Double-Gyroid Network Morphology in Tapered Diblock Copolymers

Abstract

We report the formation of a double-gyroid network morphology in normal-tapered poly(isoprene-b-isoprene/styrene-b-styrene) [P(I-IS-S)] and inverse-tapered poly(isoprene-b- styrene/isoprene-b-styrene) [P(I-SI-S)] diblock copolymers. Our tapered diblock copolymers with overall poly(styrene) volume fractions of 0.65 (normal-tapered) and 0.67 (inverse-tapered), and tapered regions comprising 30 volume percent of the total polymer, were shown to self-assemble into the double-gyroid network morphology through a combination of small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The block copolymers were synthesized by anionic polymerization, where the tapered region between the pure poly(isoprene) and poly(styrene) blocks was generated using a semi-batch feed with programmed syringe pumps. The overall composition of these tapered copolymers lies within the expected network-forming region for conventional poly(isoprene-b-styrene) [P(I-S)] diblock copolymers. Dynamic mechanical analysis (DMA) clearly demonstrated that the order-disorder transition temperatures (TODT’s) of the network-forming tapered block copolymers were depressed when compared to the TODT of their non-tapered counterpart, with the P(I-SI-S) showing the greater drop in TODT. These results indicate that it is possible to manipulate the copolymer composition profile between blocks in a diblock copolymer, allowing significant control over the TODT, while maintaining the ability to form complex network structures.

Controlling Macroscopic Properties by Tailoring Nanoscopic Interfaces in Tapered Copolymers

“…Previously, Epps and co-workers have demonstrated that styrene−isoprene copolymers can adopt double-gyroid morphologies, with reductions in order−disorder temperatures for tapered block copolymers relative to discrete block copolymers. 22 While we have not detected this complex morphology in our styrene−butadiene systems, it is clear that simply varying the order of introduction and relative concentration of comonomers in the tapered regions of a copolymer can significantly impact final molecular and physical properties. This important conclusion has broad implications for tailored polymer properties using both traditional and novel monomer feeds.…”

Design and Synthesis of Network-Forming Triblock Copolymers Using Tapered Block Interfaces

“…This reduction in χ eff leads to lower order-to-disorder transition temperatures relative to the corresponding non-tapered block copolymers. 24–26 Thus, TBCs can be used to create high molecular weight materials while retaining access to the network phases found at weak and intermediate segregation strengths. 26 Though a well-ordered network structure has been found at high molecular weight following additional post-processing in a few select cases, 27 our TBCs permit the facile design of network materials with improved mechanical properties (due to higher molecular weights), combined with lowered interfacial energetics for a wider array of potential applications.…”

Effect of sequence dispersity on morphology of tapered diblock copolymers from molecular dynamics simulations

“…A major driver of interest in such systems is that, by adjusting the length of the tapered region, one can tune microphase behavior and physical properties such as glass transition temperature (T g ) and orderdisorder transition temperature (T ODT ), as has been found in experiments by multiple groups. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] As would be intuitively expected, adding a taper generally increases the miscibility of the system, effectively decreasing the segregation strength (quantified by χN, the Flory χ parameter times polymer length) and widens the interfacial regions of the microphase separated structures. Furthermore, tapering has been shown to change the microphase behavior and dynamics versus typical diblocks in ways that cannot be explained by a simple shift in effective segregation strength.…”

“…Furthermore, tapering has been shown to change the microphase behavior and dynamics versus typical diblocks in ways that cannot be explained by a simple shift in effective segregation strength. [16][17][18][19][20] The promise of tapered polymers was highlighted in a recent work showing that intermediate length tapers can enhance polymer dynamics, improving ion transport in lithium ion battery electrolyte materials. 21 Simulation and theory can provide insight into the physical origins of such behavior and potentially provide guidance in implementing this new control parameter a) E-mail: hall.1004@osu.edu effectively.…”

“…26 One way tapered copolymers can be formed experimentally is via a semi-batch process of many sequential living anionic polymerization steps; during each step the two different types of monomers are injected in different amounts and are polymerized approximately randomly. 4,5,16,[27][28][29][30][31][32] A very recent work showed an excellent agreement between tapered copolymer density profiles from experiment and fDFT (with a fixed sequence), 17 though comparisons between experiment and theory with respect to order-disorder transitions or dynamics have not been as specific and precise.…”