Statistical copolymers of styrene and 2-vinylpyridine with trimethylsilyl methacrylate and trimethylsilyloxyethyl methacrylate

Statistical copolymers of styrene with trimethylsilyl methacrylate, STMS, and trimethylsilyloxyethyl methacrylate, STME, and of 2-vinylpyridine with trimethylsilyloxyethyl methacrylate, VTME were prepared by free radical copolymerization in benzene with 2,2′-azobisisobutyronitrile, AIBN. The reactivity ratios of the different monomers were estimated using the Finemann-Ross, the inverted Finemann-Ross, and the Kelen-Tüdos or the extended Kelen-Tüdos graphical methods. Structural parameters of the copolymers were obtained by calculating the diad sequence fractions, which were derived using the monomer reactivity ratios. The results were compared with those obtained from the copolymerization of styrene and 2-vinylpyridine with methacrylic acid and 2-hydroxyethyl methacrylate.     

Titanium‐mediated [CpTiCl2(OEt)] ring‐opening polymerization of lactides: A novel route to well‐defined polylactide‐based complex macromolecular architectures

Among three cyclopentadienyl titanium complexes studied, CpTiCl₂(OEt), containing a 5% excess CpTiCl₃, has proven to be a very efficient catalyst for the ring‐opening polymerization (ROP) of L ‐lactide (LLA) in toluene at 130 °C. Kinetic studies revealed that the polymerization yield (up to 100%) and the molecular weight increase linearly with time, leading to well‐defined PLLA with narrow molecular weight distributions (M_w/M_n ≤ 1.1). Based on the above results, PS‐b‐PLLA, PI‐b‐PLLA, PEO‐b‐PLLA block copolymers, and a PS‐b‐PI‐b‐PLLA triblock terpolymer were synthesized. The synthetic strategy involved: (a) the preparation of OH‐end‐functionalized homopolymers or diblock copolymers by anionic polymerization, (b) the reaction of the OH‐functionalized polymers with CpTiCl₃ to give the corresponding Ti‐macrocatalyst, and (c) the ROP of LLA to afford the final block copolymers. PMMA‐g‐PLLA [PMMA: poly(methyl methacrylate)] was also synthesized by: (a) the reaction of CpTiCl₃ with 2‐hydroxy ethyl methacrylate, HEMA, to give the Ti‐HEMA‐catalyst, (b) the ROP of LLA to afford a PLLA methacrylic‐macromonomer, and (c) the copolymerization (conventional and ATRP) of the macromonomer with MMA to afford the final graft copolymer. Intermediate and final products were characterized by NMR spectroscopy and size exclusion chromatography, equipped with refractive index and two‐angle laser light scattering detectors. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1092–1103, 2010     

Response Surface Methodology to Optimize the Isolation of Dominant Volatile Compounds from Monofloral Greek Thyme Honey Using SPME-GC-MS

This study aimed at an experimental design of response surface methodology (RSM) in the optimization of the dominant volatile fraction of Greek thyme honey using solid-phase microextraction (SPME) and analyzed by gas chromatography-mass spectrometry (GC-MS). For this purpose, a multiple response optimization was employed using desirability functions, which demand a search for optimal conditions for a set of responses simultaneously. A test set of eighty thyme honey samples were analyzed under the optimum conditions for validation of the proposed model. The optimized combination of isolation conditions was the temperature (60 °C), equilibration time (15 min), extraction time (30 min), magnetic stirrer speed (700 rpm), sample volume (6 mL), water: honey ratio (1:3 v/w) with total desirability over 0.50. It was found that the magnetic stirrer speed, which has not been evaluated before, had a positive effect, especially in combination with other factors. The above-developed methodology proved to be effective in the optimization of isolation of specific volatile compounds from a difficult matrix, like honey. This study could be a good basis for the development of novel RSM for other monofloral honey samples.     

Ring‐opening polymerization of lactones using zirconocene catalytic systems: Block copolymerization with methyl methacrylate

The ring‐opening polymerization of ε‐caprolactone (ε‐CL) and δ‐valerolactone (δ‐VL) using nine catalytic systems consisting of a combination of three C_2v zirconocene complexes and three borate cocatalysts is discussed. The polymerizations proceed in a well‐controlled manner, producing polymers with relatively high molecular weights and narrow molecular weight distributions. Kinetic experiments of the polymerization of ε‐CL with the catalytic system Cp₂ZrMe₂/B(C₆F₅)₃ (1) showed a linear dependence between polymerization yield and molecular weight with time, as well as between the molecular weight with the molar ratio of the monomer over the catalyst [ε‐CL]/[Zr], indicating sufficient control of the polymerization reaction. The catalytic system (1) was utilized for the synthesis of well‐defined block copolymers of MMA with ε‐CL and δ‐VL. All samples were characterized by size exclusion chromatography, nuclear magnetic resonance, and differential scanning calorimetry. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3524–3537, 2007     

Polymerization of acrylates and bulky methacrylates with the use of zirconocene precursors: Block copolymers with methyl methacrylate

The polymerization behavior of cyclohexyl methacrylate and trimethylsilyloxyethyl methacrylate with the catalytic system Cp₂ZrMe₂/B(C₆F₅)₃/ZnEt₂ was examined. Block copolymers of these bulky methacrylates with methyl methacrylate (MMA), having high molecular weights and relatively narrow molecular weight distributions, were prepared. n‐Butyl acrylate and tert‐butyl acrylate were polymerized with various catalytic systems based on zirconocene complexes. These polymerizations seemed to proceed to a nonquantitative yield, producing polymers with high molecular weights and relatively low polydispersities. This behavior indicated the presence of termination reactions in the initiation step, which appeared to be faster than the propagation step. Block copolymers of these acrylates with MMA were synthesized with the catalytic system rac‐Et(Ind)₂ZrMe₂/[B(C₆F₅)₄]⁻[Me₂NHPh]⁺/ZnEt₂, starting from the polymerization of MMA. The block copolymers produced were well defined in most cases, as indicated by size exclusion chromatography, NMR, and differential scanning calorimetry measurements. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3337–3348, 2005     

