Focused on biomedical applications of thermo-responsive polymers, low-doses of gamma radiation from a Co-60 source were applied in a simple one-pot method to synthesize graft copolymers of alginate and poly(N-isopropylacrylamide) (PNIPAAm) with different compositions. The molar percentage of grafted NIPAAm (% molar NIPAAm) was determined by thermogravimetric analysis (TGA) and elemental analysis (EA), being the copolymer structure-property relationship studied in terms of thermo-associative and rheological behavior in aqueous solutions. The addition of more NIPAArn monomer in the initial mixture of reaction, as well as, increasing absorbed dose lead to a greater grafting. However, increasing radiation dose produces copolymers with diminished viscoelastic properties caused by the alginate backbone scission. From rheological curves, two transition temperatures, Ta and Tgel, were determined as a consequence of the thermo-responsiveness of PNIPAAm side chain. Storage (G') and loss (G '') modulus curves undergo a slope inversion at Ta temperature, where both moduli begin to increase caused by an associative behavior of PNIPAAm domains. While, Tgel temperature is related to the onset of the gelation process at the G'/G '' crossover. In order to design samples with liquid-gel transitions close to the human body, able to form gels in situ once inoculated, it was possible to tailor both transition temperatures selecting copolymers with an appropriate PNIPAAm content and optimizing the copolymer concentration in the aqueous solution. A good agreement between transition temperatures and viscoelastic properties was achieved for 5 wt% aqueous solutions of copolymers with low NIPAAm content synthesized at the lowest absorbed dose (0.5 kGy).

Synthesis of starch-graft-poly(-caprolactone) copolymers (St-g-PCL) was achieved under vacuum by employing low doses of 60Co γ-radiation. Irradiation synthesis was carried out by using glass vials containing gelatinized starch suspension and ε-caprolactone (-CL) monomer. Two starch:-CL mass ratios were employed 1:0.1 and 1:10. Irradiated samples were exhaustively treated with chloroform in order to remove homopolymer traces. Fourier transform infrared spectra of extracted samples showed a characteristic band associated to stretching vibration of carbonyl group, an indicative that PCL was grafted onto starch backbone. A grafting degree between 9 and 12% was achieved according to thermogravimetric analysis. Thermoplastic starch/PCL blends (TPS/PCL) with different amounts of St-g-PCL copolymers were prepared in order to test their thermal and mechanical properties. The addition of the synthesized copolymer did not show substantial changes over thermal properties, meanwhile significantly increased their maximum tensile strength and Young’s modulus since St-g-PCL enhances the interfacial adhesion between starch and PCL chains.

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.

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.

•Alginate-g-poly(N-isopropylacrylamide) (PNIPAAm) copolymers were synthesized.•Low doses of 60Co gamma radiation lead to thermosensitive water-soluble copolymers.•Hydrogels were formed using calcium ions to crosslink alginate-based copolymers.•Swelling ratios were lower at 37°C than at 24°C, due to PNIPAAm contribution.

Nowadays, the understanding of the interaction of ionizing radiations with polymeric materials is becoming increasingly important. It is well known that many parameters regarding the synthesis of the polymers noticeably affect the irradiation process. In this work, an analysis of the effect of the type and the position of unsaturations in the molecular structure of crosslinkable polymers is performed. For such purpose, two solid semycristalline metallocenic ethylene 1-olefin copolymers (mEOC) which contain a low concentration of unsaturations from the synthesis, and their hydrogenated samples, were irradiated along with liquid poly(dimethylsiloxane) (PDMS) homo and copolymers containing different location and concentration of vinyl groups, which were structurally tailored through anionic synthesis. The source of irradiation was 60Co, under vacuum at room temperature, in all the cases. The results indicated that terminal vinyls drastically accelerate the crosslinking to lower doses, even at much lower concentrations than other type and location of unsaturations for both, mEOC and PDMS, type of polymers.

