Controlled Chain-Growth Kumada Catalyst Transfer Polycondensation of a Conjugated Alternating Copolymer

Abstract

The Ni-catalyzed Kumada catalyst transfer polycondensation of a novel biaryl monomer, 2-(4-bromo-2,5-bis(2-ethylhexyloxy)phenyl)-5-chloromagnesiothiophene (2), afforded the respective π-conjugated alternating copolymer poly(thiophene-alt-p-phenylene) (PTPP). Under optimized conditions, the polystyrene-equivalent number-average molecular weight (M n ) of the copolymers prepared using this method were varied between 6.4 and 39 kDa by adjusting the initial monomer-to-catalyst ratios and, in all cases, the resulting materials exhibited narrow polydispersity indices (PDIs ≤ 1.33). Moreover, the M n of the copolymers produced were found to increase linearly with monomer conversion. The ability of PTPP to be utilized as a macroinitiator for further copolymerization was confirmed through a series of chain extension experiments as well as block copolymerizations involving 2-bromo-5-chloromagnesio-3-hexylthiophene. MALDI-MS analysis showed that the major population of the PTPP prepared using the aforementioned method contained H/Br end groups, as would be expected for efficient catalyst transfer during the polymerization with minimal occurrence of chain termination. Collectively, these results were consistent with a controlled polymerization reaction and constituted the first such example in which a conjugated polymer with an alternating repeat unit was produced via a chain-growth process.

Synthesis of poly(thiophene-alt-pyrrole) from a difunctionalized thienylpyrrole by Kumada polycondensation

“…57 It has been shown the addition of LiCl to Kumada catalyst transfer polycondensation could have beneficial effects on the chain-growth polymerization characteristics of arylGrignard monomers. 41,36 Bielawski and coworkers reported the addition of LiCl led to controlled chain-growth polymerization of 2-(4-bromo-2,5-bis(2-ethylhexyloxy)phenyl)-5-chloromagnesiothiophene to afford poly(thiophene-alt-p-phenylene). 41 However, in our case, LiCl did not show this effect; on the contrary, the M w /M n (4.6) value was much higher with much bigger M n (29500) ( Table 2, entry 10).…”

“…41,36 Bielawski and coworkers reported the addition of LiCl led to controlled chain-growth polymerization of 2-(4-bromo-2,5-bis(2-ethylhexyloxy)phenyl)-5-chloromagnesiothiophene to afford poly(thiophene-alt-p-phenylene). 41 However, in our case, LiCl did not show this effect; on the contrary, the M w /M n (4.6) value was much higher with much bigger M n (29500) ( Table 2, entry 10). The polymer had only H/H as the main end group in the presence of LiCl ( Figure 1D).…”

Evidence for the Chain-Growth Synthesis of Statistical π-Conjugated Donor-Acceptor Copolymers

“…This can introduce variation that negatively affects material, and subsequently device, reproducibility. Kumada catalyst‐transfer polymerization (KCTP) is one of the only controlled chain‐growth routes for synthesizing π‐conjugated polymers, whereby a nickel catalyst remains associated with a single polymer chain throughout polymerization . In this way, molecular weight and dispersity are well controlled, along with polymer composition and end‐group functionality.…”

Gradient Sequence π-Conjugated Copolymers

“…15). This synthetic method, now known as catalyst transfer polycondensation (CTP) (13)(14)(15)(16)(17)(18)(19), paved the way for synthesizing all-conjugated diblock copolymers (20)(21)(22)(23)(24)(25)(26)(27), star polymers (28,29) and surface-grafted polymers (30)(31)(32). CTP also provides access to all-conjugated gradient sequence copolymers (33)(34)(35)(36).…”