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A new pathway was explored for the direct synthesis of poly(ether ester)s (PEEs) via polycondensation of diacids and diols without dihydroxyl-terminated polyethers as starting materials. Herein, sulfonic acid (SA) or the bicomponent catalysts of SA and titanium isopropoxide (TPT) were found to be exceptionally active catalysts for in situ dehydration of 1,3-propanediol (PDO) to afford dihydroxyl-terminated ethers during the polycondensation of terephthalic acid (TPA) and PDO, capable of producing one kind of poly(ether ester) (PEE) comprising a hard poly(trimethylene terephthalate) (PTT) segment, poly(dipropylene terephthalate) (PDPT) segment and soft poly(trimethylene oxide terephthalate) (PTrMOT) moiety, namely PTT-co-PDPT-co-PTrMOT. Two-dimensional and one-dimensional nuclear magnetic resonance (2D and 1D-NMR) techniques have been used to reveal the copolymer structures. The ether contents and intrinsic viscosity of the resulting PEEs were tunable by adjusting the feeding molar ratios of TPT and SA. In particular, the intrinsic viscosity of the PEEs reached up to 1.06 dL g−1 accompanied by 46 wt% of the PTT contents, when methylsulfonic acid (MSA) was used at the triple molars of TPT. These PEE copolymers showed improved thermal stability when compared to poly(trimethylene oxide terephthalate) (PTrMOT) and PTT homopolymers. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) revealed that these PEE copolymers had random segment distribution, and the melting temperatures and glass transition temperatures were monotonically decreased with increasing ether content. To our knowledge, these are the first reported PEEs with odd-numbered ether segments.

New poly(ethylene terephthalate) (PET)-based poly(ether-ester)s were successfully synthesized, by using the bicomponent catalyst of titanium isopropoxide (TPT) and methanesulfonic acid (MSA) to directly catalyze polycondensation of terephthalic acid and ethylene glycol, for randomly copolymerizing poly(ethylene terephthalate) (PET), poly(diethylene terephthalate) (PDET) and poly(ethylene oxide terephthalate) (PEOT), which denoted as linear PET-co-PDET-co-PEOT. The chemical structures of PET-co-PDET-co-PEOT were evidenced by two-dimensional and one-dimensional nuclear magnetic resonance (2D and 1D-NMR) techniques, and the segment contents of the poly(ether-ester) were tunable by adjusting the feeding molar ratios of catalytic systems. The thermal properties, mechanical properties and rheological behavior of linear PET-co-PDET-co-PEOTs were studied in detail. In particular, the branched PET-co-PDET-co-PEOT were afforded via introducing the multifunctional reagents, such as 1,1,1-tris(hydroxymethyl) ethane (TME), 2,2-dimethylolpropionic acid (DMPA) or 1,2,3-propanetricarboxylic acid (PTA). Compared to linear PET-co-PDET-co-PEOTs, the elongation at break of the branched PET-co-PDET-co-PEOTs were strongly enhanced to 409%, and their flow properties were accordingly altered, as revealed by rheological analysis. The novel PET-based poly(ether-ester)s will be promising as potential thermal elastomers.