Postpolymerization modification

In addition to such postpolymerization modification methods, it is possible to directly include functionalities in PIB during the polymerization process by using pseudohalide initiators, such as azide and thiocyanate, instead of halides [35], Cheradame reported the use of cumyl azide and bifunctional l,4-bis(l-azidomethylethyl)benzene initiators with AlEt2Cl as Lewis acid activator for the polymerization of isobutene directly resulting in the mono-azido and bisazido telechelic PIBs, respectively (Scheme 8.8) [36, 37]. 

The inclusion of additives in the aqueous phase has several objectives. These additives can be used to control the pore and interconnect sizes but, most importantly, they can be used to chemically modify the polymer after polymerization. Surface as well as bulk modification of PHP cannot be achieved through post-polymerization impregnation especially when the pore/interconnect sizes are small and when the sample is thick. Since the additives are uniformly distributed in the aqueous phase droplets, at the postpolymerization modification stage, the additives are uniformly distributed within the pores. As the aqueous phase is the major emulsion phase, large quantities of desired substances can be incorporated within PHP at levels comparable to that of the polymer phase. 

In summary, EUV activation although currently strongly dependent on access to a dedicated synchrotron beamline allows well-controlled grafting of polymer brushes from polymer surfaces with high spatial resolution capabilities. The availability of a large variety of monomers suitable for this grafting process, combined with postpolymerization modification processes, opens a wide field to introduce surface functionalities. Select examples are discussed in Chapter 4. 

GRAFTING FUNCTIONAL MONOMERS VERSUS POSTPOLYMERIZATION MODIFICATION... 

Duebner M, Spencer ND, Padeste C. Light-responsive polymer surfaces via postpolymerization modification of grafted polymer-brush structures. Langmuir 2014 30(49) ... 

Tsarevsky, N.V. Bemaerts, K.V. Dufour, B. Du Prez, F.E. Matyjaszewski, K. Well-defined (cojpoly-mers with 5-vinyltetrazole units via combination of atom transfer radical (cojpolymerization of acrylonitrile and click chemistry -type postpolymerization modification. Macromolecules 2004, 37 (25), 9308-9313. 

Another distinction should be made regarding the extent of functionalization. Whereas endcapping and copolymerization are performed during polymer synthesis and therefore involve all the polymer chains, the postpolymerization modifications do not necessarily affect the complete bulk of the material. Depending on the experimental procedure applied, it is also possible that only the PLA chains on the surface (of a manufactured device or likewise) are modified (surface functionalization). 

W. Chen, et al.. Versatile synthesis of functional biodegradable polymers by combining ring-opening polymerization and postpolymerization modification via Michael-type addition reaction. Macromolecules 43 (2010) 201-207, doi 10.1021/ma901897y. 

Multifunctionality can be introduced not only through copolymerization but also by polymer analogous reactions in a postpolymerization modification step, often in combination with the introduction of additional comonomers during the polymerization process. Well-known technical examples are copolymers of polyvinyl alcohol and polyvinyl acetate with different amounts of vinyl acetate (see Section 3.1.3), which all derive from homopoly(vinyl acetate) and are the result of acetate hydrolysis to a different extent. The content of remaining vinyl acetate groups defines the hydrophilicity/hydrophobicity of the copolymer and thus the amphiphilic and stabilizing character of the material. 

ATRP initiators or RAFT CTAs containing protein-reactive moieties can be used to yield a-functionalized polymers, while postpolymerization modifications can be performed to yield ffi-ftmctionalized polymers. Figure 3 contains examples of functionalized ATRP initiators and RAFT CTAs. The resulting polymers can then be used to produce protein-polymer conjugates consisting of a single polymer chain and a single protein. These techniques can also be combined to synthesize polymer-linked protein dimers. 

ATRP produces polymers with a readily accessible site for postpolymerization modification. The majority of the polymer... 

Postpolymerization modification is yet another method of tailoring polymer properties and can be considered a modular attribute of a macromolecule [37]. Given that the metals in the bis(NHC) polymers are coordinatively unsaturated, the use of an exogenous ligand added postpolymerization was expected to bind to the metal thus altering the physical and electronic properties of the polymer. Addition of PPhj or PCyj to a suspension of polymer 53a in THF quickly affected complete dissolution of the phosphine-bound polymer. Ligation was confirmed by H and P NMR spectroscopy. 

With the thiol-ene (click) reaction unsaturated moieties in a polymer can be modified. This is of interest, because some monomers are not readily pol5mcierizable to give the desired polymer. In fact, postpolymerization modification of a polymer backbone is an important strategy in pol5mcier science. 

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