News


  • David Hewitt's paper with the Bhatia Group (August 2018)
    Impact of stereochemistry on rheology and nanostructure of PLA–PEO–PLA triblocks: stiff gels at intermediate L/D-lactide ratios

    Xuechen Yin, David R. O. Hewitt, Suan P. Quah, Bingqian Zheng, Gerard S. Mattei, Peter G. Khalifah, Robert B. Grubbs and Surita R. Bhatia*


    Abstract

    We report rheology and structural studies of poly(lactide)–poly(ethylene oxide)–poly(lactide) (PLA–PEO–PLA) triblock copolymer gels with various ratios of L-lactide and D-lactide in the PLA blocks. These materials form associative micellar gels in water, and previous work has shown that stereoregular triblocks with a L/D ratio of 100/0 form much stiffer gels than triblocks with a 50/50 L/D ratio. Our systems display an unexpected maximum in the storage modulus, G′, of the hydrogels at intermediate L/Dratio. The impact of stereochemistry on the rheology is very striking; gels with an L/Dratio of 85/15 have storage moduli that are ∼1–2 orders of magnitude higher than hydrogels with L/D ratios of 100/0. No stereocomplexation is observed in the gels, although PLLA crystals are found for gels with L/D ratios of 95/5 and 90/10, and SANS results show a decrease in the intermicellar spacing for intermediate L/D ratios. We expect the dominant contribution to the elasticity of the gels to be intermicellar bridging chains and attribute the rheology to a competition between an increase in the time for PLA endblocks to pull out of micelles as the L/D ratio is increased and PLLA crystallization occurs, and a decrease in the number of bridging chains for micelles with crystalline PLA domains, as formation of bridges may be hindered by crowded crystalline PLA domains. These results provide a new strategy for controlling the rheology of PLA-based hydrogels for potential applications in biomaterials, as well as fundamental insights into how intermicellar interactions can be tuned via stereochemistry.

    Posted Oct 4, 2018, 11:34 AM by Robert Grubbs
  • Feng-Yang Shih's paper on ipso-arylative polymerization (May 2018)
    ipso-Arylative polymerization as a route to π-conjugated polymers: synthesis of poly(3-hexylthiophene)
    Feng-Yang Shih,  Sisi Tian,  Nicholas Gallagher,  Young S. Park  and  Robert B. Grubbs*

    Abstract
    ipso-Arylative cross-coupling with two 3-hexylthiophene derivatives, (5-bromo-4-hexylthiophen-2-yl)diphenylmethanol and 2-(5-bromo-4-hexylthiophen-2-yl)propan-2-ol, has been used to prepare poly(3-hexylhiophene) (P3HT) as a model conjugated polymer. P3HT with number-average molecular weights ranging from 8–20 kg mol−1 (Đ 1.4–2.2) was prepared from 5-bromo-4-hexylthiophen-2-yl)diphenylmethanol with a Pd(OAc)2/PCy3/Cs2CO3 catalyst system. Only oligomerization of 2-(5-bromo-4-hexylthiophen-2-yl)propan-2-ol (Mn ≈ 3 kg mol−1) was observed under similar conditions. Studies with model compounds suggest that side reactions involving end-group loss limit ultimate molecular weights.

    Graphical abstract: ipso-Arylative polymerization as a route to π-conjugated polymers: synthesis of poly(3-hexylthiophene)

    Posted Oct 4, 2018, 11:30 AM by Robert Grubbs
  • 2017 Updates
    Some long overdue updates from the previous year:

    * Zhe Sun completed his PhD and is now a post-doc at SUSTech in Shenzhen. His last paper:

    Sun, Z.; Tian, Y.; Hom, W. L.; Gang, O.; Bhatia, S. R.; Grubbs, R. B. “Translating thermal response of triblock copolymer assemblies in dilute solution to macroscopic gelation and phase separation.” Angew. Chem. Int. Ed. 2017, 56, 1491-1494. (doi: 10.1002/anie.201609360)

    * Our collaborator, Dr. Chang-Yong Nam at BNL, published a paper on making ZnO patterns on surfaces:

