- Award ID(s):
- 1905487
- NSF-PAR ID:
- 10329154
- Date Published:
- Journal Name:
- Frontiers in Chemistry
- Volume:
- 10
- ISSN:
- 2296-2646
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
This work reveals the influence of pendant hydrogen bonding strength and distribution on self-assembly and the resulting thermomechanical properties of A-AB-A triblock copolymers. Reversible addition-fragmentation chain transfer polymerization afforded a library of A-AB-A acrylic triblock copolymers, wherein the A unit contained cytosine acrylate (CyA) or post-functionalized ureido cytosine acrylate (UCyA) and the B unit consisted of n-butyl acrylate (nBA). Differential scanning calorimetry revealed two glass transition temperatures, suggesting microphase-separation in the A-AB-A triblock copolymers. Thermomechanical and morphological analysis revealed the effects of hydrogen bonding distribution and strength on the self-assembly and microphase-separated morphology. Dynamic mechanical analysis showed multiple tan delta (δ) transitions that correlated to chain relaxation and hydrogen bonding dissociation, further confirming the microphase-separated structure. In addition, UCyA triblock copolymers possessed an extended modulus plateau versus temperature compared to the CyA analogs due to the stronger association of quadruple hydrogen bonding. CyA triblock copolymers exhibited a cylindrical microphase-separated morphology according to small-angle X-ray scattering. In contrast, UCyA triblock copolymers lacked long-range ordering due to hydrogen bonding induced phase mixing. The incorporation of UCyA into the soft central block resulted in improved tensile strength, extensibility, and toughness compared to the AB random copolymer and A-B-A triblock copolymer comparisons. This study provides insight into the structure-property relationships of A-AB-A supramolecular triblock copolymers that result from tunable association strengths.more » « less
-
The tunable properties of thermoplastic elastomers (TPEs), through polymer chemistry manipulations, enable these technologically critical materials to be employed in a broad range of applications. The need to “dial-in” the mechanical properties and responses of TPEs generally requires the design and synthesis of new macromolecules. In these designs, TPEs with nonlinear macromolecular architectures outperform the mechanical properties of their linear copolymer counterparts, but the differences in deformation mechanism providing enhanced performance are unknown. Here, in situ small-angle X-ray scattering (SAXS) measurements during uniaxial extension reveal distinct deformation mechanisms between a commercially available linear poly(styrene)-poly(butadiene)-poly(styrene) (SBS) triblock copolymer and the grafted SBS version containing grafted poly(styrene) (PS) chains from the poly(butadiene) (PBD) mid-block. The neat SBS (φSBS = 100%) sample deforms congruently with the macroscopic dimensions with the domain spacing between spheres increasing and decreasing along and traverse to the stretch direction, respectively. At high extensions, end segment pullout from the PS-rich domains is detected, which is indicated by a disordering of SBS. Conversely, the PS-grafted SBS that is 30 vol% SBS and 70% styrene (φSBS = 30%) exhibits a lamellar morphology and in situ SAXS measurements reveal an unexpected deformation mechanism. During deformation there are two simultaneous processes: significant lamellar domain rearrangement to preferentially orient the lamellae planes parallel to the stretch direction and crazing. The samples whiten at high strains as expected for crazing, which corresponds with the emergence of features in the two-dimensional SAXS pattern during stretching consistent with fibril-like structures that bridge the voids in crazes. The significant domain rearrangement in the grafted copolymers is attributed to the new junctions formed across multiple PS domains by the grafts of a single chain. The in situ SAXS measurements provide insights into the enhanced mechanical properties of grafted copolymers that arise through improved physical crosslinking that leads to nanostructured domain reorientation for self-reinforcement and craze formation where fibrils help to strengthen the polymer.more » « less
-
The long-standing goal in membrane development is creating materials with superior transport properties, including both high flux and high selectivity. These properties are common in biological membranes, and thus mimicking nature is a promising strategy towards improved membrane design. In previous studies, we have shown that artificial water channels can have excellent water transport abilities that are comparable to biological water channel proteins, aquaporins. In this study, we propose a strategy for incorporation of artificial channels that mimic biological channels into stable polymeric membranes. Specifically, we synthesized an amphiphilic triblock copolymer, poly(isoprene)– block –poly(ethylene oxide)– block –poly(isoprene), which is a high molecular weight synthetic analog of naturally occurring lipids in terms of its self-assembled structure. This polymer was used to build stacked membranes composed of self-assembled lamellae. The resulting membranes resemble layers of natural lipid bilayers in living systems, but with superior mechanical properties suitable for real-world applications. The procedures used to synthesize the triblock copolymer resulted in membranes with increased stability due to the crosslinkability of the hydrophobic domains. Furthermore, the introduction of bridging hydrophilic domains leads to the preservation of the stacked membrane structure when the membrane is in contact with water, something that is challenging for diblock lamellae that tend to swell, and delaminate in aqueous solutions. This new method of membrane fabrication offers a practical model for making channel-based biomimetic membranes, which may lead to technological applications in reverse osmosis, nanofiltration, and ultrafiltration membranes.more » « less
-
ABSTRACT Ternary block copolymer (BCP)‐homopolymer (HP) blends offer a simple method for tuning nanostructure sizes to meet application‐specific demands. Comprehensive dissipative particle dynamic (DPD) simulations were performed to study the impact of polymer interactions, molecular weight, and HP volume fraction (
) on symmetric ternary blend morphological stability and domain spacing. DPD reproduces key features of the experimental phase diagram, including lamellar domain swelling with increasingφ HP , the formation of an asymmetric bicontinuous microemulsion at a critical HP concentration , and macrophase separation with further HP addition. Simulation results matched experimental values for and lamellar swelling as a function of HP to BCP chain length ratio,φ HP . Structural analysis of blends with fixedα =N HP/N BCP but varyingφ HP confirmed that ternary blends follow the wet/dry brush model of domain swelling with the miscibility of HPs and BCPs depending onα . Longer HPs concentrate in the center of domains, boosting their swelling efficiencies compared to shorter chains. These results advance our understanding of BCP‐HP blend phase behavior and demonstrate the value of DPD for studying polymeric blends. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.α 2019 ,57 , 794–803 -
Abstract Therapeutic proteins are utilized in a variety of clinical applications, but side effects and rapid in vivo clearance still present hurdles. An approach that addresses both drawbacks is protein encapsulation within in a polymeric nanoparticle, which is effective but introduces the additional challenge of destabilizing the nanoparticle shell in clinically relevant locations. This study examined the effects of crosslinking self‐assembled poly(
l ‐lysine)‐grafted‐poly(ethylene glycol) nanoparticles with redox‐responsive 3,3′‐dithiobis(sulfosuccinimidyl propionate) (DTSSP) to achieve nanoparticle destabilization in a reductive environment. The polymer‐protein nanoparticles (DTSSP NPs) were formed through electrostatic self‐assembly and crosslinked with DTSSP, which contains a glutathione‐reducible disulfide. As glutathione is upregulated in various cancers, DTSSP NPs could display destabilization within cancer cells. A library of DTSSP NPs was formed with varying copolymer to protein (C:P) and crosslinker to protein (X:P) mass ratios and characterized by size and encapsulation efficiency. DTSSP NPs with a 7:1 C:P ratio and 2:1 X:P ratio were further characterized by stability in the presence proteases and reducing agents. DTSSP NPs fully encapsulated the model protein and displayed 81% protein release when incubated with 5 mM dithiothreitol for 12 hr. This study contributes to understanding stimulus‐responsive crosslinking of polymeric nanoparticles and could be foundational to clinical administration of therapeutic proteins.