Block ionomers

Reverse micelles from PMAA and PAA-containing copolymers have been extensively studied by Eisenberg and coworkers [104,105]. These authors considered the micellization of the so-called "block ionomers formed of a major PS block linked to ionized PAA and PMAA segments. Stable spherical micelles were formed by these copolymers in organic solvents such as toluene. Their characteristic size was systematically investigated by a combination of experimental techniques including TEM, SAXS, DLS, and SLS. The micelles were shown to consist of an ionic core and a PS corona. The mobility of the PS segments located near the ionic core was found to be restricted, as discussed in Sect. 2.4. 

Similar IPEC-based aqueous micelles can be obtained from the mixing of a double-hydrophilic copolymer AB with a homopolymer C or a diblock copolymer AC or a diblock copolymer DC, provided that IPECs can form between the B and C blocks. This kind of electrostatic complex has also been referred to as block ionomer complexes, or BIC. 

Fang Z, Kennedy JP. Novel block ionomers. I. Synthesis and characterization of polyisobuty-lene-based block anionomers. J Polym Sci Part A Polym Chem 2002 40 3662-3678. 

A block ionomer of poly(i.-glutamic acid)-poly(L-leucine) was studied in aqueous solution using ultramicroscopy (Section 1.4.18) and DLS by Price et al. 

Figure 9.4 Core-shell polyplex structures (A) cationic particles with a core from neutralized DNA and polycation and a corona from polycation chains adsorbed on the core (B) electroneutral particles ( polyion complex micelles or block ionomer complex ) with a core from neutralized DNA and poly cation and a corona from nonionic water soluble polymer.

Bronich, T.K., Nehls, A, Eisenberg, A, Kabanov, V.A. and Kabanov, A.V. (1999) Novel drug delivery systems based on the complexes of block ionomers and surfactants of opposite charge. Colloids Surf. B, 16, 243-251. 

It is an important aspect that block-copolymer micelles are characterized by much longer relaxation times than compared to low molecular surfactants. Non-equilibrium morphologies can easily be obtained in a vitrified state due to the efficient suppression of structural reorganization, because of the corresponding very slow response of the micelles to changes of temperature, solvent and concentration. In the case of a block-ionomer, i.e. a diblock copolymer where one block consists of ionic units, it was observed that micelles which formed in non-polar solution needed weeks to re-equilibrate after dilution of the solvent [226-228]. 

Figure 47.1. Types of naiiocaniers for dmg delivery. A liposomes B nanopaiticles C nanospheres D nanosuspensions E polymer micelles F- nanogel G block ionomer complexes H nanofibers and nanot ...

The most important ionic groups are carboxylates and sulfonates, but other groups like ammonium have also been reported. " Special classes of ionomers are zwitterionic ionomers, which contain both cationic and anionic groups, as well as ionomers with regular architectures like block ionomers, mono- or telechelic ionomers, star ionomers, or ionenes, which have regularly spaced ionic groups. ... 

A third approach towards the production of vesicles involves complementary supramolecular complexation, for instance by mixing oppositely charged block ionomers or by cofactor-enzyme interactions - two examples are presented in Sect. 2.3. 

We are currently exploring new routes to the synthesis of ionomers with controlled architecture, i.e. with control over the amount and location of ionic groups in the polymer backbone. One of our main interests is the synthesis of ion containing block copolymers. The applicability of anionic polymerization in the synthesis of block copolymers and other well defined model systems is well documented (22-24) Not as well appreciated, however, is the blocky nature that certain emulsion copolymerizations may provide. Thus, we have utilized both anionic and free radical emulsion polymerization in the preparation of model ionomers of controlled architecture. In this paper, the synthesis and characteristics of sulfonated and carboxylated block ionomers by both free radical emulsion and anionic polymerization followed by hydrolysis will be discussed. 

B) Block Ionomers Through Anionic Polymerization and Hydrolysis... 

ALLEN ET AL. Studies on the Synthesis of Novel Block Ionomers... 

Figure 4. FT-IR spectra of (A) polystyrene/poly(isobutyl methacrylate) diblock copolymer and (B) carboxylated block ionomer obtained after hydrolysis with K0-.

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