Living Polymer Chains with Predictable Molecular Weight and Dispersity via Carbanionic Polymerization in Continuous Flow: Mixing Rate as a Key Parameter

Abstract

Aiming at systematic variation of the parameter dispersity, Đ (or "polydispersity"), living polymers with predictable dispersity (Đ = 1.15−2.20) and controlled molecular weights (M n = 3200−18 500 g mol −1 ) were prepared via carbanionic polymerization. The approach relies on a continuous flow reactor equipped with a tangential fourway jet micromixing device. By varying the total flow rate, the mixing efficiency of the initiator (sec-BuLi) and the corresponding vinyl monomers is controlled, resulting in polymers with predefined dispersity, while the number-average molecular weight, M n , is kept constant. In this manner living polystyrene (PS), poly(p-methylstyrene) (PpMeS), and poly-(2-vinylpyridine) (P2VP) samples with systematically varied Đ (studied by SEC) were prepared. All polymerizations were carried out at room temperature in a 50:50 solvent mixture of THF with either hexane for PS and PpMeS or with benzene for the polymerization of 2VP. To prove the living character of all polymer chains of the distributions obtained, all carbanionic chains were labeled, i.e., end functionalized via addition of an epoxide (benzyl glycidyl ether, BGE) as a termination reagent, when full conversion of the monomer was reached. Subsequent MALDI-ToF characterization confirmed the living character of all chains of the distributions. This is key for the further generation of complex polymer architectures with tailored polydispersity. Using the living carbanions with different dispersity, in an exploratory study, PS-b-PI block copolymers with controlled dispersity of the styrene block have been prepared via direct addition of isoprene as a second monomer.

Tuning Dispersity by Photoinduced Atom Transfer Radical Polymerisation: Monomodal Distributions with ppm Copper Concentration

“…[32,33] To overcome these challenges,wesought arobust ATRP system where the molecular weight distribution could be controlled by simply tuning the amount of catalyst (copper/ ligand). Importantly,a nd unlike many previous methods, [22,27] notable tailing within the distribution is avoided, and the molecular weight distributions remained monomodal throughout the polymerisation. [34][35][36] High end-group fidelity can be maintained with this low ppm ATRP system, as only small amounts of Cu I Br are generated from Cu II Br 2 species.T his pushes the system strongly to the dormant state,a llowing for fast deactivation, and thus reducing the lifetime of active radicals.…”

“…[1] Indeed, the molecular weight distribution can significantly affect the processability of polymer melts, [11] the glass transition temperature of the material, [12] and rheological properties [13][14][15] (e.g.s hear and elongational viscosities, storage moduli, etc.) [22,23] In addition, the groups of Boyer, Leibfarth, and others [24][25][26][27][28] exploited flow chemistry to successfully tailor the dispersity by adjusting reagent concentrations,p ump flow rates,v iscosity,a nd residence times.G oto and co-workers were also able to control molecular weight distributions through at emperature-selective metal-free organocatalysed living radical polymerisation system forming complex blocks,s tars,a nd brush polymers. [16][17][18] Perhaps the most traditional way to tailor the molecular weight distribution is to blend presynthesised polymer samples consisting of multiple molecular weights.…”

“…[22,23] In addition, the groups of Boyer, Leibfarth, and others [24][25][26][27][28] exploited flow chemistry to successfully tailor the dispersity by adjusting reagent concentrations,p ump flow rates,v iscosity,a nd residence times.G oto and co-workers were also able to control molecular weight distributions through at emperature-selective metal-free organocatalysed living radical polymerisation system forming complex blocks,s tars,a nd brush polymers. [27,28] Further limitations of existing strategies include complex multicomponent systems,e xtremely low polymerisation rates,l ack of temporal control, narrow range of dispersities obtained, thorough deoxygenation of the polymerisation solutions and high temperatures ( Figure 1). While this led to ab roadening of the molecular weight distribution, the termination of chain ends prevented chain extension and the synthesis of block copolymers.…”

“…[19][20][21] Although, this is certainly an efficient method to tune dispersity,i ti sq uite tedious and often results in multimodal molecular weight distributions.Recently,Fors and co-workers introduced am odular strategy to tune the dispersity of polymers by feeding initiator species during nitroxide-mediated polymerisation (NMP) and anionic polymerisation through the use of as yringe pump. [22,23] In addition, the groups of Boyer, Leibfarth, and others [24][25][26][27][28] exploited flow chemistry to successfully tailor the dispersity by adjusting reagent concentrations,p ump flow rates,v iscosity,a nd residence times.G oto and co-workers were also able to control molecular weight distributions through at emperature-selective metal-free organocatalysed living radical polymerisation system forming complex blocks,s tars,a nd brush polymers. [29] Despite these great developments,c urrent reported strategies are limited to bimodal molecular weight distributions,a dulterated polymer chains,a nd/or low endgroup fidelity.F or instance,arecent publication has reported the addition of phenylhydrazine over the course of the polymerisation.…”

Linking two worlds in polymer chemistry: The influence of block uniformity and dispersity in amphiphilic block copolypeptoids on their self‐assembly

“…Similar thoughts were expressed decades ago by some of the most renowned polymer scientists . David Tirrell for example stated in 1997 that a “…critical comparison of theory and experiment has been complicated by the polydisperse nature of the [polymers] available to date.” Even though the last decade has seen important synthetic advances that allow to control and tailor the dispersity of polymers to some extent, the effects of dispersity between classic low‐dispersity polymers (Poisson distribution) and uniform polymers remains largely uninvestigated. In contrast, the importance of dispersity on the microphase separation of polymers with a Poisson distribution or broader has been well documented .…”