Yes. The OED supplies both adjectival and noun meanings. The latter are senses B1 and B2a & b.
B1 is the grammar sense, of 'the imperative' - that part of the verb expressing command.
2a derives from the grammatical sense as a command of someone for something of great importance.
2b concerns the the categorical imperative a philosophical concept propounded inter alia by Emmanuel Kant (1724-1804).
But the noun is nowadays used loosely in English as an action of essential necessity. e.g. The first imperative of any government is the protection of its own citizens.
1. Grammar. The imperative mood, or a verbal form belonging to it (see A. 1).
1530 J. Palsgrave Lesclarcissement Introd. 36 Je puis wanteth his
present imparatyve and his present optatyve.
1624 N. De Lawne tr. P. Du Moulin Elements Logick 108 Imperatives,
Optatives, and Subjunctives enter not into an Enuntiation.
1728 E. Chambers Cycl. Imperative,..is one of the Modes or Manners
of Conjugating a Verb, serving to express a Commandment.
1755 Johnson Gram. Eng. Tongue in Dict. The Imperative prohibitory
is seldom applied in the second person..without the word do; as Stop
him, but do not hurt him.
1871 H. J. Roby Gram. Latin Lang. §581 The imperative present
appears to consist of shortened forms of the indicative present.
2. An imperative action, speech, condition, etc.; an action, etc. involving or expressing a command; a command.
1606 W. Birnie Blame of Kirk-buriall xvi. sig. D4v, The Lords lawes are either imperatiues of good or inhibitiues of ill.
1633 T. Adams Comm. 2 Peter (iii. 16) 1452 There be..such mysticall allusions, such majesticall imparatives.
a1856 W. Hamilton Lect. Metaphysics (1859) II. xlvi. 516 The unconditional imperative of the moral law.
1868 A. Bain Mental & Moral Sci. (1875) 459 There is no act however trivial which cannot be raised to the position of a moral act, by the imperative of society.
2b. Categorical imperative: see categorical adj. 1c.
1796 F. A. Nitsch Gen. View Kant's Princ. conc. Man 195 An Imperative..which is founded upon reason itself..is a Categorical Imperative which represents an action as necessary in itself.
1817 S. T. Coleridge Biogr. Lit. 70 The unconditional command, or (in the technical language of his school) the categorical imperative, of the conscience.
1888 Pall Mall Gaz. 29 Oct. 2/2 The practical importance of the doctrine of the Divinity of Christ has always seemed to me to lie in the fact that it invests His teaching with the authority of the Categorical Imperative.