Highly Branched Poly(ether ester)s via Cyclization-Free Melt Condensation of A₂ Oligomers and B₃ Monomers

Abstract

This paper reports the first synthesis of A2 + B3 highly branched polyesters with the minimal formation of cyclics in the absence of a polymerization solvent. Highly branched poly(ether ester)s were synthesized in the melt phase using an oligomeric A2 + B3 polymerization strategy. Condensation of poly(propylene glycol) (M n ∼1060 g/mol) and trimethyl 1,3,5-benzenetricarboxylate in the presence of titanium tetraisopropoxide generated highly branched structures with high molar mass when the reaction was stopped immediately prior to the gel point. Size exclusion chromatography (SEC) and 1H NMR spectroscopy were used to monitor molar mass as a function of monomer conversion and to determine the gel point. Monomer conversions at both the theoretical and experimental gel points for an A2:B3 = 1:1 molar ratio agreed well. Thus, cyclization reactions, which are common in A2 + B3 polymerization in solution, were negligible in the melt phase. The degree of branching (DB) increased with an increase in monomer conversion and molar mass, and the final product contained 20% dendritic units. Monofunctional end-capping reagents were also used to avoid gelation in the melt phase, and high molar mass final products were obtained with nearly quantitative monomer conversion in the absence of gelation. The presence of a monofunctional comonomer did not affect the molar mass increase or the formation of branched structures due to desirable ester interchange reactions.

Polycondensation of ‘a − bn’ or ‘a2 + + bn’ Monomers ‐ A Comparison

“…Trifunctional monomers used for the syntheses of (hyper)branched polymers by 'a 2 þ b 3 ' polycondensations. [147][148][149][150][151][152][153][154][155][156][157][158][159][160][161][162][163][164][165] Macromol. Rapid Commun.…”

“…Equimolar 'a 2 þ b 3 ' polycondensations with the purpose to prepare hyperbranched or randomly branched polymers (point III) have been studied by numerous research groups over the past two decades. [128,[147][148][149][150][151][152][153][154][155][156][157][158][159][160][161][162][163][164][165] Branched polyesters, polyethers, polyamides, and polyimides were prepared from the trifunctional monomers compiled in Figure 7. The reaction products were not characterized by MALDI-TOF mass spectrometry, and all authors were convinced to have non-cyclic (hyper)branched polymers in hand.…”

Hyperbranched poly(ether sulfone)s: preparation and application to ion-exchange membranes

“…39,61,62 The copolymerization of hyperbranched monomers as the random component of the block copolymer results in controlled branching and enhanced linear polymer properties. 63,64 Hyperbranched polymers are frequently used as the core of core-shell block copolymers, where the shell block is grown from the functional groups of the hyperbranched polymer. [65][66][67] Hyperbranched polymers have also been grown from linear polymers to form diblock, 68 gridlock 69,70 and graft copolymers.…”

Multicyclic Poly(ether sulfone)s Derived from Tris(4‐hydroxyphenyl)ethane

“…condensation [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] with the intention to prepare (hyper)-branched polymers free of cycles.…”