An official website of the United States government
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
Guanine and cytosine‐containing acrylic supramolecular networks
Abstract This manuscript describes the synthesis and characterization of guanine and cytosine‐containing supramolecular copolymers, which are inspired from the guanine and cytosine nucleobase pair in deoxyribonucleic acid. Regioselective Michael‐addition allowed the efficient installation of the nucleobases on acrylate‐containing monomers, which enabled the preparation of a series of nucleobase‐functionalized acrylate andn‐butyl acrylate copolymers using conventional free radical copolymerization. Guanine‐containing copolymers exhibited superior thermal properties, thermomechanical performance, and more defined morphological structure than cytosine‐containing copolymer analogs due to the relatively strong guanine self‐association, thus expanding the potential applications for mechanically reinforced polymeric networks. Blending guanine‐ and cytosine‐containing copolymers formed a supramolecular structure through multiple hydrogen bonding between guanine and cytosine units. The supramolecular blend exhibited intermediate thermomechanical and morphological properties, which suggested that guanine and cytosine units were not fully associated in the random copolymer composition. This work provides valuable fundamental understanding of structure–property‐morphology relationships in acrylic copolymers with the presence of guanine‐cytosine self‐ and complementary interactions, suggesting new understanding in supramolecular design for enhanced mechanical and morphological properties.
more »
« less
- Award ID(s):
- 2018258
- PAR ID:
- 10491061
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Polymer Science
- Volume:
- 62
- Issue:
- 4
- ISSN:
- 2642-4150
- Format(s):
- Medium: X Size: p. 733-742
- Size(s):
- p. 733-742
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The effect of vortex‐induced mechanical stresses on the fluorescent properties of dye‐containing poly(ethylene glycol)‐block‐poly(lactic acid) (PEG‐b‐PLA) block copolymer micelles has been investigated. PEG‐b‐PLA block copolymer micelles containing fluorescent dyes, 3,3′‐dioctadecyloxacarbocyanine perchlorate (DiO) and/or 1,1′‐dioctadecyl‐3,3,3′,3′‐tetramethylindocarbocyanine perchlorate (DiI), are prepared by a simple one‐step procedure that involves the self‐assembly of block copolymers and spontaneous incorporation of hydrophobic dyes into the core of the micelles. Upon vortexing, the micelle dispersion samples showed a decrease in fluorescence intensity in a rotational speed‐ and time‐dependent manner. The results demonstrated that the vortexing can alter the fluorescent properties of the dye‐containing PEG‐b‐PLA block copolymer micelle dispersion samples, suggesting the potential utility of block copolymer micelles as a mechanical stress‐responsive nanomaterial.more » « less
-
Abstract In an effort to synthesize chemically recyclable thermoplastic elastomers, a redox‐switchable catalytic system was developed to synthesize triblock copolymers containing stiff poly(lactic acid) (PLA) end blocks and a flexible poly(tetrahydrofuran‐co‐cyclohexene oxide) (poly(THF‐co‐CHO) copolymer as the mid‐block. The orthogonal reactivity induced by changing the oxidation state of the iron‐based catalyst enabled the synthesis of the triblock copolymers in a single reaction flask from a mixture of monomers. The triblock copolymers demonstrated improved flexibility compared to poly(l‐lactic acid) (PLLA) and thermomechanical properties that resemble thermoplastic elastomers, including a rubbery plateau in the range of −60 to 40 °C. The triblock copolymers containing a higher percentage of THF versus CHO were more flexible, and a blend of triblock copolymers containing PLLA and poly(d‐lactic acid) (PDLA) end‐blocks resulted in a stereocomplex that further increased polymer flexibility. Besides the low cost of lactide and THF, the sustainability of this new class of triblock copolymers was also supported by their depolymerization, which was achieved by exposing the copolymers sequentially to FeCl3and ZnCl2/PEG under reactive distillation conditions.more » « less
-
Substrate identification of putative NCS1 and NCS2 nucleobase transporters in Pseudomonas aeruginosaMathee, Kalai; Dandekar, Ajai A (Ed.)ABSTRACT Pseudomonas aeruginosais an opportunistic pathogen that can salvage nucleobases from the environment to conserve nutrients that would otherwise be spent onde novonucleotide biosynthesis. However, little is known regarding the substrate specificity of the 13 putative nucleobase transporters inP. aeruginosa. Here, using a combination of genetic and chemical approaches, we report substrate identifications for 10 putative nucleobase transporters inP. aeruginosa. Specifically, we individually expressed each transporter in a genetic background lacking all 13 putative nucleobase transporters and quantified growth on a panel of 10 nucleobases as sole nitrogen sources. We confirmed these expression-based substrate identifications using targeted genetic knockouts. In a complementary approach, we utilized four toxic nucleobase antimetabolites to characterize antimicrobial activity in these same strains. We identified the sole allantoin transporter as well as transporters for guanine, xanthine, uric acid, cytosine, thymine, uracil, and dihydrouracil. Furthermore, we associated at least five nucleobase transporters with hypoxanthine, which has been recently reported to be an antibiofilm cue inP. aeruginosa. These results provide an initial characterization of the putative nucleobase transporters inP. aeruginosa, significantly advancing our understanding of nucleobase transport in this clinically relevant organism. IMPORTANCEPseudomonas aeruginosais a frequently multidrug-resistant opportunistic pathogen and one of the most common causes of healthcare-acquired infections. While nucleobases are known to support growth in nutrient-limited conditions, recent work showed that adenine and hypoxanthine can also decreaseP. aeruginosabiofilm formation by disrupting c-di-GMP metabolism. Thus, nucleobase transport may be relevant to multiple aspects ofP. aeruginosabiology and pathogenesis. However, there is currently little known about the transport of nucleobases inP. aeruginosa. Our work reports initial substrate identifications for 10 putative nucleobase transporters inP. aeruginosa, providing new tools to address previously difficult-to-test hypotheses relating to nucleobase transport in this organism.more » « less
-
Abstract Synthesizing soft polymers with uncommon architectural elements is critical for enhancing our understanding of fundamental structure–property relationships in macromolecules. Terpenoid materials are interesting candidates for addressing this grand challenge, as their constituent monomers can exhibit a diverse array of structural and functional groups. Moreover, these biologically‐derived materials can potentially expand the sphere of knowledge surrounding trends in related petrochemically‐derived polymers. For example, vinyl‐addition copolymers of norbornene and acyclic olefins can exhibit predictable properties (e.g., linear changes inTgas a function of composition). Due to synthetic limitations, however, it is not well understood if other rigid carbocycles engender similar behavior in a range of copolymers. As numerous terpene scaffolds display rigid motifs (such as pinane systems), terpenoid polymers are uniquely positioned to address this deficiency. Here, we report the synthesis and characterization of terpenoid copolymers (both statistical and block) with systematically tailored compositions of pinene‐based comonomers. We found that the pinane core (which is a constitutional isomer of norbornene) appears to promote ideal behavior with regard to bulk thermal properties of statistical copolymers, which mirrors the behavior of norbornene‐based systems. We also found that block copolymers exhibited thermomechanical properties that were highly tunable (and apparently correlated to carbocycle composition).more » « less
