Dynamics of poly(vinyl butyral) studied using dielectric spectroscopy and 1H NMR relaxometry.

Dielectric spectroscopy and NMR relaxometry unveiled the PVB segmental dynamics across the glass transition temperature

Copolymerization of styrene with methyl-substituted styrenes in the presence of titanium monometallocenes

AbstractThis paper investigates the homo- and copolymerization of styrene with p-methylstyrene, m-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene and 2,4,6-trimethylstyrene using a Cp*TiCl3 (Cp: cyclopentadienyl) semimetallocene catalyst activated with methylaluminoxane. Syndiotactic homo- and copolymers were obtained only for the monosubstituted monomers. For the di- or trisubstituted monomers, reduced reactivities, stereoregularities, and degrees of polymerization were obtained with respect to the monosubstituted monomers. More specifically, the homopolymerization of 2,5-dimethylstyrene and 2,4,6-trimethylstyrene and their copolymerization with styrene was inhibited. The reason for this are combined steric and inductive effects. The presence of methyl groups in para position seems to inhibit crystallization of the syndiotactic polymers. In contrast, crystallinity was evidenced in the materials produced in the presence of m-methyl substituted monomers

Biocomposites Based on Polyhydroxyalkanoates and Natural Fibres from Renewable Byproducts

Background and Objective: The use of biopolyesters and natural fibres or fillers for production of biobased composites has attracted interest of various application sectors ranging from packaging to automotive components and other high value applications in agreement with a bioeconomy approach. In the present paper biobased composites were produced by using compostable polymers degradable even in soil and marine water such as polyhydroxyalkanoates with natural fibres or fillers derived by food wastes (legumes by-products) and by wood industry.Material and Methods: Polyhydroxyalkanoates were processed with a biobased, biodegradable plasticizer such as acetyltributylcitrate and calcium carbonate as inorganic filler. The selected polymeric matrix was used for the production of composites with variable amounts of natural fibres. Green composites were manufactured by extrusion and injection moulding. Thermal, rheological, mechanical and morphological characterizations of the developed composites were performed.Results and Conclusion: The bio composites properties match the requirements for production of rigid food packaging or other single use items where the market is looking for more sustainable solutions versus the products actually used and hardly recyclable, opening a route for valorization of food residue. Pukanzsky’s model predicts with good accuracy the tensile behavior of the composites showing a medium intensity adhesion between fibres and polymer matrix in both cases analyzed.Conflict of interest: The authors declare no conflict of interest.

Unprecedented comonomer dependence of the stereochemistry control in Pd-catalyzed CO/vinyl arene polyketone synthesis

Two pyrene-tagged iminopyridines (N-N') were used to synthesize neutral and monocationic, palladium(II) complexes, [Pd(Me)Cl(N-N')] and [Pd(Me)(MeCN)(N-N')][PF6]. The monocationic complexes generated active catalysts in the CO/vinyl arene copolymerization leading to polyketones with yields and molecular weight strongly dependent on N-N', being the ketimine catalysts one order of magnitude more productive than the aldimine counterpart. The stereochemistry of polyketones synthesized with the aldimine catalyst was found to be dependent on the vinyl comonomer: prevailingly syndiotactic copolymers were obtained for styrene, prevailingly isotactic copolymers were produced for 4-methyl styrene, and atactic macromolecules were formed for the 4-tbutyl styrene. The statistical analysis demonstrated that the control of the stereochemistry switched from enantioselective site control for 4-methyl styrene to a combination of chain-end and enantioselective site control for styrene

Injectable thermosensitive gels for the localized and controlled delivery of biomolecules in tissue engineering/regenerative medicine

