Isospecific, Chain Shuttling Polymerization of Propylene Oxide Using a Bimetallic Chromium Catalyst: A New Route to Semicrystalline Polyols

Abstract

Hydroxy-telechelic poly(propylene oxide) (PPO) is widely used industrially as a midsegment in polyurethane synthesis. These atactic polymers are produced from racemic propylene oxide using chain shuttling agents and double-metal cyanide catalysts. Unlike atactic PPO, isotactic PPO is semicrystalline with a melting temperature of approximately 67 °C. Currently there is no practical route to hydroxy-telechelic isotactic PPO using racemic propylene oxide as the monomer. In this paper, hydroxy-telechelic isotactic PPO is synthesized from racemic propylene oxide with control of molecular weight using enantioselective and isoselective bimetallic catalysts in conjunction with chain shuttling agents. The discovery of an easily accessible bimetallic chromium catalyst is reported for this transformation. Diol, triol, and polymeric chain shuttling agents are used to give hydroxy-telechelic isotactic PPO of varying functionality and structure. Detailed quantum chemical studies are used to reveal the polymerization mechanism and origin of stereoselectivity.

Bimetallic Chromium Catalysts with Chain Transfer Agents: A Route to Isotactic Poly(propylene oxide)s with Narrow Dispersities

“…[1] Whereas aPPO is amorphous, isotactic PPO (iPPO) is as emi-crystalline analogue that has the promise to lead to improved properties and therefore new applications.H owever, there are few catalysts that display sufficient stereocontrol to produce semi-crystalline polymers from racemic epoxides.Furthermore,these systems generally suffer from poor control of molecular weight and high dispersity. [2] Yet, the industrial use of telechelic polyethers in polyurethanes requires low dispersities.W et herefore sought anew class of catalysts that would enable the synthesis of isotactic PPO with low dispersities from racemic propylene oxide.…”

Thiol‐Ene Cationic and Radical Reactions: Cyclization, Step‐Growth, and Concurrent Polymerizations for Thioacetal and Thioether Units

“…[2][3][4][5][6][7][8][9] In addition, concurrently occurring polymerizations of common monomers by different propagating species such as radicals,c ations,a nd anions are attractive because they can dramatically widen the scope of accessible polymer structures with novel and/or tunable properties. [10][11][12][13][14][15][16][17][18] Athiol and olefin usually undergo radical addition, that is, at hiol-ene reaction, which is one of the most efficient and robust click reactions,e ither in the presence of ar adical initiator or under UV irradiation to result in the anti-Markovnikov adduct with high selectivity and high yield. [19][20][21] Under radical conditions,athiyl radical is generated from thiol and adds to the olefin to form ac arbon radical, which then abstracts ah ydrogen atom from thiol to result in athioether product and regeneration of another thiyl radical (Scheme 1A).…”

High‐Activity Organocatalysts for Polyether Synthesis via Intramolecular Ammonium Cation Assisted SN2 Ring‐Opening Polymerization

“…Nevertheless,t he M n of the generated PPO does not exceed 13 kg mol À1 . [5] With the development of Group 13 and transition-metal-based catalysts, [6][7][8][9][10][11][12][13] polyethers with high molecular weights (M n up to 25 kg mol À1 )a nd even high regio-and stereoselectivity could be efficiently produced under mild conditions in ac ontrolled manner. [12,13] Despite significant progress,aconcern regarding metal-based catalysis systems is the metal residue,especially for the toxic cobalt and chromium systems,leading to limitations of their applications.…”