Degradable polyolefins prepared by integration of disulfides into metathesis polymerizations with 3,6-dihydro-1,2-dithiine

Abstract

Disulfide-containing polyolefins were synthesized by ring-opening metathesis polymerization (ROMP) of the 6-membered disulfide-containing cyclic olefin, 3,6-dihydro-1,2-dithiine, which was prepared by ring-closing metathesis of diallyl disulfide. This approach facilitated the production of disulfide-containing unsaturated polyolefins as copolymers with disulfide monomer units embedded within a poly(cyclooctene) or poly(norbornene) framework. The incorporation of disulfides into the polymer backbone imparts redox responsiveness and enables polymer degradation via chemical reduction or thiol-disulfide exchange. This ROMP copolymerization strategy yielded both linear polyolefins, as well as bottlebrush polymers, with degradable segments, thereby broadening the scope of responsive polymer architectures synthesized by ROMP.

Fig. 1. Synthesis of disulfide-containing polyolefins by ROMP: (a) prior multistep synthesis of the 8-membered disulfide-containing cyclic olefin, (Z)-3,4,7,8-tetrahydro-1,2-dithiocine and (b) its copolymerization with cyclic olefins; (c) ring-closing metathesis (RCM) of LDS affords (Z)-3,6-dihydro-1,2-dithiine (CDS); (d) CDS copolymerization with cis-cyclooctene or norbornene derivatives gives entry into disulfide-containing polyolefins by ROMP.

Fig. 2. (a) Metathesis CDS–LDS equilibria ; (b) chemical structures of the ruthenium benzylidene catalysts employed in this work; (c) ¹H NMR spectra of LDS and CDS (from Entry 3 in Table 1).

Fig. 3. (a) ROMP copolymerization of COE and CDS; (b) ¹H NMR spectrum of P-20 from Entry 2 in Table 2; SEC curves eluting with THF with various (c) CDS mol% while fixing [monomer]/[initiator] ratio at 200, (d) total monomer concentration at [COE] : [CDS] = 4 : 1 with [monomer]/[initiator] ratio at 200, (e) [monomer]/[initiator] at [monomer] = 2 M and [COE] : [CDS] = 4 : 1, and (f) impact of reaction time following introduction of G_III.

Fig. 4. (a) Copolymerization of COE/CDS/LDS mixture; (b) SEC (eluting with THF) curves resulting from polymerizations with 0, 10, or 20 mol% LDS; (c) Plot of M_{n, SEC} and PDI vs. LDS mol%.

Fig. 5. (a) ROMP of CDS with norbornene derivatives 1–4; (b) ¹H NMR spectrum of P1-20 from Entry 2 in Table 3; SEC curves with variation of (c) total monomer concentration at [1] : [CDS] = 4 : 1 with [monomer]/[initiator] ratio at 200; (d) temperature; (e) [monomer]/[initiator] at 2 M monomer and [1] : [CDS] = 4 : 1; and (f) ROMP copolymerization of CDS with norbornene derivatives with containing pendent, hydroxy, t-butyl ester, and t-boc amine groups.

Fig. 6. (a) P-20-k and PS BP-10 degradation by (i) reduction of disulfide or (ii) thiol-disulfide exchange; SEC curves eluting with THF of (b) P-20-k reduction of disulfide with n-TBP, (c) P-20-k thiol-disulfide exchange with 1-dodecanethiol, and (d) PS BP degradation by n-TBP as a reducing agent before and after disulfide reduction.