Stefan, Mihaela C.
Permanent URI for this collectionhttps://hdl.handle.net/10735.1/3165
Mihaela Stefan is a member of the faculty in the Department of Chemistry. Her expertise is in polymer and organic chemistry and her research has centered on the synthesis and characterization of novel polymeric materials for applications in organic electronics and medicine.
Learn more about Dr. Stefan's work on her Faculty and Research, Research Group 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 of P3HT Base Semiconducting Hybrid Films and Their Photocatalytic Properties(Springer New York LLC, 2019) Ramírez-Aparicio, J.; Pathiranage, Taniya M. S. K.; Nguyen, Hein Q.; Stefan, Mihaela C.; Samaniego-Benítez, J. E.; Salinas-Bravo, V. M.; Ramírez-Bon, R.; 55039821 (Stefan, MC); Pathiranage, Taniya M. S. K.; Nguyen, Hein Q.; Stefan, Mihaela C.Regioregular poly(3-hexylthiophene) (rr-P3HT) was employed as the supporting polymeric matrix to generate hybrid composite films by mixing with natural zeolites, ZnO, and TiO₂. Several P3HT-based hybrid composite films were deposited by a convenient method, characterized, and applied to the photocatalytic degradation of rhodamine 6G (R6G). The photocatalytic activity of the hybrid composite films was analyzed by degradation of R6G solutions (blank) under UV radiation (365 nm) and sunlight. It was observed that the photocatalytic activity of the composite films was higher as compared to the neat films of P3HT. This behavior was attributed to the extended photoresponse of the coupled organic–inorganic semiconductor system, facilitating separation of photogenerated carriers due to the strong interfacial interaction. The highest proportion of decolorization ratio of R6G obtained was close to 100%, and it was observed for the composite films P3HT/TiO₂/ZnO and P3HT/chabazite/TiO₂/ZnO under UV irradiation. Under sunlight, 99% and 97% decolorization ratios were obtained for P3HT/TiO₂ and P3HT/TiO₂/ZnO composite films, respectively. ©2019, American Coatings Association.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 Novel Chlorhexidine-Loaded Polymeric Nanoparticles for Root Canal TreatmentQuiram, Gina; Montagner, Francisco; Palmer, Kelli L.; Stefan, Mihaela C.; Washington, Katherine E.; Rodrigues, Danieli C.; Quiram, Gina; Palmer, Kelli L.; Stefan, Mihaela C.; Washington, Katherine E.; Rodrigues, Danieli C.Persistence of microorganisms in dentinal tubules after root canal chemo-mechanical preparation has been well documented. The complex anatomy of the root canal and dentinal buffering ability make delivery of antimicrobial agents difficult. This work explores the use of a novel trilayered nanoparticle (TNP) drug delivery system that encapsulates chlorhexidine digluconate, which is aimed at improving the disinfection of the root canal system. Chlorhexidine digluconate was encapsulated inside polymeric self-assembled TNPs. These were self-assembled through water-in-oil emulsion from poly(ethylene glycol)-b-poly(lactic acid) (PEG-b-PLA), a di-block copolymer, with one hydrophilic segment and another hydrophobic. The resulting TNPs were physicochemically characterized and their antimicrobial effectiveness was evaluated against Enterococcus faecalis using a broth inhibition method. The hydrophilic interior of the TNPs successfully entrapped chlorhexidine digluconate. The resulti ng TNPs had particle size ranging from 140–295 nm, with adequate encapsulation efficiency, and maintained inhibition of bacteria overItem 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 Biocompatible Organic Charge Transfer Complex Nanoparticles Based on a Semi-Crystalline Cellulose Template(Royal Society of Chemistry, 2015-06-19) Nagai, A.; Miller, J. B.; Du, Jia; Kos, P.; Stefan, Mihaela C.; Siegwart, D. J.; 55039821 (Stefan, MC); Stefan, Mihaela C.Using a bio-inspired cellulose template, new charge transfer (CT) nanoparticles (NPs) with unique and intriguing emission properties are reported. Pyrene-modified 2,3-di-O-methyl cellulose formed CT complexes with small molecule acceptors, e.g. 7,7,8,8-tetracyanoquinodimethane (TCNQ), and exhibited aggregation-induced emission (AIE) in aqueous medium upon nanoparticle formation. The TCNQ-CT NPs showed multicolor fluorescence emissions at 370-400 nm, 602 nm and 777 nm, when excited at 330 nm, 485 nm and 620 nm respectively. The cellulose-TCNQ NPs are biocompatible and demonstrate an advance in the use of the CT mechanism for biomedical imaging applications both in vitro and in vivo.