Tara Y. Meyer

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Name: Meyer, Tara

Organization: University of Pittsburgh , USA

Department: Department of Chemistry

Title: Associate(PhD)

TOPICS

Polymer

Inorganic Chemistry

Chemicals
References

Sequence Effects in Donor–Acceptor Oligomeric Semiconductors Comprising Benzothiadiazole and Phenylenevinylene Monomers

Co-reporter:Shaopeng Zhang, Nicole E. Bauer, Ilana Y. Kanal, Wei YouGeoffrey R. Hutchison, Tara Y. Meyer

Macromolecules January 10, 2017 Volume 50(Issue 1) pp:

Publication Date(Web):December 22, 2016

DOI:10.1021/acs.macromol.6b02215

To understand the influence of monomer sequence on the properties and performance of conjugated oligomers, a series of dimers, trimers, and tetramers were prepared from phenylene (P) and benzothiadiazole (B) monomers linked by vinylene groups. Optical and electrochemical studies established the influence of sequence on both the λmax and redox potentials of this series of structurally related oligomers. For tetramers with bromo end groups (PBBP, BPPB, PBPB, PPBB), the λmax ranged from 493 to 512 nm (Δ = 19 nm), the electrochemical oxidation potential from 0.65 to 0.82 (Δ = 0.17 V) and the reduction potential from −1.45 to −1.31 (Δ = 0.14 V), all of which are sequence-dependent. The effect of end groups (cyano, bromo, and alkyl) was also demonstrated to be important for the properties of these oligomers. DFT calculations of the tetramers were performed and the energy levels were correlated well with the experimentally determined spectroscopic data. Bulk heterojunction (BHJ) solar cells fabricated with selected tetramers as the donor and PC61BM as the acceptor exhibited power conversion efficiencies that varied by a factor of 3 as a function of sequence (0.47–1.85%). These results suggest that sequence control is important for tuning optoelectronic properties and photovoltaic performance of these structurally related conjugated oligomers.

Determining Sequence Fidelity in Repeating Sequence Poly(lactic-co-glycolic acid)s

Co-reporter:Ryan M. Weiss, Jian Li, Han H. Liu, Michael A. Washington, Joseph A. Giesen, Scott M. Grayson, and Tara Y. Meyer

Macromolecules 2017 Volume 50(Issue 2) pp:

Publication Date(Web):January 5, 2017

DOI:10.1021/acs.macromol.6b02202

The synthesis and characterization of sequenced copolymers is a relatively underdeveloped field despite the fact that biological polymer properties are known to depend directly on sequence. The concept of sequence fidelity is introduced and defined for repeating sequence copolymers as the ratio of repeat units of the target sequence to the total number of repeat units. 1H NMR spectroscopy and matrix-assisted laser desorption/ionization time-of- flight mass spectrometry (MALDI–ToF MS) are used to characterize the sequence fidelity of repeating sequenced copolymers comprising poly(lactic-co-glycolic acid)s. Both characterization methods are found to have both advantages and weaknesses with regard to identifying and quantifying error in these copolymers. A method for using routine MALDI–ToF MS data to quantify sequence fidelity is proposed and applied to a series of copolymers with synthetically defined error rates. The MS-determined sequence fidelities are comparable to those obtained by NMR analysis.

Sequence Effects in Conjugated DonorAcceptor Trimers and Polymers

Co-reporter:Shaopeng Zhang;Geoffrey R. Hutchison

Macromolecular Rapid Communications 2016 Volume 37( Issue 11) pp:882-887

Publication Date(Web):

DOI:10.1002/marc.201600086

Sequence-Controlled Copolymers Prepared via Entropy-Driven Ring-Opening Metathesis Polymerization

