Marco Frediani

Poly(lactic acid) as a transparent matrix for luminescent solar concentrators: a renewable material for a renewable energy technology

The suitability of L-poly(lactic acid) (L-PLA) as a transparent matrix, alternative to poly(methylmetacrilate) (PMMA), for use in luminescent solar concentrators is herein demonstrated. Low molecular weight L-PLA-based films, both chemically modified or blended with an oligothiophene luminescent dye (T5OH), showed excellent processability, photostability, and exhibited fluorescence quantum yields (of about 35%) even higher than T5OH-doped PMMA.

Low density polyethylene by tandem catalysis with single site Ti(IV)/Co(II) catalysts

A variety of branched polyethylenes (PE), ranging from semicrystalline linear low density polyethylene to completely amorphous low density polyethylene and rubbery PE, can be produced from ethylene alone by tandem catalysis using as oligomerization catalysts the (imino)pyridyl Co(II) complexes NBTCoCl2 (1) ({6-(benzo[b]thiophen-2-yl)-2-(imine)pyridyl)}CoCl2), NETCoCl2 (2) ({6-(4-ethylthiophen-2-yl)-2-(imine)pyridyl)}CoCl2), or NPhCoCl2 (3) ({6-(phenyl)-2-(imine)pyridyl)}CoCl2) and as a copolymerization catalyst [η5-C5Me4)SiMe2(t-BuN)]TiCl2 (4). The catalytic activity of the systems 1/4/MAO, 2/4/MAO, and 3/4/MAO has been evaluated under comparable experimental conditions (T = 30°C, [ethylene] = 0.35 mol/l), varying the molar fraction of the cobalt precursors. A positive comonomer effect was observed for all the systems investigated. The maximum productivity (4570 kg PE (mol Ti)−1 h−1) was obtained for the benzothiophenyl-substituted cobalt complex. An effective control of the branching in the polymer backbone was achieved by varying either the oligomerization catalyst or its molar fraction. Completely amorphous materials with Tg as low as-60°C could be obtained.

Synthesis of the first polymer-supported tripodal triphosphine ligand and its application in the heterogeneous hydrogenolysis of benzo[b]thiophene by rhodium catalysis

A p-styrenyl substituent attached to the ligand framework allows the tripodal triphosphine moiety –C(CH2PPh2)3 to be introduced as a pendant group in polystyrene matrices via free-radical copolymerisation; in conjunction with rhodium(I), the polytriphos material forms an effective heterogeneous catalyst for the hydrogenolysis of benzo[b]thiophene to 2-ethylthiophenol and ethylbenzene.

L-Lactide polymerization by calix[4]arene-titanium (IV) complex using conventional heating and microwave irradiation

Abstract Since the first contributions by Gedye and Giguere in 1986, growing attention has been registered on the use of microwave heating in organic synthesis. However still many aspects need to be clarified especially about the so called “microwave effect” and the possible degradation phenomena that may be recognized during polymer synthesis. In this work the complex cone-25,27- dipropyloxy-26,28-dioxo-calix[4]arene titanium (IV) dichloride (1) has been tested for the ring opening polymerization of L-lactide, comparing the effect of conventional heating with a possible microwave assisted strategy. The polymers obtained were fully characterized (NMR, IR, HPLC-SEC, DSC, MALDI-TOF and WAXD analysis). As expected the use of microwave irradiation induced an increase of the polymerization rate. On the other side the use of microwaves resulted in a slight loss of the control over molecular weight and molecular weight distribution if compared with a conventional thermal treatment.

Microwave pyrolysis of polymeric materials

The consumption of polymeric materials is growing ceaselessly in the world even in spite of the financial crisis. World’s plastics production in 2009 was 2.3·108 tons and in Europe it was 4.5·107 tons whose 54% is disposed as waste. The annual average production of tires in Europe is more than 2.5 106 tons. In the 2008 in Italy were produced 3.5·106 tons of plastics among which 4.1·105 tons of tires, and 1.5·106 of waste plastics tons were collected for disposal. (Chen et al., 2007; Federazione Imprese e Servizi, Unione Nazionale Imprese Recupero [FISE UNIRE], 2009; PlasticsEurope, 2010). World rubber demand is foreseen to increase up to 4% annually to 26.5 million metric tons in 2011 (Freedonia, 2010). Therefore the disposal of waste polymers is a serious environmental problem against which public is becoming more aware. The interest of waste polymeric materials disposal is focused on new uses rather than land filling or incineration. Regarding scrap tires, a strong attention has been paid over last years to the claims for their recycling or reprocessing. In consideration of their complex composition, slow degradation rate in landfill, high calorific value and shape hindrance they may be burned hardly but otherwise they cannot send to landfill anymore and an alternative methodology must be eligible in order to dispose scrap tires. European Directive No. 31/1999 states that the disposal of scrap tires in landfills is banned with the exclusion of bicycle tires and tires with an external diameter greater than 1400mm. Since July 2006 the ban has been extended also to shredded tires. Waste plastics and tires are very attractive as a source of renewed raw materials and chemical substances. These products may be achieved by pyrolysis, heating usually in the absence, but sometimes in the presence, of an oxidative agent, and these processes may be viewed as a promising technology. The pyrolysis of polymeric materials or plastic-containing wastes including scrap tires is a possible answer to the problem of their disposal because it let recover of gas, oil and solid able to be employed as a source of products and energy. Therefore the relevance of the pyrolysis processes of plastic waste has been growing. A plethora of studies over the thermal degradation of polymeric materials are carried out using conventional heating method with internal or external heating source, under inert or oxidizing atmosphere. Generally the thermal decomposition needs operating temperature above 450°C (Kaminsky et al., 2004; Mastral et al., 2002; Whesterhout et al., 1998).

