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1. Guanine and cytosine‐containing acrylic supramolecular networks

   https://doi.org/10.1002/pol.20230320  

   Liu, Boer ; Spiering, Glenn A. ; McDonough, Rose K. ; Moore, Robert B. ; Long, Timothy E. ( August 2023 , Journal of Polymer Science)

   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.

    

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2. Sustainable glucose-based block copolymers exhibit elastomeric and adhesive behavior

   https://doi.org/10.1039/c6py00700g  

   Nasiri, Mohammadreza ; Reineke, Theresa M. ( January 2016 , Polymer Chemistry)

   Herein, we present the direct modification of glucose, an abundant and inexpensive sugar molecule, to produce new sustainable and functional polymers. Glucose-6-acrylate-1,2,3,4-tetraacetate (GATA) has been synthesized and shown to provide a useful glassy component for developing an innovative family of elastomeric and adhesive materials. A series of diblock and triblock copolymers of GATA and n -butyl acrylate (n-BA) were created via Reversible Addition–Fragmentation Chain Transfer (RAFT) polymerization. Initially, poly(GATA)- b -poly(n-BA) copolymers were prepared using 4-cyano-4-[(ethylsulfanylthiocarbonyl)sulfanyl] pentanoic acid (CEP) as a chain transfer agent (CTA). These diblock copolymers demonstrated decomposition temperatures of 275 °C or greater and two glass transition temperatures ( T g ) around −45 °C and 100 °C corresponding to the PnBA and PGATA domains, respectively, as measured by differential scanning calorimetry (DSC). Triblock copolymers of GATA and n-BA, with moderate dispersities ( Đ = 1.15–1.29), were successfully synthesized when S , S -dibenzyl trithiocarbonate (DTC) was employed as the CTA. Poly(GATA)- b -poly(nBA)- b -poly(GATA) copolymers with 14–58 wt% GATA were prepared and demonstrated excellent thermomechanical properties ( T d ≥ 279 °C). Two well-separated glass transitions near the values for homopolymers of n-BA and GATA (∼−45 °C and ∼100 °C, respectively) were measured by DSC. The triblock with 14% GATA exhibited peel adhesion of 2.31 N cm −1 (when mixed with 30 wt% tackifier) that is superior to many commercial pressure sensitive adhesives (PSAs). Use of 3,5-bis(2-dodecylthiocarbonothioylthio-1oxopropoxy)benzoic acid (BTCBA) as the CTA provided a more efficient route to copolymerize GATA and n-BA. Using BTCBA, poly(GATA)- b -poly(nBA)- b -poly(GATA) triblock copolymers containing 12–25 wt% GATA, with very narrow molar mass distributions ( Đ ≤ 1.08), were prepared. The latter series of triblock copolymers showed excellent thermal stability with T d ≥ 275 °C. Only the T g for the PnBA block was observed by DSC (∼−45 °C), however, phase-separation was confirmed by small-angle X-ray scattering (SAXS) for all of these triblock copolymers. The mechanical behavior of the polymers was investigated by tensile experiments and the triblock with 25% GATA content demonstrated moderate elastomeric properties, 573 kPa stress at break and 171% elongation. This study introduces a new family of glucose-based ABA-type copolymers and demonstrates functionality of a glucose-based feedstock for developing green polymeric materials. 

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3. Sticky ends in a self-assembling ABA triblock copolymer: the role of ureas in stimuli-responsive hydrogels

   https://doi.org/10.1039/C8ME00063H  

   Shafranek, Ryan T. ; Leger, Joel D. ; Zhang, Song ; Khalil, Munira ; Gu, Xiaodan ; Nelson, Alshakim ( February 2019 , Molecular Systems Design & Engineering)

