Poly aromatic amides, aramids, have attracted a lot of attention because of their excellent physical properties like high strength, flame resistance, durability. Polymer backbone contains rigid aromatic rings linked by amide bridges which experience additional attractive forces of Hydrogen bonding. The microstructure may be crystalline in nature if rings have p- linkages or amorphous if connectivity is at O-or m- positions. The properties have been modified in several ways to suit the specific applications. Poly dimethyl siloxanes, PDMS are known as specialty polymers for their unique properties. The backbone is very soft but thermally stable.
The block copolymers of aramids and PDMS are one of the new active research fields. The hard and soft blocks are connected together to achieve the desirable properties like thermal stability, physical strength and controllable processibility.
In the present work, various combinations of the aramid and PDMS blocks have been studied. The aramid blocks in the form of oligomers were prepared under inert and moisture tree environment set at low temperature around zero degree Celsius. The diamines were dissolved in DMAc and chilled. The diacids were also dissolved in DMAc and added drop-wise to the chilled solution. Triethylamine was later used to remove the HC1 and the mixtures were stirred for overnight. To prepare the block copolymers, PDMS oligomers were dissolve in THF and added drop-wise to the aramid oligomers solutions, both in equimolar quantities. The copolymers were precipitated out with methanol, washed and dried.
A total of 37 block copolymers have been synthesized. For reference purposes, 5 pure aramid polymers were also prepared. All the samples have been characterized for their chemical structure by FTIR. proton NMR, DV-Visible, TGA and Elemental analysis techniques.
The FTIR spectra of the block copolymers show the presence of all the active functional groups present in the aramid and PDMS parts. The assigned peaks can also be located on the individual relevant spectra of pure aramid polymer and PDMS oligomer. Similarly the NMR results have also proved the presence of all the respective types of protons in the block copolymer.
The results of UV-Visible scans have shown clearly the presence and effect of hydrogen bonding in the aramid blocks. The shift in peak position is indicative of the increase in magnitude of such interaction in the samples resulting from the increase in aramid block length.
The thermal stability concluded from the TGA curves have been found in accordance with the nature of the backbone. The block copolymers with longer aramid blocks need higher temperature to reach the ten percent degradation mark.
The elemental analyses have provided almost the same contents of carbons, hydrogen and nitrogen as expected in the chemical formulae of one pair of an aramid and a PDMS blocks.
Summarizing the results, it can be concluded that the aramid-PDMS block copolymers have been synthesized successfully according to the plan.