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Ultradrawing semicrystalline polymers is an intriguing approach to develop stiff, strong, and tough polymeric fibers. In the research field of polyurethane copolymer elastomers the term “soft segment” usually refers to the medium molecular weight glycol while the term “hard segment” stands for the urethane rich or isocyanate-short glycol segments. Here we investigate the influence of semiflexible segment content in the urethane rich phase on the mechanical properties and morphology of polyurethanes synthesized with a crystalline polyol as a “soft” segment. Materials with lower semiflexible urethane segment content developed stiffer and stronger materials upon drawing. This was related to greater soft segment crystallization along the draw direction. Materials with a higher fraction of semiflexible urethane segments were more elastic (higher yield strains and strengths) but exhibited more brittle-like fracture. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41281.

Bacterial cellulose (BC) with different morphologies was biosynthesized by Gluconacetobacter medellinensis strain under static and dynamic culture conditions using sugar cane juice and pineapple residues as sources of carbon and other nutrients. Hestrin and Schramm's standard culture medium was used as reference. The fermentation condition and resulting yield, physico-chemical properties, and morphology relationships of obtained cellulose were analyzed. Pineapple agroindustrial residues can be envisaged as an inexpensive and sustainable alternative resource for the production of different BC morphologies. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41237.

The impact of the incorporation of 10 wt.% of hydrolyzable chestnut tannin (CT) into pigskin gelatin (G) films plasticized with glycerol (Gly) on the physico-chemical properties as well as the in vitro antioxidant and antibacterial effectiveness against food-borne pathogens such as Escherichia coli and Streptococcus aureus was investigated. A higher tendency to both, redness (a*) and yellowness (b*) coloration characterized gelatin films incorporated with CT. The reduced lightness (L) and transparency of gelatin-CT films plasticized with 30 wt.% Gly might be associated with certain degree of phase separation which provoked the migration of the plasticizer to the film surface. The incorporation of CT and glycerol affected the chemical structure of the resultant films due to the establishment of hydrogen interactions between components as revealed by Fourier transform infrared spectroscopy. These interactions reduced gelatin crystallinity and seemed to be involved in the substantial decrease of the water uptake of films with tannin, irrespective of the glycerol level. Such interactions had minor effect on tensile properties being similar to those of the control films (without CT) at the same glycerol level. Films modified with 10wt.% CT showed significant (P

In the present work, thermoplastic maize starch based bionanocomposites were prepared as transparent films, plasticized with 35% of glycerol and reinforced with both waxy starch (WSNC) and cellulose nanocrystals (CNC), previously extracted by acidic hydrolysis. The influence of the nanofiller content was evaluated at 1 wt.%, 2.5 wt.% and 5 wt.% of WSNC. The effect of adding the two different nanoparticles at 1 wt.% was also investigated. As determined by tensile measurements, mechanical properties were improved at any composition of WSNC. Water vapour permeance values maintained constant, whereas barrier properties to oxygen reduced in a 70%, indicating the effectiveness of hydrogen bonding at the interphase. The use of CNC or CNC and WSNC upgraded mechanical results, but no significant differences in barrier properties were obtained. A homogeneous distribution of the nanofillers was demonstrated by atomic force microscopy, and a shift of the two relaxation peaks to higher temperatures was detected by dynamic mechanical analysis.

cited By 7; International audience; The layer-by-layer technique has been widely adopted for the fabrication of nanostructures with tailored properties. In this work, photoactive multilayer films consisting of alternating layers of chitosan and an azopolymer were developed by this method. Taking into account that pH is the factor controlling the charge of weak polyelectrolytes, the influence of this parameter on the structure and properties of the multilayer films was evaluated. Thus, different films were prepared by varying pH conditions as well as bilayer number. The morphology and properties of the films were analyzed by diverse advanced techniques, such as ultraviolet-visible spectroscopy, X-ray diffraction, and atomic force microscopy equipped with PeakForce QNM (Quantitative Nanomechanical Property Mapping). It was found that the thickness, roughness and elastic modulus of the developed multilayer films increased with the decrease of the chitosan solution pH and the increase of the bilayer number. Furthermore, induced birefringence measurements revealed that a higher level of photo-orientation was attained with the decrease of pH and the increase of bilayer number. © 2014 American Chemical Society.

