Dependence of the luminescent properties and chain length of poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylene vinylene] on the formation of cis‐vinylene bonds during Gilch polymerization

Abstract

The presence of cis-vinylene bonds in Gilch-polymerized poly[2-methoxy-5-(2 0 -ethyl-hexyloxy)-1,4-phenylene vinylene] is reported. Through fractionation, species with a weight-average molecular weight of less than 37,000 exhibited an abnormal blueshift of photoluminescence spectra in toluene solutions, and this was attributed to the presence of cis-vinylene bonds, as verified by NMR spectroscopy. Surprisingly, the fractionated species ($1 wt %) with a weight-average molecular weight of 5000 were mostly linked by the cis-vinylene bonds. The concentration decreased with the molecular weight until a molecular weight of 37,000 was reached; at that point, the polymer chains contained mainly trans-vinylene bonds. Obviously, the formation of cis-vinylene bonds strongly inhibited the growth of polymer chains during Gilch polymerization.

Origin of the methylene bonds in poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylenevinylene] prepared according to Gilch's method: novel applications

“…It is generally agreed that cis ‐vinylene protons also resonate at δ = 6.5–6.8 ppm for the PPV derivatives prepared by the Wittig reactions 24–26. In our previous study, we have mistakenly attributed the peak at δ = 6.6–6.7 ppm for the MEH‐PPV prepared from monomer I to the formation of cis ‐vinylene bonds during Gilch polymerization 15. As the resulting polymer was subjected to thermal treatment at 200 °C for 1–2 h, half of the methylene bonds were broken as indicated by the decrease of the peak at δ = 6.6–6.7 ppm 16.…”

“…Lately, we discovered the presence of methylene defects (or bonds) in MEH‐PPV chains—defects that are prone to break at 200 °C, at least 150 °C lower than the major degradation temperature of defect‐free MEH‐PPV. This bond has been mistakenly assigned to the cis defect in our previous studies because of the similarity between their 1 H‐NMR spectra 15. Through thermal annealing of MEH‐PPV in order to break the methylene bonds at 200 °C, the extent of chain aggregation was significantly reduced, so that the maximum quantum yield of photoluminescence (PL) was increased to six times that of untreated MEH‐PPV 16…”

Polarized optical spectroscopy applied to investigate two poly(phenylene-vinylene) polymers with different side chain structures

“…The molecular weights of these two polymers are markedly different; for poly͑2Ј-methoxy-5-2-ethyl-hexoxy͒-1,4-phenylene vinylene ͑MEH-PPV͒ the upper limit is ϳ300 000 g / mol, while for poly͑2-͑3Ј ,7Ј-dimethyloctyloxy͒-5-methoxy-1,4-phenylenevinylene͒ ͑OC 1 C 10 -PPV͒ the molecular weight can be as high as 1 900 000 which corresponds to ϳ7000 repeat units. 41,42 Dry powder was dissolved under stirring in toluene. For films the concentration was ϳ5 mg/ ml, and films were made by spin coating at 1500 rpm/ 30 s deposition on a glass plate.…”

Enhancing the electroluminescent efficiency of poly{5‐methoxy‐2‐[(2′‐ethyl‐hexyl)‐oxy]‐p‐phenylenevinylene}/poly(2,3‐diphenyl‐5‐octyl‐p‐phenylenevinylene) polyblends by the introduction of chemical bonding through a thermal treatment

“…The copolymerization of MEH–PPV monomers with DPO–PPV monomers via the Gilch route22 is prone to form an alternative copolymer:23 That is, MEH–PPV monomers prefer to react with DPO–PPV monomers and vice versa. We also found that MEH–PPV molecular chains were easily cleaved from their cis‐linkage defects by a thermal treatment in our previous study 24, 25. Thus, we thought that if MEH–PPV/DPO–PPV polyblends were thermally treated in vacuo , their constituent polymers would be able to react and link with each other and turn the polyblend into a system more like a block copolymer.…”