Reactive processing of polymers:melt grafting of glycidyl methacrylate on ethylene propylene copolymer in the presence of a coagent

Glycidyl methacrylate (GMA) was grafted on ethylene-propylene copolymer during melt processing with peroxide initiation in the presence and absence of a more reactive comonomer (coagent), trimethylolpropane triacrylate (Tris). The characteristics of the grafting systems in terms of the grafting reaction yield and the nature and extent of the competing side reactions were examined. The homopolymers of GMA (Poly-GMA) and Tris (Poly-Tris) and the GMA-Tris copolymer (GMA-co-Tris) were synthesized and characterized. In the absence of the coagent, high levels of poly-GMA, which constituted the major competing reaction, was formed, giving rise to low GMA grafting levels. Further, this grafting system resulted in a high extent of gel formation and polymer crosslinking due to the high levels of peroxide needed to achieve optimum GMA grafting and a consequent large drop in the melt index (increased viscosity) of the polymer. In the presence of the coagent, however, the grafting system required much lower peroxide concentration, by almost an order of magnitude, to achieve the optimum grafting yield. The coagent-containing GMA-grafting system has also resulted in a drastic reduction in the extent of all competing reactions, and in particular, the GMA homopolymerization, leading to improved GMA grafting efficiency with no detectable gel or crosslinking. The mechanisms of the grafting reactions, in the presence and absence of Tris, are proposed.

Preparation of a poly(L-lactide-co-caprolactone) copolymer using a novel tin(II) alkoxide initiator and its fiber processing for potential use as an absorbable monofilament surgical suture

A poly(L-lactide-co-caprolactone) copolymer, P(LL-co-CL), of composition 75:25 mol% was synthesized via the bulk ring-opening copolymerization of L-lactide and ε-caprolactone using a novel bis[tin(II) monooctoate] diethylene glycol coordination-insertion initiator, OctSn-OCH2CH2OCH2CH2O-SnOct. The P(LL-co-CL) copolymer obtained was characterized by a combination of analytical techniques, namely nuclear magnetic resonance spectroscopy, gel permeation chromatography, dilute-solution viscometry, differential scanning calorimetry, and thermogravimetric analysis. For processing into a monofilament fiber, the copolymer was melt spun with minimal draw to give a largely amorphous and unoriented as-spun fiber. The fiber's oriented semicrystalline morphology, necessary to give the required balance of mechanical properties, was then developed via a sequence of controlled offline hot-drawing and annealing steps. Depending on the final draw ratio, the fibers obtained had tensile strengths in the region of 200–400 MPa.

Study of the kinetics and mechanism of rapid self-assembly in block copolymer thin films during solvo-microwave annealing

Microwave annealing is an emerging technique for achieving ordered patterns of block copolymer films on substrates. Little is understood about the mechanisms of microphase separation during the microwave annealing process and how it promotes the microphase separation of the blocks. Here, we use controlled power microwave irradiation in the presence of tetrahydrofuran (THF) solvent, to achieve lateral microphase separation in high- lamellar-forming poly(styrene-b-lactic acid) PS-b-PLA. A highly ordered line pattern was formed within seconds on silicon, germanium and silicon on insulator (SOI) substrates. In-situ temperature measurement of the silicon substrate coupled to condition changes during "solvo-microwave" annealing allowed understanding of the processes to be attained. Our results suggest that the substrate has little effect on the ordering process and is essentially microwave transparent but rather, it is direct heating of the polar THF molecules that causes microphase separation. It is postulated that the rapid interaction of THF with microwaves and the resultant temperature increase to 55 degrees C within seconds causes an increase of the vapor pressure of the solvent from 19.8 to 70 kPa. This enriched vapor environment increases the plasticity of both PS and PLA chains and leads to the fast self-assembly kinetics. Comparing the patterns formed on silicon, germanium and silicon on insulator (SOI) and also an in situ temperature measurement of silicon in the oven confirms the significance of the solvent over the role of substrate heating during "solvo-microwave" annealing. Besides the short annealing time which has technological importance, the coherence length is on a micron scale and dewetting is not observed after annealing. The etched pattern (PLA was removed by an Ar/O-2 reactive ion etch) was transferred to the underlying silicon substrate fabricating sub-20 nm silicon nanowires over large areas demonstrating that the morphology is consistent both across and through the film.

