Mihaela C. Stefan

Grignard metathesis (GRIM) polymerization for the synthesis of conjugated block copolymers containing regioregular poly(3-hexylthiophene)

The synthesis of various conjugated block copolymers of regioregular poly(3-hexylthiophene) by Grignard metathesis (GRIM) polymerization is described.

Regioregular poly(3-hexylthiophene) in a novel conducting amphiphilic block copolymer

Regioregular poly(3-hexylthiophene) has been successfully incorporated into a novel amphiphilic block copolymer. The amphiphilic nature of poly(3-hexylthiophene)-block-poly(acrylic acid) has been investigated using spectroscopic methods and has yielded solvatochromic behavior in several solvents of varying polarity. Evidence suggests that a supramolecular, long range ordering of block copolymer occurs in polar solvents, resulting in the formation of aggregates. Despite relatively large amounts of non-conductive blocks, the poly(3-hexylthiophene) diblock copolymer yields a high conductivity of 1 S · cm(-1) , and atomic force microscopy shows the formation of a highly organized nanofibrilar morphology in the solid state.

Thermally Controlled Release of Anticancer Drug from Self-Assembled γ-Substituted Amphiphilic Poly(ε-caprolactone) Micellar Nanoparticles

A thermo-responsive poly{γ-2-[2-(2-methoxyethoxy)ethoxy]ethoxy-ε-caprolactone}-b-poly(γ-octyloxy-ε-caprolactone) (PMEEECL-b-POCTCL) diblock copolymer was synthesized by ring-opening polymerization using tin octanoate (Sn(Oct)(2)) catalyst and a fluorescent dansyl initiator. The PMEEECL-b-POCTCL had a lower critical solution temperature (LCST) of 38 °C, and it was employed to prepare thermally responsive micelles. Nile Red and Doxorubicin (DOX) were loaded into the micelles, and the micellar stability and drug carrying ability were investigated. The size and the morphology of the cargo-loaded micelles were determined by DLS, AFM, and TEM. The Nile-Red-loaded polymeric micelles were found to be stable in the presence of both fetal bovine serum and bovine serum albumin over a 72 h period and displayed thermo-responsive in vitro drug release. The blank micelles showed a low cytotoxicity. As comparison, the micelles loaded with DOX showed a much higher in vitro cytotoxicity against MCF-7 human breast cancer cell line when the incubation temperature was elevated above the LCST. Confocal laser scanning microscopy was used to study the cellular uptake and showed that the DOX-loaded micelles were internalized into the cells via an endocytosis pathway.

Recent developments in micellar drug carriers featuring substituted poly(ε-caprolactone)s

In the field of drug delivery, synthetic polymers have been widely explored due to their range of properties and functions achievable by tuning their structures. Poly(e-caprolactone)s in particular have established themselves as excellent candidates for biomedical applications because of their biocompatibility, biodegradability, and synthetic versatility. In this review, applications of functional poly(e-caprolactone)s in drug delivery systems are highlighted. Recent studies regarding the encapsulation or direct conjugation of drugs, bioactive molecules and moieties for targeting are discussed. Also considered are advances in amphiphilic polymers with functional poly(e-caprolactone)s that exhibit stimuli-responsive behavior: pH-, thermo-, photo-, and reduction-sensitive. Ongoing research and development of functional poly(e-caprolactone)s continues to expand their potential for use in micellar drug delivery systems.

Synthesis and Characterization of a Block Copolymer Containing Regioregular Poly(3‐hexylthiophene) and Poly(γ‐benzyl‐L‐glutamate)

Poly(3-hexylthiophene)-b-poly(γ-benzyl-L-glutamate) (P3HT-b-PBLG) rod-rod diblock copolymer was synthesized by a ring-opening polymerization of γ-benzyl-L-glutamate-N-carboxyanhydride using a benzylamine-terminated regioregular P3HT macroinitiator. The opto-electronic properties of the diblock copolymer have been investigated. The P3HT precursor and the P3HT-b-PBLG have similar UV-Vis spectra both in solution and solid state, indicating that the presence of PBLG block does not decrease the effective conjugation length of the semiconducting polythiophene segment. The copolymer displays solvatochromic behavior in THF/water mixtures. The morphology of the diblock copolymer depends upon the solvent used for film casting and annealing results in morphological changes for both films deposited from chloroform and trichlorobenzene.

Developments of furan and benzodifuran semiconductors for organic photovoltaics

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.

Electronic Properties-Morphology Correlation of a Rod–Rod Semiconducting Liquid Crystalline Block Copolymer Containing Poly(3-hexylthiophene)

The influence of the solvent and annealing temperature on the field-effect mobilities and morphologies of poly(3-hexylthiophene)-b-poly(γ-benzyl-L-glutamate) (P3HT-b-PBLG) rod-rod diblock copolymer has been investigated. Thin film X-ray diffraction studies show peaks originating from both P3HT and PBLG indicating that the crystalline nature of both the blocks is conserved after the formation of the block copolymer. It has been observed that the field-effect mobilities of the diblock copolymer are independent of the annealing temperatures for thin films deposited from both 1,2,4-trichlorobenzene and chloroform solvents. The correlation between the field-effect mobility and morphology indicates that the P3HT block self-assembles at the surface SiO(2) dielectric.

Nickel(II) α-Diimine Catalyst for Grignard Metathesis (GRIM) Polymerization

A nickel α-diimine catalyst was used for Grignard metathesis (GRIM) polymerization of 2,5-dibromo 3-hexylthiophene and 2-bromo-5-iodo-3-hexylthiophene monomers. GRIM polymerization of 2-bromo-5-iodo-3-hexylthiophene generated regioregular polymers with molecular weights ranging from 3,000 to 12,000 g · mol(-1). The nickel α-diimine catalyst was also successfully used for the GRIM polymerization of a bulky benzodithiophene monomer.

Structural variation of donor–acceptor copolymers containing benzodithiophene with bithienyl substituents to achieve high open circuit voltage in bulk heterojunction solar cells

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.

Benzodifuran and benzodithiophene donor–acceptor polymers for bulk heterojunction solar cells

Four new donor–acceptor copolymers were synthesized by using benzo[1,2-b:4,5-b′]dithiophene and benzo[1,2-b:4,5-b′]difuran as donors and thieno[3,4-b]thiophene was used as the acceptor building block. A systematic study was performed to determine the influence of the combinations of different heteroatoms in the donor–acceptor copolymer. In bulk heterojunction solar cells, the polymer with all furan building blocks in the electron donating units, poly[(4,8-bis(5-dodecyl-2-furanyl)benzo[1,2-b:4,5-b′]difuran-2-yl)-alt-(2-ethyl-1-(3-fluorothieno[3,4-b]thiophen-2-yl)-1-hexanone)] (P4) (Mn = 66.7 kDa), achieved the highest power conversion efficiency of 5.23%.