Organocatalyzed controlled ROP of β-lactones towards poly(hydroxyalkanoate)s: from β-butyrolactone to benzyl β-malolactone polymers

Basic organocatalysts of the guanidine (1,5,7-triazabicyclo[4.4.0]dec-5-ene, TBD), amidine (1,8-diazabicyclo[5.4.0]-undec-7-ene, DBU) and phosphazene (2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2 diazaphosphorine, BEMP) type effectively polymerize benzyl β-malolactone (MLABe) under mild operating conditions. Poly(3-benzyloxybutyrate)s (PMLABe)s with controlled molecular features, i.e. controlled molar masses, narrow dispersities (1.12 < ĐM < 1.39) and well-defined end-groups, are thus formed at 60 °C from bulk monomers, with Mn,NMR up to 80 500 g mol−1. The formation of α-guanidine/amidine/phosphazene,ω-benzyloxycarbonyl-crotonate telechelic polymers, [base{MLABe}nC(O)CHCH(CO2Be)], was demonstrated from hydrolysis and methanolysis experiments along with detailed NMR and MALDI-ToF mass spectrometry analyses. A similar mechanism to that suggested for the ROP of β-butyrolactone (BL) is proposed.