    Ye, X.; Kestell, J.; Kisslinger, K.; Liu, M.; Grubbs, R. B.; Boscoboinik, J. A.; Nam, C.-Y. “Effects of residual solvent molecules facilitating the infiltration synthesis of ZnO in a non-reactive polymer.” Chem. Mater. 2017, 29, 4535-4545. (doi: 10.1021/acs.chemmater.7b01222)

    * Barney and Bob wrote a perspective on living polymerization for Macromolecules:

    Grubbs, R. B.; Grubbs, R. H. “50th Anniversary Perspective: Living Polymerization—Emphasizing the Molecule in Macromolecules.” Macromolecules 2017, 50, 6979-6997. (doi: 10.1021/acs.macromol.7b01440)

    * Some of Tianyuan's PhD work (a collaboration with Michael Hadjiargyrou, Ben Hsiao, and Ben Chu) has finally seen publication:

    Wu, T.; Cai, Y.; Zhao, X.; Ngai, C. K.; Chu, B.; Hsiao, B.; Hadjiargyrou, M.; Grubbs, R. B. “Synthesis and Characterization of Poly(ethylene oxide)/polylactide/polylysine Tri-arm Star Copolymers for Gene Delivery.” J. Polym. Sci., Part A: Polym. Chem., published on-line 12/26/2017. (doi: 10.1002/pola.28938)


    Posted Jan 2, 2018, 8:41 AM by Robert Grubbs
  • Two Publications by Bingyin Jiang

    Phase Behavior of Alkyne-Functionalized Styrenic Block Copolymer/Cobalt Carbonyl Adducts and in Situ Formation of Magnetic Nanoparticles by Thermolysis

    Department of Chemistry, Department of Materials Science and Engineering and Chemical and Molecular Engineering Program, and §Department of Geosciences, Stony Brook University, Stony Brook, New York 11794, United States
     Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States
    Macromolecules201649 (3), pp 853–865
    DOI: 10.1021/acs.macromol.5b02515
    Publication Date (Web): January 27, 2016

    Abstract Image
    A series of polystyrene-block-poly(4-(phenylethynyl)styrene) (PS-b-PPES) diblock copolymers with a range of compositions were prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization. Block copolymer/cobalt carbonyl adducts (PSx-PPESy[Co2(CO)6]n) were subsequently prepared by reaction of Co2(CO)8 with the alkyne groups of the PPES block. Phase behavior of the block copolymer/cobalt carbonyl adducts (PSx-PPESy[Co2(CO)6]n, 8% ≤ wt % PS ≤ 68%) was studied by small-angle X-ray scattering and transmission electron microscopy (TEM). As the composition of PSx-PPESy[Co2(CO)6]n copolymers was shifted from PS as the majority block to PPESy[Co2(CO)6]n as the majority block, the morphology was observed to shift from lamellar with larger PS domains to cylindrical with PS as the minority component and then to spherical with PS as the minority component. These observations have been used to map out a partial phase diagram for PSx-PPESy[Co2(CO)6]n diblock copolymers. Heating of PSx-PPESy[Co2(CO)6]n samples at relatively low temperatures (120 °C) results in the formation of nanoparticles containing crystalline cobalt and cobalt oxide domains within the PPESy[Co2(CO)6]nregions as characterized by TEM, X-ray diffraction (XRD), and X-ray scattering.

    Magnetic Hydrogels from Alkyne/Cobalt Carbonyl-Functionalized ABA Triblock Copolymers

     Department of Chemistry, Stony Brook University, Stony Brook, New York 11794-3400, United States
     Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States
    § Department of Geosciences, Stony Brook University, Stony Brook, New York 11794-2100, United States
    J. Am. Chem. Soc.2016138 (13), pp 4616–4625
    DOI: 10.1021/jacs.6b01271
    Publication Date (Web): March 09, 2016
    Copyright © 2016 American Chemical Society