Since polyol is one of the major components in polyurethane foam synthesis, introducing renewably sourced polyols in the foam formulation leads to materials with high renewable carbon content. A series of flexible polyurethane foams with variations in polyol composition were synthesized with castor oil based Lupranol Balance ® 50 polyether polyol and corn based polytrimethylene ether glycol mixtures. Water was used as the unique and eco-friendly blowing agent. The effect of the relative amount of each polyol on the structure and properties was analyzed by optical microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, tensile and compressive tests, dynamic mechanical analysis and atomic force microscopy. The average molecular weight and hydroxyl number of the polyol components showed to influence the foaming reaction and hence the structure and properties of the polyurethane foam. The newly developed peak force quantitative nano-mechanics technique was used to map the elastic modulus values of foam cell struts and it seemed to be adequate to assess the purity of the different phases. Authors thank financial support from University of the Basque Country (PIFUPV047/2011), Basque Government (IT776-13 and S-PE13UN091), Spanish Ministry of Economy and Competitiveness (MINECO) (IPT-2012-0728-420000) and European Union (PIRSES-2012-318996). Technical support provided by SGIker (UPV/EHU, MINECO, GV/EJ, ESF) is gratefully acknowledged. info:eu-repo/semantics/publishedVersion

A high-temperature thermosetting bisphenol-A dicyanate, BADCy was modified with polyetherimide, PEI, at various compositions. Phase separation and rheokinetics through curing were studied by optical microscopy, dynamic and isothermal differential scanning calorimetry, and rheological measurements. The PEI phase separated at the early stages of curing, well before gelation, and did not affect the polycyclotrimerization kinetics. The phase structure and thermal properties of the final network were investigated as a function of the PEI content and cure temperature. For this purpose, dynamic mechanical analysis, scanning electron microscopy studies, and thermogravimetrical analysis were carried out. The morphological changes were interpreted in terms of a spinodal decomposition mechanism in the composition range studied. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1037–1047, 2000

Chemorheology of curing as well as the phase separation behavior of polysulfone (PSU)-modified diaminodiphenylmethane-cureddiglycidylether of bisphenol-A epoxy mixtures have been studied using several techniques. The delay in polymerization for the modifiedmixtures with respect to that of the neat epoxy can be explained by dilution and viscosity effects. The immiscibility of these mixtures hasbeen proved for various PSU contents and as a function of the precuring conditions used as well. The control of the generated morphologiescan be performed only by varying the processing temperature. The thermal and dynamic viscoelastic behavior of the modified matrices hasbeen examined and compared to the parent epoxy matrix. Finally, the mechanical properties, including fracture toughness, have beendiscussed in terms of the morphological behavior for an epoxy matrix modified with various amounts of PSU and for a 15 wt.% PSUcontainingmatrix precured at different temperatures. Fil: Martinez, I.. Universidad del País Vasco; España Fil: Martin, M.D. Universidad del País Vasco; España Fil: Eceiza, A.. Universidad del País Vasco; España Fil: Oyanguren, Patricia Angelica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Mondragon, I.. Universidad del País Vasco; España

In the present work, the kinetics of the reaction of p-tolyl isocyanate with a polycarbonate diol has been studied, as a model for similar urethane systems. Liquid chromatography has been used to monitor the reaction, which allows direct measurement of the reaction of isocyanate group. The results obtained have enabled us to propose a reaction path and an autocatalyzed third-order kinetic model. Activation energy values have been determined from measurements taken at different isothermal temperatures.

