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The increasingly intense consumption of plastics and, above all, their improper disposal in the environment are causing serious environmental concerns. Great efforts have been made for the development of new methods aimed at facilitating and speeding up the identification and sorting of different materials in the plastic recycling process. In this field, new strategies based on fluorescent tagging have been developed. This work concerns the synthesis and characterization of new fluorescent copolymers of polyethylene (PE) and polystyrene (PS), which are among the most produced and consumed plastic materials. The synthesized copolymers are potentially suitable for use as fluorescent markers of PE and PS. Ethylene-co-N-pentenyl carbazole (P(E-co-PK)) and styrene-co-4-(N-carbazolyl)methyl styrene (P(S-co-SK)) copolymers were prepared by Ziegler–Natta and free radical polymerization, respectively. If excited at 300 nm, both P(E-co-PK)s and P(S-co-SK)s give fluorescence emissions resulting in them being optically active. Moreover, due to the low amount of fluorescent units, they show chemico-physical properties such as those of their corresponding homopolymers (PE and PS). P(E-co-PK)s and P(S-co-SK)s have been also tested as fluorescent markers of PE and PS. The experimental results demonstrate that from PE/P(E-co-PK) and PS/P(S-co-SK) blends prepared using only 1% by weight of fluorescent copolymer, distinguishable fluorescent emissions can be still detected.

Fe–Pr co-doped TiO2 photocatalysts are synthetized by sol–gel method using titanium tetraisopropoxide, praseodymium nitrate and iron acetylacetonate as precursors of titania, praseodymium and iron, respectively. The chemical-physical properties of all prepared samples are analysed by X-ray diffraction (XRD), Raman spectroscopy, UV–vis diffuse reflectance spectroscopy (UV–vis DRS), photoluminescence (PL) spectroscopy and N2 adsorption at −196 °C. XRD patterns show the main peaks of anatase phase in all photocatalysts and evidence that Fe and Pr ions are effectively introduced into the TiO2 lattice. UV–vis DRS spectra indicate the reduction of the band gap value of Fe-Pr co-doped TiO2 with respect to TiO2 and Pr-doped TiO2 thank to co-doping of TiO2 with Pr and Fe ions. The photocatalytic performances of all prepared samples are investigated for the degradation of Acid Orange 7 azo dye (AO7) and also of phenol under visible light irradiation. Photocatalytic efficiency obtained using Fe–Pr co-doped TiO2 markedly increases compared to un-doped TiO2, Pr-doped TiO2 and Fe-doped TiO2 photocatalysts. Fe-Pr co-doped TiO2 prepared with 8.5 mg of praseodymium nitrate gave the best photocatalytic activity. The enhanced photocatalytic activity should be associated with the simultaneous doping of TiO2 with Pr3+ and Fe3+ ions that induces a marked decrease of band gap value together with an enhanced generation of oxygen vacancies, which can trap electrons, and therefore reducing their recombination with photogenerated positive holes. Indeed, using the optimized Fe-Pr co-doped TiO2, the dye discoloration and mineralization is about 87 and 80 %, respectively, after 60 min of LEDs visible light irradiation, underlining the best performances of the optimized Fe–Pr co-doped TiO2 in terms of treatment time. Finally, the optimized Fe-Pr co-doped TiO2 is tested for visible light degradation of phenol in aqueous solution, confirming the absence of possible sensitization phenomena of photocatalyst surface by the AO7 dye.

This mini review summarizes the preparation and testing of polymeric composites with a N-doped TiO2 photocatalyst to effectively design a photocatalytic system for water pollutant degradation under visible light. In detail, the various N-doped TiO2/polymer composites reported in the literature are briefly discussed along with some examples dealing with the use of N-doped TiO2 particles, both supported on the external surface of polymers and dispersed within the structure of visible-light-transparent polymeric aerogels. Finally, the scope for future works and challenges for the commercialization of such materials are highlighted.

