The effects on different synthetic polymers of distinct types of radiation, gamma rays and electron beam, under different atmospheres are followed by changes in their viscoelastic behavior. Taking ...into account the two main radioinduced reactions, crosslinking and scissioning of polymeric chains, liquid polydimethylsiloxane has been used as example of crosslinkable polymer and semi crystalline polypropylene as example of scissionable polymer. Propylene − 1-hexene copolymers have been also evaluated, and the effects of both reactions were clearly noticed. Accordingly, samples of those aforementioned polymers have been irradiated with 60Co gamma irradiation in air and under vacuum, and also with electron beam, at similar doses. Sinusoidal dynamic oscillation experiments showed a significant increase in branching and crosslinking reactions when specimens are irradiated under vacuum, while scissioning reactions were observed for the different polymers when irradiation takes place under air with either gamma irradiation or electron beam.
•Analysis of gamma and EB irradiated scissionable iPP and crosslinkable PDMS.•Similar decrease of viscoelasticity of all irradiated samples with air gamma and EB.•Crosslinking in vacuum irradiation for PDMS, and sort of in iPP copolymers.•Amorphous iPP tend to branching when irradiated, specially, under vacuum.
The physical properties of glycopolymers based on
d-(+)-glucosamine,
d-(+)-galactosamine and
d-(+)-mannosamine derivatives and obtained from two ethylene–vinyl alcohol, EVOH, copolymers with ...different vinyl alcohol compositions have been analyzed. The thermal degradation of these glycopolymers is almost independent of the type and amount of saccharide incorporated but slightly dependent on the initial EVOH copolymer composition. The glycopolymers derivate from the EVOH copolymer with lower ethylene content present two relaxation processes, while those derivatives from the EVOH copolymer with lower vinyl alcohol composition essentially show three relaxations processes. In both sets of glycopolymers, the relaxation process associated with the cooperative motions that take place at the glass transition is located at analogous temperatures to those previously determined by differential scanning calorimetry, both results being rather consistent.
A family of amphiphilic poly(acrylic acid-
g-styrene), P(AA-
g-S), graft copolymers has been prepared by quantitative hydrolysis from poly(
tert-butyl acrylate-
g-styrene), P(
tBA-
g-S), precursors ...and evaluated by
1H NMR and FTIR. The thermal characterization of these copolymers as a function of the number of grafted repeat units has been performed by thermogravimetric analysis, TGA, differential scanning calorimetry, DSC, and dynamic mechanical experiments. A higher thermal stability of the PAA main chain was observed by TGA as incompatible PS is grafted onto it. Small-angle X-ray scattering, SAXS, measurements have confirmed the existence of phase separation in the graft copolymers and the morphological behavior was analyzed. An increase on microdomains size is observed when the number of grafts diminishes. Moreover, the presence of polar functional groups in the backbone chain leads to the formation of hydrogen bonds giving rise to a substantial modification of the linear viscoelastic response compared with that exhibited by the unhydrolyzed precursory copolymers, as observed by analysis of melt rheological measurements.
Novel glycopolymers based on ethylene–vinyl alcohol copolymers and lactones have been developed. Their solutions in water lead to the formation of reversible thermallyinduced networks as well as ...exhibit molecular recognition to specific lectins.
Novel glycopolymers have been prepared from ethylene–vinyl alcohol copolymers, EVOH. For that purpose, three distinct aminosaccharides (
N-(4-aminobutyl)-
d-gluconamide (NABG),
N-(4-aminobutyl)-
O-β-
d-galactopyranosyl-(1
→
4)-
d-gluconamide (NABL) and
N-(4-aminobutyl)-
O-β-
d-glucopyranosyl-(1
→
4)-
d-gluconamide (NABM) have been synthesized. The previous functionalization of these EVOH copolymers is mandatory to activate their hydroxyl reactivity before the subsequent coupling reaction with the aminosaccharides. The activation with carboxylic acid groups by reaction with phthalic anhydride has been chosen in the current investigation because of its almost quantitative yield and the subsequent high modification extent reached (>60%). The glycopolymers that turned out water-soluble (i.e., those based on NABL and NABM) have shown a reversible network formation unusually described in glycopolymers. In addition, their capability to interact with lectins, particularly Concanavalin A and
Ricinus communis Agglutinin, has confirmed the specificity of lectin recognition in these glycopolymers.
MCM‐41 micro‐ and nanoparticles are prepared and functionalized with silane coupling agents. These pristine and silane‐decorated mesoporous MCM‐41s are further used in the synthesis of ...MCM‐41/ethylene nanocomposites by in situ polymerization, utilizing either supported or non‐supported catalytic systems. The catalytic behavior of those systems is discussed, taking into consideration the effects of the particle size, surface characteristics, and functionalization. The results have shown that the initial surface state of MCM‐41 is of paramount importance to achieve high catalytic activity if a polymerization catalyst is to be supported. Functionalization changes the surface chemistry, thus, a positive or negative effect may be observed, depending on the previous features of the surface. The particle size of MCM‐41 and its functionalization affect its final dispersion within the polymeric matrix, this distribution is evaluated by SEM, TEM, and microhardness measurements.
