A-B-A stereoblock copolymers of N-isopropylacrylamide

作者：Nuopponen Markus; Kalliomaeki Katriina; Laukkanen Antti; Hietala Sami; Tenhu Heikki^*

来源：Journal of Polymer Science Part A: Polymer Chemistry , 2008, 46(1): 38-46.

DOI：10.1002/pola.22355

• amphiphiles
• hydrophilic polymers
• isotactic
• macromonomers
• reversible addition fragmentation chain transfer (RAFT)

A-B-A stereoblock polymers with atactic poly(N-isopropylacrylamide) (PNIPAM) as a hydrophilic block (either A or B) and a non-water-soluble block consisting of isotactic PNIPAM were synthesized using reversible addition fragmentation chain transfer (RAFT) polymerizations. Yttrium trifluoromethanesulfonate was used in the tacticity control, and bifunctional S,S'-bis(alpha,alpha'-dimethyl-alpha ''-acetic acid)-trithiocarbonate (BDAT) was utilized as a RAFT agent. Chain structures of the A-B-A stereoblock copolymers were determined using (1)H NMR, SEC, and MALDI-TOF mass spectrometry. BDAT proved to be an efficient RAFT agent in the controlled synthesis of stereoregular PNIPAM, and both atactic and isotactic PNIPAM were successfully used as macro RAFT agents. The glass transition temperatures (T(g)) of the resulting polymers were measured by differential scanning calorimetry. We found that the T(g) of isotactic PNIPAM is molecular weight dependent and varies in the present case between 115 and 158 degrees C. Stereoblock copolymers show only one T(g), indicating the miscibility of the blocks. Correspondingly, the T(g) may be varied by varying the mutual lengths of the A and B blocks. The phase separation of aqueous solutions upon increasing temperature is strongly affected by the isotactic blocks. At a fixed concentration (5 mg/mL), an increase of the isotacticity of the stereoblock copolymers decreases the demixing temperature.

• 出版日期2008-1-1