Compounded Interplay of Kinetic and Thermodynamic Control over Comonomer Sequences by Lewis Pair Polymerization

Abstract

The design of facile synthetic routes to well-defined block copolymers (BCPs) from direct polymerization of one-pot comonomer mixtures, rather than traditional sequential additions, is both fundamentally and technologically important. Such synthetic methodologies often leverage relative monomer reactivity toward propagating species exclusively and therefore are rather limited in monomer scope and control over copolymer structure. The recently developed compounded sequence control (CSC) by Lewis pair polymerization (LPP) utilizes synergistically both thermodynamic (K eq ) and kinetic (k p ) differentiation to precisely control BCP sequences and suppress tapering and misincorporation errors. Here, we present an in-depth study of CSC by LPP, focusing on the complex interplay of the fundamental K eq and k p parameters, which enable the unique ability of CSC-LPP to precisely control comonomer sequences across a variety of polar vinyl monomer classes. Individual Lewis acid equilibrium and polymerization rate parameters of a range of commercially relevant monomers were experimentally quantified, computationally validated, and rationalized. These values allowed for the judicious design of copolymerizations which probed multiple hypotheses regarding the constructive vs conflicting nature of the relationship between K eq and k p biases, which arise during CSC-LPP of comonomer mixtures. These relationships were thoroughly explored and directly correlated with resultant copolymer microstructures. Several examples of higher-order BCPs are presented, further demonstrating the potential for materials innovation offered by this methodology.

Cyclic and Linear Tetrablock Copolymers Synthesized at Speed and Scale by Lewis Pair Polymerization of a One-Pot (Meth)acrylic Mixture and Characterized at Multiple Levels

“…−1 for the LPP of MMA under nearly identical conditions (Figure S2). 47 The heavily biased equilibrium and kinetic values predict high sequence control for MAD-catalyzed LPP of this comonomer pair. Indeed, the one-pot CSC-LPP of this monomer pair showed rapid (<7 s) and complete consumption of AIA before MMA began to polymerize (Figure 2).…”

“…Additionally, the k p for AlA was impressively high at k p , obs = 8.14 × 10 4 [M]·s –1 ·[LA] t –1 ·[LB] 0 –1 , significantly higher than the recently reported k p,obs = 3.96 × 10 2 [M]·s –1 ·[LA] t –1 ·[LB] 0 –1 for the LPP of MMA under nearly identical conditions (Figure S2). The heavily biased equilibrium and kinetic values predict high sequence control for MAD-catalyzed LPP of this comonomer pair. Indeed, the one-pot CSC-LPP of this monomer pair showed rapid (<7 s) and complete consumption of AIA before MMA began to polymerize (Figure ).…”

“…46 Monomers allyl acrylate (AlA) and MMA were selected for mixed-feed CSC-LPP due to their known high differentiation by K eq (for the [M1]/[M2]/[LA] coordination equilibrium) and propagation rate (k p ). 47 Using variable-temperature 1 H NMR to track the [AlA]/[MMA]/ [MAD] equilibrium at −20 °C, MMA/MAD coordination could not be observed, thus implying a heavy K eq bias (>1000) for MAD preferential coordination to AlA over MMA (Figure S1). Additionally, the k p for AlA was impressively high at k p , obs = 8.14…”

“…Specifically, Lewis base (LB) tricyclohexylphosphine (PCy 3 ) was employed as the linear polymer initiator and ethyl sorbate/MAD/I t Bu (1,3-di- tert -butylimidazol-2-ylidene) (1:1:1) ion pair 1 as the cyclic polymer initiator . Monomers allyl acrylate (AlA) and MMA were selected for mixed-feed CSC-LPP due to their known high differentiation by K eq (for the [M1]/[M2]/[LA] coordination equilibrium) and propagation rate ( k p ) . Using variable-temperature 1 H NMR to track the [AlA]/[MMA]/[MAD] equilibrium at −20 °C, MMA/MAD coordination could not be observed, thus implying a heavy K eq bias (>1000) for MAD preferential coordination to AlA over MMA (Figure S1).…”

%VBur index and steric maps: from predictive catalysis to machine learning

“…Overall, it must be assessed that quantitatively the use of the concepts of steric maps is frankly focused on ligands such as NHCs, 24,65 but especially the explosion has come in the reproduction of catalytic surfaces where simple polymerization, 284,285 or hydrogenation reactions take place. 31,149…”