1,721,126 research outputs found
Water extraction and degradation of a sterically hindered phenolic antioxidant in polypropylene films
No full textWater extraction of the sterically hindered phenolic antioxidant Irganox 1010 from three polypropylene based polymeric films has been studied in isothermal conditions at 40, 50 and 70 °C. The films made of isotactic polypropylene and two different heterophasic polypropylene/ethylene–propylene monomers copolymers (PP/EPM copolymers) were immersed in closed water baths under nitrogen atmosphere in order to minimise the oxidative process. The amounts of antioxidant that have left the films and are dissolved in the water bath have been monitored over time by HPLC analysis and faster extraction kinetics were observed from the polymers than from the homopolymer. No appreciable amounts of Irganox 1010 were found in the extraction water at any time, whereas its degradation by-products were found by LC/MS analysis in the extraction water.
The experimental extraction kinetics from the three polymers were compared with the theoretical curves based on the Fick's diffusion equations solved both for a semi-infinite (degradation reaction faster than extraction) and a finite system (no degradation reaction) and Irganox 1010 was demonstrated to be extracted by water from polypropylene based material faster than predictable only on the basis of the values of its coefficient of diffusion in the polymers and of partition between water and polymer
Defined Chitosan-based networks by C-6-Azide-alkyne “click” reaction
No full textChitosan was converted to its -NH(2)-protected derivative by reacting with phthalic anhydride and then selectively functionalized with an azido group in C-6 position. Two different procedures were employed. The first was a "one-pot" procedure and the second was a two steps reaction through the tosylated intermediate. Both methods resulted in an effective functionalization of chitosan with azido groups. For the two before mentioned procedures, the functionalization degree was estimated by elemental analysis as number of azido groups per pyranoside ring and was 0.28 mol/mol and 0.26 mol/mol, respectively. The azido-functionalized derivatives underwent further modification by Cu(I) catalyzed dipolar cycloaddition with mono- or di-alkynes. The reaction with phenylacetylene produced soluble derivatives that were fully characterized at molecular level by FT-IR and NMR spectroscopies, elemental analysis and size exclusion chromatography (SEC). Crosslinked derivatives were obtained by reactions with 1,7-octadiyne or 1,4-diethynylbenzene and subsequently deprotected to restore the free amino groups. These last systems showed selective swellability in acid medium
Easy detectable isocyanate in the reaction with gelatin RID E-9799-2011
No full textGelatin reactivity with isocyanate was studied by using the easy detectable 1-naphthyl-isocyanate (NphI). Four different NphI/gelatin feed ratios were investigated with NphI molar amount ranging between 1/10 and 1/1 with respect to the possible reactive groups of gelatin. The reactions were carried out at 45 A degrees C in DMSO as solvent, under nitrogen atmosphere. Modified gelatin samples were characterized by IR, UV-VIS, fluorescence spectroscopies as well as by proton and DOSY NMR. Spectroscopy results allow to evidence the presence of both bonded and unbonded naphthyl derivatives in the gelatin samples. Unbonded species were present particularly at the highest NphI/gelatin feed ratio and their formation was correlated to the increasing competition of the reaction with water since the amount of available reactive groups on gelatin was comparable or smaller than the amount of residuum water in dry gelatin.Gelatin reactivity with isocyanate was studied by using the easy detectable 1-naphthyl-isocyanate (NphI). Four different NphI/gelatin feed ratios were investigated with NphI molar amount ranging between 1/10 and 1/1 with respect to the possible reactive groups of gelatin. The reactions were carried out at 45 °C in DMSO as solvent, under nitrogen atmosphere. Modified gelatin samples were characterized by IR, UV-VIS, fluorescence spectroscopies as well as by proton and DOSY NMR. Spectroscopy results allow to evidence the presence of both bonded and unbonded naphthyl derivatives in the gelatin samples. Unbonded species were present particularly at the highest NphI/gelatin feed ratio and their formation was correlated to the increasing competition of the reaction with water since the amount of available reactive groups on gelatin was comparable or smaller than the amount of residuum water in dry gelatin. © 2010 Springer-Verlag
Synthesis and characterization of thienyl- and terthienyl-group-bearing methacrylic polymers as precursors for grafting reactions of thiophene side-chains
