Tailoring of polypyrrole backbone by optimizing synthesis parameters for efficient EMI shielding properties in X-band (8.2-12.4 GHz)

- Optimized ratio of dopant: oxidant: monomer for PPy synthesis was found to be 1: 2: 1.
- PPy synthesized using SLS as dopant gave best combination of properties.
- PPy synthesized had highest conductivity (42 S/cm) and EMI shielding (-126 dB).

This paper describe the effect of reaction conditions i.e. oxidant concentration (ferric chloride), dopant concentration and nature of dopant (sodium lauryl sulphate [SLS], sodium dodecyl benzene sulphonate [SDBS], lithiosulphoisophthalic acid [LiSiPA] and naphthalene disulphonic acid [NDSA]) on the conductivity and electromagnetic shielding properties of polypyrrole (PPy). PPy was synthesized using one mole of dopant [SLS] and varying concentrations of oxidant (2, 3, 4 and 5 mol per mole of pyrrole). The conductivity and shielding effectiveness of PPy obtained was found to be dependent on the concentration of oxidant and it was highest when the molar ratio of pyrrole: oxidant: dopant was 1:2:1. In the second set of experiments, dopant concentration [0.6, 1, 1.4 and 1.8 mol per mole of pyrrole] was varied keeping the concentration of pyrrole: oxidant as 1:2 to determine the optimum concentration of dopant. The polymer prepared using pyrrole: oxidant: dopant ratio as 1:2:1 showed the highest conductivity as well as the shielding effectiveness. Using these optimized conditions polypyrrole was synthesized using different dopants [i.e. SLS, SDBS, LiSiPA and NDSA]. Polypyrrole synthesized using optimized conditions and SLS as dopant had highest conductivity (42 S/cm) and electromagnetic shielding effectiveness of −126 dB in the X-band [8.2-12.4 GHz] which is the highest value ever reported for the PPy synthesized by chemical oxidative polymerization. The shielding properties discussed in the present paper are very close to the conventional metals with an additional advantage that the primary mechanism of shielding is absorption dominant.

Polypyrrole backbone was tailored to achieve highest EMI shielding value (-126 dB and an average of −110 dB for samples of 3 mm thickness).152