Controlled Synthesis of Hyperbranched Polyglycerols by Ring-Opening Multibranching Polymerization

TLDR

Glycidol, a latent cyclic AB₂ monomer, can undergo ring‑opening multibranching polymerization (ROMBP). The polymerization was initiated by 10 % deprotonated 1,1,1‑tris(hydroxymethyl)propane under slow addition to suppress unwanted polymerization and cyclization, and the resulting hyperbranched polyethers were characterized by 13C NMR, MALDI‑TOF, VPO, and GPC. The resulting hyperbranched polyethers exhibited controlled molecular weights (Mn 1250–6500 g mol⁻¹), narrow polydispersities (Mw/Mn 1.13–1.47), a degree of branching of 0.53–0.59, and glass transition temperatures between –20 °C and –26 °C, with MALDI‑TOF confirming complete initiator attachment and no macrocyclics.

Abstract

Glycidol represents a latent cyclic AB2-type monomer that can be polymerized in a ring-opening multibranching polymerization (ROMBP). Hyperbranched aliphatic polyethers with controlled molecular weights and narrow molecular weight distribution have been prepared via anionic polymerization of glycidol with rapid cation-exchange equilibrium. 1,1,1-Tris(hydroxymethyl)propane (TMP) was partially deprotonated (10%) and used as initiator for the anionic polymerization carried out under slow addition conditions to minimize polymerization without initiator as well as cyclization. 13C NMR spectra were employed to assess the degree of branching (DB), which was in the range 0.53−0.59. 13C NMR, MALDI-TOF mass spectrometry, vapor pressure osmometry (VPO), and GPC were used to characterize molecular weights and polydispersities of the polyols formed, showing good agreement. n for the polymers prepared was in the range 15−83 (M̄n = 1250−6500), and M̄w/M̄n obtained was 1.13−1.47, being exceptionally low for hyperbranched polymers. MALDI-TOF spectra evidenced complete attachment of the hyperbranched structures to the TMP initiator and the absence of macrocyclics as well as hyperbranched macromolecules without initiator, due to the slow addition. The hyperbranched polyethers prepared showed Tg's between −20 and − 26 °C.