Block copolymers are a class of materials that are particularly interesting with respect to their capability to self-assemble in ordered structures. In this context, the coupling between environment and dynamics is particularly relevant given that movements at the molecular level influence various properties of macromolecules. Mixing the polymer with a second macromolecule appears to be an easy method for studying these relationships. In this work, we studied blends of poly(methyl methacrylate) (PMMA) and a block copolymer composed of PMMA as the first block and poly(3-methyl-4-[6-(methylacryloyloxy)-hexyloxy]-4′-pentyloxy azobenzene) as the second block. The relaxational properties of these blends were investigated via electron spin resonance (ESR) spectroscopy, which is sensitive to nanometric length scales. The results of the investigations on the blends were related to the dynamic behavior of the copolymers. At the nanoscale, the study revealed the presence of heterogeneities, with slow and fast dynamics available for molecular reorientation, which are further modulated by the ability of the block copolymers to form supramolecular structures. For blends, the heterogeneities at the nanoscale were still detected. However, it was observed that the presence of the PMMA as a major component of the blends modified their dynamic behavior.

A study of local relaxation is presented in a series of poly(methyl methacrylate)s (PMMAs) of varying molar mass from oligomers to polymers. Decoupling phenomena from the viscous flow in the rotational relaxation at temperature T-c and violations of the Debye-Stokes-Einstein relation characterize the rotational dynamics of the series, also evidencing the influence exerted by the chain length on segmental relaxation. We discuss different dynamics regimes, coupling degrees of local relaxation to viscosity, and step-like behaviors with mass. The latter is a recurrent result in rotational relaxation and its dynamic parameters, discriminating the molecular-like behavior of the oligomers from a more specific polymeric response. Particular attention has been devoted to the onset of the Rouse dynamics in polymer samples. Scaling laws of the relaxation times with the mass are considered in the different temperature regions. Above T-c the results agree with the forecasts of the Rouse theory. Below T-c the scaling exponent could be accounted for by considering the Guenza theory of the cooperative interchain dynamics.

Current standards introduce different test methods to be used for the determination of the dynamic properties of polymers. Some of these have been applied in the last years for the evaluation of the thermoviscoelastic properties of interlayer in laminated glass. Even the latest draft standards, which provide test methods for the determination of mechanical properties of laminated glass interlayers, hesitate in providing a definite test procedure and thus allow the use of three different test methods depending on the kind of interlayer. Here, a short review of the test methods collected from the literature is proposed and some considerations are made regarding their strengths and weaknesses. The scope of studies surveyed does not claim to be exhaustive, but simply to be representative of the variety of procedures employed in research. The necessity is stressed to converge to as limited a number of test methods as possible that are also adequately simple and can therefore be applied in most research laboratories. (C) 2016 American Society of Civil Engineers.

Many studies reported in the literature are able to demonstrate significant influence of weathering on physical and mechanical properties of PVB. In this paper, the results of these researches are compared and discussed. The effects of rheological parameters modifications on the coupling capability of laminated glass structural elements and on the mechanical response to loads are then evaluated through numerical analysis. Real structures are often exposed to direct sunlight or to temperature or humidity levels that can induce damage phenomena in the interlayer; the modification of mechanical coupling capability and of adhesion properties of interlayer that effectively take place in laminated glass structures have to be taken into account in the design process as they probably affect the behavior of the structure not only in the serviceability state but especially in the ultimate limit state.

The dynamic response at nanometers and nanoseconds was investigated by electron spin resonance spectroscopy in random and block copolymers of an azobenzene methacrylate (MA4) and methyl methacrylate (MMA) with cholestane molecular tracer. The study evidenced the presence of different molecular sites for the reorientation at nanoscale, that were modulated by the amount of MA4 counits in the random copolymers and by the self-assembly in supramolecular structures in the block copolymers. A number of dynamics features was revealed, such as the presence of memory effects, the existence and the degree of coupling of the rotational dynamics to the structural relaxation of the matrix or to its viscosity, and the population of dynamic sites. This provided a detailed characterization of the mechanisms dictating the dynamic response of the structurally different copolymers. The influence of microstructure on the relaxation properties of the random copolymers was also discussed by considering the evaluated cooperativity coefficients, cooperativity indices, and packing lengths.

