Living Radical Polymerization to New Macromolecules
The discovery of ‘‘living’’ or ‘‘controlled’’ radical polymerizations has spurred extensive research efforts during the past decade. The ability to achieve a high degree of control over polymer microstructure under relatively mild conditions signifies a marked increase in the ease with which structures such as di- and triblock polymers, star polymers, and comb-like graft polymers can be prepared.
(D) The DTC radicals then re-cap the new carbon radical.
Steps (A)through (D) continue until UV light is terminated or all of the materials are consumed.
RAFT and utilize a chain transfer agent that reacts with a propagating macroradical initiated by a conventional free radical initiator.
Structures of RAFT agents commonly used in (mini)emulsion
ATRP, whose origins lie in atom transfer radical addition chemistry, relies on the transfer of a halide atom from a catalyst/ligand complex to a propagating macroradical
Only really sensitive to oxygen Wide range of operating conditions. Control of Macromolecular Structure
•Very good control over molecular weight and
polydispersity.
Enright et al. designed a continuous tubular reactor for the TEMPOmediated polymerization of styrene in miniemulsion
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Atom transfer radical polymerization (ATRP)
polymerization.
Stable-free radical polymerization (SFRP)
SFRP employs a stable nitroxide (e.g. TEMPO; 2,2,6,6tetramethyl-1-piperidinyloxy) to reversibly terminate macroradicals, thereby yielding a dormant chain
(A)The CLiPP photopolymer system forms a crosslinked polymer network upon exposure to UV light, incorporating DTC groups as polymer chain end-caps. DTC groups remain on the polymer surface. (B) Upon subsequent exposure to UV light, DTC andcarbon radicals are reformed. (C) Carbon radicals can propagate through other vinyl groups.
SFRP two-step emulsion polymerization process, initiated with MAMA. Reproduced with permission
Considerable progress has been made in developing an emulsion polymerization process using thewater-soluble SG1-based alkoxyamine ‘‘Bloc-Builder’’, using styrene and/or n-butyl acrylate.
height is adjusted and the setup is exposed to UV light for 500 s.
(F) The top glass with attached photomask is removed leaving a polymer lid layer attached to the middle layer of photomask and glass. (G) The glass-top layer assembly and the bottom layer are aligned so that the polymer layers are facing each other.
Widespread commercialization of L/CRP will likely require the use
of aqueous dispersions.
As basic understanding of the three major types of
L/CRP (stable-free radical polymerization (SFRP),
scale production, providing excellent heat transfer, ease of mixing,
process flexibility such as semi-batch addition of reagents during polymerization, and ease of handling/ transporting the final latex.
(H) Device monomer is placed between the top and base polymer
layers, height is adjusted and the setup is exposed to UV light. (I) Both sets of glass with attached photomasks are removed and device channels are cleaned out with low-pressure air.
•Applicable to a wide range of monomers.
•Inert to many functional groups.
•Robust.
The incentives to progress to aqueous dispersions are important; many polymers made by a free radical process are polymerized in emulsion-based systems, primarily for economic reasons. Aqueous dispersions are the best alternative for large-
atom transfer radical polymerization (ATRP), reversible addition–fragmentation-transfer (RAFT)) developed, so did interest in adapting these systems to aqueous dispersed environments, such as emulsion and miniemulsion
Smulders et al. demonstrated that the RAFT agent PEPDTA(1-苯乙 基二硫代苯乙酸酯 ) can be used to produce styrene/butyl acrylate block copolymers with a high degree of chain end livingness in a train of four CSTRs, and that the process was quite flexible in allowing changes in polymer properties through changes in flow rate, injection point of the second monomer and temperature
This process enables facile modification of polymer surfaces with brush
grafted functional materials (E), or with crosslinkable materials (F).
(A)Glass and photomask are aligned over device monomer. (B) The photomask is brought into contact with device monomer, height is adjusted and setup is exposed to UV light. C) Glass and photomask are removed leaving a polymerized base