Corn starch melt-processing in the presence of a commonly used plasticizer mixture (water/glycerol) and a non-conventional alternative (alginate/glycerol) was evaluated. All assayed formulations were successfully processed by melt-mixing and injected in circular probes. It was determined that all samples presented a typical viscoelastic behavior, observing a decrease in storage and loss modulus with water and alginate concentration, which facilitated samples processability. Concerning to thermal stability, it was not affected neither for water nor alginate presence. From injected probes, flexible films were obtained by thermo-compression. Films with the highest assayed water content presented a sticky appearance, whereas those containing alginate were non-tacky. Plasticizing action of water and alginate was evidenced by the occurrence of homogeneous fracture surfaces, without the presence of unmelted starch granules. Besides, the shift of glass transition temperature to lower values also corroborated the plasticizing effect of both additives. In conclusion, obtained results demonstrated the well-plasticizing action of sodium alginate on starch matrix, turning this additive into a promissory alternative to replace water during melt-processing of thermoplastic corn-starch.

Final properties of two thermoplastic corn starch matrices were improved by adding poly(epsilon-caprolactone), PCL, at 2.5, 5, and 10% w/w. One of the thermoplastic starch matrices was processed using water and glycerol as plasticizers (S-G) and the other one was plasticized with a mixture of glycerol and sodium alginate (SG,). Blends were suitably processed by melt mixing and further injected. Films obtained by thermo-compression were flexible and easy to handle. Microstructure studies (SEM and FTIR) revealed a nice distribution of PCL within both matrices and also a good starch-PCL compatibility, attributed to the lower polyester concentration. The crystalline character of PCL was the responsible of the increment in the degree of crystallinity of starch matrices, determined by XRD. Moreover, it was demonstrated by TGA that PCL incorporation did not affect the thermal stability of these starch-based materials. In addition, a shift of T-g values of both glycerol and starch-rich phases to lower values was determined by DSC and DMA tests, attributed to the PCL plasticizing action. Besides, PCL blocking effect to visible and UV radiations was evident by the incremented opacity and the UV-barrier capacity of the starch films. Finally, water vapor permeability and water solubility values were reduced by PCL incorporation. (C) 2015 Elsevier Ltd. All rights reserved.

The phase behavior for the very diluted DDAB-NaDHC-water system was investigated at 25°C. Fluorescence, conductivity, and surface tension experiments were carried out to determine the cac values. Comparison between experimental and calculated values shows the suitability of the regular theory to predict the critical aggregation concentrations for the tested systems. The interaction between both amphiphiles inside aggregates is not ideal, showing a large synergism. Such fact is reflected by the activity of coefficients values. The aggregates are mainly comprised by DDAB (18–30 % mol NaDHC) regardless of the NaDHC solution molar fraction; these molecules act as a good solvent of bile salt type molecule. Nevertheless, the gradual inclusion of NaDHC molecules inside DDAB bilayers leads to structural transformations. These facts are supposed to be due the combination of two effects: (i) the reduction of head groups hydration and (ii) the increment of chain repulsion.

Alginate is the generic name given to the salts of alginic acids. Alginic acids are polyuronides, i.e., polysaccharides molecules which are built up of uronic acid residues, molecules with a carboxyl group on the carbon that is not part of the ring, Commercial alginates are currently obtained by extraction from brown seaweeds such as Laminaria digitata, Laminaria hyperborea, and Macrocystis pyrifera. However, several bacteria such as the nitrogen-fixing aerobe Azotobacter vinelandii and the opportunistic pathogen Pseudomonas aeruginosa also produce alginate. Alginates are unique in terms of their properties such as emulsifiers, thickeners, stabilizers, gelling and film forming, resulting in several applications for the food and pharmaceutical industries. Alginate has been regarded as an excellent polysachaccharide for gel systems because of its unique features such as biocompatibility, biodegradability, immnogenecity, and non-toxicity. In the biomedical area, alginates have been used as devices in several human health applications, such as excipients in drug delivery (DDS), wound dressings, as dental impression materials and in some formulations preventing gastric reflux, among others. Main characteristics and chemical modification, along with some interesting properties and applications are reviewed along this chapter.