Chemometric Study of Fatty Acid Composition of Virgin Olive Oil from Four Widespread Greek Cultivars

Virgin olive oil (VOO) is one of the key components of the Mediterranean diet owing to the presence of monounsaturated fatty acids and various bioactive compounds. These beneficial traits, which are usually associated with the cultivar genotype, are highlighting the demand of identifying characteristics of olive oil that will ensure its authenticity. In this work, the fatty acid (FA) composition of 199 VOO samples from Koroneiki, Megaritiki, Amfissis, and Manaki cultivars was determined and studied by chemometrics. Olive cultivar greatly influenced the FA composition, namely, oleic acid (from 75.36% for Amfissis to 65.81% for Megaritiki) and linoleic acid (from 13.35% for Manaki to 6.70% for Koroneiki). Spearman’s rho correlation coefficients revealed differences and similarities among the olive oil cultivars. The use of the forward stepwise algorithm identified the FAs arachidonic acid, gadoleic acid, linoleic acid, α-linolenic acid, palmitoleic acid, and palmitic acid as the most significant for the differentiation of samples. The application of linear and quadratic cross-validation discriminant analysis resulted in the correct classification of 100.00% and 99.37% of samples, respectively. The findings demonstrated the special characteristics of the VOO samples derived from the four cultivars and their successful botanical differentiation based on FA composition.     

pH-responsive aggregates from double hydrophilic block copolymers carrying zwitterionic groups. Encapsulation of antiparasitic compounds for the treatment of leishmaniasis

A series of well-defined poly[(ethylene oxide)-b-2-(dimethylamino)ethyl methacrylate] (PEO-b-PDMAEMA) diblock copolymers were synthesized by atom transfer radical polymerization (ATRP) techniques. Post-polymerization reactions were performed to transform a portion of the tertiary amine groups of the PDMAEpsilonMA into phosphorozwitterions. The aggregation behavior of the prepared zwitterionic block copolymers was investigated by static and dynamic light scattering techniques at 25 and 37 degrees C, in weakly basic and acidic aqueous solutions. Antiparasitic drugs used for the treatment of Leishmania were incorporated into the copolymer aggregates. The effect of the solution pH, the zwitterion content, temperature, and the quantity of the incorporated drug on the aggregation behavior of the copolymers was tested.     

Synthesis and characterization of brush diblock and triblock copolymers bearing polynorbornene backbone and poly(l‐lactide) and/or poly(hexyl isocyanate) side chains by a combination of coordination and ring opening metathesis polymerization

We report the synthesis of poly(l ‐lactide) and poly(hexyl isocyanate) macromonomers using bischloro‐η⁵‐cyclopentadienyl(bicyclo[2.2.1]‐hept‐5‐en‐2‐oxy) Titanium (IV), [CpTiCl₂(O‐NBE)]. These macromonomers bearing a norbornene end group were polymerized towards brush copolymers employing Grubbs' first generation catalyst. Brush copolymers consisting of blocks with different side chains were synthesized. The polymers were characterized by Size Exclusion Chromatography, Nuclear Magnetic Resonance, and their thermal properties were investigated by Thermogravimetric Analysis, and Differential Scanning Calorimetry analysis. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3455–3465     

Metallocene‐mediated cationic ring‐opening polymerization of 2‐methyl‐ and 2‐phenyl‐oxazoline

The cationic ring‐opening polymerization of 2‐methyl‐2‐oxazoline and 2‐phenyl‐2‐oxazoline was efficiently used using bis(η⁵‐cyclopentadienyl)dimethyl zirconium, Cp₂ZrMe₂, or bis(η⁵‐tert‐butyl‐cyclopentadienyl)dimethyl hafnium in combination with either tris(pentafluorophenyl)borate or tetrakis(pentafluorophenyl)borate dimethylanilinum salt as initiation systems. The evolution of polymer yield, molecular weight, and molecular weight distribution with time was examined. In addition, the influence of the initiation system and the monomer on the control of the polymerization was studied. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 000: 000–000, 2011     

Anionic polymerization of n‐hexyl isocyanate with monofuctional initiators. Synthesis of well‐defined diblock copolymers with styrene and isoprene

Several monofunctional initiators, such as s‐BuLi, 1,1‐diphenyl‐4‐methylpentyl lithium (DPMPL), benzyl potassium (BzK), triphenylmethyl sodium (trityl sodium, TrNa) and benzyl sodium (BzNa) were tested and evaluated for the polymerization of n‐hexyl isocyanate (HIC) in THF at ?98 °C. The polymerizations were conducted either without or with additives, such as LiBPh₄, NaBPh₄, and crown ether 18C6. The products were characterized by size exclusion chromatography (SEC), membrane osmometry (MO), and ¹H NMR spectroscopy. The best results regarding polymerization yield, molecular weight distribution, and agreement between the stoichiometric and the experimentally observed molecular weight were obtained by the initiating system BzNa/NaBPh₄ in a molar ratio 1/10. By using BzNa/NaBPh₄ system, well‐defined block copolymers of HIC with styrene or isoprene were synthesized for the first time. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3533–3542, 2005