Plastics are a heterogeneous class of synthetic compounds that, due to their unique characteristics find numerous applications both in industrial and civil fields. However, despite the great advantages that these materials brought in everyday life, the plastic wastes resulting from their massive use represent one of the main environmental problems at the global level. Once released, plastics persist for a long time and are subjected both to biotic and abiotic processes leading to the formation of small particles, known as micro and to nanoplastics, that interact with organisms, accumulating inside tissues and risking to enter in the trophic chain. Among the different types of plastic, polypropylene (PP) is one of the diffused, widely exploited in food and textile industries for disposable packaging and to produce surgical masks. Owing to the huge distribution and the resultant abundant presence of PP waste products, it results necessary investigate the possible toxicity on living organisms. For these reasons, here we analyzed the effects of PP micro and nanoplastics dispersed in freshwater, using the medicinal leech Hirudo verbana as invertebrate model. To better follow the plastics fate, fluorescent particles, labeled with a fluorophore, have been used. Animals were examined at various timings after plastics exposure and results were analyzed by means of microscopy, immunofluorescent and molecular biology analyses. After assessing the entrance of PP fragments into leech tissues, the activation of the innate immune response was evaluated. The results show that the presence of micro and nanoplastics induces an initial physical protection that consists in the secretion of mucus, followed by an increase of blood vessels and the recruitment of immune cells, in particular macrophages. Moreover, macrophages were directly involved in both phagocytic and encapsulation processes, as demonstrated by acid phosphatase (ACP) histoenzymatic and Thioflavin-T assays, expressing specific pro-inflammatory factors, such as HvRNASET2 and HmAIF-1, as demonstrated by immunolocalization and qPCR experiments. Finally, the expression levels of genes related to oxidative stress-induced enzymes have been investigated, in order to evaluate the possible increase in reactive oxygen species (ROS), due to the entry into the leech tissues of PP micro and nanoplastics. This work allows deepening the current knowledge of the possible harmful effects on human health deriving from micro and nanoplastics dispersion, leading new insight about freshwater ecosystems that often represent the first environments interested in plastic pollution.

Fluorescent polypropylenes for the detection of PP-derived microplastic pollutants in organic tissues.

The analysis of FT-IR spectra of isotactic and syndiotactic poly(N-pentenylcarbazole) (i-PPK and s-PPK) amorphous film samples are reported in the present paper. A comparison with FT-IR spectrum of a non stereoregular polyvinylcarbazole (PVK) commercial sample is also presented. Calculated vibration spectra of both i-PPK and s-PPK are obtained through the Density Functional Theory (DFT) method. Theoretical results are interpreted in terms of potential energy distribution (PED) analysis, and compared with i-PPK and s-PPK FT-IR experimental spectra. Only a few differences, due to the conformational constrain imposed by tacticity, are detected between the two fully amorphous polymer stereoisomers. Moreover, the observed differences between PPKs and PVK spectra are attributed to the presence of the alkylene linker (-(CH2)3-) in PPK samples, distancing the carbazole groups to the main chain. The alkylene linker allows more flexibility to both the side and main chain of PPK samples, giving rise to new vibrational mixed modes which are not detected in PVK.

Stereospecific cis-1,4 polymerization of 1,3 butadiene is carried out by using CpTiCl3/MAO and Cp*TiCl3/MAO catalysts in solvents (mesitylene, toluene, benzene, chlorobenzene, m-chlorobenzene, hexafluorobenzene) having different nucleophilicity. The influence of nucleophilicity of used solvent on activity and selectivity of the two considered catalytic systems is evaluated. Catalyst activity is strongly affected by used solvent, while polymer microstructure remains almost unchanged. The formation of a labile specie anti-η3-π-butenyl-Ti coordinated to solvent molecule, able to increase the rate of polymerization reaction, is hypothesized. The effect of two different external electron donors, N(C2H5)3 and P(C6H5)3, in the polymerization environment on activity and selectivity of the two considered catalytic systems is also investigated. Both N(C2H5)3 and P(C6H5)3 induce a sweeping decrease of catalyst activity, but do not cause changes in polymer microstructures.

The most recent results concerning the stereospecific synthesis and the microstructural, chemico-physical and optical characterization of polymers containing pendant carbazolyl groups are reviewed for the first time. Stereoregular poly(N-alkenyl-carbazole)s, poly(4-(Ncarbazolyl) methyl styrene), poly(ω-(N-carbazolyl)alkyl acrylate)s and poly(ω-(N-carbazolyl)alkyl metacrylate)s are considered in this review, with a particular focus on the influence of polymer stereochemistry on photophysical behavior. Potential applications of these materials in light-emitting diodes (LEDs), electrochromic devices, electrophotography and holographic memories are also discussed. Among these, we show the appealing results of our experiments, concerning the color tuning in organic LEDs based on poly(N-pentenyl-carbazole) by means of the polymer chain stereoregularity.

