In this study, nanocomposites based on polypropylene are synthesized by the in situ polymerization of propene in the presence of mesoporous SBA-15 silica, which acts as a carrier of the catalytic system (zirconocene as catalyst and methylaluminoxane as cocatalyst). The protocol for the immobilization and attainment of hybrid SBA-15 particles involves a pre-stage of contact between the catalyst with cocatalyst before their final functionalization. Two zirconocene catalysts are tested in order to attain materials with different microstructural characteristics, molar masses and regioregularities of chains. Some polypropylene chains are able to be accommodated within the silica mesostructure of these composites. Thus, an endothermic event of small intensity appears during heating calorimetric experiments at approximately 105 °C. The existence of these polypropylene crystals, confined within the nanometric channels of silica, is corroborated by SAXS measurements obtained via the change in the intensity and position of the first-order diffraction of SBA-15. The incorporation of silica also has a very significant effect on the rheological response of the resultant materials, leading to important variations in various magnitudes, such as the shear storage modulus, viscosity and δ angle, when a comparison is established with the corresponding neat iPP matrices. Rheological percolation is reached, thus demonstrating the role of SBA-15 particles as filler, in addition to the supporting role that they exert during the polymerizations.

Nanocomposites based on isotactic polypropylene (iPP) and mesoporous silica particles of either MCM-41 or SBA-15 were prepared by melt extrusion. The effect of the silica incorporated into an iPP matrix was firstly detected in the degradation behavior and in the rheological response of the resultant composites. Both were ascribed, in principle, to variations in the inclusion of iPP chains within these two mesostructures, with well different pore size. DSC experiments did not provide information on the existence of confinement in the iPP-MCM-41 materials, whereas a small endotherm, located at about 100 °C and attributed to the melting of confined crystallites, is clearly observed in the iPP-SBA-15 composites. Real-time variable-temperature Small Angle X-ray Scattering (SAXS) experiments with synchrotron radiation turned out to be crucial to finding the presence of iPP within MCM-41 pores. From these measurements, precise information was also deduced on the influence of the MCM-41 on iPP long spacing since overlapping does not occur between most probable iPP long spacing peak with the characteristic diffractions from the MCM-41 hexagonal nanostructure in comparison with existing superposition in SBA-15-based materials.

Different nanocomposites based on two isotactic polypropylenes (iPP) and mesoporous SBA-15 silica have been attained by melt extrusion as an attempt to understand the influence of average molecular weight in the rheological behavior, morphological and crystalline features and in the final properties (thermal stability and mechanical response) as well as in the capability of incorporating iPP chains within the nanometric SBA-15 pores. Closeness to rheological percolation and a significant increase of viscosity are observed as SBA-15 content is raised, this effect being more evident for the materials prepared from the iPP with the lowest molecular weight. These composites also shift their maximum degradation to lower values under inert atmosphere but keep rather unchanged decomposition behavior in oxidant conditions. No considerable changes are found with molecular weight in their morphological characteristics, nor in the type of iPP polymorph developed. The confinement of iPP chains in the SBA-15 channels, implied by a small endotherm in the DSC melting curves, is definitely ascertained by real-time variable-temperature Small Angle X-ray Scattering measurements with synchrotron radiation, suggesting, additionally, that somewhat thicker crystallites are developed within the mesostructure in the materials prepared from the iPP with inferior molecular weight. Moreover, the SBA-15 mesoporous particles exert a reinforcing role in all cases and reduce the deformation capacity of the ultimate materials as their content is increased.

Prodegradant additives (PDA) came up in the last few decades as a possible solution to the low degradability of polyolefins. PDAs attack polyolefins chains cutting and degrading them to a degree that eventually may allow phagocytosis by microorganisms. Also, considering that the PDA is added in very low quantities, main additives suppliers affirm that a priori they neither alter mechanical properties nor the recyclability of the polymer. In order to verify these claims, this work comprehends a systematic study to analyze the effectiveness of some commercially available PDAs on different polyolefins. Diverse degradability analysis of LDPE, HDPE and PP additivated with 1 and 2wt% of PDA were performed comparing changes on molecular weights, rheological and mechanical properties among them and base polyolefins, all under two kinds of experiments: natural and UV accelerated aging. It was found that the addition of PDA accelerates degradation since after both aging processes samples with PDA were significantly more degraded than base polyolefins under same conditions. Moreover, processing also contributes to the degradation process, being more noticeable in PP. However, results demonstrate that chain scission of polyolefins additivated with PDA is not being improved to an extent that would allow biodegradation.

