Synthesis, characterization, electrochromic properties, and electrochromic device application of a novel star polymer consisting of thiophene end‐capped poly(ε‐caprolactone) arms emanating from a hexafunctional cyclotriphosphazene core

Hexa‐armed and thiophene (Thi) end‐capped poly(ε‐caprolactone) star polymer (N3P3‐(PCL‐Thi)6), containing cyclotriphosphazene core, was prepared in a four‐step reaction sequence. Ring‐opening polymerization (ROP) and “click chemistry” techniques were employed in the first and final steps, respectively. Hexa‐armed PCL star polymer (N3P3‐(PCL‐OH)6) was successfully synthesized via ROP of ε‐caprolactone (ε‐CL) by using hekzakis(p‐(hydroxymethyl)phenoxy) cyclotriphosphazene as the multisite initiator and tin(II) 2‐ethylhexanoate (Sn(Oct2)) as the catalyst in bulk at 115 °C. Further modifications of the N3P3‐(PCL‐OH)6 were accomplished by derivatization of the hydroxyl‐functional chain ends. The obtained N3P3‐(PCL‐OH)6 was then reacted with 2‐bromo‐2‐methylpropanoyl bromide, and this led to a star polymer with bromide end groups, N3P3‐(PCL‐Br)6. In the third step, N3P3‐(PCL‐Br)6 was azidified with sodium azide (NaN3) in DMF affording N3P3‐(PCL‐N3)6. Conversion of the azide chain end groups into Thi was quantitatively accomplished via the “click reaction” between N3P3‐(PCL‐N3)6 and prop‐2‐yn‐1‐yl 3‐thienyl acetate in the final step. Subsequently, the star polymer with six Thi chain ends (N3P3‐(PCL‐Thi)6) was employed in electrochemical copolymerization with both pyrrole and Thi. Electrochromic properties and electrochromic device application of N3P3‐(PCL‐Thi)6/PThi were also investigated.