Polypropylene oxide (PPO) and poly(9-(2,3-epoxypropyl) carbazole) (PEPK) di-block copolymers are prepared in one pot via sequential monomer addition by using i-PrONa/i-Bu3Al as an anionic catalytic system. An almost 100% monomer conversion is obtained, and the length of each block is controlled through the monomer/catalyst ratio used. Copolymer molecular weights are quite close to theoretical values calculated assuming the formation of one polymer chain per catalyst, therefore, it is hypothesized that the polymerization reaction proceeds with a living character. The synthesis appears to be particularly efficient and versatile. The calorimetric properties of copolymers obtained in this work are remarkable, since they show two distinct Tg values, corresponding to the PPO and PEPK blocks. The optical measurements of di-block copolymers show more analogous features than those of PEPK homopolymer. Copolymer solution emission spectra just exhibit isolated carbazole fluorescence, whereas in the solid state, film spectra show excimer fluorescence.

Synthesis and characterization of chromium(III) complexes with 2-thenoyltrifluoroacetone ligand are described and the crystal structures of the two possible geometric isomers, efficiently obtained by crystallization, are reported for the first time. In the solid state structure, both isomers reveal a distorted octahedral geometry of the metal ion. In addition, absorption and emission properties of the complex are determined in solution and in a polymethylmethacrylate (PMMA) matrix.

Fe0 (ZVI) is one of the most effective reactants for treatment of water contaminated with chlorinated hydrocarbons, pollutants recalcitrant to degradation. Unfortunately, ZVI use is limited by corrosion and loss of reactivity over time. In order to suppress oxidation and passivation phenomena of iron, in this study ZVI was coupled to a suitable semiconductor (ZnS). Under UV light, electrons in the valence band of ZnS are promoted in the conducting band (ECB = − 1.04 eV vs NHE) and are able to reduce Fe2+ to Fe0 (E0 = − 0.44 eV vs NHE). The ZnS_ZVI composite was simply prepared by coating commercial ZnS with Fe0 obtained by reducing Fe (II) salt with sodium borohydride. The achieved ZnS_ZVI catalytic system was characterized by FESEM, WAXD, Raman and N2 adsorption at −196 °C, with the aim to analyze morphology and crystalline structure of both components of the ZnS_ZVI system. Catalytic activity tests showed that ZnS_ZVI is effective in degrading probe molecules, eriochrome black T dye (EBT) and chlorobenzene (PhCl), from aqueous solutions under UV light irradiation. The experimental results show that in both cases the reductive action of Fe0 on the N = N bond of EBT and C-Cl of PhCl is synergistically coupled to the oxidative action of ZnS towards by-products. OH radicals, generated by the reaction between the electron holes in the valence band of ZnS and H2O (OH−), were indeed confirmed by photoluminescence analysis. Recyclability tests indicate that ZnS_ZVI is highly stable since its catalytic activity, on both probe molecules, remains unchanged even after several cycles of reuse under UV irradiation. ZnS_ZVI catalytic behavior towards EBT has been carefully analyzed and a possible mechanism of EBT degradation has been proposed, which involves the formation of a Fe2+-EBT complex whose structure has also been suggested.

A new norbornene dicarboximide presenting a pendant carbazole moiety linked by a p-methylene benzyl spacer is synthesized. This carbazole-functionalized monomer is polymerized via ring-opening metathesis polymerization using Grubbs third-generation catalyst. Microstructural analysis of resulting polymers performed by Nuclear Magnetic Resonance (NMR) shows that they are stereoirregular. Wide-angle X-ray diffraction (WAXD) and thermal (DSC) analysis indicate that polymers are also amorphous. With respect to the fluorescence analysis, both solution and film polymer samples exhibit only “normal structured” carbazole fluorescence, while excimer formation by overlap of carbazole groups is not detected.

