Polyoxazolines (PAOx)

Properties and Applications

Polyoxazolines are amorphous to semicrystalline polymers that have been known for over 40 years. This class of polymers is produced by cationic ring-opening polymerization (CROP) of 2-oxazolines. More than a hundred different 2-oxazoline polymers have been reported in the literature to date.¹ Their properties range from rubbery and soft with glass transition temperatures well below room temperature to hard and brittle with melting/softening points well above 200°C.¹ Their solubility in solvent and water depends on the substituent next to the carbonyl group. Those with small side groups are strongly hydrophilic and water-soluble whereas those with long hydrocarbon side-chains are hydrophobic and water-insoluble.

Many PAOx are highly biocompatible² and have been intensively studied as materials for biomedical and pharmaceutical applications such as polymer-drug and polymer-protein conjugates, drug delivery micelle carriers, hydrogels, antifouling and antimicrobial devices, and wound healing.^1,2 Outside of these applications, oxazoline polymers have found no noteworthy commercial applications.
The monomer oxazoline itself has been used to functionalize acrylic and styrene-acrylic copolymers.³ These reactive resins find uses as polymer crosslinkers and adhesion promotors in numerous water- and solvent-borne products including coatings, paints, inks, and pressure sensitive adhesives.⁴ They can also be used as compatibilizers in thermoplastics and as binders and surface conditioners in textile products.

¹M. Glassner, M. Vergaelen and R. Hoogenboom, Polym. Int., 67, 32–45 (2018)
²A. Dworak, B. Trzebicka, A. Kowalczuk, C. Tsvetanov, S. Rangelov, Polimery, 59, 1 (2014)
³EPOCROS Brochure: Novel Low toxic Polymer Crosslinker and Adhesion Promoting Agent, Nippon Shokubai Co. 2016
⁴Oxazolines readily react with carboxyl, thiol and phenol groups but not with alcohols. The reaction with carboxyl groups
proceeds rapidly at elevated temperatures (80-100°C).³