Polymerization with Universal/Switchable RAFT Agents

Product Description

RAFT (Reversible Addition-Fragmentation chain Transfer) is a form of living radical polymerization involving conventional free radical polymerization of a monomer in the presence of a suitable chain transfer (RAFT) reagent. RAFT technology can be used with a wide range of monomers by all modes of free radical polymerization (solution, emulsion and suspension). The appropriate RAFT agent must be selected for the monomer of interest. Historically there have been no "universal" RAFT agents, capable of preparing block copolymers comprised of both lower activity monomers (LAMs; e.g., N-vinylpyrrolidone (Aldrich Prod. No. V3409), vinyl acetate (Aldrich Prod. No. V1503), etc.), along with more active monomers (MAMs; e.g., acrylates, methacrylates, styrenes, etc.). However, with the development of a new class of stimuli responsive, "pH-switchable" RAFT agents, poly(MAM)-block-poly(LAM) copolymers with narrow molecular weight distributions can be readily achieved. For a further explanation of RAFT technology and its advantages, please read the technical article by researchers at CSIRO.

Reagents

RAFT Agent Catalog Number
Methyl 2-propionate methyl(4-pyridinyl)carbamodithioate   735639
2-Cyanopropan-2-yl N-methyl-N-(pyridin-4-yl)carbamodithioate   736236
S-cyanomethyl-N-methyl-N-(pyridin-4-yl)carbamodithioate 738689
N,N′-Dimethyl N,N′-di(4-pyridinyl)thiuram disulfide   735973

Precautions and Disclaimer

These products are for R&D use only, not for drug, household, or other uses. Please consult the Safety Data Sheet for information regarding hazards and safe handling practices.

Storage/Stability

The products are light sensitive. Store the products at 2–8 °C and keep tightly closed.

RAFT Polymerization Procedures

Example procedures of RAFT polymerization utilizing "Switchable" RAFT reagents (as performed by researchers at CSIRO):

  1. Poly(methyl methacrylate) homopolymer
  2. Poly(vinyl acetate) homopolymer
  3. Poly(methyl methacrylate)-block-poly(vinyl acetate) copolymer



  1. Methyl Methacrylate Polymerization using methyl methacrylate (MMA, Aldrich Prod. No. M55909) as the monomer, 2,2'-Azobis(2-methylpropionitrile) (AIBN) (Aldrich Prod. No. 441090) as the initiator, and a Switchable RAFT agent (Aldrich Prod. No. 736236).
    1. A stock solution (A) of trifluoromethanesulfonic acid (100 μL or 170 mg, Aldrich Prod. No. 347817) in acetonitrile (5.0 mL) was prepared.
    2. A second stock solution (B) containing methyl methacrylate (7.0 mL), AIBN (10 mg), 2-Cyanopropan-2-yl N-methyl, N-(pyridin-4-yl)carbamodithioate (50.02 mg), acetonitrile (2.0 mL) and stock solution A (1.0 mL) was prepared.
    3. 2.0 mL of stock solution B was transferred to an ampoule, degassed by three repeated freeze-evacuate-thaw cycles and sealed. Other glassware suitable for handling air sensitive reactions, such as a schlenk reaction tube, may be used as an alternative to a sealed ampoule.
    4. The ampoule was polymerized at 60 ˚C for 16 hours. Characterization data for this polymerization is presented in Table 1.
    5. To remove color from the final product the polymer was dissolved in excess dichloromethane and passed through a crushed sodium carbonate bed. A color change from yellow to colorless occurs.


    Table 1. Characteristics of PMMA synthesized by switchable RAFT polymerization using Aldrich Prod. No. 736236.

    Reaction Time Mn PDI % Conv.
    3 h 15,500 1.56 27.6%
    6 h 19,200 1.58 51.1%
    16 h 33,050 1.25 98.0%


  2. Vinyl Acetate Polymerization - Using vinyl acetate (Aldrich Prod. No. V1503) as the monomer, 1,1'-Azobis(cyclohexanecarbonitrile) (ACHN) (Aldrich Prod. No. 380210) as the initiator, S-cyanomethyl N-methyl,N-(pyridin-3-yl) carbamodithioate (Aldrich Prod. No. 738689) as the Switchable RAFT agent, and ethyl acetate as solvent (Aldrich Prod. No. 270989).

    1. A stock solution of ACHN (10.3 mg), vinyl acetate (10 mL) and ethyl acetate (5.0 mL) was prepared. An aliquot (3.0 mL) of this stock solution was transferred into an ampoule containing S-cyanomethyl N-methyl,N-(pyridin-3-yl) carbamodithioate (35.0 mg), which was degassed by three repeated freeze-evacuate-thaw cycles and sealed.
    2. The ampoule was heated at 75 °C for 3 days. After the reaction, the un-reacted monomer was removed on rotary evaporator. The resulting poly(vinyl acetate) displayed a low polydispersity as shown in Table 2.


    Table 2. Characteristics of poly(vinyl acetate) synthesized by switchable RAFT polymerization using Aldrich Prod. No. 738689.

    Reaction Time Mn PDI % Conv.
    3 days 8900 1.24 54.8


  3. Poly(methyl methacrylate)-block-poly(vinyl acetate) copolymer prepared using vinyl acetate (Aldrich Prod. No. V1503) as the monomer, ACHN (Aldrich Prod. No. 380210) as the initiator, and the PMMA macro chain transfer agent (MacroCTA) prepared in Procedure A (PMMA, 33,050 Da, PDI = 1.25). The poly(methyl methacrylate)-block-poly(vinyl acetate) copolymer was synthesized under reaction conditions similar to Procedure B.

    Table 3. Characteristics of poly(methyl methacrylate)-block-poly(vinyl acetate) copolymer synthesized by switchable RAFT technology.

    Reaction Time Mn PDI % Conv.
    3 days 55,900 1.39 80


    The Switchable RAFT agents are able to successfully polymerize monomers of different reactivity and achieve narrow molecular weight distributions as shown in Figure 1.

    Figure 1. GPC analysis of poly(methyl methacrylate)-block-poly(vinyl acetate) polymerized for 16 hours using PMMA as a macroCTA. Reprinted from Ref. 1 with permission from the American Chemical Society.



    1 Gel permeation chromatography (GPC) method: Waters Associates liquid chromatograph equipped with differential refractometer and 3×mixed C and 1 mixed E PLgel column. Tetrahydrofuran (flow rate of 1.0 mL/min) was used as eluent at 22 ± 2 °C. The columns were calibrated with narrow polydispersity polystyrene standards. The molecular weights are reported as polystyrene equivalents.

Materials

     

References

  1. Benaglia, M.; Chiefari, J.; Chong, Y.K.; Moad, G.; Rizzardo, E.; Thang, S.H. J. Am. Chem. Soc. 2009, 131, 6914.


Patents WO98/01478 and WO99/311444

Please see sigma-aldrich.com/raftlicense for license details.

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