The morphology of ordered block copolymer patterns as probed by high resolution imaging

The microphase separation of block copolymer (BCP) thin films can afford a simple and cost-effective means to studying nanopattern surfaces, and especially the fabrication of nanocircuitry. However, because of complex interface effects and other complications, their 3D morphology, which is often critical for application, can be more complex than first thought. Here, we describe how emerging microscopic methods may be used to study complex BCP patterns and reveal their rich detail. These methods include helium ion microscopy (HIM) and high resolution x-section transmission electron microscopy (XTEM), and complement conventional secondary electron and atomic force microscopies (SEM and TEM). These techniques reveal that these structures are quite different to what might be expected. We illustrate the advances in the understanding of BCP thin film morphology in several systems, which result from this characterization. The systems described include symmetric, lamellar forming polystyrene-b-polymethylmethacrylate (PS-b-PMMA), cylinder forming polystyrene-b-polydimethylsiloxane (PS-b-PDMS), as well as lamellar and cylinder forming patterns of polystyrene-b-polyethylene oxide (PS-b-PEO) and polystyrene-b-poly-4-vinylpyridine (PS-b-P4VP). Each of these systems exhibits more complex arrangements than might be first thought. Finding and developing techniques whereby complex morphologies, particularly at very small dimensions, can be determined is critical to the practical use of these materials in many applications. The importance of quantifying these complex morphologies has implications for their use in integrated circuit manufacture, where they are being explored as alternative pattern forming methods to conventional UV lithography.

Formation of sub-7 nm feature size PS-b-P4VP block copolymer structures by solvent vapour process

The nanometer range structure produced by thin films of diblock copolymers makes them a great of interest as templates for the microelectronics industry. We investigated the effect of annealing solvents and/or mixture of the solvents in case of symmetric Poly (styrene-block-4vinylpyridine) (PS-b-P4VP) diblock copolymer to get the desired line patterns. In this paper, we used different molecular weights PS-b-P4VP to demonstrate the scalability of such high χ BCP system which requires precise fine-tuning of interfacial energies achieved by surface treatment and that improves the wetting property, ordering, and minimizes defect densities. Bare Silicon Substrates were also modified with polystyrene brush and ethylene glycol self-assembled monolayer in a simple quick reproducible way. Also, a novel and simple in situ hard mask technique was used to generate sub-7nm Iron oxide nanowires with a high aspect ratio on Silicon substrate, which can be used to develop silicon nanowires post pattern transfer.

Influence of additives on the performance of a PVDF membrane

The field of use of membranes is wide and ranges from the automotive industry to biomedical uses. Many formulations and compositions find a niche where they are able to improve efficiency, running cost and quality of the product. The aim of this research is to expand GVS’s product portfolio introducing a new membrane formulation. A series of additives were researched and evaluated, adding them to the membrane solutions, which were then cast and characterised using techniques like Scanning Electron Microscopy (SEM), poroscopy, FT-IT ATR and measurements like Water Break Through (WBT), Air Flow (AF), thickness. This study ultimately focused on one additive, which effect on the membranes was studied in various compositions. Interesting insights were also collected on the stability of the polymer solutions over time, which was found to change the membrane properties significantly, mainly affecting airflow and water breakthrough. Properties of the membranes were studied to find possible correlations to the amount of additive. The additive seems however to change the membrane porometry considerably depending on the time of immersion in the water bath. A new procedure to yield uniform unsupported polymeric membranes for tensile tests was developed. The additive was found to reduce elongation at break and decrease tensile strength of the membranes, possibly hinting toward plasticization of the product.

