Convenient Access to α‐Amino‐ω‐Hydroxyl Heterobifunctional peg and ppo via a Sacrificial Hexahydro‐Triazine Star Strategy

Experimental Section

Instrumentation and reagent details are given in the Supporting 

Information.

Preparation of an Ethylene Oxide Stock Solution: An ethylene oxide 

(EO) stock solution in DMSO was prepared by the following protocol. 

Under reduced pressure 6 mL of EO was transferred into a graduated 

ampule cooled to 

−70  °C with an ethanol/nitrogen cooling bath. 

Subsequently, EO was transferred by distillation in high vacuum in the 

cold into a frozen flask with 20 mL dry DMSO. The flask 

was sealed, and the EO solution was slowly allowed to 

reach room temperature. Then the flask was backfilled 

with argon.

Synthesis of TrAz-PEG Star Polymers: The following 

exemplary protocol describes the synthesis of 

TrAzPEG

61

. 300 mg of 1,3,5-triethanol hexahydro-1,3,5-

triazine (TrAz) (75%) (1 eq, 1.0 mmol), 57.6 mg KO

t

Bu 

(0.5 eq, 0.5 mmol) and 272 mg 18-crown-6 (1 eq, 

1 mmol) were dissolved in 10 mL methanol. 5.5 mL 

of this solution (TrAz: 1eq, 0.46 mmol) were then 

added to a Schlenk flask. The solvents were removed 

in high vacuum at room temperature. Subsequently 

the temperature was raised to 40 

°C and last traces of 

solvent were removed overnight. The flask was then 

filled with argon and cooled to room temperature. Via 

a syringe 7 mL of the EO stock solution (corresponds 

to 1.4 g EO (67 eq, 31.8 mmol)) was transferred to the 

dried initiator. The polymerization was carried out at 

room temperature for 24 h. The full conversion of EO 

was monitored by 

1

H NMR. Then, 5 mL concentrated 

sodium bicarbonate solution was added, and the 

mixture extracted with 25 mL dichloromethane. 

The organic layer was then washed four times with 

brine to remove the majority of DMSO. Last traces were 

removed under reduced pressure. The isolated products 

were recovered in yields between 76% and 91%.

Synthesis of TrAz-PPO Star Polymers: The following 

exemplary protocol describes the synthesis of 

TrAzPPO

47

. 300 mg TrAz (75%) (1 eq, 1.0 mmol), 

57.6 mg KO

t

Bu (0.5 eq, 0.5 mmol) and 272 mg 

18-crown-6 (1 eq, 1 mmol) were dissolved in 5 mL 

methanol. 2.5 mL of this solution (TrAz: 1 eq, 

0.46 mmol) were then added to a Schlenk flask. The 

solvents were removed in high vacuum at room 

temperature. The temperature was raised to 40 

°C and last traces of 

solvent were removed overnight. The flask was then filled with argon and 

cooled to room temperature. 1.6 mL dry propylene oxide (PO) (50 eq., 

23 mmol) was added via syringe. The polymerization was conducted 

at room temperature and stirring for 5 days. Unreacted PO was then 

removed under reduced pressure. The obtained polymer was purified by 

extraction with petroleum ether and two washings with water. The yields 

of isolated TrAz-PPO star polymers were between 71% and 88%.

Cleavage of TrAz-PEG and TrAz-PPO Stars: A slightly modified 

procedure of Pradipta et al. was employed to cleave the aminal core.

[12]

 

100 mg of the star polymer was dissolved in 4 mL methanol (for 

TrAz-PPO stars ethanol) containing 5% hydrochloric acid and stirred at 

60 

°C for 18h. Then 2 mL of an aqueous 10% ammonia solution was 

added and stirred for 15 min. 2 mL concentrated NaHCO

3

 solution was 

then added and the solution was extracted with 15 mL dichloromethane. 

The organic phase was dried with Na

2

SO

4

 and the solvent removed 

under reduced pressure. Typical yields of the isolated heterobifunctional 

polyether were between 75% and 85%.

Synthesis of Acid Labile Polyurethane Structures: 100 mg (1 eq, 

0.03 mmol) of TrAzPPO

47

 was mixed with 9 mg hexamethylene 

diisocyanate (HDI). 4 mg (0.2 eq, 0.007 mmol) dibutyltin dilaurate 

(DBTL) was added and mixed in thoroughly. The solution solidified 

within 10 min to an elastomer. To study the degradation, two 50 mg 

samples of the synthesized polyurethane were transferred into 1 mL 

methanol and 1 mL of 5% HCl in methanol, respectively and gently 

shaken over the course of 10 min. Results are shown in Figure S15, 

Supporting Information.