[4][5] With the CSA, which had joined the Ligue de Football Association (LFA) in 1910, Poullain was able to measure himself against the best Parisian clubs, such as CA Paris, FEC Levallois, and Jules Rimet's Red Star AC, and even play friendly matches in the ranks of the Red Star, alongside Eugène Maës, but he did not impose himself because of his style, which was always discussed, since he placed efficiency above technique, often shooting on goal, including from afar, which was uncommon at the time.

[5] Despite his lack of technique, his game married that of Maës, who was basically a "target man" or "poacher", and therefore, on 27 February 1913, both of them were called up by France for a friendly match against England amateurs at Colombes, which ended in a 1–4 loss;[2][3][5] Poullain scored his side's only goal in the 75th minute, with a shot from 25 meters out that beat the English goalkeeper Horace Bailey, a 1912 Olympic champion.

[3] During the First World War, Poullain was taken prisoner very early, at the end of August 1914, and transferred to the Altengrabow camp, near Magdeburg, where he found several fellow international footballers, such as Victor Denis, Henri Lesur, Charles Renaux, among others, and naturally, all of them formed a team, despite the prisoners not being allowed to cross the barbed wire that separated the barracks, so the games were often interrupted by the German sentries.

[5] He eventually became ill, and since the Germans had little concern for taking care of the sick, Poullain was repatriated, which allowed him not only to return to France, but to play football again, this time at CA Paris, from 1917.

[5] Poullain went on to wear the national jersey again, but this time unofficially, in a friendly against Belgium on 21 April 1918 (2–5), alongside Devaquez and Darques, and his old comrade Dartoux.