Stereoregular polymers like isotactic poly(N-butenyl-carbazole) (i-PBK), isotactic and syndiotactic poly(N-pentenyl-carbazole) (i-PPK and s-PPK), and poly(N-hexenyl-carbazole) (i-PHK and s-PHK) are synthesized using the stereospecific homogeneous “single site” Ziegler-Natta (Z-N) catalysts: rac-dimethylsilylbis(1-indenyl)zirconium dichloride (1)/methylaluminoxane (MAO) and diphenylmethylidene(cyclopentadienyl)-(9-fluorenyl)zirconium dichloride (2)/MAO. Catalytic activity is rationalized by density functional theory (DFT) calculations. All synthesized polymers are fully characterized by NMR, thermal, wide-angle X-ray diffraction, and fourier transform infrared spectroscopy analysis. Fluorescence measurements on isotactic and syndiotactic polymer films indicate that all polymers give rise to excimers, both “sandwich-like” and “partially overlapping.” Excimer formation is essentially driven by the polymer tacticity. Isotactic polymers generate both sandwich-like and partially overlapping excimers, while syndiotactic polymers give rise especially to partially overlapping ones. A theoretical combined molecular dynamics–time dependent DFT approach is also used to support the experimental results. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017

Organic light emitting diodes (OLEDs) are fabricated using two novel polymers, isotactic and syndiotactic poly(N-pentenyl-carbazole) (i-PPK and s-PPK), as emitting layers. The electroluminescence spectra of the devices are analyzed in comparison with the photoluminescence spectra of polymer films and are related to their microstructure properties. Blue light emitting diodes are obtained, except for the i-PPK based multilayer OLED, which emits white light due to three contributions (electroplex fluorescence, excimer phosphorescence and electromer emission). The results show that the polymer tacticity strongly affects the photoconductive properties of the devices.

The synthesis and the microstructural characterization of isotactic poly (N-pentenyl-carbazole) (i-PPK) are reported. The achieved polymer is semicrystalline, the melting temperature is 138°C. i-PPK Fourier transform infrared spectroscopy (FTIR) spectrum and X-ray diffraction pattern are compared with those of polyvinylcarbazole. The observed differences are tentatively associated to higher flexibility of the i-PPK chains due to the alkylene group connecting the carbazole group to the main chain. The presence of intrachain and interchain interactions between carbazole units, which bring these groups to stack each other, is assumed. i-PPK optical properties are investigated and an electroluminescent behaviour of polymer is observed. Organic light emitting diodes based on i-PPK layers are founded to emit white light. POLYM. COMPOS., 36:1110–1117, 2015. © 2015 Society of Plastics Engineers

The electroluminescence (EL) of isotactic and syndiotactic poly(N-pentenyl-carbazole) (PPK), achieved by coordination polymerization, is studied in order to investigate the interrelation between the polymer tacticity and their physical-chemical properties. The use of these polymers in organic light-emitting diode (OLED) fabrication is also explored. Thermal and x-ray diffraction analyses of PPKs show that the isotactic stereoisomer is semicrystalline, whereas the syndiotactic one is amorphous. Optical analysis of both stereoisomers, carried out on film samples, reveals the presence of two different excimers: 'sandwich-like' and 'partially overlapping'. Nevertheless, the emission intensity ratio between 'sandwich-like' and 'partially overlapping' excimers is higher in the isotactic than in the syndiotactic stereoisomer. Using the synthesized polymers as OLED emitting layers, the influence of the polymer tacticity on the EL properties of the device is highlighted. In detail, while blue OLEDs are obtained by using the syndiotactic stereoisomer, OLEDs with a multilayer structure fabricated with the isotactic stereoisomer emit white light. The contribution of three different emissions (fluorescence, phosphorescence and electromer emissions) with comparable intensities to the detected white light is discussed. © 2017 IOP Publishing Ltd.

13 C NMR analysis of poly(4-methyl-1,3-pentadiene) (poly(4-MPD)) obtained by using the C 2 symmetric zirconocene based catalytic system: rac -[CH 2 (3- tert -butyl-1-indenyl) 2 ]ZrCl 2 ( 1 )/ 13 C enriched methylaluminoxane (MAO) shows strong differences between the microstructure of the first inserted monomer unit and the in-chain inserted ones. The first insertion step results regiospecific, but not stereospecific, while the propagation step is regio- and stereoselective producing 1,2 syndiotactic poly(4-MPD). This feature is justified by assuming a “chain end” controlled mechanism working for the propagation step of polymerization. 13 C NMR analysis of isotactic poly(4-methyl-1-pentene) (poly(4-MP)) obtained by using the same catalytic system shows that the first monomer insertion is partially enantioselective.

Aqueous emulsion polymerization of styrene in the presence of half-titanocenes which CpTiCl 3 , (CpCH 2 CH 2 OCH 3 )TiCl 3 , and of the titanocene (Ph) 2 C[(Cp)(Flu)Ti]Cl 2 is effected. The polymer features are compared with those of polystyrene obtained in the same reaction conditions, by using Cp 2 TiCl 2 as initiator. Titanocene (Ph) 2 C[(Cp)(Flu)Ti]Cl 2 does not show any activity in styrene polymerization. On the contrary, by using both half-titanocenes CpTiCl 3 and (CpCH 2 CH 2 OCH 3 )TiCl 3 , stereoirregular polystyrene is produced. Aqueous emulsion polymerization of substituted styrenes (3-methyl-styrene, 4-methyl-styrene, 3-chloro-styrene, 4-chloro-styrene) is also performed in the presence of Cp 2 TiCl 2 . From all monomers, stereoirregular polymers are obtained. Monomer reactivity results dependent on the substituent on the aromatic ring. Aqueous emulsion styrene – 4-chloro-styrene copolymerizations are performed by using Cp 2 TiCl 2 , too. Copolymer composition totally reflects that of comonomers used in the feeding. According to a statistical distribution of comonomers, the product of the reactivity ratios is 1.1.

Bis-cyclopentadienyl titanium dichloride (Cp2TiCl2) is utilized as initiator for aqueous emulsion homopolymerization of 1,3-butadiene and isoprene and for copolymerization of the same diene monomers with styrene. The obtained homo- and copolymers are fully characterized by 13C nuclear magnetic resonance spectroscopy, thermal analysis and gel permeation chromatography.

Group 4 metals complexes bearing anilidomethylpyridine ligands have been synthesized and characterized by nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and single-crystal X-ray...

Ethene-1,3-butadiene copolymerizations in the presence of CpTiCl3/MAO catalytic system were performed. The microstructure of the obtained copolymers and the activity were reported as a function of the Al/Ti ratio. At high Al/Ti ratio prevailingly 1,4-cis butadiene homosequences were obtained, whereas, at low Al/Ti ratio, over 50% of alternating ethene-1,4-trans-butadiene was produced. The activity shows a minimum value at Al/Ti = 128.

Rac-[CH 2 (2,4-di-tert-butyl-cyclopentadienyl) 2 ]-ZrCl 2 (1), rac-[CH 2 (3-tert-butyl-4,5,6,7-tetrahydroindenyl) 2 ]-ZrCl 2 (2), rac-[CH 2 (3-isopropyl-4,5,6,7-tetrahydroindenyl) 2 ]-ZrCl 2 (3), and rac-[CH2(3-methyl-4,5,6,7-tetrahydroinde-nyl) 2 ]ZrCl 2 (4) were synthesized and characterized by 1 H NMR analysis. These C 2 symmetric ansa-zirconocenes, activated with methylaluminoxane (MAO), were able to promote copolymerization of ethene and 1,3-butadiene. The structures of the copolymers are strongly influenced by zirconocene utilized as catalytic precursor. Depending on the reaction conditions polyethenes containing cyclopropane and cyclopentane rings, or 1,1- 1,3-butadiene inserted constitutional units, were obtained.

The activity and the polymer microstructures obtained for polymerizations of four different conjugated dienes catalyzed by CpTiCl3−MAO have been closely compared for a broad temperature range (−45 to +70 °C). Apparent activation energies of 16.1 and 13.1 kcal/mol have been obtained for the poorly chemoselective butadiene and (E)-1,3-pentadiene polymerizations, while an apparent activation energy close to 8 kcal/mol has been obtained for the highly 1,2-syndiospecific polymerization of 4-methyl-1,3-pentadiene. As for (Z)-1,3-pentadiene polymerization, previous experimental evidences of two competing mechanisms have been confirmed. A molecular modeling analysis, comparing three possible polymerization mechanisms for the four considered dienes, contributes to rationalization of the available polymerization results.

In the presence of rac-[CH2(3-tert-butyl-1-indenyl)2]ZrCl2 (1) activated by methylaluminoxane (MAO) 1,4-pentadiene (1,4-PD), if copolymerized with ethene (E), gives unprecedented formation of methylene-1,3-cyclobutane units and a large amount of cross-links. Instead, in the presence of the same catalytic system, copolymerization of ethene with 1,3-butadiene (1,3-BD) or with 1,5-hexadiene (1,5-HD) gives exclusively a cyclization reaction, producing cyclopropane and cyclopentane units. The experimental results were rationalized by a theoretical approach, comparing the minimum energy pathways for the ring formation, after a diene insertion, with the competing ethene insertion reaction.

The polymerization of 1,3-butadiene to a 1,4-cis polymer is promoted by several nickel compounds activated by methylaluminoxane (MAO). The polymerization mechanism has been investigated with computational studies, and this motivating subject has been reported in several publications. Nickel-catalyzed and other transition-metal-catalyzed butadiene polymerizations are insertion polymerizations. Chain propagation proceeds in two steps

Cpolymerizations of propene and buta-1,3-diene performed in the presence of rac-[CH 2 (3-tert-butyl-1-indenyl) 2 ]ZrCl 2 and methylaluminoxane (MAO) have been investigated. Buta-1,3-diene gives prevailingly primary coordination to the metal, producing overall 1,2 units. Cyclopropane and cyclopentane rings, although in low amounts, are also obtained. The presence of butadiene would be responsible for some regioirregular 2,1-inserted propene units, which at high temperatures give rearrangement to 3,1 units.

Polymer microstructures obtained by copolymerizations of (Z)-1,3-pentadiene with ethene, conducted at different temperatures by the CpTiCl3−MAO catalytic system, have been characterized by detailed 13C NMR analyses. The observed microstructures indicate an essential role of the backbiting of the allyl-terminated growing chain on the occurrence of 1,2 syndiotactic and 1,4-cis high selectivities, which are observed for (Z)-1,3-pentadiene homopolymerizations at low and high temperatures, respectively. Molecular modeling studies suggest that the occurrence of 1,2-syndio and 1,4-cis stereoselectivities would be determined by the steric constrain (and stereorigidity) associated with the maintenance, in monomer bound intermediates, of the backbiting coordination of syn and anti allyl-terminated growing chains, respectively.

Four samples of syndiotactic poly(propylene) were synthesized by changing either the polymerization temperature or the catalytic system. Samples with different molecular weights were obtained, ranging between 27 000 and 826 000, whereas the fraction of syndiotactic pentads was found very near in the different samples, ranging between 88 and 91%. The polymer powders were quenched from the melt in an ice-water bath, extracted at room temperature and aged for 1 month. Changes in the structural organization during the ageing time at room temperature were followed by X-rays, transport properties and infrared analysis. The X-ray diffrac- tograms showed that all the fresh samples crystallized in the disordered helical form I, containing also a fraction of chains in trans-planar conformation. The helical crystallinity was found very similar for all the samples, and a small increase of this parameter, not higher than 4-6%, was observed during the ageing time. At variance, the study of sorption of a vapor at low activity indicated the presence of an intermediate phase not crystalline, yet impermeable to the vapors, increasing during the ageing at room temperature. The fraction of the intermediate phase was very high in the lowest molecular weight sample, and decreased on increasing the molecular weight, reaching a constant value for molecular weights higher than 80 000. The analysis of the infrared spectra showed that the helical bands increase during the ageing, indicating that the intermediate phase is composed by very small and disordered helical crystals. The elastic modulus of each sample was measured soon after quenching and during the ageing. It was found a consistent increase of this parameter, not ascribable only to the small increase of crystallinity. The increase of the elastic modulus of all the samples was correlated to the increase of the intermediate phase derived by sorption, and a good dependence on this parameter was found.

2-Phenyl-1,3-butadiene and (E)-1-phenyl-1,3-butadiene were polymerized in the presence of homogeneous Ziegler-Natta catalytic systems. The products were analyzed by means of 13C NMR spectroscopy. Monomer reactivities and polymer structures were compared with those obtained by using the same catalytic systems in the polymerizations of isoprene, (E)-1,3-pentadiene and 1,3-butadiene. The results were tentatively rationalized by considering the stability of the allyl groups resulting after any insertion of the monomer into the growing chain.

