Biewer, Michael C.
Permanent URI for this collectionhttps://hdl.handle.net/10735.1/3699
Michael Biewer is an Associate Professor of Chemistry. His research is "focused on the understanding of intermolecular effects in ordered media. In particular we are investigating the effect different media impart upon chemical reactivity with the goal of designing organic systems with specific functional control. This broad research goal encompasses a number of different fields including semiconducting polymers for molecular electronics, biodegradable polymers for drug delivery and the synthesis of carbon nanotubes of one type through topochemical reactions." Learn more about Dr. Biewer on his laboratory site, Chemistry Faculty and Research and Research Explorer pages.
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Recent Submissions
Item Halide-Free Neodymium Phosphate Based Catalyst for Highly cis-1,4 Selective Polymerization of Dienes(Royal Soc Chemistry, 2019-01-24) Ren, Yixin; Miller, Justin T.; Polderman, Stefanie T.; Vo, Trinh D.; Wallace, Adele C. M.; Cue, John Michael O.; Tran, Sarah T.; Biewer, Michael C.; Stefan, Mihaela C.; 0000-0001-5374-8600 (Stefan, MC); Ren, Yixin; Miller, Justin T.; Polderman, Stefanie T.; Vo, Trinh D.; Wallace, Adele C. M.; Cue, John Michael O.; Tran, Sarah T.; Biewer, Michael C.; Stefan, Mihaela C.Neodymium-based Ziegler-Natta type catalytic systems are known to produce polydienes with high cis-1,4 content. It is generally believed that in Ziegler-Natta catalytic systems, a halide or pseudohalide, whether in the catalyst itself or a separate source, is required for the success of the polymerization. In this work, we have synthesized an unusual halide-free neodymium diethyl phosphate catalyst for diene polymerization. This neodymium complex combined with triisobutylaluminum (TIBA), formed a binary catalytic system and was used to polymerize β-myrcene. The catalytic system displays high stereospecificity and produces poly(β-myrcene) with 96% cis-1,4 content and a relatively narrow molecular weight distribution (Mᵥᵥ/Mₙ = 1.80). Also, kinetic studies indicated the catalytic system gives a pseudo-living polymerization. The block copolymer poly(β-myrcene)-b-poly(isoprene) was successfully synthesized by sequential monomer addition, further demonstrating the pseudo-living nature of polymerization with the neodymium diethyl phosphate catalyst.Item Synthesis and Opto-Electronic Properties of Functionalized Pyrimidine-Based Conjugated Polymers(John Wiley and Sons Inc.) Karmegam, Vasanthy; Udamulle Gedara, Chinthaka M.; Biewer, Michael C.; Stefan, Mihaela C.; 55039821 (Stefan, MC); Karmegam, Vasanthy; Udamulle Gedara, Chinthaka M.; Biewer, Michael C.; Stefan, Mihaela C.Side chain engineering has been used for tuning the opto-electronic properties of organic semiconductors. In this work, a series of pyrimidine-based donor-acceptor (D-A) conjugated polymers functionalized with electron-withdrawing or electron-donating side chains were synthesized. The opto-electronic properties of the pyrimidine D-A conjugated polymers were investigated focusing on the dependence on the electron withdrawing strength of the acceptor moiety, while maintaining the same donor moiety. Fine-tuning of the energy levels was achieved by introducing electron donating (alkoxy [—OR] and alkylthio [—SR]) or electron withdrawing (alkylsulfinyl [—SOR] and alkylsulfonyl [—SO₂R]) side chains onto the acceptor moiety. The effects of side chain modification have been investigated through DFT calculations, UV–vis analysis, and electrochemical measurements.Item Peg Based Anti-Cancer Drug Conjugated Prodrug Micelles for the Delivery of Anti-Cancer Agents(Royal Soc Chemistry, 2015-12-09) Senevirathne, Suchithra A.; Washington, Katherine E.; Biewer, Michael C.; Stefan, Mihaela C.; 55039821 (Stefan, MC); Senevirathne, Suchithra A.; Washington, Katherine E.; Biewer, Michael C.; Stefan, Mihaela C.Due to the high cost and uncertain success of new drug development, tremendous effort is devoted to increasing the efficacy of established anti-cancer drugs. Development of polymer prodrug conjugates has evolved recently in the nano-medicine field for cancer diagnosis and treatment. The major advantage of using polymer drug conjugates is that the chemical and physical properties of polymers can be tuned to increase the efficacy and to reduce the toxicity of the drug. The stimuli responsiveness provides the release of the prodrug in a controlled manner which avoids undesired side effects, organ damage, and toxicity caused by the fluctuations associated with periodic