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A reaction, combining labeled oligomers included in an anisotropic matrix, was monitored with small-angle neutron scattering. The initial "butterfly pattern" was strongly enhanced during the reaction, indicating that the growing branched structures are constrained to particular regions within the network. The real-time measurement was continued until the growing clusters had reached their final size. After removal of the constraints the sample completely recovered its original shape. The relaxed isotropic sample exhibits the history of its production bya highly anisotropic scattering pattern. It resembles ellipses whose longer axes are aligned along the stretching direction. [ABSTRACT FROM AUTHOR]

The structures and kinetics of the thermal degradation of three polymer networks have been studied. In the course of the thin polyurethane network degradation, the evolution of the MWD of polymer chains has a nonmonotonous character, but the sample mass decrease is described by the equations for two parallel first-order reactions. Activation parameters are shown to depend on the polymer curing conditions. The kinetics of the dense polymer network (the polymer of dimethacrylic ester of triethylene glycol, the epoxyanhydride polymer) degradation depends on the hardness of the polymer samples: soft polymer samples are degradated following a mechanism of radical-chain depolymerization, while for hard polymer samples the degradation proceeds mainly by a decay of unstable functional groups through a molecular mechanism. The results of an NMR study of molecular mobility during PTGM degradation are explained by the microheterogeneous structure of this polymer. It has been shown that the kinetic regularities of the dense polymer network degradation strongly depend on the presence of inert fillers. [ABSTRACT FROM AUTHOR]

The bulk PUs obtained with the use of diol and triol have been studied by electron microscopy. The fracture surface morphology of these samples has been compared. It has been found that the degree of crosslinking can be responsible for different mechanisms of fracture and, thus, various fracture curves are observed. The solvent cast PUs (obtained with the use of diol) have been studied by polarized light and electron microscopy. The birefringent and non-briefringent elements have been found under polarized light. Both appear to have a spherulite-like feature when observed under parallel polarizers and care must be taken in their interpretation. [ABSTRACT FROM AUTHOR]

A novel technique for the analysis of the molecular weight distribution functions of crosslinked polymer chains is proposed. The technique is based on the relation between the high-temperature nuclear magnetic resonance free induction decay and the network structure. The method is used to study thermally and mechanically activated degradation of polyesterurethane networks. [ABSTRACT FROM AUTHOR]

Polymer blends and semi-1-IPN's based on EVA and PMMA were evaluated with regard to phase dispergation and glass transition behavior. The size of the dispersed PMMA phase in melt-mixing blends, linear blends and semi-1-IPN's was examined. It can be concluded that the prepared blends and IPN's are phase separated, but in semi-IPN's the degree of dispergation is enhanced. The dependence of the glass transition temperature on the degree of crosslinking of EVA and the EVA content in the prepared blends and IPN's is discussed. [ABSTRACT FROM AUTHOR]

The paper demonstrates how a characterization of unfilled, amorphous rubber networks can be evaluated from uniaxial stress-strain measurement data. A network model is proposed that includes finite chain extensibility, topological constraints, and a trapped entanglement constribution to the reduced stress, which does not vanish in the infinite strain limit. Beside their influence on topological constraints, trapped entanglements are assumed to act like additional junctions, which also reduce the limiting extensibility of the network. In this framework a relation between the crosslink contribution and the topological constraint contribution to the reduced stress is derived, which allows the determination of the trapping factor from experimental stress-strain measurement data. The experimental results found for NR-networks cured with thiuram (TMTD) and peroxide (DCP), respectively, confirm the proposed model. It becomes obvious that the low topological constraint contribution found for the DCP-cured networks is related to a lower trapping rate, which results from main-chain scission during the curing procedure. [ABSTRACT FROM AUTHOR]

Fluorescence experiments were carried out on polymer films composed of poly (vinyl acetate) (PVAc, 91.7 mol%) and poly (2-methylhexyl methacrylate) (PEHMA, 8.3 mol%) (all the PEHMA present as a graft copolymer), which were prepared by solvent casting. The PEHMA phase was labeled with a low concentration (0.7 mol% PEHMA) of naphthalene groups. Exposure of the films to a pentane solution of 9-anthrylmethyl pivalate (AMP) transferred the AMP molecules exclusively to the PEHMA phase of the material. Direct energy transfer studies showed that the energy transfer rate was proportional to the AMP concentration, and that the process was characterized by an effective dimensionality $$\bar d$$ =1.3. This result can be explained by the Exponential Series Method (ESM) in terms of a crossover phenomenon in restricted geometries, if the PEHMA is present in the film in the form of interconnected, long, thein (ca. 25 Å diameter) cylinders. Supporting this idea is our finding that swelling agents for PHEMA such as hexadecane are also taken up by the film from pentane solution. Experiments on these materials give $$\bar d$$ values that increase with increasing hexadecane until $$\bar d$$ becomes equal to 3.0. These final results support the idea that PEHMA forms an interpenetrating network in glassy PVAc film. [ABSTRACT FROM AUTHOR]

Time-temperature dependence of mechanical loss factor and crack resistance parameters — critical stress intensity factor KIc and critical strain energy release rate GIc for the cured epoxy/amine polymer have been studied. Mechanical loss and crack resistance master curves have been obtained using time-temperature superposition principle. Activation energies fo relaxation processes and crack growth have been estimated. It was shown that the crack resistance is defined by the relaxation spectrum of the epoxy polymer. [ABSTRACT FROM AUTHOR]

Epoxy networks on the basis of diglycidyl ether of bisphenol-A (DGEBA) cured with aliphatic diols of different chain length in the presence of magnesium perchlorate or with 4,4′-diaminodiphenylmethane (DDM) and imidazole, respectively, were investigated by FTIR spectroscopy. The influence of the accelerator on the epoxy/amine system was studied. The addition of a low amount of imidazole leads to a decrease of the epoxy abssorption band at 915 cm−1 and to the appearance of a shoulder at 1132 cm−1 assigned to branched ether structures due to the reaction of epoxy groups with secondary hydroxyl groups. At higher concentrations only minimum changes of these bands are observed, but absorptions of unreacted amine functionalities near 3300 cm−1 remain in the spectra. — In the spectra of the epoxy/diol networks the epoxy bands have disappeared. The formation of ether structures indicated by absorption bands near 1120 cm−1 and the behavior of the hydroxyl band are strongly dependent on diol chain length and concentration. Only a small amount of diol is incorporated into the network by covalent bonding. The remaining diol acts as platicizer. [ABSTRACT FROM AUTHOR]

The peculiarities of highly crosslinked epoxy-amine polymer relaxation studied by pulse NMR method have been analyzed. A qualitative model of large-scale motion of highly crosslinked polymers based on the supposition of an anisotropic character of the interknot chain segmental motion and its dependence on the chain rigidity and connectivity of knots that adjoined to it has been developed. On the basis of this model the probable molecular and topological structure of epoxy-amine network fragments responsible for the α-relaxation has been given. The undissolved problems of highly crosslinked polymer α-relaxation have been discussed. [ABSTRACT FROM AUTHOR]

Quantum chemical investigations of the electronic structure of the design carbazole (Cz)-containing supermolecules, supramolecules, oligovinylcarbazole (OVK) and oligoepoxypropylcarbazole (OEPK) were performed in the framework of the semiempirical modified neglect of differential overlap (MNDO) method. The data obtained show that donor-acceptor properties of supermolecules: Cz-σ (or π) bridge-acceptors slightly depend on: 1) the number of alkane or alkene groups in the bridges, 2) the presence of π bonds, and 3) the various conformations in the bridge. Equilibrium distances between Cz and acceptor molecules in the supramolecular complexes and the sequence of the stability are found taken into account the oriented electrostatic attraction forces. There is a small charge redistribution in the ground state of the Cz-containing supermolecules and supramolecules. These designed derivatives are potential molecular photodiodes. The MNDO calculation data obtained show that the valence bands of the OVK and OEPK are narrow, therefore there is a electron hole hopping transfer mechanism in these systems. [ABSTRACT FROM AUTHOR]

A solution of polymer macromolecules in the presence of an external electric field is considered. Dipole-like interactions between polymer chain segment-vectors and the electric field are assumed to be proportional to cosv, where v is the angle between the segment-vector and the direction of the electric field. Parameters describing the local order at the segmental and chain level, i.e., moments of the first and second Legendre polynomials 〈P1(v)〉 and 〈P2(v)〉 are expressed as power series on parameter q, where q is the intensity of the external electric field in kT units. The optical anisotropy induced by the external electric field and the possibility of application of the Kerr equation for description of this effect are discussed. [ABSTRACT FROM AUTHOR]

The network formed by arm-linked charged polymer stars was considered as a model of a polyelectrolyte network with a large number of free branches. It is shown that the relation between the number of free branches and the number of charges on each branch determines the character of swelling/collapse transition caused by the decrease in the solvent strength: if the number of branches is small and the charge density is high, the collapse occurs as the first-order phase transition below the Θ-point, just as in ordinary polyelectrolyte networks. In the opposite case the collapse of the network occurs smoothly due to strong interchain interactions, the width of the transition range increases with degree of branching. In contrast to previous results, it is shown that under the conditions of good solvent the dependence of the network swelling coefficient on the solvent strength is always of the power character. This effect is independent of the number of free ends, but has different physical origin (intra- or interbranch interactions) in the cases of weak and strong branching, respectively [ABSTRACT FROM AUTHOR]

An interesting case of soft condensed matter are microemulsion-mediated polymer networks. Depending on the strength of the polymerwater or polymer-oil domain interactions, a variety of networks is formed extending from stable gels to fluids, displaying purely viscous flow. Details of the formation and properties of the networks formed will be discussed. Of particular interest is the regime of viscoelastic networks. It is tempting to compare experimental data from rheometric oscillatory measurements of such systems with predictions of the mode coupling theory. Preliminary results are presented. [ABSTRACT FROM AUTHOR]

A fundamental distinction between the mesophases formed by ABA triblock copolymers and by AB diblock copolymers is the bridging of A domains by B blocks. The ABA mesophases form physically crosslinked networks characterized by non-uniform spatial distribution of high-functionality crosslinks. The swelling of these networks by selective solvents gives rise to novel "mesogels". Three theoretical aspects of these systems, focusing on the lamellar case, are considered: i) The SCF theory of the equilibrium fraction of bridging chains in mesophases formed by a melt of ABA triblock copolymers. ii) The swelling equilibrium and the deformation behavior of mesogels swollen by a selective solvent for the B blocks. iii) The deformation behavior of lamellar gels immersed in a poor solvent for the B blocks. [ABSTRACT FROM AUTHOR]

The dependence of the elasticity modulus and the equilibrium swelling of the endlinked PDMS networks on the thermodynamical quality of the solvent in which the networks are formed and in which they swell is studied. The molar masses of crosslinked oligomers are 800 and 11000. the solvent quality is changed by the increase in the amount of nonsolvent in binary liquids mixture. The correlation between ternary phase diagrams and properties of swollen and dry networks (elasticity modulus, swelling, density) is established. The study of network deswelling in solvents of worsening quality shows that the abrupt collapse proceeds for the networks formed in good solvents at high dilution. The collapse results in an increase of the exponent value of the power law of elasticity modulus concentration dependence. [ABSTRACT FROM AUTHOR]

The effects of the physical and chemical networks on the relaxation processes and on the morphology of polyester-based polyurethane elastomers were studied by thermal, thermomechanical, and dielectric methods. Two series of polyester-based polyurethane elastomers were prepared by varying the NCO/OH ratio during the second step of polymerization while the hard segment content was maintained almost constant, at about 30% in the first series and at about 39% in the second. Differential Scanning Calorimetry (DSC), dielectric ac and Thermally Stimulated Depolarization Current (TSDC) measurements and Dynamic Mechanical Analysis show a main relaxation related to the glass transition of the soft parts of the polyurethane copolymers. The results of all the techniques used have shown that the increase of the NCO/OH ratio produces an increase in the glass transition temperature and a more homogeneous morphology. Dielectric ac and TSDC relaxation spectroscopy provided more information about the dynamics of the glass transition. [ABSTRACT FROM AUTHOR]

A new statistical theory of polymer networks is presented. In contrast to the Gaussian chain model, the idea of the theory is to include the effects of limited chain extensibility, stiffness, confiturational constraints of each network strand, and constraints of overall orientation. The theory uses the Roncal/Yoon worm-like chain model in spherical approximation. The configurational constraints are modeled by virtual tubes. The partition function of the network is formulated in single-chain approximation. The model describes, in a consistent manner, the fact that, at large extensions, the entropy decreases, and when the polymer is stretched out there is no further configuration left which the polymer can ocucpy. The elastic free energy and the stress-strain relationship are derived. The results show, for example, the typical upturn behavior in the Mooney-plot. The location of the upturn depends on the length of the network chains. Furthermore, it is shown how the action of configurational constraints becomes weaker in the case of predominance of shorter network strands and finite chain extensibility. The extension of the theory to the effects of constraints of overall orientation is discussed. [ABSTRACT FROM AUTHOR]