The shear rheological behavior is investigated in this work for a series of poly(ethyl acrylate) samples, whose molar mass ranges from oligomers to high polymers. The focus was on studying the onset of entanglement effects over selected reptation models in order to ascertain their ability to reproduce the complex shear modulus of the polymers and to provide consistent values of the microscopic parameters driving the structural relaxation of the polymer system. Among ordinary reptation topological models, we found that the Doi–Edward model, implemented with contour length fluctuation and constraint release mechanism for the tube relaxation, better reproduced the rheological response of the materials. Most importantly, we were able to simulate material functions to obtain consistent microscopic information on the materials, such as Rouse time and entanglement molar mass, over the whole range of investigated molar masses, therefore overcoming the discrepancy usually found, mostly in the mass region of partial entanglement. Finally, descriptions of the polymer entanglement features, in agreement with the experimental and microscopic model findings, are provided in the framework of the packing-length phenomenological model and by means of analytical calculations of the polymer viscosity according to the Milner–McLeish–Likhtman model.

Mechanical properties of interlayer polymers are recognized to be essential for a correct design of laminated glass structures. Although several researches have been carried out on the consequences of weathering actions on a laminated glass, few quantitative data on the properties of polymers are available. The response of structures to a long duration load is therefore evaluated taking into account the effects of viscosity of the interlayer, but in the hypothesis that the interlayer material does not degrade over time. In this paper the results are reported of an experimental analysis of the thermo-viscoelastic properties of polyvinyl butyral used as interlayer of laminated glass, subjected to weathering actions (humidity, thermal cycles and UV radiation). The results were interpreted in the light of the connection between microstructure and rheology of polymers, and highlight two different damage mechanisms, promoted in different extents by the different weathering actions.

The mechanical behaviour of laminated glass is strongly influenced by the coupling capability of interlayer that, in turn, depends on the shear modulus of the polymer. An accurate determination and a comprehensive description of the thermo-viscoelastic properties of polymeric interlayer is necessary to reliably predict the laminate behaviour in structural applications, both by simplified methods in which the mechanical behaviour of the polymer is described as elastic (“secant stiffness” approaches) and by step by step analysis, in which articulated load and temperature histories are reproduced. In this paper, a test procedure is proposed to perform dynamic tests on polymer interlayer, that revels to be more simple and more reliable than the procedures presently in use; the first results of an experimental analysis on polyvinyl butyral laminated glass specimens are reported and the generalyzed Maxwell constitutive model obtained from the tests on the material is compared with analogous models reported in the literature. Some case studies are considered in order to evaluate the influence of the assumed constitutive behaviour on the response of structural elements.

The shear rheological behavior was investigated in a series of high molar mass liquid-crystalline polymers (PMA4 homopolymer and copolymer samples) carrying an azobenzene mesogenic group in the side chains (MA4). The focus was on studying the entanglement effects and testing selected reptation models to ascertain their ability to reproduce the complex shear modulus of the copolymers. We found that ordinary dynamic models worked for the nematic PMA4 copolymers with methyl methacrylate (MMA), nicely reproducing the rheological response of the materials. We were able to obtain microscopic information on the materials, such as Rouse time and entanglement molar mass, in a consistent way, as well as to get insight on the macroscopic effects of tube dilatation induced by the nematic order on the master curves of the entangled polymers. Model improvements, accounting for the different nature of the counits, were also proposed in this work that singled out the friction coefficients of the counits MMA and MA4. The monomeric friction coefficient zeta(MA4)(0) was found to be constant throughout the series, (5 +/- 2) X 10(-9) kg s(-1). Likewise, zeta(MMA)(0) had the same value throughout the series, very similar to literature data for PMMA homopolymers, (2.0 +/- 0.6) x 10(-8) kg s(-1). Finally, in the framework of the packing-length model, constant packing lengths of 3.5 and 13 angstrom throughout the series were found for MMA and MA4 counits, respectively. Also, it resulted that the viscoelastic behavior of any PMA4 random copolymer could be predicted, provided that the response of the extreme homopolymers of the series has been characterized.

In this study for the first time we investigate the most common reticulated N-isopropylacrylamide (pNIPAAM) macrohydrogel for both its mechanical response and shear rheological behavior in time and frequency domains. Hydrogels are characterized by water content volume and weight measurements, FT-IR spectroscopy, scanning electron microscopy and reflecting index. Compressive uniaxial tests on equilibrated hydrogels individuate a hookean response within a 30% strain range with Ec modulus of 12.2kPa, and a neo-hookean response within a 79% strain range which upper limit corresponds to material rupture with Gc modulus of 3.8kPa. Tensile experiments performed for the first time on the pure material evidence a rupture limit for a strain around 30% with hookean modulus Et of 24.8kPa and neo-hookean modulus Gt of 7.3kPa. Rheological studies, carried out in linear response regime around the hydrogel swelling–deswelling transition, report relaxation times of the kinetics towards the equilibrium at different temperatures. The phase transition of pNIPAAM is monitored and the transition temperature is determined following the temperature dependence of the shear modulus. We apply different literature models to the rheological response and to the swelling–deswelling transition of the hydrogel. Finally, we analyze the results providing values for microscopic material parameters such as crosslink density and mesh size.

In this work, we provide more insight into the rheological properties of functionalized polypropylene copolymers with modified architectures, which originate long-chain branching. The evaluation of the average distance between branches and the fraction of long-chain branch points has been carried out quantitatively, by numerical fitting of experimental data according to a literature model, and the viscoelastic response of the samples has been analyzed in terms of a Carreau-Yasuda-like model and ColeCole plots. These analyses allowed us to discriminate the viscoelastic behavior of the samples on the basis of their feed composition. Moreover, we were able to highlight direct correlations between viscosity, long-chain branching level, distance between branching points and functionalization degrees of PP polymers. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

We report on the rheological investigation of a nematic block copolymer of an azobenzene methacrylate (MA4) and methyl methacrylate (MMA). Relaxation processes are discussed in terms of chain architecture and viscoelastic response of the polymer. In contrast to analogous random copolymers of MMA and MA4, the present block copolymer did not show validity of the time-temperature superposition (TTS) principle for all material functions. TTS was found to work only for the storage modulus. Rheological steady-state and oscillatory measurements were thus compared in order to obtain further insight into such a peculiar phenomenon.

The grafting of polar monomers to polyolefin backbones carried out in the melt in the presence of peroxides is accompanied by a restructuring of the pristine macromolecule architecture depending on reaction conditions and original polyolefin structure In the case of polypropylene (PP), side reactions, mainly degradation, are often controlled by the use of coagents which also provide a more complex scenario as far as possible reactions and final polymer structure are concerned We have demonstrated that 2 furyl acrylates are very active in maintaining the high molecular weight of PP during various functionalization processes carried out in the melt in the presence of peroxides In the study reported here, PP samples modified in the melt by free radical processes initiated with peroxides in the presence of butyl-3-(2-furyl) propenoate and its mixture with maleic anhydride were examined, and the effect of structural changes achieved were related to the rheology of the melt and morphological behaviour under heating Rheological analysis is consistent with the formation of long branched macromolecules to an increasing extent with increasing content of reagents with respect to the polyolefin Differential scanning calorimetry shows that the amount of long-chain branching is responsible for a decrease of the melting temperature and an increase of the crystallization temperature These results confirm that the functionalization coagent and monomer can give large macromolecule structure changes which can be driven in different directions depending on feed composition (C) 2010 Society of Chemical Industry

It is widely accepted that a temperature region exists above the glass transition temperature, playing a fundamental role in the physics of polymers and glass formers. In this region, several dynamic crossovers have been experimentally and numerically revealed in the past years and the onset of glassy behavior is generally located, because of cooperative and heterogeneous features exhibited by the dynamics. In this Article, the rotational dynamics of two different stiff molecular spin probes dissolved in poly(propylene glycol) has been investigated by electron spin resonance spectroscopy in a wide temperature range. Decoupling phenomena between macroscopic and microscopic transport properties have been observed in the crossover region. A comparison with previous studies carried out with the same tracers dissolved in different polymers and glass formers strongly supports the idea that the observed crossover signals the onset of spatial correlations of dynamics on the length scale probed by the tracers.

The rheological behavior of a nematic polymethacrylate containing an azobenzene side group was investigated. The time-temperature superposition principle was found to hold over a large temperature range, as no discontinuities were detected at the isotropic-nematic transition temperature, despite the relatively high molar mass of the polymer. A direct proof of the unentangled behavior of the polymer is provided, which stems from a dynamic model able to predict the relaxation mechanisms by simply knowing the molar mass distribution of the polymer sample.

The aim of this work is to explore the consequences on the kinetics of structural relaxation of considering a glass-forming system to consist of a series of small but macroscopic relaxing regions that evolve independently from each other towards equilibrium in the glassy state. The result of this assumption is a thermorheologically complex model. In this approach each relaxing zone has been assumed to follow the Scherer-Hodge model for structural relaxation (with the small modification of taking a linear dependence of configurational heat capacity with temperature). The model thus developed contains four fitting parameters. A least-squares search routine has been used to find the set of model parameters that fit simultaneously four DSC thermograms in PVAc after different thermal histories. The computer-simulated curves are compared with those obtained with Scherer-Hodge model and the model proposed by Gómez and Monleón. The evolution of the relaxation times during cooling or heating scans and also during isothermal annealing below the glass transition has been analysed. It has been shown that the relaxation times distribution narrows in the glassy state with respect to equilibrium. Isothermal annealing causes this distribution to broaden during the process to finally attain in equilibrium the shape defined at temperatures above Tg.