administration. A large number of anti-cancer drug polymer conjugates have been studied for cancer therapy due to their promising clinical applications in chemotherapy. In this paper, poly(ethylene glycol) (PEG) based anti-cancer drug conjugates will be discussed followed by a review of different types of PEG-b-poly(epsilon-caprolactone) (PEG-b-PCL) copolymer drug conjugates and histone deacetylase inhibitor polymer conjugates as novel therapeutics. The pH sensitive release of prodrugs will be discussed for polymer prodrug conjugates that are currently under investigation.Item Developments of Furan and Benzodifuran Semiconductors for Organic Photovoltaics(Royal Society of Chemistry, 2015-02-13) Huang, Peishen; Du, Jia; Biewer, Michael C.; Stefan, Mihaela C.; 55039821 (Stefan, MC); Biewer, Michael C.; Stefan, Mihaela C.This review describes the developments of organic photovoltaic materials containing furan or benzo[1,2-b:4,5-b']difuran (BDF) building blocks. Promising power conversion efficiencies above 6% have been achieved in the past two years for the BDF donor-acceptor polymers. Fundamentals of organic photovoltaics are briefly introduced at the beginning of this review. The uniqueness and advantages of BDF building block in semiconducting materials are discussed and compared with benzo[1,2-b:4,5-b']dithiophene analogues.Item Fine-tuning Thermoresponsive Functional Poly(ε-caprolactone)s to Enhance Micelle Stability and Drug Loading(Royal Society of Chemistry, 2015-01-16) Rainbolt, Elizabeth A.; Miller, J. B.; Washington, Katherine E.; Senevirathne, Suchithra A.; Biewer, Michael C.; Siegwart, D. J.; Stefan, Mihaela C.; 55039821 (Stefan, MC); Biewer, Michael C.; Stefan, Mihaela C.Block copolymers synthesized by the ring-opening polymerization of γ-2-[2-(2-methoxyethoxy)ethoxy]ethoxy-ε-caprolactone (ME₃CL), γ-2-methoxyethoxy-ε-caprolactone (ME₁CL), and ε-caprolactone (CL) are reported. Previously, diblock copolymers of PME₃CL-b-PME₁CL displayed excellent thermoresponsive tunability (31-43 ⁰C) and self-assembled into micelles with moderate thermodynamic stability. In this report, two strategies are employed to enhance thermodynamic stability of PME₃CL/PME₁CL-type block copolymer micelles while maintaining their attractive thermoresponsive qualities: modification of the end group position and alteration of hydrophobic block composition by using both ME₁CL and CL. These new thermoresponsive amphiphilic block copolymers showed lower critical micelle concentration (CMC) values by one order of magnitude and formed thermodynamically stable micelles. Furthermore they demonstrated good biocompatibility and up to 4.97 wt% doxorubicin loading, more than double the amount loaded into the PME₃CL-type polymeric micelles previously reported.Item Nitrogen Containing Graphene-Like Structures from Pyrolysis of Pyrimidine Polymers for Polymer/graphene Hybrid Field Effect Transistors(Royal Soc Chemistry, 2014-09-02) Gunathilake, Samodha S.; Huang, Peishen; Bhatt, Mahesh P.; Rainbolt, Elizabeth A.; Stefan, Mihaela C.; Biewer, Michael C.; 55039821 (Stefan, MC); Stefan, Mihaela C.; Biewer, Michael C.Nitrogen containing graphene like structures were obtained by the pyrolysis of two pyrimidine polymers at 600 degrees C. Pyrimidine polymers were prepared by the base catalyzed aldol condensation reactions between 2-decyloxy-4,6-dimethylpyrimidine and two aromatic dialdehydes. Pyrolyzed products were shown to have a graphitic structure by Raman spectroscopy, scanning electron microscopy, and powder X-ray diffraction studies. The presence of nitrogen in the graphitic structures was proved by elemental analysis and energy dispersive X-ray analysis experiments. Fluorescence quenching experiments with poly(3-hexylthiophene) (P3HT) showed that the resultant graphitic material can act as an acceptor. These materials were tested in P3HT/graphene hybrid field effect transistors which exhibited higher mobilities and comparable on/off ratios compared to P3HT only devices.Item A Semiconducting Liquid Crystalline Block Copolymer Containing Regioregular Poly-(3-hexylthiophene) and Nematic Poly(n-hexyl Isocyanate) and its Application in Bulk Heterojunction Solar Cells(Royal Soc Chemistry, 2014-08-06) Bhatt, Mahesh P.; Du, Jia; Rainbolt, Elizabeth A.; Pathiranage, Taniya M. S. K.; Huang, Peishen; Reuther, James F.; Novak, Bruce M.; Biewer, Michael C.; Stefan, Mihaela C.; 0000 0000 8413 1147 (Novak, BM); 98037603 (Novak, BM); 55039821 (Stefan, MC); Novak, Bruce M.; Biewer, Michael C.; Stefan, Mihaela C.A liquid crystalline diblock copolymer containing regioregular poly(3-hexylthiophene) (P3HT) and