Anionic ring-opening polymerization (AROP) was employed for the controlled synthesis of linear model block copolymers of 1,3,5,7-tetrametil-1,3,5,7-tetravinyl(cyclotetrasiloxane) (V-4) and 1,3,5-dimethyl(cyclotrisiloxane) (D-3) monomers by using sec-butyl lithium (sec-Bu-Li+) as initiator, and high-vacuum anionic polymerization techniques. V-4 copolymerization was promoted by employing D-3 and sec-Bu-Li+ producing living silanolates that open the stable V-4 ring. For this purpose, two strategies were applied: (a) sequential addition of monomers, and (b) one-step copolymerization at different reaction temperatures. According to the experimental results, higher levels of V-4 incorporation (similar to 18.14 mol %) were obtained by mixing both co-monomers and performing the reaction at high temperature (80 degrees C). This strategy allowed the control of the V-4 incorporation into the copolymer structure, giving the opportunity of synthesizing model vinyl-siloxane polymers. The gamma radiation of these materials showed that lower doses are needed to achieve the same gel content as in a model poly(dimethylsiloxane) (PDMS). In such a sense, these results constitute one of the first reports regarding the effect of gamma radiation on vinyl-containing silicon polymers, and may be of fundamental importance if a biomedical cross-linked rubber-type PDMS is needed at earlier doses of sterilization. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Metallocenic polypropylene and copolymers with 3.7, and 9.2mol% of hexene and 3.0mol% of octadecene comonomer content were synthesized without the presence of additives and irradiated with 60Co gamma radiation under vacuum at room temperature. Size Exclusion Cromatography and gel extraction data showed that scission reactions predominate over crosslinking in the homopolymer and that there is a dose from where crosslinking started to increase considerably, in the irradiated copolymers. Rheology also showed evidence of chain-enlargements on the copolymers by means of an increase in the viscoelastic properties of the irradiated material.

Different molecular weight chitosans were evaluated on the decay of coated Anquito squashes (Cucurbita moschata) as well as the maintenance of the fruit quality along five storage months. The original chitosan (Mw=391kDa, 83% DD), was depolymerized by gamma radiation. Apart from chain scission, other chemical changes were not detected by FTIR or UV–vis analyses. The molecular weight characterization of chitosans was done by size exclusion chromatography with dual light scattering and concentration detection (SEC-MALLS-RI). The coating effectiveness was evaluated on the following parameters: fungal decay incidence, weight loss, firmness, total reducing sugar, soluble solid, flesh color, carotene content, pH and titratable acidity. No sign of fungal decay was observed in squashes coated with 122 and 56kDa chitosans, which were also the most effective treatments in reducing the weight loss. The chitosan with Mw=122kDa was also the best treatment considering firmness, internal aspect, sugar and carotene content. Then, radiation degraded chitosan was better in C. moschata preservation than the original chitosan.

An anionic almost monodisperse linear polydimethylsiloxane (PDMS) was subjected to gamma irradiation under vacuum at room temperature. The molecular weight changes induced by the radiation process have been investigated using size exclusion chromatography (SEC) with refraction index (RI) and multi angle laser light scattering (MALLS) detectors, to obtain the number and weight average molecular weights of the irradiated samples.The analysis of the data indicates that crosslinking reactions predominated over scission reactions. The results obtained by an SEC-RI have confirmed the presence of small, but measurable amounts of scission.A previously developed mathematical model of the irradiation process that accounts for simultaneous scission and crosslinking and allows for both H- and Y-crosslinks, fitted well the measured molecular weight data. This prediction is in accordance with the experimental data obtained by 29Si-Nuclear Magnetic Resonance spectroscopy (NMR) and previously reported data for commercial linear PDMS (Satti et al., 2008).

