import re
s = "I have a string ^submarine I want to be able to detect ^marines as a match"
kw = "^submarine"
r = re.compile(r"(?<!\w)[{0}]+(?!\w)".format(re.escape(kw)))
print(r.findall(s))
aW1wb3J0IHJlCnMgPSAiSSBoYXZlIGEgc3RyaW5nIF5zdWJtYXJpbmUgSSB3YW50IHRvIGJlIGFibGUgdG8gZGV0ZWN0IF5tYXJpbmVzIGFzIGEgbWF0Y2giCmt3ID0gIl5zdWJtYXJpbmUiCnIgID0gcmUuY29tcGlsZShyIig/PCFcdylbezB9XSsoPyFcdykiLmZvcm1hdChyZS5lc2NhcGUoa3cpKSkKcHJpbnQoci5maW5kYWxsKHMpKQ==