In conclusion, both the hydrolysis in a flask and in a microwave synthesizer results in a degree of hydrolysis above 99%. LPEIs with differentmolar masses (430 g · mol -1 to 8 600 g · mol -1) were synthesized using both methods. However, compared to the conventional heating in a flask, the hydrolysis in amicrowave synthesizer proceeded much faster. Since the batch processing is automated, it ispossible to synthesize larger amounts of LPEI. The fast and efficient hydrolysis and the good heat distribution render the microwave synthesizer to be very energy saving, compared to conventional heating in a flask. Further advantages of a microwave synthesizer are the excellent control of the heating rate and time, making the hydrolysis highly controllable and reproducible. This is important with respect to the development of a certified synthesis method for larger amounts of "pharmagrade" LPEI. The synthesis conditions were optimized to obtain the maximum of side chain cleavage (99%) within the shortest time range. Although incomplete cleavage (>1%) was obtained even by increasing the reaction time and the temperature, the best and most efficient hydrolysis conditions were found to be 130 8C for 1 h using a microwave synthesizer. The maximum concentration of PEtOx, which can be hydrolyzed, was found to be 0.33 g PEtOx per mL 6 M hydrochloric acid. An increase of the concentration led to a decrease of the degree of hydrolysis. A methyl and a proton-initiated LPEI were prepared via the improved protocol. Several parameters, which can be used as specification for a "pharmagrade" pro- duction of LPEI, were identified and systematically investigated. The developed protocol showed a high reproducibility, and the identity and purity of the LPEIs was proven by means of 1H NMR and IR spectroscopy as well as MALDI-TOF- and ESI-Q-TOF-MS. To the best of our knowledge, this contribution contains the first report of a proton-initiated LPEI. Theprimary aminogroup of 4 enables the possibility of a selective end group functionalization of the LPEI.
- Electrospray ionization mass spectrometry
- Linear polyethyleneimine
- Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS)