Olefin polymerization in liquid sulfur dioxide initiated by m-chloroperbenzoic acid. I. Homopolymerization of styrene and α-methylstyrene

Homopolymerizations of styrene (Sty) and α-methylstyrene (AMS) in liquid sulfur dioxide were carried out in the temperature range from ?10°C to ?78°C, using m-chloroperbenzoic acid as initiator. It is shown, through the effect of initiator concentration, temperature, and times of reaction on the conversion and molecular weight of the polymers, that AMS is more reactive than Sty because it requires a smaller amount of initiator for the same conversion to be reached, although the molecular weight of the resulting polymer is lower. A linear relationship has been observed for Sty between the degree of polymerization and the initiator concentration. Within the experimental conditions employed, the presence of polysulfones has been discarded by elemental analysis. The polymerization reactions are considered to be cationic in mechanism.     

Magnetic properties of a polyfluorene derivative containing complexed neodymium ions

Poly[9,9′‐dihexylfluorene‐2,7‐diyl)‐6,6″‐(2,2′:6′,2″‐terpyridine)] (LaPPS75) and its complexes with neodymium were synthesized and characterized. Magnetic measurements showed that the noncomplexed polymer presented a ferromagnetic contribution due to the formation of π stacking, and that in absence of those, the ferromagnetic behavior is suppressed. The pristine polymer, the complexed one and a low‐molecular‐weight model compound with the same structure of the complexed site in the parent polymer were studied. The observed behavior found is presented and discussed, the most important finding was that when a conjugated chain is used as a host for the metallic ion, an amplification of four times for the magnetization is achieved, using the same metallic content for complexed polymer and model compound for comparison. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 304–311     

Theoretical analysis of aggregation in block‐copolymer films: The optical signature

We focus this work on the theoretical investigation of the block‐copolymer poly[oxyoctyleneoxy‐(2,6‐dimethoxy‐1,4phenylene‐1,2‐ethinylene‐phenanthrene‐2,4diyl) named as LaPPS19, recently proposed for optoelectronic applications. We used for that a variety of methods, from molecular mechanics to quantum semiempirical techniques (AM1, ZINDO/S‐CIS). Our results show that as expected isolated LaPPS19 chains present relevant electron localization over the phenanthrene group. We found, however, that LaPPS19 could assemble in a π‐stacked form, leading to impressive interchain interaction; the stacking induces electronic delocalization between neighbor chains and introduces new states below the phenanthrene‐related absorption; these results allowed us to associate the red‐shift of the absorption edge, seen in the experimental results, to spontaneous π‐stack aggregation of the chains. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

HTPB‐based polyurethanes. II. SINs with PMMA

Simultaneous interpenetrating networks from poly(methyl methacrylate‐co‐ethyleneglycol dimethacrylate) (PA) and a hydroxyl‐terminated polybutadiene‐based polyurethane (PU) were prepared with various hard‐segment contents (X) in the PU and different ratios (PU/PA) between the components. The level of the reinforcement, the mechanism of molecular failure, and the phase inversion depended strongly on X. Dynamic mechanical results indicated that the interpenetration occurred in the rigid blocks of the PU. The improved thermal and mechanical properties observed with higher values of X were interpreted in terms of the molecular weight and polydispersity of the hard blocks in the PU. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2861–2872, 2000     

Theoretical studies for forecasting the power conversion efficiencies of polymer‐based organic photovoltaic cells

Modifying the electron‐withdrawing capability in donor–acceptor conjugated copolymers allows designing new polymers with better optical properties. These materials have been successfully applied in bulk heterojunction solar cell devices, and recently a great progress in the enhancement of power conversion efficiencies (PCE) has been achieved. In 2006 Scharber proposed a design rule to obtain PCE values over 10%, optimizing the orbital energy levels of the donor material. The present work proposes a methodology capable to predict theoretically the best efficiencies imparted by a group of 65 conjugated monomeric units selected from the literature, generating 2080 possible DA combinations. The geometries, frontier levels and optical properties were estimated by DFT methods. Based on the results, it was possible to predict the PCE of the most promising 22 copolymers. The results of the calculations indicated that several polymers investigated showed the predicted PCE between 9% and 10%. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 919–927     

Photophysical behavior of block copolymers containing EDOT,thiophene, and benzodiathiazole units linked to fluorene