This study deals with the dynamic mechanical properties of a glass-reinforced vinyl ester resin. The viscoelastic parameters of the loss factor and the storage modulus as a function of the cure temperature were used as a criterion to determine the optimum cure conditions to be employed. It is shown that the cure temperature usually used to cure these resins is not enough to reach the maximum glass transition temperature, and, therefore, an additional postcure should be used. The influence of several solvents on the dynamic mechanical behavior of these resins cured following the cure pathway proposed by the supplier was also analyzed. This behavior was compared with the solvent uptake at various exposure times, and the changes observed were related to the crosslink density as well as to the chemical structure of both the resin and the solvent. Finally, the effects of varying the exposure temperature were also investigated for the resin exposed to a liquid which simulates petroleum fluid. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2595–2602, 1998

Manipulation of nanoparticles is easier when they are appropriately functionalized with adequate chemical groups. In this work, multiwalled carbon nanotubes were functionalized with different chemical groups and the influence of functionalization on their stability in different solutions and the impact on elastomeric polyurethane composites were studied. It was observed that the functionalization yielded in all cases nanotubes with approximately the same dimensions (diameter: ∼8–40 nm; length: ∼1–25 μm) and 24–29 wt% of organic tallow per mass of nanotube. The chemical behaviour of nanotubes in solutions was highly dependent on functionality. The impact on mechanical properties was function of the chemical nature of the nanotube functional groups and moderately followed the expected tendency according to their solubility in solvents.

cited By 31; International audience; Shape-memory bionanocomposites based on a naturally sourced segmented thermoplastic polyurethane and chitin nanocrystals were synthesized, and their mechanical properties and thermally activated shape-memory behavior were studied. The chitin nanocrystals were incorporated during the synthesis of the prepolymer made from a castor oil-based difunctional polyol and hexamethylene diisocyanate. The polymerization was completed by addition of propanediol, as a corn-sugar based chain extender, bringing the weight content of components from renewable resources to >60%. Thermal analysis of the bionanocomposites revealed a phase-separated morphology, which is composed of soft and hard domains, which bestow the material with two melting transitions at 60 and 125 C, that are exploitable for a shape memory effect. The soft segment is responsible for temporary shape fixing, while the hard segment crystallites are responsible for the permanent shape. The introduction of small amounts (0.25-2 wt %) of chitin nanocrystals was found to increase the crystallinity of the hard segment by way of nucleation, which in turn improves the shape recovery considerably. The thermally activated shape-memory behavior of the synthesized bionancomposites is exploitable with a programming and release temperature of 60 C. The materials display good in vitro cell response, as shown by short-term cytotoxicity assays, and therefore, the bionanocomposites appear to be potentially useful for biomedical applications. © 2013 American Chemical Society.

In this manuscript mixtures of a poly(styrene)-b-poly(thiophene) (PS-b-PT) copolymer with fullerenes (C60) as a dopant were prepared in order to evaluate their optical/surface properties through optical microscopy (OM) and atomic force microscopy (AFM) measurements respectively, as well as their conductivity through the four probe technique under variable conditions such as: temperature (room temperature and 150 � C), solvent (toluene and chlorobenzene) and dopant concentration (2 and 5 wt %). The results exhibited that thermal treatment; solvent polarity and dopant concentration influence significantly the optical absorbance val- ues. Ultraviolet-visible spectroscopy (UV-Vis) was also adopted to examine the optical absorbance of the mixtures and how it can be affected by the structures obtained in each case. The results for the variables involved in this study were very interesting and led to significant conclusions concerning the potential application of the proposed mixture for improved organic solar cells. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40084.

CdSe nanoparticles with polystyrene (PS) brushes are obtained by "grafting through" technique starting from solely aqueously synthesized nanoparticles. Mercaptoethanol (ME) capped nanoparticles are used to achieve double bond functional groups on the surface by condensation reaction with methacryloxypropyltrimethoxysilane (MPS). PS polymerization starts from these double bonds. Spectroscopic, diffraction and thermal techniques are used to characterize the nanoparticles. Infrared spectroscopy shows the formation of robust bonding between CdSe nanoparticles and the organic ligand, as well as the presence of the functional double bond on the surface of nanoparticles. Thermal analysis reveals changes in thermal properties of PS, as thermal stability of PS in the functionalised nanoparticles is improved. UV-vis and fluorescence measurements show that PS-CdSe nanoparticles exhibit good optical properties and transmission electron microscope (TEM) micrographs shows good level of dispersion of CdSe nanoparticles in a PS matrix.

