Selective Partial Hydrolysis of Amphilic Copoly(2-Oxazoline)s and Responsive Micellization of the Resulting Poly(Ethylene Imine) Copolymers
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Lambermont-Thijs, Hanneke M. L.; Heuts, Hans; Höppener, Stephanie; Schubert, Ulrich S.; Hoogenboom, Richard
- Abstract:
- The acidic and basic hydrolyses of gradient and diblock copolymers based on 2-methyl-2-oxazoline
(MeOx) and 2-phenyl-2-oxazoline (PhOx) were investigated. Various reaction times were examined
revealing polymers with varying ratios of PMeOx, PPhOx and poly(ethylene imine) (PEI). It could be
shown that under acidic conditions, PMeOx as well as PPhOx are readily cleaved while under basic
conditions PPhOx was almost not hydrolyzed leading to higher selectivity. However, partial
degradation of the polymers occurred under basic conditions as evidenced by SEC. Thermal
investigations of the polymers cleaved under acidic conditions revealed that most obtained copolymers
exhibited a melting temperature due to the large PEI content. Self-assembly studies revealed that the
partially hydrolyzed copolymers formed micelles at both ambient and elevated temperatures in acidic
medium due to protonation of the ethylene imine units leading to good solubility. In contrast, the
copolymers were insoluble at ambient temperature in water or basic medium, but self-assembled into
spherical micelles at elevated temperatures as evidenced by transmission electron microscopy and
dynamic light scattering. As such, these novel PEI–PPhOx copolymers exhibit thermoresponsive
micellization behavior based on the crystallization induced phase separation of linear PEI at lower
temperatures. Moreover, the copolymer consisting of 84 ethylene imine repeat units, 16 PPhOx groups
also revealed pH responsive micellization due to increased solubility of the ethylene imine units upon
protonation in acidic solution.
- Year:
- 2011
- Type of Publication:
- Article
- Journal:
- Polymer Chemistry
- Volume:
- 2
- Pages:
- 313 - 322