Mathias Destarac

On the Critical Role of RAFT Agent Design in Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization

There are a certain number of precautions a polymer chemist should take before undertaking a reversible addition-fragmentation chain transfer (RAFT) polymerization with a view of obtaining a polymer with controlled macromolecular characteristics (, PDI) and little or no change of rate of polymerization in comparison with conventional radical polymerization. Among them, a proper selection of the so-called R and Z groups borne by the thiocarbonyl thio skeleton of the RAFT agent is essential and is strongly dependent on the considered monomer. In this review, we introduce the basic concepts associated with the RAFT process like its mechanism and kinetics, and how the RAFT agent structure can strongly influence its reactivity and sometimes lead to undesired kinetic behaviors.

Low temperature RAFT/MADIX gel polymerisation: access to controlled ultra-high molar mass polyacrylamides

We pushed back the limits of molar mass control in aqueous RAFT/MADIX polymerisation through a fast and quantitative gel polymerisation of a series of acrylamido monomers. Unprecedentedly high Mn up to 106 g mol−1 with low dispersities (Đ < 1.2) was achieved in homopolymerisation, statistical and block copolymerisation of a selection of acrylamido monomers such as AM, DMA, AMPS and NIPAM. The reasons for access to an abnormally high kinetic chain length in the presence of a RAFT/MADIX agent are discussed.

Aqueous RAFT/MADIX polymerisation of vinylphosphonic acid

RAFT/MADIX polymerisation of vinylphosphonic acid (VPA) was controlled in water with an O-ethyl xanthate transfer agent. This represents the first example of reversible deactivation radical polymerisation of a monomer bearing an unprotected phosphonic acid function. Hence, macromolecular engineering of polyphosphonates can now be envisioned by directly polymerising VPA in water.

Selective and Quantitative Oxidation of Xanthate End‐Groups of RAFT Poly(n‐butyl acrylate) Latexes by Ozonolysis

Although various successful strategies have been reported in the past for the postpolymerization modification of the reversible addition-fragmentation chain transfer (RAFT) terminal group in homogeneous media, no solution is proposed for the tedious case of aqueous polymer dispersions where most of the thiocarbonylthio terminal group is buried into the core of the polymer particle. In this work, ozone is proposed to tackle this important academic and industrial challenge. After preliminary model ozonolysis reactions performed on a xanthate RAFT agent and a derived low molar mass poly(n-butyl acrylate) (PBA) in dichloromethane solution, it is shown that the hydrophobic nature and strong oxidant properties of ozone are responsible for its efficient diffusion in aqueous PBA latex particles obtained by RAFT and selective and complete transformation of the xanthate terminal group into a thiocarbonate end-group. In addition to the beneficial total discoloration of the final product, this chemical treatment does not generate any volatile organic compound and leaves the colloidal stability of the polymer particles unaffected, provided that a PBA latex with a sufficiently high Mn of 5000 g mol(-1) is selected.

Thermosensitive spontaneous gradient copolymers with block- and gradient-like features

Reversible addition–fragmentation chain transfer (RAFT) copolymerization was used to prepare copolymers of N-isopropyl acrylamide (NIPAM) and vinyl acetate (VAc) with mole fractions of NIPAM ranging from 0.1 to 0.6 and targeted degrees of polymerization of 100 and 250. The measured kinetic parameters and obtained experimental results revealed that this copolymerization system leads to a “one pot” synthesis of amphiphilic gradient copolymers, which have thermoresponsive and self-assembly characteristics resembling those of the analogous block copolymers but with some intriguing differences. Their self-assembly behavior in water suggests the formation of dynamic aggregates which respond rapidly to changes in solubility as revealed by 1H NMR spectroscopy, in contrast to the kinetically frozen aggregates formed by block copolymers. Furthermore, despite their block-like composition profiles, these copolymers display a single and broad glass transition, as is typically found in linear gradient copolymers. The synthetic approach presented in this contribution could readily be adapted to other comonomer systems to provide an accessible and economic alternative to the conventional multi-step preparation of block copolymers.

Dixanthate-terminated poly(butylene terephthalate). A novel RAFT/MADIX agent for the synthesis of well-defined triblock copolymers resulting from consecutive step- and chain-growth polymerization processes

Well-defined triblock copolymers comprising a poly(butylene terephthalate) (PBT) mid-block and three different hydrophobic blocks (poly(tert-butyl acrylate) P(t-BA), poly(n-butyl acrylate) P(n-BA) and poly(tert-butyl acrylamide) P(t-BAm)) were successfully prepared by the combination of step-growth and RAFT/MADIX polymerizations. Two different synthetic strategies were investigated for the preparation of O-ethylxanthate-terminated PBT RAFT/MADIX agent. Firstly α,ω-dihydroxy-PBT synthesized by a step-growth polymerization was transformed into the corresponding dixanthate-functionalized PBT according to a two-step procedure. An alternative approach was performed by using a hydroxyl-functional xanthate as chain stopper in a single step-growth polymerization process. In both cases, the presence of xanthate terminal groups was confirmed by NMR spectroscopy and MALDI-TOF mass spectrometry. The resulting PBT with xanthate end-groups was used as a macro-chain transfer agent for the RAFT/MADIX polymerization of n-BA, t-BA and t-BAm. The synthesis of well-defined PBT-based triblock copolymers was confirmed by SEC analysis.

Scope and limitations of ring-opening copolymerization of trimethylene carbonate with substituted γ-thiolactones

Functional (co)polymers are increasingly developed by ring-opening polymerization of functional cyclic esters and cyclic carbonates for a wide range of applications. Following this trend and aiming to challenge the polymerization of substituted γ-thiolactones, we studied the ring-opening copolymerization of recently developed γ-thiolactones with trimethylene carbonate in order to prepare new poly(carbonate-co-thioester)s with phosphonated or fluorinated pendant groups.

Acceleration and improved control of aqueous RAFT/MADIX polymerization of vinylphosphonic acid in the presence of alkali hydroxides

The effect of adding various alkali hydroxides to the conventional and reversible RAFT/MADIX radical polymerizations of vinylphosphonic acid (VPA) has been investigated. The addition of up to 1 equivalent of NaOH increases the rate and the final conversion of both conventional and RAFT/MADIX polymerizations. Larger quantities of NaOH retard the polymerization. LiOH, KOH and NH4OH also increase the rate of polymerization, to a lesser extent. In all cases, the most pronounced effect is observed in the presence of 0.5 equivalents of hydroxide relative to VPA. In RAFT/MADIX polymerizations, the dispersity of the final polymer decreases as the ionic radius of the counterion increases (H+ > Li+ > Na+ > K+ > NH4+), while the acceleration of polymerization follows the order Na+ > K+ > NH4+ > Li+ > H+. Thus the use of 0.5 eq. NaOH leads to the fastest polymerizations, while 0.5 eq. KOH and NH4OH provide a moderate increase in rate coupled with a significant reduction in dispersity of the final polymer.

Industrial development of reversible-deactivation radical polymerization: is the induction period over?

Reversible-deactivation radical polymerisation (RDRP) techniques are essential in modern polymer chemistry. Over the years, they have become not only fantastic lab tools for the easy preparation of structurally complex polymers but also an industrial reality. This article reviews industrial developments and commercial success based on RDRP processes. The nature of RDRP control agents is discussed and numerous industrial polymers and their applications are exemplified. While RDRP is firmly established as a powerful means for the development of next generation high-valued polymer products, there is room for improvement in terms of the cost/performance ratio for a broader adoption by industry. Some directions are proposed for the future.