Copolymerizations of ethylene with 1,3-butadiene in the presence of catalytic systems based on C 2 -symmetric zirconocenes rac -(CH 3 ) 2 Si(2-R-4-R′-1-indenyl) 2 ZrCl 2 (where R = CH 3 – or H and R′ = C 6 H 5 – or H) are compared. The chemical nature and the relative amount of constitutional comonomer units from butadiene (1,4- trans , methylene-1,2-cyclopentane and methylene-1,2-cyclopropane) are strongly affected by the bulkiness of the substituent on the indenyl ligands. The unsubstituted indenyl zirconocene system rac -(CH 3 ) 2 Si(indenyl) 2 ZrCl 2 /methylalumoxane (MAO) inserts 1,3-butadiene leading to both cyclopentane and 1,4- trans units, whereas exclusively cyclopentane constitutional units are obtained from rac -(CH 3 ) 2 Si(2-methyl-1-indenyl) 2 ZrCl 2 /MAO. The catalytic system rac -(CH 3 ) 2 Si(2-methyl-4-phenyl-1-indenyl) 2 ZrCl 2 /(MAO) is able to incorporate about 30% of butadiene units into polymer chains and to form up to 10% of cyclopropane units. An unusual insertion mechanism for conjugated diolefins, that involves a butadiene η 2 primary coordination and insertion leading to formation of cycloalkane units, is largely predominant for all used catalytic systems. Mechanistic studies and DFT calculations indicate that the chemoselectivity of the reaction depends on the bulkiness of the substituents on the indenyl ligands of catalyst.

The synthesis and the microstructural, morphological, optical characterization of poly (N-pentenyl-carbazole) are reported. The obtained polymer present a stereoregular isotactic microstructure and is cristalline with a Tm of 138°C. Photoluminescence analysis of chlorobenzene polymer films, having high homogeneity and low roughness, show that PPK emits in a broad spectrum range 350-600 nm.

C 2 -symmetric zirconocenes activated by methylaluminoxane were utilized as catalysts in the polymerization of 1.3-diolefins. The results indicate that the most crowded catalytic precursor rac[CH 2 (3-tert-butyl-1-indenyl) 2 ]ZrCl 2 (1) is also the most active one, giving 1,4-polymerization of 1,3-butadiene and (Z)-1,3 pentadiene and 1,2-polymerization of (E)-1,3-pentadiene and 4-methyl-1,3-pentadiene. Probably, the different behavior of 1 with respect to other C 2 -symmetric zirconocenes utilized is due to the different stability of the bond between the last inserted monomer unit and the metal, as well as to the coordination of incoming monomer.

SUMMARY: Stable free radical polymerization has been used in the controlled synthesis of poly(2,5-bis[(4butylbenzoyl)oxy]styrene), PBBOS. This “mesogen-jacketed liquid crystalline polymer”, which has mesogenic units attached directly to the backbone in a side-on mode, has been found to exhibit thermotropic liquid crystallinity similar to more conventional main-chain architectures. Stable free radical polymerization of PBBOS consistently produced molecular weight distributions below the theoretical limiting polydispersity of 1.5 calculated for a conventional free radical polymerization process. Surprisingly, a comparison of the synthesis of polystyrene to the polymerization of PBBOS under nearly identical conditions showed that the PBBOS polymerized with a significantly higher reaction rate and monomer conversion efficiency. The nematic phase of these polymers was determined to be stable over the temperature range spanning the polymer glass transition temperature up to the temperature for thermal decomposition. The molecular arrangement of the PBBOS polymers was examined by wide-angle X-ray diffraction and is described here.

Crystalline methylene-1,2-cyclopentane (E-1,2CP) random copolymers, containing up to 15% of cyclic units, are obtained in high yields by copolymerization of ethylene and 1,3-butadiene in the presence of rac-[CH2(3-methyl-1-indenyl)2]ZrCl2/MAO catalyst. The highly selective formation of trans methylene-1,2-cyclopentane units occurs by an intramolecular insertion of the double bond pendant from polymeril chain after an unusual primary vinyl insertion of 1,3-butadiene. Thermal properties and structure of E-1,2CP copolymers, as function of 1,2-cyclopentane molar content, are analyzed and compared with those of other ethylene copolymers. The variation in melting temperature and crystallinity observed in E-1,2CP copolymers is consistent with that observed for ethylene copolymers with comonomers bulkier than propylene. Moreover, the 1,2-cyclopentane units, as well as comonomers bulkier than propylene, cause only slight deformations of polyethylene orthorhombic unit cell parameters. These data are rationalized by assuming that 1,2-cyclopentane units, are confined in amorphous phase, while the polyethylene crystalline phase remains pure.