Co-reporter:Ryan M. Weiss, Amy L. Short, and Tara Y. Meyer

ACS Macro Letters 2015 Volume 4(Issue 9) pp:1039

Publication Date(Web):September 2, 2015

DOI:10.1021/acsmacrolett.5b00528

A new general synthetic approach to sequenced macromolecules was developed and applied to the synthesis of polymers comprising lactic acid (L), glycolic acid (G), and ε-caprolactone (C)-derived monomer units. The new method employs entropy-driven ring-opening metathesis polymerization (ED-ROMP) to prepare copolymers with embedded sequences and controlled molecular weights. Cyclic macromonomer precursors were prepared by ring-closing metathesis of ethylene glycol (Eg)-linked sequenced oligomers bearing terminal olefins. ED-ROMP of the resulting macrocycles using Grubbs’ second generation catalyst yielded poly(CL-Eg-LC-Oed), poly(CLL-Eg-LLC-Oed), poly(LGL-Eg-LGL-Oed), and poly(LGL-Eg-LGL-Hed) (Oed = octenedioc acid; Hed = hexenedioc acid). Hydrogenation produced the saturated sequenced copolymers. Molecular weight was well-controlled and could be adjusted by varying the monomer-to-catalyst ratio. Mns of 26–60 kDa were obtained (dispersities = 1.1–1.3). The methodology proved general for three different sequences and two olefinic metathesis groups.

Stimuli-Responsive Iron-Cross-Linked Hydrogels That Undergo Redox-Driven Switching between Hard and Soft States

Co-reporter:Jeffrey T. Auletta, Gregory J. LeDonne, Kai C. Gronborg, Colin D. Ladd, Haitao Liu, William W. Clark, and Tara Y. Meyer

Macromolecules 2015 Volume 48(Issue 6) pp:1736-1747

Publication Date(Web):March 9, 2015

DOI:10.1021/acs.macromol.5b00142

A unique class of stimuli-responsive hydrogels, termed electroplastic elastomers (EPEs), whose mechanical properties can be reversibly tuned between hard and soft states with the application of an electric potential, is described. Electrochemically reversible cross-links formed within a permanent, covalently cross-linked polymeric hydrogel network are switched between strongly binding Fe3+ and weak to nonbinding Fe2+, as determined by potentiometric titration. With the incorporation of graphene oxide (GO) into the EPE, a significant enhancement in modulus and toughness was observed, allowing for the preparation of thinner EPE samples, 80–100 μm in thickness, which could be reversibly cycled between soft (Young’s modulus: ∼0.38 MPa) and hard (∼2.3 MPa) states over 30 min. Further characterization of EPE samples by magnetic susceptibility measurements suggests the formation of multinuclear iron clusters within the gel.

Chemical and Electrochemical Manipulation of Mechanical Properties in Stimuli-Responsive Copper-Cross-Linked Hydrogels

Co-reporter:Rachel D. Harris, Jeffrey T. Auletta, S. Amin Mohaghegh Motlagh, Matthew J. Lawless, Nicholas M. Perri, Sunil Saxena, Lisa M. Weiland, David H. Waldeck, William W. Clark, and Tara Y. Meyer

ACS Macro Letters 2013 Volume 2(Issue 12) pp:1095

Publication Date(Web):December 3, 2013

DOI:10.1021/mz4004997

Inspiration for the design of new synthetic polymers can be found in the natural world, where materials often exhibit complex properties that change depending on external stimuli. A new synthetic electroplastic elastomer hydrogel (EPEH) that undergoes changes in mechanical properties in response to both chemical and electrochemical stimuli has been prepared based on these precedents. In addition to having the capability to switch between hard and soft states, the presence of both permanent covalent and dynamic copper-based cross links also allows this stimuli-responsive material to exhibit a striking shape memory capability. The density of temporary cross links and the mechanical properties are controlled by reversible switching between the +1 and +2 oxidation states.

Sequence Matters: Modulating Electronic and Optical Properties of Conjugated Oligomers via Tailored Sequence

Co-reporter:Benjamin N. Norris, Shaopeng Zhang, Casey M. Campbell, Jeffrey T. Auletta, Percy Calvo-Marzal, Geoffrey R. Hutchison, and Tara Y. Meyer

