Shifting Boundaries: Controlling Molecular Weight Distribution Shape for Mechanically Enhanced Thermoplastic Elastomers

Abstract

Thermoplastic elastomers (TPEs) based on polystyrene (PS) are commonplace in society. The elastomeric properties of these materials are often sacrificed to increase mechanical properties such as stiffness, strength, and toughness. We sought to produce stiff, strong, and tough TPEs that retain their elastomeric properties by shifting the lamellar phase boundary toward higher PS content. By precisely controlling the molecular weight distribution (MWD) shape of one PS block in polystyrene-block-polyisoprene-block-polystyrene (SIS), we produced elastomeric continuous phase TPEs at atypically high PS volume fractions, shifting the lamellar phase boundary from 0.33 in triblocks with a narrow MWD PS block to ∼0.39 in triblocks with a broadened MWD PS block. Furthermore, we observed hexagonal/lamellar phase coexistence at a PS volume fraction of 0.39 when the MWD shape of the first PS block was asymmetric. These materials exhibit enhanced mechanical properties consistent with high volume fractions of PS and elastomeric properties consistent with continuous morphologies.

Effect of Hydrophilic Monomer Distribution on Self‐Assembly of a pH‐Responsive Copolymer: Spheres, Worms and Vesicles from a Single Copolymer Composition

“…For G20 , aggregates of spherical assemblies were observed at pH 5, while at pH 4 a mixture of vesicles and wormlike micelles was observed. The presence of wormlike micelles and vesicles rather than only vesicles as in the other structures may be related to the larger dispersity of the gradient copolymer, as increased dispersity is known to displace the phase diagrams of block copolymers, [40–44] for example pushing the cylinder/lamellar phase boundary of polystyrene‐ block ‐polyisoprene‐ block ‐polystyrene elastomers to higher volume fractions of polystyrene [44] . Wormlike structures have previously been observed in aqueous dispersions of block copolymers of BA and AA prepared at low pH; these irreversibly transform into spheres when the pH is raised [35, 45] …”

“…Thep resence of wormlike micelles and vesicles rather than only vesicles as in the other structures may be related to the larger dispersity of the gradient copolymer, as increased dispersity is known to displace the phase diagrams of block copolymers, [40][41][42][43][44] for example pushing the cylinder/lamellar phase boundary of polystyrene-block-polyisoprene-blockpolystyrene elastomers to higher volume fractions of polystyrene. [44] Wormlike structures have previously been ob-served in aqueous dispersions of block copolymers of BA and AA prepared at low pH;t hese irreversibly transform into spheres when the pH is raised. [35,45] Finally,a ssemblies of T10 remained small ( % 10 nm) and spherical from pH 10 to pH 5, while only vesicles of 100 to 300 nm in diameter were observed at pH 4.…”

Einfluss der Verteilung hydrophiler Monomere auf die Selbstassemblierung eines pH‐responsiven Copolymers: Kugeln, Würmer und Vesikel aus einer einzigen Copolymerkomposition

“…Forschungsartikel 4978 www.angewandte.de zellen beobachtet wurde.D ie Anwesenheit von wurmartige Mizellen und Vesikeln und nicht nur reinen Vesikeln wie in den anderen Proben, kçnnte mit der grçßeren Dispersitätder Gradienten-Copolymer zusammenhängen, da erhçhte Dispersitätb ekanntlich die Phasendiagramme von Blockcopolymeren beeinflusst, [40][41][42][43][44] indem zum Beispiel die Zylinder/ Lamellen-Phasengrenze von Elastomeren aus Polystyrolblock-Polyisopren-block-Polystyrol zu hçheren Volumenfraktionen von Polystyrol verschoben wird. [44] Wurmartige Strukturen wurden zuvor in wässrigen Dispersionen von Blockcopolymeren von n-BuA und AA beobachtet, die bei niedrigem pH-Wert hergestellt wurden;d iese wandeln sich irreversibel zu Kugeln um, wenn der pH-Wert erhçht wird. [35,45] Die Assemblierungen von T10 führte zur Ausbildung von kleinen ( % 10 nm) kugelfçrmigen Strukturen im Bereich von pH 10 bis pH 5, während Vesikel mit einem Durchmesser von 100 bis 300 nm nur bei einem pH-Wert von 4b eobachtet wurden.…”

Bromoform-assisted aqueous free radical polymerisation: a simple, inexpensive route for the preparation of block copolymers

“…It should be noted that the molar mass dispersity, Ð, of the final polymers was high in all cases (2.8-3.5), with no suggested relationship between Ð and bromoform content. As previously discussed, high Ð values may not inherently have an adverse impact on the desired application 15,[23][24][25][26][27][28][29][30] .…”

“…Such well-defined macromolecules are crucial for structure-property relationship studies 15 , bulk block copolymer self-assembly (where low mass dispersities are required to produce sharp nanophase boundaries [16][17][18][19] ) and in the pursuit of sequence-controlled macromolecules for biomimicry [20][21][22] . Despite the drive for narrow molar mass distributions, this is not always necessary to prepare materials with desired characteristics and performance [23][24][25][26][27][28][29][30] . In industrial settings, polymers with broader molar mass distributions are often easier to process 31 and the breadth and shape of the molar mass distribution 32 can impart desirable physical properties (e.g.…”