Synthesis of Poly(p-phenyleneethynylene)s with Crosslinkable End or Side Groups and Its Solid State Structure and Optical Properties Before and after Crosslinking

Two crosslinkable poly(p-phenyleneethynylene)s(PPEs): poly [2,5-di(2'-ethyl-hexyloxy)-1,4-phenyleneethynylene] with end-capped vinyl(PPE1) and poly [2,5-di(allyloxy)-1,4-phenyleneethynylene-2,5-di(2'-ethyl-hexyloxy)-1,4-phenyleneethynylene](PPE2) were synthesized. Via the thermal addition reactions of vinyl end groups of PPE1 and allyloxy side groups of PPE2, crosslinked polymers C-PPE1 and C-PPE2 were obtained, respectively. The two polymers were characterized by wide-angle X-ray diffraction(WXRD), ultraviolet-visible(UV-Vis) absorption, and photoluminescence(PL). The results indicate that in the solid state, the polymer chains of PPE1 were packed with a low degree of crystallinity because of the sterically hindered(2'-ethyl-hexyl)oxy branched side chains, but, because of the introduction of allyloxy side chains, the polymer chains of PPE2 were packed in an order fashion with a high degree of crystallinity. Because of the high crosslinking density in C-PPE2, the formation of aggregates and excimer was hampered by the formed crosslinking network more effectively in C-PPE2 film than in C-PPE1 film.