Core diblock copolymer side chains

Core-Shell Diblock Copolymer Side Chains... 

Scheme 10.9 Synthetic procedure of amphiphilic core-shell cylindrical brushes with PS-b-PAA diblock copolymer side chains [100]. (Reproduced with permission of the American Chemical Society.)...

H) Core-shell diblock copolymer side chains If side chains are built from diblock copolymers, molecular bmshes will exhibit a core-shell-type stmeture. The polymerization techniques that were involved in the stepwise growth of diblock side chains included ATRP, NMP, ROP, or their com-... 

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. 

From a stmctural point of view, assembled polymer cylinders are naturally of 100% grafting density. Each polymer chain that is either crosslinked or fixed in the backbone domain possesses a corresponding block that stretches out of the core as a side chain this is because they are from an identical diblock copolymer molecule, and so wiU always be covalently bonded. 

Among a variety of present stmctures, core-shell molecular bmshes that contain diblock copolymers in the side chains are of special interest. A judicious choice of the two blocks in the side chains may result in an intramolecular phase separation in solution due to their unlike interactions with the solvent. This can aeate a ID channel in the core surrounded by a protective shell. The anisotropically shaped core can be practically used as a nanoreactor to synthesize and accommodate ID inorganic or hybrid nanostmctures. According to the chemical nature of the core and shell, the templates can be classified roughly into three forms, namely, amphiphilic, bishydrophilic, and self-templating core-shell molecular bmshes. 

Figure 4.7 exhibits examples of diblock copolymers with irreversible photo-response. Polymer 30 contains photolabile protecting groups attached to carboxylic groups in the side chains. Upon UV irradiation, photosolvolysis of the pyrenylmethyl ester occurs, 1-pyrenemethanol is cleaved from the polymer chain and carboxylic add groups are released. As a consequence, the hydrophobic block turns into a hydrophilic PMAA block. Core-shell micelles formed by 30 disappeared after irradiation with UV light at 365 nm. This design was further validated with other chromophores (polymers 31-34). °... 

---