Scaffold piezoelettrici in PVDF/PCL per la rigenerazione del tessuto nervoso periferico

Le lesioni del sistema nervoso periferico, causate da eventi traumatici o da patologie degenerative, costituiscono un danno che può portare alla perdita di specifiche funzionalità motorie o sensoriali. In questi casi, la terapia chirurgica è necessaria per riparare la perdita di continuità assonale. Il gold standard operatorio attuale è costituito dal trapianto nella sede lesionata di un nervo da donatore o dallo stesso soggetto affetto dal danno. Recentemente, un approccio basato su tecniche di ingegneria dei tessuti propone l’impianto di biomateriali modellati come condotti che favoriscano la rigenerazione assonale. Ne è un esempio chiaro un recente lavoro di ricerca, nel quale Cheng et al. propongono una strategia basata sull’impiego di scaffold piezoelettrici prodotti attraverso una tecnica di "casting annealing displacement " che utilizza Polivinilidenfluoruro (PVDF) e Policaprolattone (PCL). Confrontando in vitro scaffold in PCL, in PVDF e PCL/PVDF, in particolare analizzandone le proprietà piezoelettriche e quelle meccaniche, si rilevano i vantaggi della copolimerizzazione. Questi risultati di interesse vengono inoltre confermati dai risultati funzionali ottenuti con l’impianto in vivo in topi con una lesione di 15 mm al nervo sciatico.

Corona Poling per film polimerici di P(VDF-TrFE): applicazione e ottimizzazione

Negli ultimi anni, il copolimero piezoelettrico P(VDF-TrFE), poli(vinildenfluoruro-trifluoroetilene), ha suscitato un grande interesse nella ricerca scientifica per le potenziali applicazioni elettroniche come, ad esempio, l’energy harvesting per la produzione di dispositivi indossabili e auto-alimentabili, sensori biocompatibili e memorie non volatili. In questo elaborato viene descritta l'indagine sperimentale di ottimizzazione eseguita su campioni di P(VDF-TrFE) polarizzati tramite la tecnica innovativa del corona poling, la quale è stata applicata con l'ausilio di una cella appositamente progettata per lo scopo. Questa tecnica si distingue dalle precedenti per il fatto che non sia necessario un diretto contatto tra gli elettrodi e il materiale da polarizzare. Per questo motivo essa presenta numerosi vantaggi rispetto alle tecniche tradizionali, riservando grandi potenzialità. I risultati sulla risposta piezoelettrica, matematicamente rappresentata dal coefficiente di deformazione d33 [C/N], dimostrano che sia possibile ottenere valori comparabili a quelli ottenibili con la tecnica tradizionale di DC poling.

Estudo inicial da degradação in vivo de poli(L-co-D,L ácido lático), sintetizado em laboratório, aplicado como prótese tibial em coelhos

The copolymer poly (L-co-D,L lactic acid), PLDLA, has gained prominence in the field of temporary prostheses due to the fact that their time of degradation is quite compatible with the requirement in the case of osseous fracture. In this work the in vivo degradation of devices from copolymer, as a system of plates and screws, used in fixation of the tibia of rabbits was studied. The devices were implanted in 15 adult rabbits, albinos, New Zealand race, and they were used as control devices of alloys of titanium (Ti-6Al-4V/ V grade). The use of copolymers, synthesized in the laboratory, was tested in the repair of fracture in rabbits'tibias, being assessed in the following times: 2 weeks, 2 months and 3 months. Morphological analysis of tissue surrounding the plate and screw system, for 2 weeks of implantation, showed the presence of osteoblasts, indicating a pre bone formation. After 2 months there was new bone formation in the region in contact with the polymer. This bone growth occurred simultaneously with the process of PLDLA degradation, invading the region where there was polymer and after 3 months there was an intense degradation of the copolymer and hence greater tissue invasion compared to 2 months which characterized bone formation in a region where the polymer degraded. The in vivo degradation study of the devices for PLDLA by means of histological evaluations during the period of consolidation of the fracture showed the efficiency of plate and screw system, and it was possible to check formation of bone tissue at the implantation site, without the presence of inflammatory reaction

Synthesis and structural characterization of block and random low molecular weight copolymers composed of L-lactic acid and isosorbide succinate moieties

Isosorbide succinate moieties were incorporated into poly(L-lactide) (PLLA) backbone in order to obtain a new class of biodegradable polymer with enhanced properties. This paper describes the synthesis and characterization of four types of low molecular weight copolymers. Copolymer I was obtained from monomer mixtures of L-lactide, isosorbide, and succinic anhydride; II from oligo(L-lactide) (PLLA), isosorbide, and succinic anhydride; III from oligo(isosorbide succinate) (PIS) and L-lactide; and IV from transesterification reactions between PLLA and PIS. MALDI-TOFMS and 13C-NMR analyses gave evidence that co-oligomerization was successfully attained in all cases. The data suggested that the product I is a random co-oligomer and the products II-IV are block co-oligomers.