poly-(n-hexyl isocyanate) (PHIC) was synthesized by the combination of Grignard metathesis polymerization (GRIM) and titanium mediated coordination polymerization methods. The poly(3-hexylthiophene)-b-poly(n-hexyl isocyanate) (P3HT-b-PHIC) diblock copolymer used in this study contained ~10 mol% of P3HT and ~90 mol% of PHIC. The diblock copolymer displayed solvatochromism in THF-water and THF-methanol mixtures. The field-effect mobilities of the synthesized block copolymer were measured in bottom gate-bottom contact organic field-effect transistors (OFETs). The surface morphology of the polymer thin film was investigated in the channel region of the OFET devices by tapping mode atomic force microscopy (TMAFM). The diblock copolymer displayed nanostructured morphology in thin film and had good mobility despite the low content of the semiconducting P3HT block. The diblock copolymer was also used as an additive to improve the performance of P3HT/PCBM bulk heterojunction (BHJ) solar cells. Liquid crystalline characteristics of the diblock copolymer were examined by cross-polarizing microscopy and X-ray diffraction.Item Benzodithiophene Homopolymers Synthesized by Grignard Metathesis (GRIM) and Stille Coupling Polymerizations(Royal Soc Chemistry, 2014-04-16) Magurudeniya, Harsha D.; Kularatne, Ruvini S.; Rainbolt, Elizabeth A.; Bhatt, Mahesh P.; Murphy, John W.; Sheina, Elena E.; Gnade, Bruce E.; Biewer, Michael C.; Stefan, Mihaela C.; 0000 0003 8371 1336 (Gnade, BE); 00049719 (Gnade, BE); 55039821 (Stefan, MC); Gnade, Bruce E.; Biewer, Michael C.; Stefan, Mihaela C.Poly{4,8-bis(95-dodecylthiophene-2-yl) benzo[1,2-b: 4,5-b'] dithiophene} has been synthesized by both Grignard metathesis (P1) and Stille coupling polymerizations (P2). Polymers P1 and P2 were characterized and their optoelectronic properties, charge carrier mobilities, and photovoltaic properties were compared. The field-effect mobilities of the polymers were measured on both untreated and heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane (FS) treated organic field effect transistor (OFET) devices. The polymers were also evaluated in bulk heterojunction (BHJ) solar cells with [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) as the acceptor.Item Structural Variation of Donor-Acceptor Copolymers Containing Benzodithiophene with Bithienyl Substituents to Achieve High Open Circuit Voltage in Bulk Heterojunction Solar Cells(Royal Soc Chemistry, 2013-11-06) Kularatne, Ruvini S.; Taenzler, Ferdinand J.; Magurudeniya, Harsha D.; Du, Jia; Murphy, John W.; Sheina, E. E.; Gnade, Bruce E.; Biewer, Michael C.; Stefan, Mihaela C.; 0000 0003 8371 1336 (Gnade, BE); 00049719 (Gnade, BE); 55039821 (Stefan, MC); Gnade, Bruce E.; Biewer, Michael C.; Stefan, Mihaela C.Three new donor-acceptor copolymers P1, P2, and P3 were synthesized with benzodithiophene with bithienyl substituents as the donor and 5,6-difluorobenzo[c][1,2,5]thiadiazole, 4,7-di(thiophen-2-yl)benzo[c][1,2,5] thiadiazole, and 5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole as the acceptors, respectively. The insertion of thiophene spacer between the donor and the acceptor broadened the absorption of the polymers P2 and P3 and resulted in a red shift of ~30 nm as compared to that of the polymer P1. However, the inclusion of fluorine atoms on the polymer had detrimental effects on the photovoltaic properties of the polymers. The synthesized donor-acceptor polymers were tested in bulk heterojunction (BHJ) solar cells with [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) acceptor. Polymer P2 gave a PCE of 3.52% with PC71BM in which the active layer was prepared in chloroform with 3% v/v 1,8-diiodooctane (DIO) additive. The effect of fluorine substitution and thiophene group insertion on the UV/Vis absorbance, photovoltaic performances, morphology, and charge carrier mobilities for the polymers are discussed.Item Synthesis and characterization of novel semiconducting polymers containing pyrimidine(Royal Soc Chemistry, 2013-02-27) Gunathilake, Samodha S.; Magurudeniya, Harsha D.; Huang, Peishen; Nguyen, Hien; Rainbolt, Elizabeth A.; Stefan, Mihaela C.; Biewer, Michael C.; 55039821 (Stefan, MC); Stefan, Mihaela C.; Biewer, Michael C.The acidic methyl protons of 4,6-dimethylpyrimidines can be easily deprotonated with a base to generate a resonance stabilized carbanion which can be used as a substrate for aldol condensation reactions. A series of novel conjugated polymers were synthesized by the aldol condensation reaction of 2-decyloxy-4,6-dimethylpyrimidine with various aromatic dialdehydes.