Direct polymerization of functional monomers
Direct incorporation of functional groups into the polymer backbone
No post-polymerization modification required
High degree of functionality (DPfunctional monomer)
Arrangement dependent on (co)polymer architecture
Plethora of monomers with different functionality available
A number of monomers containing polar functional groups have been successfully polymerized by ATRP. They include acrylonitrile (AN),(1-5) (meth)acrylamides,(6,7) 4-vinyl pyridine (4VP),(8,9) dimethylaminoethyl methacrylate (DMAEMA),(10) and monomers containing an -OH group such as 2-hydroxyethyl acrylate (HEA)(11) and 2-hydroxyethyl methacrylate (HEMA).(12) Glycidyl acrylate(13) has also been polymerized by ATRP yielding well-defined polymers containing the reactive glycidyl group, which can be used as a precursor for other functional groups.(14) Water-soluble monomers (both neutral and ionic) can be polymerized in controlled fashion by ATRP directly in protic (aqueous) media.(15,16) Some examples of monomers, including some with polar groups that have been polymerized by ATRP, are shown below.
ATRP catalysts with strongly binding ligands should be used for copolymerization of monomers containing functional groups (mostly substituted amides, amines, or pyridines) to avoid, or reduce, competitive complex formation between the monomer or polymer and the copper center.(17) In many cases, catalyst destabilization can be suppressed by selection of the proper ligand or addition of excess ligand or excess "pseudo" ligand. For example, in the ATRP of sodium 4-styrenesulfonate in aqueous solution, there is a rapid disproportionation of the ATRP catalyst, resulting in loss of control. However, this disproportionation reaction is prevented in the presence of excess pyridine (a "pseudo" bpy ligand) or added bromide ions.(18) This is shown in the following table where water and a 1:1 water/pyridine mixture was used as the solvent for an ATRP polymerization of sodium 4-styrenesulfonate with a CuBr/bpy catalyst using a MePEOBiB initiator at 100:1 ratio at 30 0C.
The reaction was clearly controlled to a greater degree in the presence of a large molar excess of pyridine, which functions as a "pseudo" ligand, to ensure that the CuBr/bpy catalyst complex remains in solution.
While the ATRP of several types of polar monomers, particularly acidic ones, has proven to be quite challenging, progress continues to be made.(17,19,20)
Other Functional Monomers Successfully Polymerized by ATRPThe following schematic shows some of the monomers polymerized by ATRP and include styrenes, (meth)acrylates, (meth)acrylamides. While polymerization of monomers with free acidic groups remain a challenge the can be incorporated into a copolymer if attention is given to presevation of an active catalysy complex throughout the reaction since functionality often dictates the appropriate conditions for an ATRP, solvent, temp, catalyst, etc..
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