   Directing polymer self-assembly through noncovalent interactions is a powerful way to control the structure and function of nanoengineered materials. Dynamic hydrogen bonds are particularly useful for materials with structures that change over time or in response to specific stimuli. In the present work, we use the supramolecular association of urea moieties to manipulate the morphology, thermal response, and mechanical properties of soft polymeric hydrogels. Urea-terminated poly(isopropyl glycidyl ether)- b -poly(ethylene oxide)- b -poly(isopropyl glycidyl ether) ABA triblock copolymers were synthesized using controlled, anionic ring-opening polymerization and subsequent chain-end functionalization. Triblock copolymers with hydroxy end-groups were incapable of hydrogelation, while polymers terminated with meta -bis-urea motifs formed robust gels at room temperature. Rheometric analysis of the bulk gels, variable-temperature infrared spectroscopy (VT-IR), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS) confirmed the formation of structured hydrogels via association of the meta -bis-urea end-groups. Monourea end-groups did not result in the same regular structure as the meta -bis-urea. In future, the reported hydrogels could be useful for elastomeric, shape-morphing 3D-printed constructs, or as biomimetic scaffolds with precisely tailored porosity and mechanical properties. 

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4. Synthesis of a heterotelechelic helical poly(methacrylamide) and its incorporation into a supramolecular triblock copolymer

   https://doi.org/10.1039/c9py01047e  

   Deng, Ru ; Milton, Margarita ; Pomarico, Scott K. ; Weck, Marcus ( September 2019 , Polymer Chemistry)

   We report the first heterotelechelic helical poly(methacrylamide) (PMAc) bearing orthogonal supramolecular binding sites on its chain-ends synthesized through a combination of reversible addition–fragmentation chain-transfer (RAFT) polymerization and thiol–bromo “click” chemistry. The heterotelechelic PMAc was assembled with two monotelechelic polymers featuring different secondary structures, namely a coil-like poly(styrene) and a helical poly(isocyanide), resulting in the formation of a coil–helix–helix supramolecular triblock copolymer through orthogonal metal coordination and hydrogen bonding interactions. Triblock assembly was confirmed through 1 H NMR spectroscopy, isothermal titration calorimetry (ITC) and viscometry. The individual polymer blocks retained their secondary structures in the final triblock copolymer, as evidenced by circular dichroism (CD) spectroscopy. Our synthetic strategy expands the toolbox of triblock copolymers featuring structural motifs similar to the ones found in proteins and provides the potential for the development of other complex multifunctional polymeric ensembles. 

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5. Molecular Insights into the Self‐Assembly of Block Copolymer Suckerin Polypeptides into Nanoconfined β‐Sheets

   https://doi.org/10.1002/smll.202202642  

   Liu, Yuying ; Wang, Ying ; Tong, Chaohui ; Wei, Guanghong ; Ding, Feng ; Sun, Yunxiang ( July 2022 , Small)

   Suckerin in squid sucker ring teeth is a block‐copolymer peptide comprised of two repeating modules—the alanine and histidine‐rich M1 and the glycine‐rich M2. Suckerin self‐assemblies display excellent thermo‐plasticity and pH‐responsive properties, along with the high biocompatibility, biodegradability, and sustainability. However, the self‐assembly mechanism and the detailed role of each module are still elusive, limiting the capability of applying and manipulating such biomaterials. Here, the self‐assembly dynamics of the two modules and two minimalist suckerin‐mimetic block‐copolymers, M1‐M2‐M1 and M2‐M1‐M2, in silico is investigated. The simulation results demonstrate that M2 has a stronger self‐association but weaker β‐sheet propensities than M1. The high self‐assembly propensity of M2 allows the minimalist block‐copolymer peptides to coalesce with microphase separation, enabling the formation of nanoconfined β‐sheets in the matrix formed by M1–M2 contacts. Since these glycine‐rich fragments with scatted hydrophobic and aromatic residues are building blocks of many other block‐copolymer peptides, the study suggests that these modules function as the “molecular glue” in addition to the flexible linker or spacer to drive the self‐assembly and microphase separation. The uncovered molecular insights may help understand the structure and function of suckerin and also aid in the design of functional block‐copolymer peptides for nanotechnology and biomedicine applications.

    

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