The aim of this work is to present a detailed study of the changes introduced by gamma radiation on several metallocenic polyethylene copolymers. Therefore, metallocenic polyethylene and copolymers with 3.3, 9.2, and 16.1 mol % of hexene comonomer content were synthe- sized and irradiated with 60 Co gamma radiation under vac- uum at room temperature with radiation doses ranging from 0 to 100 kGy. Size Exclusion Chromatography data show that crosslinking reactions predominate over scission, even for the copolymer with the highest tertiary carbon content. Over a certain critical dose, which depends on the molecular weight and molecular structure of the initial polymer, an insoluble gel forms. The irradiated polymers also exhibit complex rheological behavior with increasing melt viscosity and elasticity, consistent with long chain branching and/or crosslinking. FTIR confirms depletion of terminal vinyl groups and increase of trans unsaturations with dose. The rate at which these two reactions evolve seems to depend on the comonomer content of the irradi- ated copolymers. Differential scanning calorimetry and Raman spectroscopy analyzes indicate less crystallinity and thicker interphases in irradiated materials. A mathematical model, which accounts for scission and crosslinking reac- tions, fitted well the evolution with radiation dose of the measured molecular weight data. V C 2010 Wiley Periodicals,

Two different post reactor processes were compared, 60Co vacuum gamma irradiation and chemical modification with 2,5-dimethyl-2,5-di(tert-butylperoxy)-hexane (DBPH), on two metallocenic copolymers. These copolymers have a similar molecular weight and crystallinity, but different side chain lengths and concentration of end vinyl groups. The influence of the crosslinking agents on the structure of the samples was studied using gel extraction, size exclusion chromatography (SEC), FTIR spectroscopy and differential scanning calorimetry (DSC). The analysis of the data indicates that crosslinking reactions predominated over scission reactions in all cases. At the same conversion, peroxide modified samples show higher crosslinking levels than irradiated samples. The modified polymers show a complex rheological behavior and an increment in their rheological properties due to crosslinking. FTIR data demonstrated a depletion of vinyl terminal groups with the increment of the absorbed dose and the peroxide concentrations applied. This depletion was more significant in the peroxide crosslinked samples. A mathematical model that accounts for scission and crosslinking reactions fitted well the experimental data.

A commercial linear polydimethylsiloxane (PDMS) was subject to gamma irradiation under vacuum and in air, as well as to accelerated electron beam radiolysis (EB). All irradiation treatments were done at room temperature. The molecular weight changes induced by the radiation processes have been investigated using size exclusion chromatography (SEC) with refraction index (RI) and multi angle laser light scattering (MALLS) detectors to obtain the number and weight average molecular weights of the irradiated samples.The analysis of the data indicates that crosslinking reactions predominated over scission reactions in all cases. Gamma irradiation under vacuum was the most efficient process within the analyzed dose range, reaching the gel point earlier. Irradiation in the presence of oxygen induces oxidative effects, both in gamma and EB irradiations. A previously developed mathematical model of the irradiation process that accounts for simultaneous scission and crosslinking and allows for both H and Y crosslinks fitted well the measured molecular weight data. (C) 2008 Elsevier Ltd. All rights reserved.

Well-characterized linear ethylene-butene copolymers with polyclispersities lower than m were modified using gamma radiation and an organic peroxide with the purpose of assessing the relative importance and form of evolution of the chain-linking processes with these two methods. The copolymers used in this work were obtained by hydrogenation of polybutaclienes, which were synthesized by anionic polymerization of butadiene. Part of these materials were irradiated by gamma rays in a Co-60 radiation facility and the rest was modified with 2,5-dimethyl-2,5 di(terbutyl peroxy)-hexane in the molten state. As expected, the critical radiation dose and the critical concentration of peroxide required for the onset of gelation decreases with average molecular weight of the original copolymer. Although, the chain-linking reactions govern the modification process, there is a fraction of molecular chains that suffers scission. The measurable fraction of molecules having molecular weights lower than the original quasi-monodisperse copolymers is, for both processes, about 5% of the total modified polymer. on the post-gel region, the gel amount increases continuously with the radiation dose and the peroxide concentration added to the copolymers. For the radiation modified polymers, the calculation of the evolution of the molecular weights assuming ideal network forming conditions agreed very well with the experiments both, before and after the gel point. This is not accomplished when the modification process is done with the use of peroxides. Also, the results obtained from the peroxide modification processes at low relative concentrations with respect to the critical one for gelation show that the evolution of the structural modification evolves at a considerable lower rate than that observed in the radiation results.