ABSTRACTBranched polypropylenes (PPb) with markedly improved melt strength were produced without significantly affecting the processability of the original PP. A two‐step process of functionalization with MA and crosslinking with m‐XDA was used, both by batch mixing and by extrusion. Branching degrees of ~0.06 LCB/1000 monomer units or smaller were obtained. All PPbs display clear and significant strain hardening, being the PPb obtained by extrusion the one that shows the largest melt strength. This polymer has a zero‐shear‐rate viscosity slightly smaller than that of PP while its strain‐hardening index is about 10 times higher. Moreover, the nonlinear behavior of PP at elongation begins at a time similar to its terminal relaxation time or larger, while the ratio of these times reduces significantly with branching. PP/PPb blends were prepared to extend the range of obtainable melt strength in PP. They display rheological behavior between those of the mixed polymers with slight positive deviation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48845.

The influence of mesoporous SBA-15 on the thermal stability of nanocomposites with isotactic polypropylene has been evaluated in detail, both under inert and air conditions, by performing dynamic weight loss measurements and by tracking the evolution of degradation species in materials prepared by melt extrusion. A superior thermal stability has been found in the composites, both under nitrogen and air, compared with that observed in the pristine PP. An almost identical effect has been found under those two atmospheres, in spite that the mechanisms involved in both of them are completely different. The rheological characteristics of these materials turn out the driving aspect in the observed thermal behaviour, prevailing on other specific detrimental parameters.

Long-chain branched polypropylenes were synthesized from a maleic anhydride grafted polypropylene (PPg). Different levels of branching were generated by reactive processing using four chain-linking agents: glycerol, 1,4-butanediol, 1,4-phenylenediamine, and the epoxy resin bisphenol-A diglycidyl ether. The results from Fourier transform infrared and size-exclusion chromatography confirm the grafting of the chain-linking agents onto grafted polypropylene and the generation of long-chain branches. In addition, the rheological and morphological results show that 1,4-phenylenediamine produces the largest increment of branching at significantly lower concentrations than the other chain-linking agents. Moreover, 1,4-phenylenediamine gives place to branched polypropylenes with narrower distribution of molecular structures. [GRAPHICS] .

Spectroscopic features in the Raman spectra of semicrystalline polyolefins that characterize different phase morphologies are reported. With growing incorporation of different 1-olefins, changes in the spectra due to different short chain branches are identified for polyethylene and polypropylene, both isotactic and syndiotactic. Bands were assigned to crystalline, semicrystalline and amorphous contents, and quantification was approached with the use of internal reference bands. The degree of crystallinity and the conformational order of the copolymers decrease with the increase in short chain branches content, and the behavior of larger short chains is different depending on the type of polymer analyzed. A semi ordered interphase was found, assigned and followed in all cases, as well as the evolution of amorphous phase with comonomer incorporation.

Nanocomposites based on isotactic polypropylene (iPP) and different content of Al nanoparticles have been prepared in order to gain knowledge of their electromagnetic interference (EMI) shielding capability. This potential has been analyzed from attenuation upon reflection measurements at microwave frequency range. Moreover, shielding characteristics have been checked by Attenuated Total Reflectance (ATR) and correlated to the ones achieved by X-ray diffraction with synchrotron radiation. Very promising results have been obtained, with an excellent balance between shielding efficiency and sample weight. Hence, these materials are potentially good alternatives to replace metals for this application, avoiding electromagnetic environmental pollution. The effect of incorporation of Al nanoparticles on the iPP processing properties has been additionally evaluated by a rheological study at a very broad frequency range.

Blends and composites were obtained by mixing commercial metallocenic linear low density polyethylene (LLDPE) and isotactic polypropylene, with different molecular weight polydimethylsiloxanes (PDMS), including a vinyl ended PDMS. Gamma ray irradiation at different atmospheres was also applied in order to enhance blending by grafting and crosslinking of the radioinduced radicals. Dynamic rheological behavior results suggested that blending increased the viscoelasticity of the blends. Improvement and changes in the abrasive wear behavior was also followed, along with structural properties.

This work aimed to design and characterize cross-linked hyaluronic acid-itaconic acid films loaded with acetazolamide-hydroxypropyl beta cyclodextrin-triethanolamine complexes. Materials & methods: Films were cross-linked with itaconic acid and poly(ethyleneglycol)-diglycidylether. Biopharmaceutical properties were assessed by evaluating in vitro drug release rate, biocompatibility in a human corneal epithelial cell line, bioadhesiveness with pig gastric mucin, in vivo bioadhesion and efficacy. Results: Showed good mechanical properties and oxygen permeability. Proliferation rate of corneal cells was affected by highest acetazolamide concentration. Bioadhesive interaction exhibited a water movement from pig mucin to the film; in vivo experiments showed strong bioadhesion for 8 h and hypotensive effect for almost 20 h. Conclusion: Experimental set showed promising performance and encouraged future studies to optimize formulation.

