Commercially available Vince lactam and its derivatives are copolymerized with 2,3-dihydrofuran (DHF) in a living fashion based on the unique reactivity of Ru Fischer carbene. The resulting copolymers can be fully degraded into small molecules under mildly acidic conditions, suggesting a uniform incorporation of the DHF units throughout the polymer backbone. The regioselective and ultrafast chain transfer of G3-benzylidene to vinyl ethers enabled us to synthesize a narrowly dispersed triblock copolymer via macroinitiation from poly(ethylene glycol) divinyl ether. This high metathesis activity and regioselectivity of vinyl ethers was further exploited in a kinetically controlled catalytic synthesis of degradable copolymers using vinyl ethers as effective chain transfer agents. This strategy paves the way for a one-pot synthesis of degradable ROMP polymers from easily accessible monomers and chain transfer agents. We report a catalytic copolymerization in which up to 500-fold savings in the expensive and toxic ruthenium carbene complex can be achieved compared to a conventional ROMP. We believe that this cost-effective and environmentally friendly synthesis of degradable polymers will be highly useful for many biomedical applications as well as for environmental sustainability.
Here, we present a detailed study of the metathesis activity of conjugated 1,3 diene derivatives in ring opening metathesis polymerization (ROMP) using Grubbs’ 3rd generation catalyst (G3). A comprehensive screening...
A catalytic living ring-opening metathesis copolymerization (ROMP) method is described that relies on a degenerative, reversible and regioselective exchange of propagating Fischer-carbenes. All characteristics of a living polymerization such as narrow dispersity, excellent molar mass control and the ability to form block copolymers are achieved by this method. The method allows the use of up to 200 times less ruthenium complex than traditional living ROMP. We demonstrate the synthesis of ROMP-ROMP diblock copolymers, ATRP from a ROMP macro-initiator and living ROMP from a PEG-based macro chain transfer agent. The cost-effective, sustainable and environmentally friendly synthesis of degradable polymers and block copolymers enabled by this strategy will find various applications in biomedicine, materials science, and technology.
Terminal alkynes display high reactivity
toward Ru-carbene metathesis
catalysts. However, the formation of a less reactive bulky carbene
hinders their homopolymerization. Simultaneously, the higher reactivity
of alkynes does not allow efficient cross propagation with sterically
less-hindered cycloalkene monomers, resulting in inefficient copolymerization.
Nonetheless, terminal alkynes undergo rapid cross-metathesis with
vinyl ethers. Therefore, an efficient cross propagation can be achieved
with terminal alkynes and cyclic enol ether monomers. Here, we show
that terminal alkyne derivatives can be copolymerized in an alternating
fashion with 2,3-dihydrofuran using Grubbs’ third generation
catalyst (G3). A linear relationship of the number-average
molecular weight versus monomer to initiator ratio and block copolymer
synthesis confirmed a controlled copolymerization. The SEC and NMR
analyses of the synthesized copolymers confirmed the excellent control
over molecular weight and exclusive alternating nature of the copolymer.
The regioselective chain transfer of G3 to vinyl ether
and the high reactivity of the Fischer-type Ru carbene toward terminal
alkynes was also exploited for polymer conjugation. Finally, the presence
of an acid labile backbone functionality in the synthesized alternating
copolymers allowed complete degradation of the copolymer within a
short time interval which was confirmed by SEC analyses.
Single chain transfer agents are used to synthesize narrowly distributed heterotelechelic ROMP polymers in one pot, exploiting a new mechanistic and synthetic approach. The chain transfer agents carrying different functional groups are synthesized in a few straightforward steps. Prefunctionalization of commercially available Grubbs' third-generation catalyst is realized in situ using regioselective chain transfer agents within a short reaction period. After monomer consumption, the excess chain transfer agent in the reaction medium automatically end-functionalizes the polymer chain, yielding a heterotelechelic polymer via a ring-opening−ringclosing sequence. 1 H NMR, MALDI-ToF, and SEC analyses confirmed end-group functionalization as well as excellent control over molecular weight and dispersity. This strategy highlights a new way of synthesizing one-pot heterotelechelic ROMP polymers straightforwardly and efficiently.
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