Easy access to oxygenated block polymers via switchable catalysis

Abstract

Oxygenated block polyols are versatile, potentially bio-based and/or degradable materials widely applied in the manufacture of coatings, resins, polyurethanes and other products. Typical preparations involve multistep syntheses and/or macroinitiator approaches. Here, a straightforward and well-controlled one-pot synthesis of ABA triblocks, namely poly(ether- b -ester- b -ether), and ABCBA pentablocks, of the form poly(ester- b -ether- b -ester’- b -ether- b -ester), using a commercial chromium catalyst system is described. The polymerization catalysis exploits mechanistic switches between anhydride/epoxide ring-opening copolymerization, epoxide ring-opening polymerization and lactone ring-opening polymerization without requiring any external stimuli. Testing a range of anhydrides, epoxides and chain-transfer agents reveals some of the requirements and guidelines for successful catalysis. Following these rules of switch catalysis with multiple monomer additions allows the preparation of multiblock polymers of the form (ABA) n up to 15 blocks. Overall, this switchable catalysis delivers polyols in a straightforward and highly controlled manner. As proof of potential for the materials, methods to post-functionalize and/or couple the polyols to make higher polymers are demonstrated.

Triblock polyester thermoplastic elastomers with semi-aromatic polymer end blocks by ring-opening copolymerization

“…58,[62][63][64] In terms of catalyst selection, many catalysts are known for either lactone ROP or epoxide/anhydride ROCOP, there are fewer active for both processes. 57,[65][66][67][68] A further complication is that many ROCOP catalysts deliver polyesters showing bimodal, or multi-modal, molar mass distributions arising from chains initiated from the catalyst, co-catalyst and residual protic compounds (see Fig. S1 † for ROCOP reaction steps).…”

“…70 At sufficiently high diol or water loading, this approach can be used to deliver monomodal molar mass distributions. 57,65,66 The obvious limitation is that N is severely reduced likely preventing phase separation in the resulting block polymers. Our group previously reported a different solution to bimodal molar mass distributions by applying catalysts featuring an organometallic with reactive initiating groups.…”

Orthogonal functionalization of alternating polyesters: selective patterning of (AB)n sequences

“…22,23 These chemistries can be successfully installed by post-functionalization reactions, perhaps most commonly by the thiol-ene reaction. [28][29][30][31][32][33][34][35][36][37][38] Relevant to this are several reports of its application using aliphatic polycarbonates prepared by CO 2 /epoxide ROCOP. [38][39][40][41][42][43][44][45][46][47][48][49][50] For example, Darensbourg and co-workers used it to make amphiphilic block polycarbonates that self-assembled into micelles.…”

“…[21][22][23] The selection of the catalyst is important to ensure the highly alternating structure and there are now quite a range of catalysts which effectively prevent epoxide homopolymerization. 21,[24][25][26][27][28][29][30] In addition to its impressive sequence selectivity, ROCOP is also amenable to manufacturing at scale since many epoxides and anhydrides are already produced and used by the chemical industry. 22 One draw-back of ROCOP is that several useful functional groups are incompatible and, in particular, substituents such as hydroxyl, primary/secondary amine, carboxylic acid and other protic species function as chain transfer agents.…”

Simple In-Based Dual Catalyst Enables Significant Progress in ε-Decalactone Ring-Opening (Co)polymerization

“…26,27 C. Williams has also reported ε-DL copolymerization of tri and tetra component monomer mixtures (epoxide / anhydride / ε-DL and epoxide / anhydride / ε-DL / CO2) promoted by Cr or Zn-based catalysts. 28,29,30 Here, the secondary metal-alkoxide propagating moiety resulting from the ring-opoening of ε-DL imparts well-balanced kinetics and prevents chain-transfer reactions.…”