The surface morphology of poly(styrene-b-4 vinyl pyridine) (PS-b-P4VP) diblock copolymer thin films after solvent vapor annealing has been studied. Morphological features can be switched upon exposure to vapors of a solvent selective for one of the blocks. Self-assembled nanostructures such as hexagonal or striped morphologies were obtained varying vapor exposure time. In addition, the effect of the presence of CdSe nanoparticles located in the P4VP block on obtained nanostructures was analyzed. Atomic force microscopy (AFM) was used for morphological characterization of the block copolymer and the nanocomposites. AFM images showed that nanostructuring was different depending on the amount of CdSe nanoparticles, due to the decrease in P4VP chain mobility.

There has been a great deal of interest in the use of nanostructured bacterial cellulose membranes for biomedical applications, including tissue implants, wound healing, and drug delivery. However, as bacterial cellulose does not intrinsically present antimicrobial properties, in the present study, antimicrobial bacterial cellulose membranes were obtained by chemical grafting of aminoalkyl groups onto the surface of its nanofibrillar network. This approach intends to mimic intrinsic antimicrobial properties of chitosan. Interestingly, these novel grafted bacterial cellulose membranes (BC-NH2) are simultaneously lethal against S. aureus and E. coli and nontoxic to human adipose-derived mesenchymal stem cells (ADSCs) and thus may be useful for biomedical applications. In addition to these biological properties, the bioactive nanostructured BC-NH2 membranes also present improved mechanical and thermal properties.

An unsaturated polyester resin was cured with different catalyst contents. The crosslinking process was followed by static and dynamic viscosimetry and by differential scanning calorimetry (d.s.c.). Activation energies were determined from the gel times obtained by viscosimetry and from the variation in the maximum exotherm temperature obtained by d.s.c. at different heating rates. The existence of a threshold in the amount of catalyst to use is shown by analysis of the gel times. The effect of catalyst content on the glass transition temperatures of the different mixtures has been analysed taking into account the crosslink density, measured by means of the rubber modulus obtained by dynamic mechanical tests.

An investigation was carried out into the effect of amine/epoxy stoichiometry and thermal history during cure on physical and mechanical properties of epoxy networks. The formulation studied consisted of a diglycidyl ether of bisphenol A epoxy resin and 4,4′-diaminodiphenyl sulfone curing agent. The experimental matrix was based upon three amine/epoxy ratios and seven different thermal histories during cure. Techniques used included dynamic mechanical and fracture analysis, and Fourier transform infra-red (FTi.r.) spectroscopy. The highest glass transition temperature (Tg) was observed in the stoichiometric formulation and the lowest in the epoxy-rich mixture. For a given stoichiometry, the value of Tg, infinity was not a function of thermal history during cure except, interestingly, in the case when the initial temperature was 180°C. The highest rubbery state modulus and the lowest average molecular weight between crosslinks were also found in the stoichiometric formulation. Our findings were rationalized in terms of the varying degrees of crosslinking in different networks. The opposite trend was observed in the glassy state at 20°C, where the lowest flexular modulus belonged to the stoichiometric formulation. An explanation for those results was offered in terms of the free volume concept. FTi.r. analysis established clearly the existence of residual epoxy groups in all formulations, even after post-cure. Etherification reaction between epoxy and hydroxyl groups takes place during post-cure, but a complete conversion of epoxy groups cannot be attained owing to the topological constraints within the three-dimensional network in the later stages of cure. This finding is of particular significance in mechanistic kinetic models based upon the absolute value of epoxy concentration at all stages of cure.