Ultrasounds in Melted Poly(ethylene glycol) Promote Copper‐Catalyzed Cyanation of Aryl Halides with K4[Fe(CN)6]

Melted poly(ethylene glycols) (PEGs) were used for the first time as solvent for the sonochemically promoted cyanation of aryl halides employing inexpensive and safe K4[Fe(CN)6] and a relatively low amount of Cu-based catalyst. The Mw (weight-average polymer molecular weight) of PEG proved to notably influence the substrate conversion, which is indicative of a strong dependence of the sonication efficacy on solvent properties. Gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) contributed to the characterization of the polymer and the elucidation of the catalytic system.

High-Pressure Reactivity of L,L-Lactide

L,L-Lactide, a dimer of L-lactic acid, is the typical monomer used for the catalytic synthesis of poly(L-lactic acid) (PLLA). We studied its phase diagram and reactivity at high pressure and high temperature by means of a diamond anvil cell. FTIR and Raman spectroscopy were employed to probe the changes occurring in the sample. An increase of temperature at pressure higher than 0.1 GPa revealed a solid-solid phase transition before the melting. A reaction was observed immediately after the melting with the almost complete transformation of the starting reactant to an amorphous poly(lactic acid) (PLA). The increase of pressure was found to accelerate the process, suggesting the reaction rate to be limited in the diffusion step. A steeper acceleration, likely due to multiphoton absorption processes of the 647.1 nm laser light by PLA, was observed in the Raman experiments.

Ring-Opening Polymerisation of rac-Lactide Using a Calix[4]arene-Based Titanium (IV) Complex

cone-25,27-Dipropyloxy-26,28-dioxo-calix[4]arene titanium (IV) dichloride (1) has been assessed in the ring-opening polymerisation of rac-lactide (L,D-LA). The polymers formed (PLDA) turned out to display an isotactic stereoblock microstructure (determined by NMR) despite the fact that the catalyst has symmetry. Two techniques were applied for initiating the polymerisation reaction, microwave irradiation, and conventional thermal treatment. The polymers obtained were all characterised by NMR, IR, HPLC-SEC, DSC, and MALDI-TOF analysis. The use of microwave irradiation, applied for the first time to calixarene-based catalysts in the presence of the rac-lactide monomer, increased the polymerisation rate compared with that obtained by the other method. On the other hand, standard thermal treatment enabled a slightly better control than microwave irradiation over the molecular weight and molecular weight distribution of the polylactides formed.

Synthesis and processing of biodegradable and bio-based polymers by microwave irradiation

Biodegradable polymers, as well as polymers produced from renewable feedstocks, are attracting increasing interests as possible substitutes for conventional plastics: a higher energy efficiency in synthesis and processing steps must be continuously pursued in order to maximize the intrinsic environmental benefits brought by this class of materials. Microwave assisted organic synthesis (MAOS) is nowadays a major topic in green chemistry and a great (yet rising) number of papers can already be found that report striking advantages over conventional thermal heating. Nonetheless microwave (MW) energy sources are recently being chosen also for several polymerization reactions. Indeed, reduced heating times and superior homogeneity provided by MW reactors may play a central role in optimizing production processes, with a dramatic improvement in the environmental performance. In the introduction of this chapter we’re briefly recalling some theoretical principles of microwave-matter interaction; several experimental setups are then examined and, eventually, thermal and non-thermal specific microwave effects are described and commented. The following paragraph is dedicated to a comprehensive survey of synthesis examples found in scientific literature and categorized by polymerization technique, in which particular relevance is given to products of increasing commercial importance like poly(e-caprolactone) (PCL) and poly(lactic acid) (PLA). A third part of the chapter deals with the employment of microwave heating for chemical modification and processing of polymers; the last paragraph summarizes advantages and drawbacks of microwave assisted polymer chemistry, stressing the energy efficiency topic and drawing conclusions.

Methyl acrylate polymers as suitable materials for the conservation of stone: performance improvements through atom transfer radical polymerization

Acrylic polymers are a suitable category of materials for application in building stone conservation mainly due to their peculiarities (i.e., easy to apply, low cost, good adhesive and cohesive properties, and high solubility in many organic solvents). The performances of polyacrylates have been improved through atom transfer radical polymerization (ATRP). Polymers were obtained with low polydispersity, controlled molecular weight, and showing better stability to UV irradiation than products obtained by radical polymerization. New poly(methyl acrylate-co-perfluoropolyethers) were also prepared via ATRP, using a perfluoropolyether derivative as initiator, showing the possibility of synthesizing copolymers between acrylates and perfluoropolyethers in common solvents. Protective efficiency of poly(methyl acrylate-co-perfluoropolyether) was close to that of commercially available products.