Effect of nonconjugated polymers on the conjugation length and structure of poly(3-octylthiophene) in ternary polymer blend

The shifting of λmax (π‐π* transition) of P3OT (poly(3‐n‐octylthiophene)) was used to monitor the degree of miscibility between P3OT and the matrix polymers. In the ternary blend system, 1% of P3OT is soluble in a uniform PMMA/EVA20 mixed matrix and does not interfere with the miscibility between PMMA and EVA20 (ethylene‐vinyl acetate copolymer with 20% of vinyl acetate). But 5% of P3OT can attract EVA20 out of the matrix and induce the separation from 95% of PMMA/EVA20 matrix and cause the doublet peak of λmax. Likewise, the DSC thermograms do not demonstrate the melting‐point depression of EVA20 in a 5% P3OT ternary system. However, the melting‐point depression did occur only for 1% of P3OT. IR‐spectra demonstrate that the methylene groups affinity contributed to the misciblity either in 1% P3OT/PMMA or in P3OT (1 and 5%)/EVA20. The solubility difference of P3OT in PMMA (poor) and EVA20 (better) creates a continuous morphology for obtaining a highly conjugated path in a nonconjugated matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 773–781, 2007