Linear Poly(ethylene imine)s by Acidic Hydrolysis of Poly(2-oxazoline)s: Kinetic Screening, Thermal Properties, and Temperature-Induced Solubility Transitions

Abstract

The kinetics for the acidic hydrolysis of two water-soluble poly(2-oxazoline)s with methyl and ethyl substituents were investigated. It could be observed that poly(2-ethyl-2-oxazoline) (PEtOx) and poly(2methyl-2-oxazoline) (PMeOx) are hydrolyzed following a linear relation with time. Various polymer lengths and concentrations were investigated, revealing that both parameters had no influence on the hydrolysis kinetics. Comparison between PEtOx and PMeOx revealed that the smaller PMeOx side group could be removed faster. Furthermore, a series of linear poly(ethylene imine) (PEI) were synthesized with varying M/I ratio from 5 to 200 to elucidate structure-property relations. Thermal measurements indicated that the T g of PMeOx was increasing up to a M/I ratio of 100. PEI, on the other hand, is crystalline and exhibits a melting temperature which shows a similar increase with M/I ratio as observed for the T g of PMeOx. Solubility measurements in water and water/ethanol mixtures indicated a solubility transition to a soluble state at elevated temperatures. The solubility transition was observed to fit with the melting temperature, indicating that the PEI crystals need to melt in solution before solubilizing. Moreover, when adding ethanol to the water solution, the formed crystals are less stable due to the improved solubility of PEI in ethanol, causing a decrease in cloud point temperature. Upon cooling, PEI crystallizes at much lower temperatures compared to dissolution, causing a large hysteresis presumably due to extensive intermolecular hydrogen bonding, which also plays a role in the formation of the hydrate crystals.

Design Strategies for Functionalized Poly(2-oxazoline)s and Derived Materials

“…Schubert, Hoogenboom and co-workers investigated the acid-mediated hydrolysis of pMeOx and pEtOx [208]. They found that the hydrolysis kinetics did not show significant dependency on polymer concentrations or polymerization degrees.…”

Charging and stability of anionic latex particles in the presence of linear poly(ethylene imine)

“…Poly(ethylene imine) is an important polyelectrolyte within this class, and is known in two different forms [38,39]. Highly branched poly(ethylene imine) (BPEI) is obtained by ring-opening polymerization of ethylenimine and linear poly(ethylene imine) (LPEI) is synthesized by the hydrolysis of poly(2-oxazoline)s. These polyelectrolytes were investigated in substantial detail [31,38,[40][41][42][43][44].…”

Oxazoline‐Based Antimicrobial Oligomers: Synthesis by CROP Using Supercritical CO2

“…[18,19] Polyethylenimine is a polyamine which possesses a high number of advantages, such as being a chelating agent, having good water solubility, and good physical and chemical stability and that can be easily obtained by oxazoline-based polymers hydrolysis. [20,21] Most of the studies of polymers with antimicrobial activity are based on compounds and materials possessing quaternary ammonium salts in their structure since its antimicrobial activity has been known for decades. [22][23][24] Waschinski and co-workers reported the synthesis of a series of oxazoline-based polymers, terminated with quaternary ammonium groups (using a series of Nalkyl-N,N-dimethylamines but also pyridine), prepared via standard CROP.…”