Chazzan: יִתְגַּדַּל וְיִתְקַדַּשׁ שְׁמֵהּ רַבָּא / May His great name be exalted and sanctified
Congregation: !אָמֵן / Amen!
Chazzan: בְּעָלְמָא דִּי בְרָא כִרְעוּתֵהּ / in the world which He created according to His will.
Chazzan: יִתְבָּרַךְ וְיִשְׁתַּבַּח וְיִתְפָּאַר וְיִתְרומַם וְיִתְנַשּא וְיִתְהַדָּר וְיִתְעַלֶּה וְיִתְהַלָּל שְׁמֵהּ דְּקֻדְשָׁא בְּרִיךְ הוּא / Blessed and praised, glorified and exalted, extolled and honoured, adored and lauded be the name of the Holy One, blessed be He,
Congregation (Some traditions): !בְּרִיךְ הוּא / Blessed be He!
Congregation (Some traditions): !אָמֵן / Amen!
לְעֵלָּא מִן כָּל בִּרְכָתָא וְשִׁירָתָא תֻּשְׁבְּחָתָא וְנֶחֱמָתָא דַּאֲמִירָן בְּעָלְמָא / above and beyond all the blessings, hymns, praises and consolations that are uttered in the world.
Translations from Wikipedia
It seems strange to me to interject these responses in the middle of a sentence, instead of or in addition to at the end of the sentence. Most of the time, when we say "Amen," it's at the end of a blessing.
Why do we interrupt like this in Kaddish?