Thioanhydride/isothiocyanate/epoxide ring-opening terpolymerisation: sequence selective enchainment of monomer mixtures and switchable catalysis

Abstract

We report a new sequence selective terpolymerisation in which three monomers (butylene oxide (BO) A, PhNCS B and phtalic thioanhydride (PTA) C) are selectively enchained into an (ABA’C)n sequence. PTA/PhNCS/BO...

Sequence Selective Ring‐opening Terpolymerisation Facilitates Higher Order Switchable Catalysis

“…It approximately comprises 43 % monothio −O−(C=S)−O− and trithio −S−(C=S)−S− links respectively and 12 % other (thio)carbonate links which is similar to results reported by Werner and coworkes on Li catalysed CS 2 /BO ROCOP [25,32] . Due to overlapping 1 H NMR resonances for the respective linkages, the linkage ratios were approximated by integration of the relative integrals of the quaternary carbon resonances (ESI Section S1 and Figure S5) [22,23] . Hence, our ϵDL ROP to PTA/CS 2 /BO ROTERP to CS 2 /BO ROCOP cascade ultimately forms a PDL‐ b ‐poly(ester‐ alt ‐ester‐ alt ‐trithiocarbonate)‐ b ‐poly(thiocarbonate) with 3 % ROCOP links in the ROTERP block and compositionally pure ROP and ROCOP blocks.…”

“…The polymers show an unusual “head‐to‐head‐ alt ‐tail‐to‐tail” selectivity, meaning that ester groups sit next to tertiary carbon centres while heterocarbonates sit next to secondary carbon centres. We furthermore reported mechanistic switching of LiOBn catalysed ϵ‐decalactone (ϵDL) ROP in BO to PTA/(CS 2 or PhNCS)/BO ROTERP through addition of PTA and the corresponding heteroallene to polymerising ϵDL in BO (Figure 1(b)) [22,23] . This procedure eventually forms polydecalactone (PDL)‐ b ‐poly(ester‐ alt ‐ester‐ alt ‐heterocarbonate) block polymers and the onset of ROTERP hence suppresses the occurrence of ϵDL ROP.…”

“…We furthermore reported mechanistic switching of LiOBn catalysed ɛ-decalactone (ɛDL) ROP in BO to PTA/(CS 2 or PhNCS)/BO ROTERP through addition of PTA and the corresponding heteroallene to polymerising ɛDL in BO (Figure 1(b)). [22,23] This procedure eventually forms polydecalactone (PDL)-b-poly(ester-alt-ester-alt-heterocarbonate) block polymers and the onset of ROTERP hence suppresses the occurrence of ɛDL ROP. A preliminary investigation into the intermediate speciation of ROTERP identified that as for ROP and ROCOP alkoxide intermediates are also involved here (Figure 1(c)) implying that all three catalytic cycles could be linked together into one cascade.…”

“…This causes the termination of ROP and the onset of heteroallene/epoxide ring‐opening copolymerisation (ROCOP) to form a heteropolycarbonate ROCOP block connected to the polyester ROP polymer [16] Switchable catalysis is enabled by the circumstance that the alkoxide resting states encountered in ROP are short living intermediates in ROCOP while the heterocarbonate/carboxylate resting states of ROCOP exclusively insert epoxide and not lactones due to chain‐end chemoselectivities and linkage stabilities [17–21] . Recently, we realised alternating ring‐opening terpolymerisation (ROTERP) of ternary monomer mixtures comprising phtatlic thioanhydride (PTA), CS 2 or PhNCS and butylene oxide (BO) or propylene oxide (PO) [22,23] . Here, simple lithium benzyloxide (LiOBn) selectively forms poly(ester‐ alt ‐ester‐ alt ‐heterocarbonates) in up to 98 % selectivity with respect to the erroneous links from ROCOP (i. e. thioesters from PTA/BO ROCOP or heterocarbonates from CS 2 /BO or PhNCS/BO ROCOP) [24–31] .…”

“…[17][18][19][20][21] Recently, we realised alternating ring-opening terpolymerisation (ROTERP) of ternary monomer mixtures comprising phtatlic thioanhydride (PTA), CS 2 or PhNCS and butylene oxide (BO) or propylene oxide (PO). [22,23] Here, simple lithium benzyloxide (LiOBn) selectively forms poly(ester-altester-alt-heterocarbonates) in up to 98 % selectivity with respect to the erroneous links from ROCOP (i. e. thioesters from PTA/BO ROCOP or heterocarbonates from CS 2 /BO or PhNCS/BO ROCOP). [24][25][26][27][28][29][30][31] The polymers show an unusual "head-to-head-alttail-to-tail" selectivity, meaning that ester groups sit next to tertiary carbon centres while heterocarbonates sit next to secondary carbon centres.…”