Cellulose nanocrystals (CNC) successfully obtained from microcrystalline cellulose (MCC) were dispersed in a thermoplastic polyurethane as matrix. Nanocomposites containing 1.5, 5, 10 and 30 wt% CNC were prepared by solvent casting procedure and properties of the resulting films were evaluated from the viewpoint of polyurethane microphase separated structure, soft and hard domains. CNC were effectively dispersed in the segmented thermoplastic elastomeric polyurethane (STPUE) matrix due to the favorable matrix–nanocrystals interactions through hydrogen bonding. Cellulose nanocrystals interacted with both soft and hard segments, enhancing stiffness and stability versus temperature of the nanocomposites. Thermal and mechanical properties of STPUE/CNC nanocomposites have been associated to the generated morphologies investigated by AFM images.

Precursors of polyurethane chains have been reacted by means of in situ polymerization with organically modified montmorillonite clay to obtain polyurethane nanocomposites containing from 1 to 4 wt % of nanoreinforcement. The effective final dispersion of inorganic component at nanometric scale was investigated by X-ray diffraction, atomic force microscopy, and transmission electron microscopy. In addition, the effect of the nanoreinforcement incorporation on thermal and mechanical behavior of polyurethane nanocomposites was evaluated. Nanocomposites showed similar mechanical properties to polyurethanes containing high-hard segment contents with higher tensile modulus and a decrease in elastomeric properties of polyurethane materials. Finally, biocompatibility studies using L-929 fibroblast have been carried out to examine in vitro cell response and cytotoxicity of the matrix and their nanocomposite materials. Results suggested that the organic modifier in the clay is unsuitable for biomedical devices in spite of the fact that the matrix is a good candidate for cell adhesion and proliferation.

Polyols derived from renewables resources are good candidates to obtaining segmented polyurethane elastomers. Diisocyanates with different chemical structure, aliphatic and aromatic, have been used to synthesize by a two step polymerization procedure polyurethane elastomers with different hard segment content. Microphase separation and thermal stability have been studied using attenuated total reflection Fourier transform infrared spectroscopy (ATR‐FTIR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The analysis of the H‐bonded and non H‐bonded urethane carbonyl stretching vibration in the amide I region, the glass transition temperature of the soft and hard segments and the melting temperature and enthalpies of hard segment reveal that aliphatic diisocyanate based polyurethanes present higher phase separation degree and harder segment crystallinity and also superior thermal stability than aromatic diisocyanate‐based polyurethanes.

Advanced oxidation technologies (AOT) were applied for the production of accurately controlled oxidized multi-walled carbon nanotubes. Fenton process is effective to get carboxylic (-COO - or -COOH) and OH groups on the surface of carbon nanotubes while Photofenton and UV/H 2O 2 processes mostly produce OH groups on surface of multiwalled carbon nanotubes (MWCNT). All of them preserve the structure of MWCNT allowing to achieve accurately controlled oxidized MWCNT. Fourier transform infrared spectroscopy (FTIR) and thermogravimetical analysis (TGA) show that the acid treatment is the more efficient technique to generate COOH groups on MWCNT surface. However, this chemical technique generates strong damages on the MWCNT structure, as demonstrated by TGA, field emission scanning electron microscopy and transmission electron microscopy results. Copyright © 2009 American Scientific Publishers. Fil: Escobar, Mariano Martin. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Goyanes, Silvia Nair. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Corcuera, M. A.. Universidad del País Vasco; España Fil: Eceiza, A.. Universidad del País Vasco; España Fil: Mondragon, I.. Universidad del País Vasco; España Fil: Rubiolo, Gerardo Hector. Comisión Nacional de Energía Atómica; Argentina. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Candal, Roberto Jorge. Universidad Nacional de San Martín; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

This paper deals with the design of biopolymeric hydrogels after the chemical cross-linking of gelatin through the Diels–Alder (DA) reaction. Furan modified gelatin (Gel-FGE) was prepared by the reaction of furfuryl glycidyl ether with the free amino groups present in the gelatin. A Jeffamine®-based bismaleimide was employed as a cross-linking agent and the influence of the amount of cross-linker used on the final hydrogel properties was studied. The DA and retro-DA reactions were followed by ultraviolet spectroscopy and the final properties of the hydrogel assessed. Scanning Electron Microscopy was used to analyze the structure of the final material and rheology studies confirmed the formation of a chemically cross-linked network. The swelling behavior in response to external stimuli such as pH and salt concentration was also studied. By virtue of the DA “click” reaction, biopolymer-based cross-linked hydrogels, with promising properties for biomedical applications, were obtained in a simple one step procedure free of catalysts, additives or coupling agents.