Functionalization matters: Beneficial and detrimental effects on catalytic activity are observed after various forms of silane functionalization are performed on MCM‐41 and used as support for metallocene catalysts in ethylene polymerization.
Viscoelastic relaxations of four poly(butyl acrylate-
g-styrene) copolymers were studied over a wide range of temperatures. The temperature location and apparent activation energy of the distinct ...relaxations found are discussed. A single relaxation associated with cooperative motion has been observed in the range of graft content analysed. In addition, the stress–strain behaviour of these graft copolymers was studied. Films of the copolymer samples were stretched at room temperature since the possible application as adhesives might take place at about room temperature. Some mechanical parameters have been estimated, such as elastic modulus, tensile strength and toughness. Moreover, microhardness has been measured and its relationship with other mechanical properties has been established.
The CMS muon system Cerrada, M.
The European physical journal. C, Particles and fields,
07/2004, Letnik:
33, Številka:
S1
Journal Article
Recenzirano
Odprti dostop
AbstractAn overview of the CMS Muon Detector System design and goals is made. The system includes several types of detectors. In the barrel part Drift Tube Chambers are used, whereas Cathode Strip ...Chambers have been chosen for the endcaps. The main features, and the performance, of both types of chambers are described. We also report on the current status of the production of these detectors.
The influence of two thermal treatments on the structure, morphology, and ultimate properties exhibited by isotactic polypropylene (iPP), synthesized by conventional Ziegler–Natta iPP (Z-iPP) or ...metallocene iPP (m-iPP) catalysts, has been investigated in the present work. Novelty of this research consisted in the incorporation of a β nucleating agent in two different contents to the m-iPP. Results attained are compared with those found in the Z-iPP and important differences are observed. Differential scanning calorimetry and X-ray diffraction experiments revealed that coexistence of different crystalline lattices took place depending on the type of iPP: β and α forms were found in the β nucleated Z-iPP specimens, whereas α, β, and γ polymorphs could be developed in the m-iPP with nucleating agent. On the other hand, the iPP glass transition temperature (Tg) did not exhibit a significant change because of the addition of β nucleant, as deduced from Dynamic Mechanical Thermal Analysis (DMTA) analysis. Moreover, the size and shape of the iPP spherulites was totally changed by the presence of the β agent. This nucleant promoted the formation of smaller spherulites in a greater amount, as demonstrated by optical microscopy. Concerning the mechanical parameters, microhardness, MH, and Young modulus, E, values were in the fast crystallized samples lower than those presented by their slowly cooled counterparts. A good balance in properties was seen for the slowly crystallized m-iPP that incorporated a 5 wt% content in β nucleating agent, this fact being ascribed to the coexistence of the three α, β, and γ polymorphs.
This study investigates the synthesis, characterization and properties of isotactic polypropylene/graphene nanosheet nanocomposites (iPP/GNS). These nanocomposites were prepared by in situ ...polymerization using the metallocene complex rac-Me2Si(Ind)2ZrCl2 and methylaluminoxane (MAO) as cocatalyst. Homogeneous graphene nanosheet dispersions within the polymeric matrix were observed by TEM and XRD. The molecular characteristics of iPP, such as molecular weight, polydispersity and tacticity, were not affected by the presence of nanoparticles. The thermal properties investigated by DSC and TGA showed that graphene nanosheets significantly improved the matrix, increasing the crystallization and the degradation temperatures. From a mechanical perspective, there was an excellent balance between a significant increase in Young’s modulus and a slight reduction in the elongation at break. The reinforcing effect of graphene incorporation was confirmed by the increase of the storage modulus with nanosheet content. An enhancement of dimensional stability was also detected, and deformability was significantly smaller in the nanocomposites than in the homopolymer. Impedance measurements showed that the electrical conductivity increased by a factor of 108 compared to that of neat iPP.
While the inclusion of TiO
2 nanoparticles in either EVOH copolymer matrix or isotactic-polypropylene matrix induces the same elastic behaviour (a), the optical behaviour (b) presents a clear anomaly ...in the case of the TiO
2 inclusions in EVOH copolymer matrix (grey down triangles).
High resolution Brillouin spectroscopy (HRBS) backscattering elastic data in nanocomposites of ethylene–vinyl alcohol copolymer (EVOH) and TiO
2 nanoparticles present anomalous dependence with concentration, while Young’s modulus and microhardness data show the expected behaviour. When performing HRBS with the 90A scattering geometry to asses the effective elastic constant, the expected behaviour for low concentration of TiO
2 nanoparticles is again obtained. This unusual disagreement can be solved assuming that the inclusion of TiO
2 nanoparticles induces anomalous refractive index behaviour at the applied laser wavelength for the different EVOH–TiO
2 nanocomposites. Comparison with experimental elastic and optical data obtained in isotactic-polypropylene–TiO
2 nanocomposites proves that EVOH–TiO
2 nanocomposites show an unusual optical behaviour at the laser wavelength, possibly due to a singular bonding between the EVOH polymer and the TiO
2 nanoparticles.
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