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 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 Self-Assembly of a Conjugated Triblock Copolymer at the Air-Water Interface(2013-06-27) Zhao, L.; Feng, C.; Pang, X.; Jung, J.; Stefan, Mihaela C.; Sista, Prakash; Han, R.; Fang, N.; Lin, Z.; Stefan, Mihaela C.Controlling the self-assembly of highly luminescent conjugated polymers is essential for preparing various optoelectronic devices. In this study, a polyisoprene-b-polystyrene-b-poly(3-hexylthiophene) (PI-PS-P3HT) triblock copolymer was synthesized and readily self-assembled into network-like morphologies via dewetting at the air-water interface. Interestingly, the monolayer thick film displayed high photoluminescence (PL) as a result of successfully transferring the amorphous conjugated P3HT chains in the PI-PS-P3HT triblock copolymer from the solution state to the solid state. A model was proposed to illustrate the supramolecular organization of the PI-PS-P3HT monolayer. To the best of our knowledge, this is the first study of a hydrophobic conjugated block copolymer at the air-water interface, from which the conjugated polymer-based monolayer with highly efficient PL formed by dewetting was achieved.Item Synthesis and Characterization of a Polyisoprene-b-polystyrene-b-poly(3-hexylthiophene) Triblock Copolymer(2012-12-06) Nguyen, Hien Q.; Bhatt, Mahesh P.; Rainbolt, Elizabeth A.; Stefan, Mihaela C.; Stefan, Mihaela C.A polyisoprene-b-polystyrene-b-poly(3-hexylthiophene) triblock copolymer was synthesized by anionic coupling of living polyisoprene-b-polystyryl lithium with allyl-terminated poly(3-hexylthiophene). The triblock copolymer retained the opto-electronic properties and morphology found in the poly(3-hexylthiophene) homopolymer despite the insulating polyisoprene and polystyrene blocks, making it potentially useful as an elastomeric semiconducting material.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.Item Role of the Transition Metal in Grignard Metathesis Polymerization (GRIM) of 3-Hexylthiophene(2013-09-09) Bhatt, Mahesh P.; Magurudeniya, Harsha D.; Sista, Prakash; Sheina, E. E.; Jeffries-El, M.; Janesko, B. G.; McCullough, R. D.; Stefan, Mihaela C.; Stefan, Mihaela C.Regioregular poly(3-alkylthiophene)s are widely used in organic electronics applications such as solar cells and field effect transistors. Nickel, palladium, and platinum diphenylphosphinoethane complexes were tested as catalysts for the Grignard metathesis (GRIM) polymerization of 2,5-dibromo-3-hexylthiophene and 2-bromo-5-iodo-3-hexylthiophene. Nickel-mediated polymerization generated regioregular, low-polydispersity poly(3-hexylthiophene) with well-defined molecular weight consistent with a "living" chain-growth mechanism. By contrast, palladium-mediated polymerization proceeded by a step-growth mechanism and generated polymers with less than 80% head-to-tail couplings. Platinum-mediated polymerization gave very low molecular weight products. Kinetic and computational results suggested that the nickel catalyst acts as an initiator and remains associated with the growing polymer chain, while palladium dissociates from the growing chain. Computational and experimental evidence was provided for various side reactions of dissociated Pd(0) catalyst, which could yield a step growth mechanism and lower regioirregularity.Item Grignard Metathesis (GRIM) Polymerization for the Synthesis of Conjugated Block Copolymers Containing Regioregular Poly(3-Hexylthiophene)(2011-11-28) Stefan, Mihaela C.; Bhatt, Mahesh P.; Sista, P.; Magurudeniya, H. D.; Stern, Robert J.The synthesis of various conjugated block copolymers of regioregular poly(3-hexylthiophene) by Grignard metathesis (GRIM) polymerization is described. © 2012 The Royal Society of Chemistry