Macromolecules 2013 Volume 46(Issue 4) pp:1384-1392

Publication Date(Web):February 11, 2013

DOI:10.1021/ma400123r

Although sequence must necessarily affect the photophysical properties of oligomers and copolymers prepared from donor and acceptor monomers, little is known about this effect, as nearly all the donor/acceptor materials have an alternating structure. A series of sequenced p-phenylene–vinylene (PV) oligomers was synthesized and investigated both experimentally and computationally. Using Horner–Wadsworth–Emmons (HWE) chemistry, a series of dimers, trimers, tetramers, pentamers, and hexamers were prepared from two building block monomers, a relatively electron-poor unsubstituted p-phenylene–vinylene (A) and an electron-rich dialkoxy-substituted p-phenylene–vinylene (B). UV–vis absorption/emission spectra and cyclic voltammetry demonstrated that the optoelectronic properties of these oligomers depended significantly on sequence. Calculations predicting the HOMO–LUMO gap of the sequenced oligomers correlated well with the experimental properties for the 2- to 4-mers, and the consensus model developed was used to design hexameric sequences with targeted characteristics. Despite the weak acceptor qualities of the “A” monomer employed in the study, HOMO–LUMO gap differences of ∼0.25 eV were found for isomeric, sequenced oligomers. In no case did the alternating structure give the largest or smallest gap. The use of sequence as a strategy represents a new dimension in tailoring properties of π-conjugated polymers.

The Effect of Monomer Order on the Hydrolysis of Biodegradable Poly(lactic-co-glycolic acid) Repeating Sequence Copolymers

Co-reporter:Jian Li ; Sam N. Rothstein ; Steven R. Little ; Harry M. Edenborn

Journal of the American Chemical Society 2012 Volume 134(Issue 39) pp:16352-16359

Publication Date(Web):September 5, 2012

DOI:10.1021/ja306866w

The effect of sequence on copolymer properties is rarely studied despite the precedent from Nature that monomer order can create materials of significant diversity. Poly(lactic-co-glycolic acid) (PLGA), one of the most important biodegradable copolymers, is widely used in an unsequenced, random form for both drug delivery microparticles and tissue engineering matrices. Sequenced PLGA copolymers have been synthesized and fabricated into microparticles to study how their hydrolysis rates compare to those of random copolymers. Sequenced PLGA microparticles were found to degrade at slower, and often more constant, rates than random copolymers with the same lactic to glycolic acid ratios as demonstrated by molecular weight decrease, lactic acid release, and thermal property analyses. The impact of copolymer sequence on in vitro release was studied using PLGA microparticles loaded with model agent rhodamine-B. These assays established that copolymer sequence affects the rate of release and that a more gradual burst release can be achieved using sequenced copolymers compared to a random control.

Manipulating Mechanical Properties with Electricity: Electroplastic Elastomer Hydrogels

Co-reporter:Percy Calvo-Marzal, Mark P. Delaney, Jeffrey T. Auletta, Tianqi Pan, Nicholas M. Perri, Lisa M. Weiland, David H. Waldeck, William W. Clark, and Tara Y. Meyer

ACS Macro Letters 2012 Volume 1(Issue 1) pp:204

Publication Date(Web):December 15, 2011

DOI:10.1021/mz2001548

The dawn of the 21st century has brought with it an increasing interest in emulating the adaptive finesse of natural systems by designing materials with on-demand, tunable properties. The creation of such responsive systems could be expected, based on historical precedent, to lead to completely new engineering design paradigms. Using a bioinspired approach of coupling multiple equilibria that operate on different length scales, a material whose bulk mechanical properties can be manipulated by electrical input has been developed. The new macroscale electroplastic elastomer hydrogels can be reversibly cycled through soft and hard states while maintaining a three-dimensional shape by sequential application of oxidative and reductive potentials. This input changes the cross-linking capacity of iron ions within the gel matrix, between a poorly coordinating +2 and a more strongly binding +3 oxidation state. Inclusion of carbon nanotubes in the hydrogel preparation increases conductivity and decreases transition time.

Exploiting Sequence To Control the Hydrolysis Behavior of Biodegradable PLGA Copolymers

Co-reporter:Jian Li ; Ryan M. Stayshich

Journal of the American Chemical Society 2011 Volume 133(Issue 18) pp:6910-6913

Publication Date(Web):April 13, 2011

DOI:10.1021/ja200895s

Monomer sequence is a potentially powerful but underutilized tool for the control of copolymer properties. Sequence is demonstrated to dramatically affect the hydrolysis profile for the degradation of poly(lactic-co-glycolic acid) (PLGA), a member of the most widely used class of biodegradable polymers employed in biomedical applications. The nearly linear molecular weight loss profile and uniform thermal behavior throughout the course of the hydrolysis differ dramatically from the behavior that is exhibited by random copolymer controls with the same comonomer ratio.

