Herein, we describe a catalyst transfer polycondensation that enabled access to well-defined poly(p-phenyleneethynylene) (PPE), a prominent conjugated polymer. Treatment of a stannylated 4-iodophenylacetylene derivative with PhPd(t-Bu3P)Br afforded the corresponding PPE in up to 94% yield. Under optimized conditions, the molecular weight of the polymer increased linearly with monomer consumption, and was controlled by adjusting the initial monomer-to-catalyst ratio. The chain-growth nature of the polymerization reaction was utilized to produce well-defined PPE-containing block copolymers, as well as to grow PPE brushes from silica nanoparticles via a surface-initiated polymerization process.
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.
A bis-phenanthroline [2]catenane copper complex, consisting of one olefinic macrocycle and one nonolefinic macrocycle, underwent an entropy-driven ring-opening olefin metathesis polymerization (ROMP) to provide a polypseudorotaxane. The polymerization featured an average degree of polymerization of ca. 63 wherein the polymer was effectively saturated with threaded macrocycles. Removal of the copper led to near complete release of the macrocycles from the polymer backbone.
Here we report the synthesis of metalated main-chain polypseudorotaxanes via ring-opening olefin metathesis copolymerization of macrocycles and metalated [2]catenanes. By varying the feed ratio of the macrocycle and the [2]catenate comonomers, we prepared metalated pseudorotaxane polymers with selected, predictable average linear densities of threaded macrocycles that ranged from 0% to 100%, thus allowing, for the first time, both full and fine control over this key parameter.
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