In this paper, the abrasive wear behavior of different metallocenic isotactic propylene homo and copolymers was studied along with their mixtures with siloxane based polymers. These mixtures were prepared with poly(dimethylsiloxane) homopolymers of different molar masses, and a block copolymer with ε-caprolactone. The crystallinity degree of the samples, as well as their thermal, mechanical and rheological properties was also studied in order to infer the effect of the presence of the PDMS based additives in the mixtures. Wear rate was decreased in most of the cases, and a dependence with the molecular architecture of the additives was observed.

Ring-opening homo- and co-polymerization reactions of ϵ-caprolactone were performed by employing anionic polymerization (high vacuum techniques) and lithium silanolates (LS) as initiators. LS were obtained by reaction between hexamethyl(cyclotrisiloxane) and sec-Bu–Li+, or from living poly(dimethylsiloxanyl)lithium chains. The results indicated that LS are efficient initiators for the ring-opening polymerization of ϵ-caprolactone, providing the respective homogeneous polymers in good yields.

A reaction between a linear polypropylene functionalized with maleic anhydride (PPg) and epoxy resin (bisphenol A diglycidyl ether) was carried out on the molten state to generate long-chain branches (LCB) in the molecular structure of the PPg. Concentrations of epoxy resin (ER) of up to 3.15 wt% were employed to obtain different levels of branching. FTIR spectroscopy analysis indicates that during the reaction, anhydride groups in PPg are consumed and new ester groups are formed. The presence of branches was verified using multiple-detection size-exclusion chromatography and rheology. The degree of long-chain branching induced in PPg augments with increasing concentration of ER. Furthermore, the materials modified with higher content of ER display gel-like behavior. The long-chain branched polymers also display thermo-rheological complexity. Thermal characterization studies show that LCBs have a nucleating effect during crystallization and cause the augment of the crystallization activation energy of PPg.

Trapped entanglements, cross-linker functionality, and elastically effective chains are the sources of elasticity of polymer networks and gels. However, despite more than 80 years of theoretical and experimental research in this field, still little is known about their relative contribution to network elasticity. In this work, we use double quantum nuclear magnetic resonance (DQ NMR) experiments to characterize the elasticity of model polymer networks prepared with cross-linkers of mixed functionality and control of structural defects. An order parameter that condensates the elastic response within the theoretical framework of the entangled phantom theory for rubber elasticity was identified. Standard lore dictates that low molecular weight precursors for the elastically active chains leads to a negligible contribution of trapped entanglements. Here we show that the contribution of trapped entanglements may equal the contribution coming from elastically active material and that it is independent of network topology.

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.

This work covers the synthesis and characterization of in-reactor Ultra-High Molecular Weight Polyethylene/ High Density Polyethylene, UHMWPE/ HDPE, blends by in situ polymerization in a single reactor, through dual catalyst immobilization. These blends are synthesized combining two different catalysts (one for each targeted molar mass) co-im-mobilized in mesoporous Santa Barbara Amorphous, SBA-15, particles. First, the ethylene polymerization behavior is investigated, under different polymerization conditions. Then, studies on the thermal, mechanical and rheological characteristics of the produced in-reactor blends are presented and their performance is compared and discussed in a comprehensive way. Moreover, the effect of different filler contents on the properties exhibited by the resulting materials is investigated. Results have shown that these in-reactor UHMWPE/ HDPE blends exhibit a complex thermal, mechanical and rheological behavior, which depends mainly on the proportion between the two polymer components and on the amount of SBA-15.

Se estudió la síntesis de copolímeros bloque de poli (estireno) y poli (metil metacrilato) (PS-b-PMMA) empleando polimerización radicalaria por transferencia atómica (ATRP). Se realizaron distintos experimentos variando las relaciones molares de monómero, ligando e iniciador para determinar su influencia en la síntesis de copolímeros PS-b-PMMA con masas molares determinadas y estructura homogénea. Los polímeros sintetizados se caracterizaron químicamente por espectroscopia infrarroja con Transformada de Fourier (FTIR) y cromatografía por exclusión de tamaños (SEC), empleando un detector de índice de refracción. Se obtuvieron los copolímeros bloque propuestos, con un buen control de su estructura macromolecular (Mw/Mn < 1,90).

The successive self nucleation and annealing (SSA) methodology has been shown to be successful to characterize the lamellae structure of many polyolefins. The differences in molecular structure of metallocenic α-olefin copolymers with varied comonomer type and content were characterized by this technique with a conventional DSC. This thermo-structural characterization process was also applied to analyze the changes induced on a 1-octadecene - ethylene copolymer modified with different post-reactor methods: several doses of gamma-radiation, peroxide modification and oxidative degradation. These modifications induced crosslinking and branching on the original copolymer affecting its molecular weight and the crystalline structure. The SSA technique revealed detailed changes in the lamellae formation of the materials obtained as a consequence of the different methods of modification employed in this work. Mainly, crosslinking and branching sites restrained the mobility and length of CH2 sequences to form lamellae, while degradation led to preferential chain scission at branched carbons making easier the formation of higher melting temperature lamellae.