Periodic Incorporation of Pendant Hydroxyl Groups in Repeating Sequence PLGA Copolymers

Co-reporter:Ryan M. Stayshich;Ryan M. Weiss;Jian Li

Macromolecular Rapid Communications 2011 Volume 32( Issue 2) pp:220-225

Publication Date(Web):

DOI:10.1002/marc.201000608

Synthesis of repeating sequence copolymers of lactic, glycolic, and caprolactic acids

Co-reporter:Ryan M. Weiss;Evan M. Jones;David E. Shafer;Ryan M. Stayshich

Journal of Polymer Science Part A: Polymer Chemistry 2011 Volume 49( Issue 8) pp:1847-1855

Publication Date(Web):

DOI:10.1002/pola.24610

Abstract

Repeating sequence copolymers of poly(lactic-co-caprolactic acid) (PLCA), poly(glycolic-co-caprolactic acid) (PGCA), and poly(lactic-co-glycolic-co-caprolactic acid) (PLGCA) have been synthesized by polymerizing segmers with a known sequence in yields of 50–85% with M_ns ranging from 18–49 kDa. The copolymers exhibited well-resolved NMR resonances indicating that the sequence encoded in the segmers used in their preparation is retained and that transesterification is minimal. The exact sequences allowed for unambiguous assignment of the NMR spectra, and these standards were compared with the data previously reported for random copolymers. The glass transition temperatures (T_gs) of the PLCA and PGCA copolymers were found to depend primarily on monomer ratio rather than sequence. Sequence dependent T_gs were, however, noted for the PLGCA polymers with 1:1:1 L:G:C ratios; poly LGC and poly GLC exhibited T_gs that differed by nearly 8 °C. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

New Insights into Poly(lactic-co-glycolic acid) Microstructure: Using Repeating Sequence Copolymers To Decipher Complex NMR and Thermal Behavior

Co-reporter:Ryan M. Stayshich

Journal of the American Chemical Society 2010 Volume 132(Issue 31) pp:10920-10934

Publication Date(Web):July 15, 2010

DOI:10.1021/ja102670n

Sequence, which Nature uses to spectacular advantage, has not been fully exploited in synthetic copolymers. To investigate the effect of sequence and stereosequence on the physical properties of copolymers, a family of complex isotactic, syndiotactic, and atactic repeating sequence poly(lactic-co-glycolic acid) copolymers (RSC PLGAs) were prepared and their NMR and thermal behavior was studied. The unique suitability of polymers prepared from the bioassimilable lactic and glycolic acid monomers for biomedical applications makes them ideal candidates for this type of sequence engineering. Polymers with repeating units of LG, GLG and LLG (L = lactic, G = glycolic) with controlled and varied tacticities were synthesized by assembly of sequence-specific, stereopure dimeric, trimeric, and hexameric segmer units. Specifically labeled deuterated lactic and glycolic acid segmers were likewise prepared and polymerized. Molecular weights for the copolymers were in the range Mn = 12−40 kDa by size exclusion chromatography in THF. Although the effects of sequence-influenced solution conformation were visible in all resonances of the 1H and 13C NMR spectra, the diastereotopic methylene resonances in the 1H NMR (CDCl3) for the glycolic units of the copolymers proved most sensitive. An octad level of resolution, which corresponds to an astounding 31-atom distance between the most separated stereocenters, was observed in some mixed sequence polymers. Importantly, the level of sensitivity of a particular NMR resonance to small differences in sequence was found to depend on the sequence itself. Thermal properties were also correlated with sequence.