The characteristic poor stability and high fluid permeability of Poloxamer®- based gels have severely limited their biomedical application. In this work, Poloxamer 407 was used as building block to synthesize a poly(ether urethane) (PEU), which aqueous solutions formed gels with improved stability and mechanics compared to Poloxamer itself. PEU chains formed micelles in aqueous solution (diameter ~40 nm at 25°C) and systems with PEU content higher than 5±1% w/v underwent a temperature- driven gelation. Gel properties were tuned acting on PEU concentration in the starting solutions, with compositions within the range 8-18% w/v showing high potential for biomedical applications (gelation at 37°C within 3-10 minutes, residence time from few days to many weeks, injectability). Model proteins (bovine serum albumin, horseradish peroxidase) were encapsulated in mild conditions and their release was modulated by gel composition (on day 3, approx. 85, 65 and 55% of encapsulated payload released from gels with 8, 15 and 18% w/v concentration). Released peroxidase retained approx. 30-40% of its activity up to 2 days, a key aspect for biomolecules in the drug delivery field

Polyketone Nanocomposites by Palladium-Catalyzed Ethylene-Carbon Monoxide-(Propene) Co(Ter)polymerization Inside an Unmodified Layered Silicate

AbstractComposites from Na-montmorillonite with a content in inorganic material ranging from 3 to 98 wt % were prepared in situ either by copolymerization of ethylene and CO or by terpolymerization of ethylene, propene and CO using a palladium(II) catalyst modified with 1,3-bis(diphenylphosphino)propane. This catalytic system is active in polar media and allowed to produce nanocomposites starting from unmodified Na-montmorillonite in water-methanol solutions. The morphological analysis, performed on samples with less than 40 wt % silicate by XRD and TEM, showed the formation of either intercalated or exfoliated (nanocomposite) structures, depending on the initial amount of the layered silicate in the reactor as well as the presence of propene as comonomer. Improved thermal stability of the hybrid materials, as compared to the corresponding organic polymers, was shown by TGA. A preliminary study of the blending of some polyketone nanocomposites with polyamide (nylon-6) was carried out by melt mixing at high temperature in a Brabender mixer

Effect of free radical reactions onto Structure and properties of poly(lactic acid) (PLA) based blends

The blending of PLA with poly(butylene-adipate-co-terephthalate) (PBAT) is a promising strategy to achieve a toughened multiphase material. The blends ductility could be further improved through reactive compatibilization, i.e. inducing the formation of comb PLA-PBAT copolymers during the melt blending. In the present work a non-selective strategy was adopted which consisted in the use of a peroxide, 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane. The phase morphology development and the final properties (torque, fluidity in the melt, tensile behaviour, thermal and dynamicalemechanical features) of the blends were studied as a function of the peroxide concentration. The elongation at break was improved up to a maximum value thanks to this approach and a corresponding minimum was observed in the value of the dispersed phase diameter. A structural characterization of the macromolecules formed during the reactive process was attempted by using size exclusion chromatography of the blends and comparison with the pure polymers obtained by processing in the presence of the peroxid

Radical functionalization of poly(butylene succinate-co-adipate): Effect of cinnamic co-agents on maleic anhydride grafting

Maleic anhydride (MAH), trans cinnamic acid (AcCin) and ethyl cinnamate (EtCin) were radically graft onto poly(butylene succinate-co-adipate) (PBSA). Samples were prepared in Brabender at 175 degrees C by addition of increasing amounts of MAH, AcCin, EtCin and their combinations, i.e. MAH/AcCin and MAH/EtCin, setting DCP content in the 0.2-0.6 wt\% range. Monomer grafting was quantitatively determined by FT-IR. MAH grafting degrees (FD(M)) resulted up to 1 molt Conversely, AcCin grafting degrees (FD(A)) were found almost negligible in all cases. EtCin was found grafted in the 0.3-1.0 mol\% range when the binary system MAH/EtCin was applied. Same MAH feeds returned almost doubled MAH grafting degrees (FD(M)) when AcCin was the stoichiometric co-agent, and even three times higher FD(M) when EtCin was the stoichiometric co-agent. On accounts of all the collected results, a kinetic model of the investigated systems is proposed. (C) 2011 Elsevier Ltd. All rights reserved

Polymers from Fossil and Renewable Resources

The book describes the development and commercialization of materials with viscoelastic properties, placing particular emphasis on the scientific and technological differences between plastics and bioplastics. The authors explain how to handle each of the two types of materials and determine the comparative environmental impact of the material life-cycle. The practical values of the overlapping aspects of the two types of materials from technical properties to eco-compatibility are also discusse