Sustainable Poly(lactide-b-butadiene) Multiblock Copolymers with Enhanced Mechanical Properties

Abstract

To develop mechanically improved polylactide (PLA)-based sustainable polymers, a series of poly(lactide-bbutadiene) (PLA−PB) multiblock copolymers were synthesized in a two-step procedure: PLA−PB−PLA (LBL) triblock copolymers were prepared using ring-opening polymerization of D,L-lactide, followed by chain extension of LBL triblock polymers with toluene-2,4-diisocyanate (TDI) and terephthaloyl chloride (TCl). Molecular characterization revealed that the synthetic procedures yielded the desired triblock and multiblock copolymers with a composition range of 0.5 ≤ f PLA ≤ 0.9. Differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) demonstrated nearly identical, well-ordered, morphologies in the homologous triblock and multiblock copolymer materials, in sharp contrast with the findings of a recent study involving poly(styrene-b-butadiene) (PS−PB) multiblock polymers. These results indicate a transition from classically ordered morphologies to a state of bicontinuous disorder for multiblocks containing ⟨n′⟩ ≥ 10, where ⟨n′⟩ is the average total number of blocks. Lamellae ( f PLA = 0.6) and cylinder ( f PLA = 0.7 and 0.8) forming PLA−PB multiblock copolymers exhibited dramatically enhanced mechanical properties compared to the corresponding LBL triblock copolymers. However, this toughening effect was not evident in samples containing a spherical morphology (f PLA = 0.9). These findings demonstrate a commercially viable approach to preparing sustainable plastics with competitive mechanical properties.

Crystallization and Mechanical Properties of Poly(l-lactide)-Based Rubbery/Semicrystalline Multiblock Copolymers

“…4 The HO-PE/E E -OH served as the macroinitiator for the polymerization of L-lactide. HO-PE/E E -OH was poured into a pressure flask containing a stir bar and was stirred overnight under dynamic vacuum to remove air and any residual solvent.…”

Wide Bicontinuous Compositional Windows from Co-Networks Made with Telechelic Macromonomers

“…20,21 An alternative strategy to increasing polydispersity is greatly increasing the number of blocks to form multiblock chains. This approach enhances the likelihood of obtaining the bicontinuous phase 22,23 since multiblock chains face both kinetic and thermodynamic barriers to the formation of ordered structures. 22,24,25 Disordered bicontinuous phases from multiblock copolymers have demonstrated improved mechanical properties including higher stress and strain at break compared to analogous triblock copolymers.…”

Fully bio-renewable multiblocks copolymers of poly(lactide) and commercial fatty acid-based polyesters polyols: Synthesis and characterization

“…Multiblocks copolymers are known to exhibit superior mechanical properties in comparison with analogous triblocks, because in these systems a single segmented polymer chain can span over several nanophase domains [35,42,[45][46][47]. Two main synthetic approaches have been adopted to prepare PLA-based multiblocks copolymers, typically belonging to the polyurethanes family.…”

“…The second commonly adopted synthetic strategy is also based on chain extension with di-isocyanate, but the diol in this case consists of a dihydroxyl-terminated PLA-softblock-PLA triblock copolymer, synthetized in advance following the above mentioned procedure [23,30,35,40,42]. Despite the fact that this second approach leads to a rigorously controlled length of the different blocks in the multiblock copolymer, a more complex synthetic procedure is required.…”

“…Despite the fact that this second approach leads to a rigorously controlled length of the different blocks in the multiblock copolymer, a more complex synthetic procedure is required. Soft blocks employed so far to build this class of multiblocks copolymers based on PLA are not derived from bio-renewable feedstocks, although some of them are bio-degradable [19,[23][24][25]30,33,35,36,42].…”