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

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chains per star polymer showing one third of the molecular 

weight of the star precursor and one primary amine end group. 

Consequently, 

α-amino-ω-hydroxyl heterobifunctional poly-

ether structures were obtained. The only side product formalde-

hyde could be easily separated by liquid–liquid extraction with 

water, while the polymers remained in the dichloromethane 

layer. Successful cleavage of the star polymers was confirmed by 

SEC measurements, resulting in a large shift of the molecular 

weight distribution (Figure 1A). The molecular weights after 

hydrolysis, determined by SEC, are approximately one third of 

the star precursor, as shown in Table 1. All heterobifunctional 

polyethers were obtained with low dispersity (Đ 

< 1.1, Table 1). 

This indicates uniform growth of all arms of the star polymer 

at a similar rate and in a random manner, as expected for the 

AROP. The successful cleavage was also verified via 

1

H NMR by 

the shift of the resonances of the methylene units linked to the 

nitrogen atom (Figure 1B and Figure S9B, Supporting Informa-

tion). Cleavage of TrazPEG

61

 to 

α-amino  ω-hydroxyl PEG can 

be further confirmed by 

13

C NMR and 2D NMR techniques 

(Figures S10–S13, Supporting Information). In addition, the 

primary amine end group of the hydrolyzed polymers could be 

assigned to the main distribution in the MALDI-TOF spectra 

of the heterobifunctional polyether (Figure 2 and Figure S15, 

Supporting Information). To sum up, the synthesis of tria-

zine-based sacrificial 

α-amino-ω-hydroxyl heterobifunctional 

polyether stars and subsequent hydrolysis of star polymers is 

confirmed by all characterization data.

The TrAz star polymers can also be used as the polyol com-

ponent in combination with a diisocyanate to form a polyure-

thane network. This network is stable in ambient conditions at 

neutral pH, but degrades rapidly in acidic conditions. Three-

arm star polyether triols consisting of PEG and PPO are major 

compound in PU foams.

[2]

 A drawback of PU is their poor 

reprocessability. Hexahydro-triazine containing thermosets 

have already been demonstrated to be strong materials that 

can be depolymerized under acidic conditions and show self-

healing properties.

[15]

 Based on these concepts, the TrAzPPO

47

 

star polymer was crosslinked in a model reaction with hexa-

methylene diisocyanate (HDI) under catalysis with dibu-

tyltin dilaurate (DBTDL) to form a PU elastomer according to 

Scheme S1, Supporting Information. The obtained crosslinked 

product was stable in pure methanol over a prolonged time and 

showed only slight swelling. Exposition to hydrochloric acid in 

methanol degraded the aminal cores and resulted in complete 

dissolution within 10 min (Figure S16, Sup-

porting Information).

In conclusion novel hexahydro-tria-

zine containing three arm star polymers 

were synthesized with molecular weights 

from 3–15 kg mol

−1

, a narrow molecular 

weight distribution and with low disper-

sity  Đ 

< 1.1. Acidic hydrolysis of the hex-

ahydro-triazine core cleaved the arms of 

the star polymers and gave access to well-

defined 

α-amino-ω-hydroxyl heterobifunc-

tional poly(ethylene glycol) (PEG) as well as 

poly(propylene oxide) (PPO). The molecular 

weights correspond to one third of the star 

polymer precursor and were in the range 

Macromol. Rapid Commun. 2019, 1900020