Ultra‐low modulus polyazomethines and enhanced adhesion strength with copper foils

Abstract

Polyazomethines (PAzMs) were prepared from dialdehydes containing different lengths of alkylene groups (m = 2–12) and an ether‐containing common aromatic diamine. The main purpose of this work is to achieve an ultra‐low modulus and a considerably high adhesion strength with a smooth surface (S‐side) of electro‐deposited copper foils for applications as novel coating‐type protective layer materials of flexible printed circuit boards. The elongation at break of the PAzM films was drastically enhanced by increasing the annealing temperature (Ta). The results are probably attributed to a chain extension effect accompanied with solid‐state polymerization promoted at elevated temperatures. An increase in the alkylene chain length (m) led to a gradual decrease in the modulus of the PAzM films owing to an increase in the chain flexibility. It also drastically improved the adhesion strength (S‐side); 8.3 N cm–1 at m = 12 in spite of the absence of anchoring effect. To further decrease the modulus, the PAzM (m = 12) was modified with another diamine comonomer containing a polybutylene oxide block. This approach was very effective for achieving the present target properties; the PAzM copolymer displayed ultra‐low tensile modulus (0.20 GPa) and a very high adhesion strength (9.8 N cm–1) with the S‐side of copper foils. Copyright © 2015 John Wiley & Sons, Ltd.