The spectral properties of two block copolymers were investigated, based on the fluorene‐EDOT (FEDOT) segment linked either to fluorene‐thiophene (FTh) or to fluorene‐benzothiadiazole (FBz) units, in an alternated fashion. Experimental data revealed that in the first material, each block keeps the spectral absorption region observed in the individual copolymers, while in the other structure new spectral characteristics were observed, as compared with each individual segment. In order to elucidate this behavior, theoretical calculations using density functional theory methods were performed. The block copolymers were reduced to a minimal representative model and the following structures were modeled: (FEDOT)₂, (FBz)₂ e (FTh)₂ relative to the alternated segments and (FEDOT)₂‐(FBz)₂ and (FEDOT)₂‐(FTh)₂ as miniblocks for the block copolymers. The theoretical results showed good agreement with experimental data and used to interpret the differences in electronic behavior of the block copolymers and their correlation with the observed photophysical behavior. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 908–915     

Correlations between the number of thiophene units and the photovoltaic behavior of fluorene–oligothiophene copolymers

The photophysical and photovoltaic properties of three alternated fluorene–thiophene copolymers were studied. With similar structure the copolymers differed by the numbers of thiophene units linked to each fluorene group:one, two and three. The electronic properties were analyzed through mobility measurements and the overall properties pointed out to the one containing the three rings as the best material, as anticipated, due to the larger number of thiophene units. However, after thermal annealing the polymer containing two thiophene rings presented the best photovoltaic efficiency, seven fold greater than the pristine material. The morphology, studied by atomic force microscopy, revealed to be one of the key factors for the performance of the materials as solar cells.     

Poly(methyl methacrylate-g-urethane). I. Synthesis

Poly(methyl methacrylate-g-urethane) was prepared by coupling between poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) and polyurethane. The polyurethane was obtained by bulk polycondensation of tolylene diisocyanate and polypropylene glycol. The two polymeric species were synthesized and characterized separately, and the composition of the grafted products varied only by the spacing of the grafted segments. Grafted copolymers with 5, 10, 20, 25, 40, 50, 70, and 90% of incorporated polyurethane have been prepared.     

Determination of polycyclic aromatic hydrocarbons in fractions in asphalt mixtures using liquid chromatography coupled to mass spectrometry with atmospheric pressure chemical ionization

An analytical method using liquid chromatography coupled to mass spectrometry with atmospheric pressure chemical ionization for the determination of polycyclic aromatic hydrocarbons in asphalt fractions has been developed. The 14 compounds determined, characterized by having two or more condensed aromatic rings, are expected to be present in asphalt and are considered carcinogenic and mutagenic. The parameters of the atmospheric pressure chemical ionization interface were optimized to obtain the highest possible sensitivity for all of the compounds. The limits of detection ranged from 0.5 to 346.5 μg/L and the limits of quantification ranged from 1.7 to 1550 μg/L. The method was validated against a diesel particulate extract standard reference material (NIST SRM 1975), and the obtained concentrations agreed with the certified values. The method was applied to asphalt samples after its fractionation according to ASTM D4124 and the method of Green. The concentrations of the seven polycyclic aromatic hydrocarbons quantified in the sample ranged from 0.86 mg/kg for benzo[ghi]perylene to 98.32 mg/kg for fluorene.     

Determination of oxygen and nitrogen derivatives of polycyclic aromatic hydrocarbons in fractions of asphalt mixtures using liquid chromatography coupled to mass spectrometry with atmospheric pressure chemical ionization

Liquid chromatography coupled to mass spectrometry with atmospheric pressure chemical ionization was used for the determination of polycyclic aromatic hydrocarbon derivatives, the oxygenated polycyclic aromatic hydrocarbons and nitrated polycyclic aromatic hydrocarbons, formed in asphalt fractions. Two different methods have been developed for the determination of five oxygenated and seven nitrated polycyclic aromatic hydrocarbons that are characterized by having two or more condensed aromatic rings and present mutagenic and carcinogenic properties. The parameters of the atmospheric pressure chemical ionization interface were optimized to obtain the highest possible sensitivity for all compounds. The detection limits of the methods ranged from 0.1 to 57.3 μg/L for nitrated and from 0.1 to 6.6 μg/L for oxygenated derivatives. The limits of quantification were in the range of 4.6–191 μg/L for nitrated and 0.3–8.9 μg/L for oxygenated derivatives. The methods were validated against a diesel particulate extract standard reference material (National Institute of Standards and Technology SRM 1975), and the obtained concentrations (two nitrated derivatives) agreed with the certified values. The methods were applied in the analysis of asphalt samples after their fractionation into asphaltenes and maltenes, according to American Society for Testing and Material D4124, where the maltenic fraction was further separated into its basic, acidic, and neutral parts following the method of Green. Only two nitrated derivatives were found in the asphalt sample, quinoline and 2‐nitrofluorene, with concentrations of 9.26 and 2146 mg/kg, respectively, whereas no oxygenated derivatives were detected.