Controlled Alternating Metathesis Copolymerization of Terminal Alkynes

Abstract

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.

Chain transfer agents for the catalytic ring opening metathesis polymerization of norbornenes

“…So far, there have been very few reports to grow ROMP polymers from a macromolecule using olen metathesis catalysts. [52][53][54] Functionalizing any metathesis catalyst using only one equivalent pre-functionalization agent attached to a polymer is exceedingly challenging. Given the speed and high regioselectivity of our CTAs, we anticipated that a monosubstituted 1,3 diene derivative attached to the chain end of a polymer could serve as a macroinitiator to initiate ROMP.…”

Catalytic Syntheses of Degradable Polymers via Ring-Opening Metathesis Copolymerization Using Vinyl Ethers as Chain Transfer Agents

“…Afterward, the Gutekunst group reported an alternating cascade copolymerization of DHF and alkynes. , A very recent report showed the synthesis of degradable polymers via ROMP of DHF with norbornene derivatives . Our group has also reported alternating metathesis copolymerization of DHF with terminal alkynes . However, in all these cases, just like in conventional living ROMP, a stoichiometric amount of ruthenium initiator with respect to the polymer chains is required.…”

“…26 Our group has also reported alternating metathesis copolymerization of DHF with terminal alkynes. 27 However, in all these cases, just like in conventional living ROMP, a stoichiometric amount of ruthenium initiator with respect to the polymer chains is required. This often leads to high catalyst loadings, which is quite expensive, as well as difficult as far as removing the toxic metal contaminants from the synthesized polymers is concerned.…”

Frontal Polymerization of Dihydrofuran Comonomer Facilitates Thermoset Deconstruction

“…An attractive method of addressing sustainability in thermosets is to incorporate cleavable units into the strands of the polymeric network. , Shieh et al recently demonstrated the ring-opening metathesis polymerization (ROMP) of p­(DCPD) thermosets having cleavable siloxane repeat units in the strands of the network. , Polymer backbone deconstruction was triggered with a fluoride reagent. Similar strategies have focused on generating thermoplastics utilizing cleavable cyclic olefin comonomers containing acetal, − disulfide, phosphoramidite, carbonate, and enol ether moieties. − Recent work from the Xia group demonstrated the synthesis of cleavable thermoplastics via the copolymerization of 2,3-dihyrdofuran (DHF) with a variety of norbornene derivatives. In addition to functioning as a cleavable unit, DHF suppressed the reactivity of Grubbs catalyst (GC) .…”