 reasonable control over molecular weight was achieved via varying the concentration of initiator, even if some non-idealities remained. Best results, also in terms of dispersity, were obtained when high initiator concentrations were employed in the synthesis [21]. It is important to note that the anionic PPV polymerization proceeds after a double action of the base LHMDS; the base is required to convert the precursor monomer, but also to deprotonate the initiator.…”

“…The mixture was stirred for 15 min and quenched with concentrated HCl (37%). Work-up was done as earlier reported [21]. For the block copolymer synthesis, the reaction was not quenched with acid, but tert-butyl acrylate (5 equivalents, 2.5 mmol, 0.36 mL) was added using a degassed syringe and the reaction was consequently stirred for another 15 min at 0 C and quenched with methanol.…”

“…All polymerization and elimination reactions were carried out as described before [21]. The polymerization temperature of À78 C was reached with an isopropanol/dry ice bath.…”

“…Under most reaction conditions these quinodimethanes are unstable and undergo spontaneous radical polymerization (it should be noted that in older literature very often anionic polymerization conditions were erroneously postulated; newer studies indicate that radical polymerization is much more likely to occur) [9]. To switch from radical to anionic polymerization, the base employed in the in-situ-formation of the actively propagating monomer was changed from tert-butoxide to the more sterically hindered base LHMDS (lithium hexamethyldisilazide) while the solvent needs to be replaced by an aprotic solvent such as THF [21].…”