Enhanced Mechanical Properties of Aliphatic Polyester Thermoplastic Elastomers through Star Block Architectures

Abstract

A series of sustainable aliphatic polyester thermoplastic elastomers (APTPEs) consisting of multi-arm star polymers with arms of poly­(l-lactide)-b-poly­(γ-methyl-ε-caprolactone) were investigated and compared to analogous linear poly­(l-lactide)-b-poly­(γ-methyl-ε-caprolactone)-b-poly­(l-lactide) triblock polymers. Linear analogues with comparable arm molar mass and comparable overall molar mass were synthesized to distinguish architectural and molar mass effects. Overall, the star block polymers significantly outperformed their linear analogues with respect to ultimate tensile strength and tensile toughness, exhibiting more pronounced strain hardening than corresponding linear APTPEs. The stars exhibited high ultimate tensile strengths (∼33 MPa) and large elongations at break (∼1400%), outperforming commercially relevant, petroleum-derived, and non-degradable styrenic TPEs. The star polymers also exhibited superior recovery characteristics during cyclic strain cycles and reduced stress relaxation compared to the linear APTPEs, highlighting the impact of architecture on improved TPE mechanical properties. Dynamic mechanical thermal analysis suggests that the star architecture increases the usage temperature range and does not negatively influence processability, an important feature for future applications. Overall, this work illustrates that simple and convenient changes in the macromolecular architecture in sustainable APTPEs result in materials with greatly enhanced mechanical properties. A comprehensive understanding of the relationship between polymer architecture and mechanical properties can be capitalized on to develop property-specific and industrially relevant sustainable materials.

Switchable Copolymerization of Maleic Anhydride/Epoxides/Lactide Mixtures: A Straightforward Approach to Block Copolymers with Unsaturated Polyester Sequences

“…1 H NMR (400 MHz, CDCl 3 , ppm) 𝛿: 7.08 (dd, J = 7.1, 3.0 Hz, 1H, Ar-H), 6.98 (dd, J = 10.6, 3.0 Hz, 1H, Ar-H), 5.60 (s, 1H, -OH), 1.38 (s, 9H, t-Bu). 19 F NMR (376 MHz, CDCl 3 , ppm) 𝛿: −122. 31.…”

“…52, 155.06, 154.20, 151.64, 140.64, 140.58, 139.40, 137.90, 129.06, 128.25, 125.32, 120.69, 119.35, 118.56, 118.49, 116.66, 116.42, 110.11, 109.88, 35.41, 31.62, 29.31, 22.68, 21.48, 14.15 (Note that the C-F coupling was not resolved). 19 F NMR (376 MHz, CDCl 3 , ppm) 𝛿: −100.00.…”

“…[15] Among various copolymers, block copolyesters can combine the properties of the respective homopolymers to furnish a new set of functionalities and exhibited adjustable and extensive macroscopic properties because of the block incompatibility. [16][17][18][19][20][21][22][23][24] Especially, block copolymers with highly reactive maleate or fumarate sequences in backbone enables further enhancement of polymer properties through post-polymerization modifications, and thus have attracted increasing attentions in recent years. For example, the poly(propylene maleate) (PPM) quasi-block copolymers afford high-performing plasticizers for commercial polylactide after post-functionality.…”

Potential of Graft Polymers Bearing Inner Molten Block and Outer Glassy Block at the Graft Chains for Thermoplastic Elastomers with Enhanced Properties

“…[ 18 ] Another reason was that the stress was carried by the core of the star shape during deformation, preventing the direct transfer of internal stress to the glassy hard domains. [ 19 ] For elastomers with graft architecture, glassy polymers can be used as either the main chain or the graft chains. In the design with glassy polymers used as the main chain, the molten chains are placed in the graft chain.…”

Investigation of eight-arm tapered star copolymers prepared by anionic copolymerization and coupling reaction

“…[30][31][32] More importantly, it has been widely recognized that star copolymers intrinsically exhibit enhanced mechanical properties compared to analogous linear block copolymers. [33][34][35] In general, the synthesis approaches of star polymers mainly include the "core-first", the "arm-first", and the "grafting-onto" methods. 36,37 The basic idea of the three strategies is to achieve efficient synthesis of star polymers by using multifunctional initiators or coupling agents.…”