    Abstract Image
    A series of alkyne-functionalized poly(4-(phenylethynyl)styrene)-block-poly(ethylene oxide)-block-poly(4-(phenylethynyl)styrene) (PPES-b-PEO-b-PPES) ABA triblock copolymers was synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. PESn[Co2(CO)6]x-EO800-PESn[Co2(CO)6]x ABA triblock copolymer/cobalt adducts (10–67 wt % PEO) were subsequently prepared by reaction of the alkyne-functionalized PPES block with Co2(CO)8 and their phase behavior was studied by TEM. Heating triblock copolymer/cobalt carbonyl adducts at 120 °C led to cross-linking of the PPES/Co domains and the formation of magnetic cobalt nanoparticles within the PPES/Co domains. Magnetic hydrogels could be prepared by swelling the PEO domains of the cross-linked materials with water. Swelling tests, rheological studies and actuation tests demonstrated that the water capacity and modulus of the hydrogels were dependent upon the composition of the block copolymer precursors.
    Posted Aug 30, 2016, 7:36 AM by Robert Grubbs
  • Two publications in collaboration with Hsiao/Chu Group

    Thiol-modified cellulose nanofibrous composite membranes for chromium (VI) and lead (II) adsorption

    • Rui Yang
    • Katherine B. Aubrecht
    • Hongyang Ma
    • Ran Wang
    • Robert B. Grubbs
    • Benjamin S. Hsiao
    • Benjamin Chu
        • Polymer 2014, 55, 1167-1176, doi:10.1016/j.polymer.2014.01.043
            Full-size image (20 K)

            Abstract

            Oxidized cellulose nanofibers (CNF), embedded in an electrospun polyacrylonitrile (PAN) nanofibrous scaffold, were grafted with cysteine to increase the adsorption capability for chromium (VI) and lead (II). Thiol-modified cellulose nanofibers (m-CNF) were characterized by titration, FT-IR, energy dispersive spectroscopy (EDS) and SEM techniques. Static and dynamic Cr(VI) and Pb(II) adsorption studies of m-CNF nanofibrous composite membranes were carried out as a function of pH and of contact time. The results indicated these membranes exhibited high adsorption capacities for both Cr(VI) (87.5 mg/g) and Pb(II) (137.7 mg/g) due to the large surface area and high concentration of thiol groups (0.9 mmol of –SH/gram m-CNF). The morphology and property of m-CNF nanofibrous composite membranes was found to be stable, and they could be used and regenerated multiple times with high recovery efficiency.

            Thiol-functionalized chitin nanofibers for As (III) adsorption

            Polymer 2015, 60, 9-17, doi:10.1016/j.polymer.2015.01.025
            Full-size image (27 K)

            Abstract

            Natural polysaccharide chitin nanofibers, prepared with a series of chemical and mechanical treatments, were used as an absorbent material for arsenic (As(III)) removal. The dimensions of chitin nanofibers, determined by small-angle X-ray scattering (SAXS), were about 6 nm in thickness, 24 nm in width and a few hundred nanometers in length. The chemical/mechanical treatment enabled the chitin nanofiber surface to be charged, thus facilitating the dispersion of nanofibers in aqueous suspension at neutral pH. The large amount of amine groups (1.7 mmol/g) on the nanofiber surface provided opportunities for further modifications, such as formation of amide bonds. In this study, grafting of cysteine was carried out to create adsorption sites for arsenic metal ion (AsO2) removal. The thiol-functionalized chitin nanofibers ([-SH] = 1.1 mmol/g) were characterized by titration, Fourier transform infrared (FT-IR) spectroscopy, energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The arsenic adsorption performance of thiol-modified chitin nanofibers was evaluated under different pH conditions and at different metal ion concentrations, where the maximum adsorption capacity was found to be 149 mg/g at pH = 7.0 using the Langmuir Model. This adsorption capacity was higher than any existing chitin/chitosan-based hydrogel or bead absorbent systems.

    Posted Feb 18, 2015, 8:37 AM by Robert Grubbs
Showing posts 1 - 5 of 17. View more »


ċ
Robert Grubbs,
Oct 5, 2015, 12:19 PM