Iterative Synthesis of Heterotelechelic Oligo(phenylene-vinylene)s by Olefin Cross-Metathesis

Co-reporter:Benjamin N. Norris, Tianqi Pan, and Tara Y. Meyer

Organic Letters 2010 Volume 12(Issue 23) pp:5514-5517

Publication Date(Web):November 11, 2010

DOI:10.1021/ol102398y

A novel iterative synthesis of heterotelechelic oligo(phenylene-vinylene)s using olefin cross-metathesis is reported. The metathesis homologation proceeds in good yields and allows for further functionalization, including the facile formation of donor-acceptor complexes and repeating sequence copolymers.

Mono- and Terfluorene Oligomers as Versatile Sensitizers for the Luminescent Eu3+ Cation

Co-reporter:D. Samuel Oxley, Robert W. Walters, James E. Copenhafer, Tara Y. Meyer, Stéphane Petoud and Harry M. Edenborn

Inorganic Chemistry 2009 Volume 48(Issue 14) pp:6332-6334

Publication Date(Web):June 12, 2009

DOI:10.1021/ic9002324

We present the design, synthesis, and physical and photophysical characterization of Eu3+ and Gd3+ complexes formed with two ligands bearing either one or three fluorene sensitizer units. As a novel sensitizing approach, the oligomer length is used to control the energies of the triplet states of the sensitizer and to mediate the sensitizer to lanthanide energy transfer.

Preparation and microstructural analysis of poly(lactic-alt-glycolic acid)

Co-reporter:Ryan M. Stayshich

Journal of Polymer Science Part A: Polymer Chemistry 2008 Volume 46( Issue 14) pp:4704-4711

Publication Date(Web):

DOI:10.1002/pola.22801

Abstract

Alternating copolymers of glycolic (G) and lactic (L) acid were prepared by the condensation of the preformed dimers: L_LG and L_racG. By size exclusion chromatography (THF, PS standards), poly(L_LG) exhibited a molecular weight (M_n) of 15.6 kg mol⁻¹, with a weight average molecular weight (M_w) of 26.9 kg mol⁻¹ and a PDI of 1.72. The M_n for poly(L_racG) was 9.2 kg mol⁻¹, with a M_w of 12.9 kg mol⁻¹ and a PDI of 1.40. The NMR spectra of poly(L_LG) were consistent with an isotactic microstructure. NMR spectra of the racemic poly(L_racG) were consistent with an atactic structure. The methylene region of the ¹H NMR spectrum showed a tetrad level of resolution of the nearby stereochemical relationships, for example, iii. Resonances for other groups in both the ¹H and ¹³C NMR spectra gave only a triad level of resolution. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4704–4711, 2008

The impact of monomer sequence and stereochemistry on the swelling and erosion of biodegradable poly(lactic-co-glycolic acid) matrices

Co-reporter:Michael A. Washington, Devin J. Swiner, Kerri R. Bell, Morgan V. Fedorchak, Steven R. Little, Tara Y. Meyer

Biomaterials (February 2017) Volume 117() pp:

Publication Date(Web):February 2017

DOI:10.1016/j.biomaterials.2016.11.037

Monomer sequence is demonstrated to be a primary factor in determining the hydrolytic degradation profile of poly(lactic-co-glycolic acid)s (PLGAs). Although many approaches have been used to tune the degradation of PLGAs, little effort has been expended in exploring the sequence-control strategy exploited by nature in biopolymers. Cylindrical matrices and films prepared from a series of sequenced and random PLGAs were subjected to hydrolysis in a pH 7.4 buffer at 37 °C. Swelling ranged from 107% for the random racemic PLGA with a 50:50 ratio of lactic (L) to glycolic (G) units to 6% for the sequenced alternating copolymer poly LG. Erosion followed an inverse trend with the random 50:50 PLGA showing an erosion half-life of 3–4 weeks while poly LG required ca. >10 weeks. Stereosequence was found to play a large role in determining swelling and erosion; stereopure analogs swelled less and were slower to lose mass. Molecular weight loss followed similar trends and increases in dispersity correlated with the onset of significant swelling. The relative proportion of rapidly cleavable G-G linkages relative to G-L/L-G (moderate) and L-L (slow) correlates strongly with the degree of swelling observed and the rate of erosion. The dramatic sequence-dependent variation in swelling, in the absence of a parallel hydrophilicity trend, suggest that osmotic pressure, driven by the differential accumulation of degradation products, plays an important role.