Acrylic acid polymerization polymer brushes

The emulsion polymerization in the third step is carried out in the presence of a water soluble monomer, such as acrylic acid. The radicals formed by the photolysis of HMEM (Fig. 6.18b) on the surface start radical chain polymerization by a grafting-from technique (see Section 6.13.3) thus generating chains of poly(acrylic acid). The polymer chains remain bound to the surface by an ester bond which can be cleaved by hydrolysis to obtain the polymer for analysis. Thus the molecular weight of the bound polymer chains can be determined which gives their contour length Lc. The thiclcness L of the brush (Fig. 6.17) attached to the surface of the particles can be deduced from the hydrodynamic radius as measured by dynamic light scattering. 

Figure 6. Interaction of a water droplet with 200 micron features of a patterned polymer brush prepared by surface-initiated polymerization. The unusual wetting profile is due to preferential interaction of the water droplet with the polymery lie acid) brush domains (light) and complete non-wetting of the hydrophobic poly(tert-butyl acrylate) domains (dark).

A solution to the steric bulk of the macromonomers is grafting from where polymerizations occur from the functionalized side chains of the ROMP-generated backbone. The copolymerization of propylene with 4mol% GOD yielded terminal vinyl groups off the main polymer chain resulting from the addition of the GOD. Attachment of the catalyst at the vinyl group via olefin metathesis enabled ROMP of nor-bomene derivatives from the polyolefin backbone.In a grafting from approach, norbornene monomers with covalently attached ATRP initiators were copolymerized with ester-functionalized norbomenes to form the polymeric backbone. The ATRP of acrylic acid successfully yielded the brush polymer. 

The synthesis of cylindrical polymer brushes with amphiphilic poly(acrylic acid)-block-poly(n-butyl acrylate) (PAA-b-PnBA) diblock copolymer side chains is shown in Fig. 13.14. The procedure includes several steps (i) synthesis of a well-defined macroinitiator, PBIEM, by esterification of poly(2-hydroxyethyl methacrylate) (PHEMA), which was synthesized via ATRP of 2-hydroxyethyl methacrylate (HEMA) or anionic polymerization of silyl-protected HEMA (ii) ATRP of t-butyl acrylate (tB A) initiated by the pendant a-bromoester groups of PBIEM, yielding cylindrical brushes with PtBA homopolymer side chains (iii) sequential ATRP of n-butyl acrylate (nBA) forming the cylindrical bmshes with diblock copolymer [poly(t-butyl acrylate)-block-poly(n-butyl acrylate) (PtBA-b-PnBA)] side chains and (iv) hydrolysis of the PtBA block to produce the hydrophilic poly(acrylic acid) (PAA) block forming the core of an amphiphilic core-shell cylinder brash [106]. By using this technique, other well-defined core-shell cylindrical polymer brashes with polystyrene (PS), PS-b-PAA or PAA-b-PS, as side chains have been successfully synthesized. 

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