On the stabilization of conducting pernigraniline salt by the synthesis and oxidation of polyaniline in hydrophobic ionic liquids

The electrochemical polymerization of aniline in a hydrophobic room-temperature ionic liquid and the spectroelectrochemical characterization of the formed film are presented. The polymerization occurs without the presence of acid in 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (BMMITFSI), leading to a very stable electroactive material where no degradation was observed even at high applied potentials. Both in situ UV-Vis and Raman spectroscopic studies provided evidence for the stabilization of pernigraniline salt at high oxidation potentials and that this polyaniline state is the conducting form, as was corroborated by in situ resistance measurements. These data are indicative that low conductivity is not an intrinsic property of pernigraniline salt and this point must be reconsidered.

Influence of the Solvent Evaporation Rate on the Crystalline Phases of Solution-Cast Poly(Vinylidene Fluoride) Films

The influence of the solvent-evaporation rate on the formation of of. and P crystalline phases in solution-cast poly(vinylidene fluoride) (PVDF) films was systematically investigated. Films were crystallized from PVDF/N,N-dimethylformamide solutions with concentrations of 2.5, 5.0, 10, and 20 wt % at different temperatures. During crystallization, the solvent evaporation rate was monitored in situ by means of a semianalytic balance. With this system, it was possible to determine the evaporation rate for different concentrations and temperatures of the solution under specific ambient conditions (pressure, temperature, and humidity). Fourier-Transform InfraRed spectroscopy with Attenuated Total Reflectance revealed the P-phase content in the PVDF films and its dependence on previous evaporation rates. Based on the relation between the evaporation rate and the PVDF phase composition, a consistent explanation for the different amounts of P phase observed at the upper and lower sample surfaces is achieved. Furthermore, the role of the sample thickness has also been studied. The experimental results show that not only the temperature but also the evaporation rate have to be controlled to obtain the desired crystalline phases in solution-cast PVDF films. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 785-791, 2010

Influence of EVA and acrylate polymers on some mechanical properties of cementitious repair mortars

In repair works of reinforced concrete, patch repairs tend to crack in the interfacial zone between the mortar and the old concrete. This occurs basically due to the high degree of restriction that acts on a patch repair. For this reason, the technology of patch repair needs to be the subject of a discussion involving professionals who work with projects, construction maintenance and mix proportioning of repair mortars. In the present work, a study is presented on the benefits that the ethylene vinyl acetate copolymer (EVA) and acrylate polymers can provide in the mix proportioning of a repair mortar with respect to compressive, tensile and direct-shear bond strength. The results indicated that the increase in bond strength and the reduction in the influence of the deficiency in Curing conditioning are the main contributions offered by the polymers studied here. (C) 2009 Elsevier, Ltd. All rights reserved.

Photodegradation of Thermodegraded Polypropylene/High-Impact Polystyrene Blends: Mechanical Properties

The influence of the addition of high-impact polystyrene (HIPS) on polypropylene (PP) photodegradation was studied with blends obtained by extrusion with and without styrene-butadiene-styrene (SBS) copolymer (10 wt % with respect to the dispersed phase). The concentrations of HIPS ranged from 10 to 30 wt %. The blends and pure materials were exposed for periods of up to 15 weeks of UV irradiation; their mechanical properties (tensile and impact), fracture surface, and melt flow indices were monitored. After 3 weeks of UV exposure, all of the materials presented mechanical properties of the same order of magnitude. However, for times of exposure greater than 3 weeks, an increasing concentration of HIPS resulted in a better photostability of PP. These results were explained in light of morphological observations. This increase of photostability was even greater when SBS was added to the blends. It was more difficult to measure the melt flow index of the binary PP/HIPS blends than that of PP for low concentrations of HIPS; this was most likely due to energy transfer between the blend domains during photodegradation. This phenomenon was not observed for the ternary blends. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 770-779, 2011