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.

Polyurethanes (PUs), in the form of coatings, adhesives, sealants, elastomers, and foams, play a vital role in the consumer goods, automotive, and construction industries. However, the inevitable disposal of nondegradable postconsumer polyurethane products constitutes a massive waste management problem that has yet to be solved. We address this challenge through the synthesis of biobased and chemically recyclable polyurethanes. Our approach employs renewable and degradable hydroxy telechelic poly(β-methyl-δvalerolactone) as a replacement for petroleum-derived polyols in the synthesis of both thermoplastic polyurethanes and flexible foams. These materials rival petroleum-derived PUs in performance and can also be easily recycled to recover βmethyl-δ-valerolactone monomer in high purity and high yield. This recycling strategy bypasses many of the technical challenges that currently preclude the practical chemical recycling of PUs.

The crystallization and mechanical properties of triblock and multiblock copolymers containing 70 vol % semicrystalline poly(L-lactide) (L) and 30 vol % rubbery poly(ethylene-co-ethylene) (E/E E ) were investigated. The multiblock copolymer was synthesized directly from the triblock copolymer (denoted LE/E E L). Specifically, the dihydroxyl-terminated LE/E E L served as a macromonomer in a step-growth polymerization in which stoichiometric quantities of sebacoyl chloride were added, resulting in (LE/ E E L) ⟨3.6⟩ , a multiblock copolymer with an average of 3.6 triblock copolymer units connected together. Additionally, triblock and multiblock copolymers were blended together in order to systematically tune ⟨n⟩ and uncover the role of block number on properties. Dynamic mechanical analysis (DMA) indicated that despite differences in ⟨n⟩, all samples had an order-to-disorder transition temperature T ODT ≈ 190°C, which is above the melting temperature (T m ) of poly(L-lactide). Small-angle X-ray scattering measurements (SAXS) of the block copolymers at T m < T < T ODT showed that the samples had identical morphology (hexagonally packed cylinders) and domain spacing. Isothermal crystallization experiments were performed using differential scanning calorimetry (DSC) and indicated that samples with higher ⟨n⟩ had a lower percentage crystallinity after 1 h of crystallization, which we associate with the differences in the average chain architecture. Uniaxial tensile measurements demonstrate a brittle-to-ductile transition at ⟨n⟩ = 1.8 for specimens with limited crystallinity. Finally, the effect of crystallinity on mechanical properties was investigated by annealing select samples. ■ INTRODUCTIONBlock polymers are an intriguing and useful class of materials due to the ability to precisely tune morphology and properties by changing parameters including composition, molecular weight, and block sequencing. 1 While diblock and triblock copolymers have been studied extensively in the literature, fewer reports have focused on multiblock copolymers. Interestingly, multiblock copolymers have been shown to have superior mechanical properties relative to diblock and triblock copolymers due to the ability of these molecules to bridge multiple nanoscale domains. 2−11 For this reason, incorporating brittle poly(lactide) (PLA) into a multiblock copolymer architecture is an attractive option for improving its mechanical properties. Additionally lactide, as well as other renewable cyclic esters such as β-methyl-δ-valerolactone, 12 menthide, 13 ε-decalatone, 9 and δ-decalactone, 14 can be polymerized with α,ω-dihydroxyl functionality by using difunctional alcohols as initiators. Hence, sustainable-based multiblock copolymers can be prepared from homopolymer and block polymer macromonomers by step-growth methods using difunctional isocyanates and acid chlorides, among other approaches. 4,15−20 Because of the potential to improve mechanical properties and the simple synthetic routes, multiblock copolymers are poised to play an important ro...