Sequence Selective Ring‐opening Terpolymerisation Facilitates Higher Order Switchable Catalysis

et al. 2023

Catal. Sci. Technol.

Self Cite

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Lithium catalysed sequence selective ring opening terpolymerisation: a mechanistic study

Deglmann

Machleit

et al. 2023

Catal. Sci. Technol.

Self Cite

“…Notably this sideprocess extends to related polymerisations and causes linkage scrambling and small molecule byproducts. [39][40][41][42][43][44][45][46] Previously it has been shown for alloxygen ROCOP that cooperative catalysts can control the reactivity of alkoxide intermediates and limit or even productively regulate side reactions. [47][48][49][50][51][52][53][54] Williams and co-workers in particular showed that a heterobimetallic Co(III)K catalyst can limit back-biting side reactions originating form alkoxides in CO2/epoxide ROCOP which lead to excellent polymer and linkage selectivities.…”

Section: B) Polymers Comprising Different Mono-(-o-c(=s)-o-oso O-c(=o...mentioning

confidence: 99%

Cooperative taming of CS2/oxetane copolymerisation: Consequences of main-chain sulfuration on polymer properties and catalysis

Plajer

Fornacon-Wood

et al. 2023

Preprint

CS2 promises easy access to degradable sulfur-rich polymers and insights into how main-group derivatisation affects polymer formation and properties, though its ring-opening copolymerisation is plagued by low linkage selectivity and small-molecule by-products. We demonstrate that a cooperative Cr(III)/K catalyst selectively delivers poly(dithiocarbonates) from CS2 and oxetanes while state-of-the-art strategies produce linkage scrambled polymers and heterocyclic by-products. The formal introduction of sulfur centres into the parent polycarbonates results in a net shift of the polymerisation equilibrium towards, and therefore facilitating, depolymerisation. During copolymerisation however the catalyst enables near quantitative generation of the metastable polymers in high sequence selectivity by limiting the lifetime of alkoxide intermediates. Furthermore, linkage selectivity is key to obtain semi-crystalline materials that can be moulded into self-standing objects. Our report demonstrates the potential of cooperative catalysis to produce previously inaccessible main-group rich materials with beneficial chemical and physical properties

“…41,[46][47][48] Combining these ROCOPs, we recently reported a Lithium catalysed PTA/CS2/epoxide ringopening terpolymerisation (ROTERP, with propylene oxide (PO) or butylene oxide (BO)) and observed the formation of poly(ester-alt-ester-alttrithiocarbonates) with a few erroneous thioester links (Figure 1). [49][50][51] The ROTERP polymers were produced in an unusual (head-to-head)-alt-(tail-totail) regioselectivity meaning that the trithiocarbonate links sit adjacent to secondary CH2 groups while the ester links sit adjacent to tertiary CH groups. This regioselectivity pointed towards a close mechanistic relation to Werner's CS2/epoxide ROCOP (ESI Figure S1) which led us to propose the reaction mechanism displayed in 4) also generates a link resulting from an isomerised epoxide (akin a virtual thiirane; A' in Figure 1) and an orthoterephtalate link in which both esters sit adjacent to tertiary CH "head" groups of the ring-opened monosubstituted epoxides.…”

Section: Introductionmentioning

confidence: 99%

Lithium Catalysed Sequence Selective Ring Opening Terpolymerisation: A Mechanistic Study

Deglmann

Machleit

et al. 2023

Preprint

The catalytic construction of well-defined materials from mixtures of building blocks is an important challenge in sustainable catalysis. In this regard, we have recently reported a new type of selective ring-opening terpolymerisation (ROTERP), in which three monomers (A, B, C) are selectively enchained into a (ABAC)n sequence, but the reasons behind this unusual selectivity remained unanswered. In this study, we present a detailed investigation into the full ROTERP mechanism based on the reactivity of model intermediates, computational studies investigating >100 possible intermediates and transition states and reaction kinetics. Experimental verification of the intermediate speciation, the primary insertion steps and the side-reactions lets us show that although most insertions and side-reactions are thermodynamically viable, kinetic selection processes at the propagating chain end determine the sequence selectivity. Computational studies elucidate the special role and speciation of the Lithium catalyst which during the catalytic cycle involves mono-metallic, bi-metallic and charge separated transitions states comprising both coordinative activation of incoming monomers and functional groups of the polymer backbone adjacent to the propagating chain. Our study not only deciphers the mechanism of a rare selective terpolymerisation but also helps answering open questions relevant to ring-opening copolymerisation (ROCOP) and alkali-metal catalysis in general, thus guiding the design of future polymerisation catalysis for degradable materials.