A new family of segmented thermoplastic polyurethanes with thermally activated shape-memory properties was synthesized and characterized. Polyols derived from castor oil with different molecular weights but similar chemical structures and a corn-sugar-based chain extender (propanediol) were used as starting materials in order to maximize the content of carbon from renewable resources in the new materials. The composition was systematically varied to establish a structure–property map and identify compositions with desirable shape-memory properties. The thermal characterization of the new polyurethanes revealed a microphase separated structure, where both the soft (by convention the high molecular weight diol) and the hard phases were highly crystalline. Cyclic thermo-mechanical tensile tests showed that these polymers are excellent candidates for use as thermally activated shape-memory polymers, in which the crystalline soft segments promote high shape fixity values (close to 100%) and the hard segment crystallites ensure high shape recovery values (80–100%, depending on the hard segment content). The high proportion of components from renewable resources used in the polyurethane formulation leads to the synthesis of bio-based polyurethanes with shape-memory properties.

The industry decarbonization has become in a fundamental challenge for the industries such as automotive or wind power. In this way, the structural components lightening is one of the principal issues for material manufacturers. For this objective, the composites are a competitive alternative, due to their unique relation between their strength and weight. Among the different structural composite part fabrication processes, liquid composite moulding (LCM) is one of the most interesting, due to its efficiency in terms of costs, time and energy consumption. In this sense, resins with fast cure and low viscosity are gaining attention, among them polyurethanes are of particular interest. This family of polymers is characterized by its great versatility, among them high-performance thermosetting polyurethanes (PUR). The advantages offered by PUR-based technology are great fatigue resistance, low viscosity and fast cure. However, the commonly used PUR’s for structural applications have some environmentally drawbacks, such as their components petrochemical origin and their low recyclability. For this reason, the aim of this work was the development of a more sustainable PUR formulation with the required mechanical properties for structural applications and suitable processability for LCM processes. Because of that, this work has focused on the analysis, synthesis and characterization of new PUR formulations and also the manufacturing process simulation and optimization.

Se ha preparado mediante hilado fibras de alginato a partir de la coagulación de una disolución de alginato empleando como baños precipitantes soluciones de sulfatos de metales divalentes. Se ha estudiado el impacto de la naturaleza del catión, de la concentración de ZnSO4 en la capacidad coagulante, y capacidad de hilado, así como en la morfología de la fibra y sus propiedades mecánicas. Se ha estudiado también el ratio de postestirado en las propiedades finales. Las fibras se han caracterizado mediante microscopía óptica, espectroscopia infrarroja de transformada de Fourier, difracción de rayos X y mediante ensayos mecánicos de tracción uniaxial. Alginate fibers have been prepared through the coagulation-spinning method using different multivalent metal sulfate salts as coagulating agents. The impact of the nature of the cation, ZnSO4 concentration on the coagulating capacity, as well as on resulting fibers morphology and mechanical properties has been studied. The impact of the drawing ratio on the mechanical properties of the fibers has also been studied. The fibers have been analyzed by optical microscopy, Fourier transformed infrared spectroscopy, X-ray diffraction and mechanically through uniaxial stretching.

The effect of temperature on the curing kinetics of two unsaturated polyester resins has been studied by Fourier transform infrared spectroscopy. It has been found that at the beginning of the reaction, the kinetic mechanism was dominated by near-azeotropic copolymerization, while conversion of polyester vinylene groups became much more favourable than styrene later in the reaction. Both styrene and vinylene group conversion at the end of isothermal cures were a function of the styrene content in the resin. The experimental results have been related to the rheological changes during cure. Activation energies have been obtained from both rheological and thermal techniques.