No full textAcrylic and methacrylic monomers bearing pyrrolyl, thienyl and terthienyl groups, were synthesized and copolymerized with various amounts of butyl acrylate and butyl methacrylate. In the resulting copolymers the heterocycle side-groups behaved as initiators in the oxidative polymerization of thiophene, allowing the polythiophene chains to grow from the side-groups and leading therefore to graft copolymers. These last were collected mostly as insoluble fractions after extraction with chloroform. Processible polymers with polythiophene side-chains were obtained when in the precursor polymer the heterocycle side-group content was very low. The presence in the graft copolymers of a significant number of stiff polythiophene side-chains was responsible for the rise in Tg values in comparison with the precursor polymers. The average number of grafted thiophene units, evaluated in the range 2-7.5, did not relate directly to measured conductivity values that were in the range 5.9 x 10(-5)-6.2 x 10(-2) Scm(-1)
Optically Responsive Polymer Nanocomposites Containing Organic Functional Chromophores and Metal Nanostructures
No full textResponsive “smart” materials are certainly one of the most intriguing research areas in modern polymer science and technology, as molecularly designed materi- als based on macromolecules offer unique opportunities in this connection. Indeed, macromolecules are able to transmit and amplify small signals through involvement of the whole chain, conferring to the material a change in properties of various level and type. We can learn from Nature how these effects may be obtained according to two distinct routes, based either on the covalent bonding of highly responsive molecular species to the chains, or on the nanodispersion of such responsive species within the polymer bulk. In the latter case, those materials based on macromolecules may also affect the behavior of guest low-molecular- weight molecules or noble metal assemblies. In addition to the molecular features of both host and guest, the supramolecular arrangement of the guest can be modulated by external events on the host material. These effects can be identified and conveniently used when easily detected and field-sensitive species are present in the low-molecular-weight component. In this chapter, we review those investi- gations conducted not only in our laboratory but also by others, that have provided clear examples of the concepts which drive the original idea. In particular, we report our data relating to the effects of external stimuli (i.e., mechanical stretching such as polymer drawing, temperature, and pressure) on the optical properties (absorption and emission) of (nano)composite materials. The (nano)dispersion of active dyes and metal nanoparticles (guest) in inert polymers (host) will then be presented as an example of the effect of the macromolecular environment on respectively the dye or metal atom aggregates (metal nanoparticles), in terms of induced optical properties
Modulation of structural and stone protective properties of fluorinated methacrylate polymers
No full textFunctionalization of polyolefins in the melt through reaction with molecules and macromolecules
No full textFunctionalization of polyolefins with diethyl maleate (DEM) is investigated to improve compatibility with other polar polymers through reactive blending. Functionalization experiments were carried out in the melt with peroxide initiator and mechanical mixers as reactors. The effect of feed composition, reactor type and duration on the functionalization degree, degradation and crosslinking reactions were examined starting with different ethylene polymers. In this way conditions were identified allowing modulation of functionalization with 2-(diethyl succinate) groups from 0.2 to 2.5% mole, and keep to negligible level undesired by-reactions such as crosslinking and degradation. The chemical reactivity of these functional groups to form interchain covalent bonds was investigated in case of the reaction of the ester groups on the polyolefin backbone with the amino end group of linear polyamides (in particular PA 6). Evidences of the formation of grafted polymer on the basis of fractionation of the resulting mixture, instrumental analysis and morphological characterization are presented
Applicability of the Photochemically Generated Pendant Benzoyl Peroxides in both “Grafting From” and “Grafting To” Techniques
No full textMethyl methacrylate and styrene copolymers containing pendant benzil groups, such as 1-[4-(2-methacroyloxyethoxy)phenyl]-2-phenyl-1,2-ethanedione-co-methyl metacrylate (BzMA/MMA), 1-[4-(2-methacroyloxyethoxy)phenyl]-2-phenyl-1,2-ethanedione-co-styrene (BzMA/S), and 1-phenyl-2-(4-propenoylphenyl)-1,2-ethanedione-co-styrene (PCOCO/S), were prepared and used as precursors for photochemically generated pendant benzoyl peroxides. Decomposition of the pendant benzoyl peroxides was subsequently used in grafting processes. Either irradiation or a combination of irradiation with subsequent thermal treatment was adopted for grafting a thin layer of BzMA/MMA copolymer onto the surface of LDPE films. The grafting resulted in a significant decrease in contact angle of the film surface. The same activation strategy was successfully adopted to initiate the polymerisation of acrylic or methacrylic acids from the surface of styrene copolymer films containing the initiator precursor in the polymer side chains (BzMA/S and PCOCO/S). The successful surface grafting was proved by contact angles measurement as well as by infrared spectroscopic analysis
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