Hyperbranched Polytriazoles: Click Polymerization, Regioisomeric Structure, Light Emission, and Fluorescent Patterning

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Abstract

Synthesis of hyperbranched poly(1,2,3-triazole)s (hb-PTAs) has been a challenge: the AB2 monomers were inclined to self-oligomerize, and their Cu(I)-catalyzed click polymerizations failed to yield soluble polymers. We tackled the challenge in this work and succeeded in generating hb-PTAs with regioregularity, processability, and functionality. We took an A2 + B3 approach and used diazides 2 and triyne 3 as monomers, which are free of self-oligomerization concerns. Thermal polymerizations of 2 and 3 produced regiorandom polymers (hb-r-P1) with high molecular weights in high yields. Metal-mediated regioselective polymerizations afforded soluble 1,4- and 1,5-linked polymers (hb-1,4-P1 and hb-1,5-P1), presenting the first examples of regioregular hb-PTAs with macroscopic processability. The reactions were affected by substrate and catalyst: electron-rich alkyne generally slowed down the cycloaddition reaction, while ruthenium catalysts (Cp*Ru(PPh3)2Cl and [Cp*RuCl2]n) exhibited higher substrate tolerance than copper catalyst [Cu(PPh3)3Br]. Regiostructures and regioregularities of the hb-PTAs were determined spectroscopically. Degrees of branching of hb-r-P1 were calculated to be ∼90%. Conformations of the hb-PTAs were affected by the steric effects between their aromatic units, which in turn affected their solubility, conjugation, luminescence, and aggregation. While the polymer solutions all emitted deep blue light, the films of hb-1,4-P1, hb-1,5-P1 and hb-r-P1 emitted blue, yellow, and white light, respectively, due to the difference in the aggregation of their chromophoric units in the solid state. Fluorescent photoresist patterns with various emission colors were readily generated from photo-cross-linking of the polymers through a nitrene-mediated photolysis mechanism.

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