Asymmetric Miktoarm Star Polymers as Polyester Thermoplastic Elastomers

Abstract

A library of polyester-based A(BA′) n asymmetric miktoarm star polymers was synthesized with A, A′ = poly(L-lactide) (PLLA) as the semicrystalline hard blocks and B = poly(4-methylcaprolactone) (PMCL) as the soft segment using a graftingthrough platform known as μSTAR. The synthetic versatility of μSTAR enabled a systematic investigation of architectural design parameters, in particular the number of BA′ arms (n), while holding the A, A′, and B block lengths constant. The value of n has a pronounced impact on the mechanical properties of these high-molecular-weight miktoarm materials. Tensile toughness increases with n, an effect likely related to bridging, as the modulus drops because the hard-block volume fraction decreases. These insights expand our understanding of architecture effects in sustainable thermoplastic elastomers.

Emergence of Connected Binary Spherical Structures from the Self-assembly of an AB2C Four-Arm Star Terpolymer

“…The ABC linear triblock copolymer can self-assemble into much more ordered nanostructures than the AB diblock copolymer due to its larger parameter space that contains at least five independent parameters. − Although some ordered structures have similar space symmetries to those formed by AB diblock copolymers, there are other structures with different symmetries. − For example, the symmetric ABC triblock copolymer can form a tetragonal array of alternating cylinders that differs from the hexagonally arranged cylinders of the AB diblock. , For polymers, a very important variable is their largely variable architecture. , Combining a changeable number of blocks with chain architectures, ABC terpolymers provide a huge space for the exploration of novel ordered nanostructures. − However, such a large parameter space and an infinite variety of architectures make it nearly impossible to find desired structures with a simple search. A feasible way is to first summarize the fundamental self-assembly mechanisms of block copolymers ,− and then establish the design rules of chain architectures based on these mechanisms . According to the target structure and abiding by the design rules, the molecular architecture of the block copolymer is designed.…”

Improved Elastic Recovery from ABC Triblock Terpolymers

“…One important conclusion from the SCFT simulations is a shift in the gyroid−lamellae (Gy-LAM) phase boundary from f A ≈ 0.32 in symmetric triblocks to f A + f C ≈ 0.36 for the ABC sequence. In principle, this shift allows for an increased loading of the hard blocks by volume fraction that is reminiscent of more complex architectures. ,, …”

“…In principle, this shift allows for an increased loading of the hard blocks by volume fraction that is reminiscent of more complex architectures. 16,22,33 Motivated by these SCFT predictions, L-C-S samples with higher loadings of the L and S hard blocks (f Hard = 0.18−0.40) that would be expected to form discrete spherical or cylindrical domains were synthesized and characterized. As plotted in Figure 7a, ABC triblocks with larger hard-block volume fractions are still extensible (900−1700%) and show strainhardening behavior typical of semicrystalline thermoplastic elastomers.…”

“…Initial theoretical and experimental efforts to increase performance and the bridging fraction involved the design of ABABA pentablock copolymers − or the synthesis of compositionally asymmetric linear ABA′ triblocks and related nonlinear architectures. − While these strategies do increase the bridging fraction of B blocks, significant loop formation still occurs. To address this limitation, ABC triblock terpolymers allow for microphase separation between the A and C blocks/domains with minimal to no loops since A chains are not miscible with C domains and C chains are not miscible with A domains (Figure a). ,− The challenge with ABC triblock terpolymers arise from introducing a third block chemistry that complicates both synthesis and the molecular designtwo independent volume fractions (f A , f B ; f C = 1 – f B – f A ) and three Flory–Huggins parameters (χ AB , χ AC , and χ BC ) must now be carefully selected.…”

High Performance Star Block Aliphatic Polyester Thermoplastic Elastomers Using PDLA-b-PLLA Stereoblock Hard Domains

“…Sustainable alternatives to incumbent petrochemical-derived TPEs that display competitive mechanical properties but are more readily degraded at their end-of-life are being actively pursued. − For example, aliphatic polyester TPEs (APTPEs) can be prepared from biomass and are susceptible to hydrolytic degradation that facilitates biodegradation under conducive conditions. Polylactide (PLA), which is both low cost and commercially available, has been widely utilized for the hard domains of APTPEs as its thermal and mechanical properties are comparable to PS .…”