Nanofoams

Last but not least, some of us have recently synthesized polyimide-aliphatic polyester triblock and graft copolymers in collaboration with Hedrick and his coworkers [ 97,98]. Well-defined aminophenyl or diaminophenyl end-functional polyester oligomers have been synthesized on purpose and used as end-cappers or macromonomers leading to the aforementioned triblock or graft copolymers, respectively. The polyimide-polyester copolymers so obtained proved to be highly efficient promoters of polyimide nanofoams (for more details see Sect. 4.2). 

Fig. 5. Illustration of the block copolymer approach to nanofoam formation...

Fig. 7. Approach to the preparation of polyimide nanofoam using microphase separated block copolymers...

The successful implementation of the block copolymer approach to polyimide nanofoams requires the judicious combination of polyimide with the thermally labile coblock. The material requirements for the polyimide block are stringent and require thermally stable, high Tg polyimides which can be readily... 

The balance of these different factors is found in the dependence of nanofoam formation on the labile block content in the copolymer [98]. For copolymers with a low composition of labile block, the degradation is rapid, forming a res-... 

New solid electrolytes with high electric conductivity from polymeric nanofoams. Development of new methods for catalysts application over electrodes for fuel cells. Nanotechnology and its application to hydrogen storage. 

The glass transition temperatures ofthe polyimides are 195-250 °C their 10% weight loss temperamres (dynamic thermogravimetric analysis, air, AT = 4.5 °C/min) are 390-422 °C. Of particular interest are the dielectric constants of these polyimides. At a relative humidity of 50% these constants are 2.70-2.90 and are comparable with constants of the best fluorinated polyimides [21, 50-55]. The lowest dielectric constant (2.70) was observed for polyimide based on 6F dianhydride, containing the highest amount of fluorine. Thermal treatment of this polymer film at 280-290 °C for 1 hour led to a decrease (2.45) of dielectric constant due to the possible formation of nanofoams [56]. 

Nawaby AV, Handa YP, Liao X, Yoshitaka Y, Tomohiro M (2007) Polymer-C02 systems exhibiting retrograde behavior and formation of nanofoams. Polym Int 56 67-73... 

After an efficient system has been found, the main open question is how to solidify the foams. One route could be to utilise water-soluble polymers or/and polymerise water-soluble monomers. Another route could be to switch to polymeric microemulsions. One would stepwisely replace the water by the preferred polymerisable hydrophilic monomer/polymer. By doing so one can be sure that the nanostructure of microemulsion remains unaffected. The generation of the nanofoam depends on the used monomer. A fixation via irradiation with fight would be preferable, when photoactive cross-linkers are... 

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