This work develops the Polyolefin Active‐Ester Exchange (PACE) process to afford well‐defined polyolefin–polyvinyl block copolymers. α‐Diimine PdII‐catalyzed olefin polymerizations were investigated through in‐depth kinetic studies in comparison to an analog to establish the critical design that facilitates catalyst activation. Simple transformations lead to a diversity of functional groups forming polyolefin macroinitiators or macro‐mediators for various subsequent controlled polymerization techniques. Preparation of block copolymers with different architectures, molecular weights, and compositions was demonstrated with ring‐opening polymerization (ROP), nitroxide‐mediated polymerization (NMP), and photoiniferter reversible addition–fragmentation chain transfer (PI‐RAFT). The significant difference in the properties of polyolefin–polyacrylamide block copolymers was harnessed to carry out polymerization‐induced self‐assembly (PISA) and study the nanostructure behaviors.
Recently
- PAR ID:
- 10236051
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie
- Volume:
- 128
- Issue:
- 42
- ISSN:
- 0044-8249
- Page Range / eLocation ID:
- p. 13204-13208
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
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Abstract This work develops the Polyolefin Active‐Ester Exchange (PACE) process to afford well‐defined polyolefin–polyvinyl block copolymers. α‐Diimine PdII‐catalyzed olefin polymerizations were investigated through in‐depth kinetic studies in comparison to an analog to establish the critical design that facilitates catalyst activation. Simple transformations lead to a diversity of functional groups forming polyolefin macroinitiators or macro‐mediators for various subsequent controlled polymerization techniques. Preparation of block copolymers with different architectures, molecular weights, and compositions was demonstrated with ring‐opening polymerization (ROP), nitroxide‐mediated polymerization (NMP), and photoiniferter reversible addition–fragmentation chain transfer (PI‐RAFT). The significant difference in the properties of polyolefin–polyacrylamide block copolymers was harnessed to carry out polymerization‐induced self‐assembly (PISA) and study the nanostructure behaviors.
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Abstract Ring‐opening polymerization (ROP) of lactones or cyclic (di)esters is a powerful method to produce well‐defined, high‐molecular‐weight (bio)degradable aliphatic polyesters. While the ROP of lactones of various ring sizes has been extensively studied, the ROP of the simplest eight‐membered lactone, 7‐heptanolactone (7‐HL), has not been reported using metal‐based catalysts. Accordingly, this contribution reports the ROP of 7‐HL via metal‐catalyzed coordinative‐insertion polymerization to the corresponding high‐molecular‐weight polyester, poly(7‐hydroxyheptanoate) (P7HHp). The resulting P7HHp is a semi‐crystalline material, with a
T mof 68 °C, which is ~10 °C higher than poly(ε ‐caprolactone) derived from the seven‐membered lactone. Mechanical testing showed that P7HHp is a hard and tough plastic, with elongation at break >670%. P7HHp‐based polyesters with higherT mvalues have been achieved through stereoselective copolymerization of 7‐HL with an eight‐membered cyclic diester, racemic dimethyl diolide (rac ‐8DLMe), known to lead to highT mpoly(3‐hydroxyburtyrate) (P3HB). Notably, catalyst's strong kinetic preference for polymerizingrac ‐8DLMeover 7‐HL in the 1/1 comonomer mixture rendered the formation of di‐block copolymer P3HB‐b ‐P7HHp, showing two crystalline domains withT m1 ~ 65 °C andT m2 ~ 160 °C. Semi‐crystalline random copolymers withT mup to 164 °C have also been obtained by adjusting copolymerization conditions. Mechanical testing showed that P3HB‐b ‐P7HHp can synergistically combine the high modulus of isotactic P3HB with the high ductility of P7HHp. -
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Abstract We introduce the heterocumulene ligand [(Ad)NCC(
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Abstract Reactions of the IrVhydride [MeBDIDipp]IrH4{BDI=(Dipp)NC(Me)CH(Me)CN(Dipp); Dipp=2,6‐
i Pr2C6H3} with E[N(SiMe3)2]2(E=Sn, Pb) afforded the unusual dimeric dimetallotetrylenes ([MeBDIDipp]IrH)2(μ 2‐E)2in good yields. Moreover, ([MeBDIDipp]IrH)2(μ 2‐Ge)2was formed in situ from thermal decomposition of [MeBDIDipp]Ir(H)2Ge[N(SiMe3)2]2. These reactions are accompanied by liberation of HN(SiMe3)2and H2through the apparent cleavage of an E−N(SiMe3)2bond by Ir−H. In a reversal of this process, ([MeBDIDipp]IrH)2(μ 2‐E)2reacted with excess H2to regenerate [MeBDIDipp]IrH4. Varying the concentrations of reactants led to formation of the trimeric ([MeBDIDipp]IrH2)3(μ 2‐E)3. The further scope of this synthetic route was investigated with group 15 amides, and ([MeBDIDipp]IrH)2(μ 2‐Bi)2was prepared by the reaction of [MeBDIDipp]IrH4with Bi(NMe2)3or Bi(Ot Bu)3to afford the first example of a “naked” two‐coordinate Bi atom bound exclusively to transition metals. A viable mechanism that accounts for the formation of these products is proposed. Computational investigations of the Ir2E2(E=Sn, Pb) compounds characterized them as open‐shell singlets with confined nonbonding lone pairs at the E centers. In contrast, Ir2Bi2is characterized as having a closed‐shell singlet ground state.
