Poly(cyclic imino ether)s

1. A gradient copolymer represented by the following formula (I):

Ini-[Ox] m -[Oz] n -Nuc  (I)

wherein:

(a) Ini represents a residue of an initiator of cationic polymerization;

(b) Nuc represents a residue of a nucleophilic agent;

(c) Ox represents N(R 1 )CHR a CHR a ; each R 1 independently represents H or C(O)R 11 ; and R 11 independently represents optionally substituted C 1-12 alkyl, optionally substituted cycloalkyl, optionally substituted aralkyl or optionally substituted aryl;

(d) Oz represents N(R 2 )CHR a CHR a CHR a ; each R 2 independently represents C(O)R 21 or H; and R 21 independently represents optionally substituted C 1-12 alkyl, optionally substituted cycloalkyl, optionally substituted aralkyl or optionally substituted aryl;

(e) each R a independently represents H, linear or branched C 1-3 alkyl;

(f) m≥5;

(g) n≥5;

(h) m+n≥20;

(i) 3:97≤m:n≤97:3;

wherein the copolymer comprises three fragments of equal size, a fragment adjacent Ini (Ini fragment), a fragment adjacent Nuc (Nuc fragment) and a central fragment that separates the Ini fragment and the Nuc fragments, wherein the monomer ratio [Oz]/[Ox] in the Ini-half of the copolymer is at least 2 times higher or lower than the same ratio in the Nuc-half of the copolymer.

2. The copolymer according to claim 1 , wherein Ra represents H.

3. The copolymer according to claim 1 , wherein 10≤m≤250.

4. The copolymer according to claim 1 , wherein 10≤n≤250.

5. The copolymer according to claim 1 , wherein each R 21 independently represents optionally substituted C1-9 alkyl.

6. The copolymer according to claim 1 , wherein each R 11 independently represents optionally substituted C 1-9 alkyl or cyclopropyl.

7. A method of preparing a gradient copolymer according to claim 1 , comprising cationic ring-opening polymerizing of a monomeric reaction mixture comprising an optionally 2-substituted 2-oxazoline and an optionally 2-substituted 2-oxazine in a molar ratio in the range of 3:97 to 97:3, wherein the optional substituent in the 2-position of the 2-substituted-2-oxazoline is a residue R 11 as defined in claim 1 , and the optional substituent in the 2-position of the 2-substituted-2-oxazine is a residue R 21 as defined in claim 1 .

8. The method according to claim 7 , wherein the cationic ring-opening polymerization is carried out in the presence of a cationic polymerization initiator selected from alkyl halides, alkyl sulfonates, acyl halides, oxazolinium salts or sulfonic acids.

9. The method according to claim 7 , wherein the copolymer comprises pendant acyl residues and at least 50% of the pendant acyl residues are removed by hydrolysis.

10. A micellar drug delivery system comprising a gradient copolymer according to claim 1 and a drug that is non-covalently bound to the copolymer.

11. A method of preparing a statistical copolymer, said method comprising cationic ring-opening polymerization of a monomeric reaction mixture comprising an optionally 2-substituted 2-oxazoline and an optionally 2-substituted 2-oxazine in a molar ratio in the range of 3:97 to 97:3, wherein the optional substituent in the 2-position of the 2-substituted-2-oxazoline is a residue R 11 as defined in claim 1 , and the optional substituent in the 2-position of the 2-substituted-2-oxazine is a residue R 21 as defined in claim 1 , wherein the statistical copolymer that is formed in the reaction mixture comprises pendant acyl residues, and wherein the statistical polymer is hydrolysed by removing at least 50% of the pendant acyl residues.