We have prepared a new series of nickel phosphine phosphonate ester complexes that feature two metal-chelating polyethylene glycol (PEG) side arms. Metal binding and reactivity studies in polar solvents showed that they readily coordinate external cations, including alkali (Li + , Na + , K + ), alkaline (Mg 2+ , Ca 2+ ), transition (Sc 3+ , Co 2+ , Zn 2+ ), post-transition (Ga 3+ ), and lanthanide (La 3+ ) metals. Although olefin polymerization reactions are typically performed in non-polar solvents, which cannot solubilize +2 and +3 metal cations, we discovered that our nickel catalysts could promote ethylene polymerization in neat tetrahydrofuran. This advance allowed us, for the first time, to systematically investigate the effects of a wide range of M + , M 2+ , and M 3+ ions on the reactivity of nickel olefin polymerization catalysts. In ethylene homopolymerization, the addition of Co(OTf) 2 to our nickel-PEG complexes provided the largest boost in activity (up to 11-fold, 2.7 × 10 6 g mol −1 h −1 ) compared to that in the absence of external salts. The catalyst enhancing effects of secondary metals were also observed in studies of ethylene and polar olefin ( e.g. , propyl vinyl ether, allyl butyl ether, methyl-10-undecenoate, and 5-acetoxy-1-pentene) copolymerization. Notably, combining either Co 2+ or Zn 2+ with our nickel complexes increased the rates of polymerization in the presence of propyl vinyl ether by about 5.0- and 2.4-fold, respectively. Although further studies are needed to elucidate the structural and mechanistic roles of the secondary metals, this work is an important advance toward the development of cation-switchable polymerization catalysts.
more »
« less
Catalyst-controlled stereoselective cationic polymerization of vinyl ethers
The tacticity of vinyl polymers has a profound effect on their physical properties. Despite the well-developed stereoselective methods for the polymerization of propylene and other nonpolar α-olefins, stereoselective polymerization of polar vinyl monomers has proven more challenging. We have designed chiral counterions that systematically bias the reactivity and chain-end stereochemical environment during cationic polymerization. This approach overrides conventional chain-end stereochemical bias to achieve catalyst-controlled stereoselective polymerization. We demonstrate that this method is general to vinyl ether substrates, providing access to a range of isotactic poly(vinyl ether)s with high degrees of isotacticity. The obtained materials display the tensile properties of commercial polyolefins but adhere more strongly to polar substrates by an order of magnitude, indicating their promise for next-generation engineering applications.
more »
« less
- Award ID(s):
- 1726291
- NSF-PAR ID:
- 10104954
- Date Published:
- Journal Name:
- Science
- Volume:
- 363
- Issue:
- 6434
- ISSN:
- 0036-8075
- Page Range / eLocation ID:
- 1439 to 1443
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract In typical cyclic polymer synthesis via ring‐closure, chain growth and cyclization events are competing with each other, thus affording cyclic polymers with uncontrolled molecular weight or ring size and high dispersity. Here we uncover a mechanism by which Lewis pair polymerization (LPP) operates on polar vinyl monomers that allows the control of where and when cyclization takes place, thereby achieving spatial and temporal control to afford precision cyclic vinyl polymers or block copolymers with predictable molecular weight and low dispersity (≈1.03). A combined experimental and theoretical study demonstrates that cyclization occurs only after all monomers have been consumed (when) via conjugate addition of the propagating chain end to the specific site of the initiating chain end (where), allowing the cyclic polymer formation steps to be regulated and executed with precision in space and time.
-
more » « less
Abstract In typical cyclic polymer synthesis via ring‐closure, chain growth and cyclization events are competing with each other, thus affording cyclic polymers with uncontrolled molecular weight or ring size and high dispersity. Here we uncover a mechanism by which Lewis pair polymerization (LPP) operates on polar vinyl monomers that allows the control of where and when cyclization takes place, thereby achieving spatial and temporal control to afford precision cyclic vinyl polymers or block copolymers with predictable molecular weight and low dispersity (≈1.03). A combined experimental and theoretical study demonstrates that cyclization occurs only after all monomers have been consumed (when) via conjugate addition of the propagating chain end to the specific site of the initiating chain end (where), allowing the cyclic polymer formation steps to be regulated and executed with precision in space and time.
-
null (Ed.)Carbon dioxide based polymers synthesized from the metal-catalyzed copolymeriation of epoxides and CO 2 containing the terpyridine ligand as an end group are reported. The strategy used was to carry out the polymerization in the presence of a carboxylic acid derivative of terpyridine, 4′-(4-carboxyphenyl)-2,2′:6′,2′′-terpyridine (HL), as a chain transfer agent. The epoxide monomer possessing a vinyl substituent, allyl glycidyl ether (AGE), was copolymerized with CO 2 employing a (salen)Co( iii ) catalyst to afford a polycarbonate which upon the addition of mercaptoacetic acid across the double bond, followed by deprotonation, yielded a water soluble polymer. In a similar manner, the sequential formation of a diblock terpolymer produced from propylene oxide, AGE, and CO 2 provided a amphiphilic polycarbonate which self-assembled upon addition to water to form micelle nanostructures. The molecular weights of these CO 2 -derived polycarbonates were shown to be easily controlled by the quantity of chain transfer agent used. These polymeric ligands were demonstrated to provide a modular design for synthesizing a wide variety of metal complexes as illustrated herein for zinc and platinum derivatives.more » « less
-
null (Ed.)Plastic production continually increases its share of global oil consumption. Thermoplastic elastomers (TPEs) are a necessary component of many industries, from automotive and construction to healthcare and medical devices. To reduce the environmental burden of TPE production on the world, we developed two new ABA triblock copolymers synthesized through cationic reversable addition–fragmentation chain transfer (RAFT) polymerization from renewable monomers. Using poly(isobutyl vinyl ether) (PIBVE) as the soft block and either poly( p -methoxystyrene) (PMOS) or poly(2,3-dihydrofuran) (PDHF) as the hard blocks, we produced triblock copolymers with varying volume fractions and characterized their material properties. PDHF-PIBVE-PDHF is sourced almost entirely from simple alcohols and exhibits mechanical properties comparable to those of commercial TPEs. This effort demonstrates the utility of cationic RAFT for the production of sustainable TPEs.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1126/science.aaw1703
