A “Catalyst Switch” Strategy for the Sequential Metal-Free Polymerization of Epoxides and Cyclic Esters/Carbonate

Phosphazene/triisobutylaluminum-promoted anionic ring-opening polymerization of 1,2-epoxybutane initiated by secondary carbamates

The deprotonation of secondary carbamates by tBuP₂ in the presence of a Lewis acid allowed initiating the polymerization of 1,2-epoxybutane.

Synthesis of linear and star poly(ε-caprolactone) with controlled and high molecular weights via cyclic trimeric phosphazene base catalyzed ring-opening polymerization

Linear and star PCLs with controlled and high molecular weights are efficiently prepared by a catalytic system of CTPB/alcohol.

Design, synthesis and ring-opening polymerization of a new iodinated carbonate monomer: a universal route towards ultrahigh radiopaque aliphatic polycarbonates

A universal route towards ultrahigh radiopaque aliphatic polycarbonates was developed based on a new iodinated carbonate monomer.

Block copolymer synthesis in one shot: concurrent metal-free ATRP and ROP processes under sunlight

A completely metal-free strategy was developed by combining Atom Transfer Radical Polymerization (ATRP) and Ring Opening Polymerization (ROP) for the syntheses of block copolymers.

Ring-opening polymerization of ω-pentadecalactone catalyzed by phosphazene superbases

A fast and living ring-opening polymerization (ROP) of ω-pentadecalactone (PDL), a representative monomer of macrolactones, was achieved using a primary alcohol as the initiator and t-BuP₄ or t-octP₄ as the catalyst.

Chemoselective Polymerizations from Mixtures of Epoxide, Lactone, Anhydride, and Carbon Dioxide

Controlling polymer composition starting from mixtures of monomers is an important, but rarely achieved, target. Here a single switchable catalyst for both ring-opening polymerization (ROP) of lactones and ring-opening copolymerization (ROCOP) of epoxides, anhydrides, and CO2 is investigated, using both experimental and theoretical methods. Different combinations of four model monomers-ε-caprolactone, cyclohexene oxide, phthalic anhydride, and carbon dioxide-are investigated using a single dizinc catalyst. The catalyst switches between the distinct polymerization cycles and shows high monomer selectivity, resulting in block sequence control and predictable compositions (esters and carbonates) in the polymer chain. The understanding gained of the orthogonal reactivity of monomers, specifically controlled by the nature of the metal-chain end group, opens the way to engineer polymer block sequences.

Noncopolymerization Approach to Copolymers via Concurrent Transesterification and Ring-Opening Reactions

Inter- and intrachain transesterification, normally regarded as a detrimental side reaction for the synthesis of polyesters, is utilized herein to formulate a novel strategy for the modification of polyesters. Addition of an organic superbase into the mixture of hydroxyl-terminated poly(ε-caprolactone) and an epoxide, for example, propylene oxide or 1,2-butylene oxide, triggers concurrent nucleophilic ring-opening of the epoxide and transesterification reaction. The synergetic effect enables convenient and efficient transformation of the polyester into poly(ester-ether) random copolymers and thus advances the preparation of functional degradable polymeric materials taking advantage of the variety of commercial and laboratory-made polyesters and epoxides.

One-pot synthesis of well-defined polyether/polyester block copolymers and terpolymers by a highly efficient catalyst switch approach

A novel catalyst switch methodology, which takes advantage of one of the best catalysts for epoxide (t-BuP₄) and cyclic ester (t-BuP₂) polymerization, is presented.

Polymerization of Ethylene Oxide, Propylene Oxide, and Other Alkylene Oxides: Synthesis, Novel Polymer Architectures, and Bioconjugation

The review summarizes current trends and developments in the polymerization of alkylene oxides in the last two decades since 1995, with a particular focus on the most important epoxide monomers ethylene oxide (EO), propylene oxide (PO), and butylene oxide (BO). Classical synthetic pathways, i.e., anionic polymerization, coordination polymerization, and cationic polymerization of epoxides (oxiranes), are briefly reviewed. The main focus of the review lies on more recent and in some cases metal-free methods for epoxide polymerization, i.e., the activated monomer strategy, the use of organocatalysts, such as N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs) as well as phosphazene bases. In addition, the commercially relevant double-metal cyanide (DMC) catalyst systems are discussed. Besides the synthetic progress, new types of multifunctional linear PEG (mf-PEG) and PPO structures accessible by copolymerization of EO or PO with functional epoxide comonomers are presented as well as complex branched, hyperbranched, and dendrimer like polyethers. Amphiphilic block copolymers based on PEO and PPO (Poloxamers and Pluronics) and advances in the area of PEGylation as the most important bioconjugation strategy are also summarized. With the ever growing toolbox for epoxide polymerization, a "polyether universe" may be envisaged that in its structural diversity parallels the immense variety of structural options available for polymers based on vinyl monomers with a purely carbon-based backbone.

Macromolecular Design via an Organocatalytic, Monomer-Specific and Temperature-Dependent "On/Off Switch". High Precision Synthesis of Polyester/Polycarbonate Multiblock Copolymers

The employment of a monomer-specific "on/off switch" was used to synthesize a nine-block copolymer with a predetermined molecular weight and narrow distribution (Đ = 1.26) in only 2.5 h. The monomers consisted of a six-membered cyclic carbonate (i.e., 2-allyloxymethyl-2-ethyl-trimethylene carbonate (AOMEC)) and ε-caprolactone (εCL), which were catalyzed by 1,5,7-triazabicyclo[4.4.0]-dec-5-ene (TBD). The dependence of polymerization rate with temperature was different for the two monomers. Under similar reaction conditions, the ratio of the apparent rate constant of AOMEC and εCL [kpapp(AOMEC)/kpapp(εCL)] changes from 400 at T = -40 °C to 50 at T = 30 °C and 10 at T = 100 °C. Therefore, by decreasing the copolymerization temperature from 30 °C to -40 °C, the conversion of εCL can be switched "off", and by increasing the temperature to 30 °C, the conversion of εCL can be switched "on" again. The addition of AOMEC at T = -40 °C results in the formation of a pure carbonate block. The cyclic addition of AOMEC to a solution of εCL along with a simultaneous temperature change leads to the formation of multiblock copolymers. This result provides a new straightforward synthetic route to degradable multiblock copolymers, yielding new interesting materials with endless structural possibilities.

Polymerization of 5-alkyl δ-lactones catalyzed by diphenyl phosphate and their sequential organocatalytic polymerization with monosubstituted epoxides

One-pot sequential organocatalytic polymerization reactions of 5-alkyl δ-lactones and monosubstituted epoxides were carried out using the base→acid “catalyst switch” strategy, leading to well-defined polyether–polyester block copolymers with various alkyl substituents.