Triblock polyester thermoplastic elastomers with semi-aromatic polymer end blocks by ring-opening copolymerization

• Published in: Chemical science (Cambridge) Vol. 11; no. 25; pp. 6567 - 6581
• Main Authors: Gregory, Georgina L, Sulley, Gregory S, Carrodeguas, Leticia Peña, Chen, Thomas T. D, Santmarti, Alba, Terrill, Nicholas J, Lee, Koon-Yang, Williams, Charlotte K
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 04.05.2020; The Royal Society of Chemistry
• Subjects: Aqueous environments; Block copolymers; Chemistry; Copolymerization; Cyclohexene; Decalactone; Differential scanning calorimetry; Elastic recovery; Equivalence; Glass transition temperature; Gravimetric analysis; Lactones; Lipase; Magnesium; Operating temperature; Phase separation; Phthalates; Phthalic anhydride; Polyester resins; Polyester thermoplastic elastomers; Ring opening polymerization; Room temperature; Stoichiometry; Stress-strain relationships; Temperature; Thermal stability; X-ray scattering
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/d0sc00463d

Thermoplastic elastomers benefit from high elasticity and straightforward (re)processability; they are widely used across a multitude of sectors. Currently, the majority derive from oil, do not degrade or undergo chemical recycling. Here a new series of ABA triblock polyesters are synthesized and show high-performances as degradable thermoplastic elastomers; their composition is poly(cyclohexene- alt -phthalate)- b -poly( -decalactone)- b -poly(cyclohexene- alt -phthalate) {PE-PDL-PE}. The synthesis is accomplished using a zinc( ii )/magnesium( ii ) catalyst, in a one-pot procedure where -decalactone ring-opening polymerization yielding dihydroxyl telechelic poly( -decalatone) (PDL, soft-block) occurs first and, then, addition of phthalic anhydride/cyclohexene oxide ring-opening copolymerization delivers semi-aromatic polyester (PE, hard-block) end-blocks. The block compositions are straightforward to control, from the initial monomer stoichiometry, and conversions are high (85-98%). Two series of polyesters are prepared: (1) TBPE-1 to TBPE-5 feature an equivalent hard-block volume fraction ( f hard = 0.4) and variable molar masses 40-100 kg mol −1 ; (2) TBPE-5 to TBPE-9 feature equivalent molar masses (∼100 kg mol −1 ) and variable hard-block volume fractions (0.12 < f hard < 0.4). Polymers are characterized using spectroscopies, size-exclusion chromatography (SEC), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). They are amorphous, with two glass transition temperatures (∼−51 °C for PDL; +138 °C for PE), and block phase separation is confirmed using small angle X-ray scattering (SAXS). Tensile mechanical performances reveal thermoplastic elastomers ( f hard < 0.4 and N > 1300) with linear stress-strain relationships, high ultimate tensile strengths ( σ b = 1-5 MPa), very high elongations at break ( b = 1000-1900%) and excellent elastic recoveries (98%). There is a wide operating temperature range (−51 to +138 °C), an operable processing temperature range (+100 to +200 °C) and excellent thermal stability ( T d,5% ∼ 300 °C). The polymers are stable in aqueous environments, at room temperature, but are hydrolyzed upon gentle heating (60 °C) and treatment with an organic acid ( para -toluene sulfonic acid) or a common lipase (Novozyme® 51032). The new block polyesters show significant potential as sustainable thermoplastic elastomers with better properties than well-known styrenic block copolymers or polylactide-derived elastomers. The straightforward synthesis allows for other commercially available and/or bio-derived lactones, epoxides and anhydrides to be developed in the future. A new series of block polyester thermoplastic elastomers are prepared by a one-pot procedure; they show properties competitive or better than conventional materials and can be fully degraded after use.