We describe and discuss the scattering l(q) of neutrons at small angle by polymer (polystyrene) networks containing either labeled (deuterated) solvent (i) or deuterated chains (ii) incorporated in the network before crosslinking, but not linked to the network ("trapped"). With labeling (i), the swelling of the gels above the volume of preparation always leads to an increase of the scattering. This is observed for gels synthesized in solution or close to the bulk state. With labeling (ii) (in undeformed state), the mixing of free chains is at random for light crosslinking. For increasing crosslinking, additional fluctuations appear and increase progressively up to complete phase separation. In deformed state (with labeling (ii)), the anisotropy is classical (elliptical, S(q‖) < S(qperp)) for short durations of relaxation after stretching. It is abnormal at low q(S(q‖) > S(qperp), "butterfly" shape) for long durations. We analyze the influence of the duration of relaxation, the crosslinking ratio, the molecular weight of trapped chains and the elongation ratio. We also show that only interchain scattering is responsible for the butterfly effect. Its origin is not attributed to a phase separation per se. We then discuss the effect of heterogeneities of crosslink density. A model where they would resemble percolation clusters, following random linking of blobs (many blobs per chain in a semidilute solution) is discussed. The structure of such clusters would be revealed by the disinterpenetration asociated with a spatial dilution, like by swelling or by stretching, in the parallel direction: in the latter case, this would indeed make parallel scattering grow. But this model does not apply to all situations observed. Another approach simply considers the mismatch between the anisotropy of the displacement of centers of mass of the chains and the weaker anisotropy of their own deformation. This model is still phenomenological. [ABSTRACT FROM AUTHOR]

The segmental orientational order generated in bimodal PDMS networks under uniaxial stress is probed, using deuterium-NMR (2H-NMR). The method consists in observing partially time-averaged nuclear (quadrupolar) interactions. The induced segmental order is measured on both kinds of network chains: "short" chains (Mn=3000) and "long" chains (Mn = 25 000). The order depends on the "long"-chain mass percentage ω (15% ⩽ ω ⩽ 80%). Moreover, for a given ω and a given applied stress the segmental orientation is very similar for both kinds of chains. This result is inconsistent with independent chain descriptions of networks. [ABSTRACT FROM AUTHOR]

Melts of polydimethylsiloxane, polyisoprene, polyisobutylene, and polyethylene were studied by the aid of proton relaxation spectroscopy predominantly using the field-cycling technique. Spin-lattice relaxation in the rotating frame (T1ρ) and transverse relaxation were investigated in addition. With spin-lattice relaxation the total frequency range was 103 to 3 · 108 Hz. Linear as well as cross-linked polymers with varying molecular weights and mesh lengths, respectively, were studied. Close to or above the critical molecular weight, peculiar frequency dependencies of the spin-lattice relaxation times were found which can be described by power laws ω1/4 or ω1/2. Depending on the molecular weight and the temperature, a crossover between these frequency dependences takes place. For low molecular weights and high temperatures the indication of a low-frequency plateau appears. Empirically the dispersion can be described well by the aid of the intensity function $$I(\omega ) = \frac{{I(0)}}{{1 + c_1 \omega ^{1/4} + c_2 \omega ^{1/2} }}$$ . The molecular weight dependences of the low-frequency spin-lattice relaxation times and of the transverse relaxation times suggest that the corresponding fluctuations have partly local and partly global features. The experimental findings are discussed in terms of the three-component scheme of chain fluctuations previously reported. [ABSTRACT FROM AUTHOR]

The segmental orientation of uniaxially strained cis-polybutadiene networks containing deuterated polybutadiene and filled with carbon black was probed by measuring the quadrupolar splitting in 2H NMR experiments. The quadrupolar splitting and the line shape are not influenced by the filler content. Possible reasons of this unexpected behavior are discussed. [ABSTRACT FROM AUTHOR]

A scale invariant model for the residual tensorial spin-spin couplings between nuclei has been used to investigate the NMR properties of deformed elastic networks. A general expression is derived which includes the effects of cross-link fluctuation dynamics and a non-isotropic deformation dependence of the fluctuation volume. The theoretical results are used to re-interpret the experimental results of Sotta and Deloche on the doublet structure observed in the 2H NMR spectra of deformed PDMS networks in terms of strain-dependent cross-link fluctuations. Previously, this feature has been used as evidence for an orientation-induced weak nematic network ordering. From the experimental results the magnitude of the junction fluctuations in the undeformed state is estimated to be approximately 1/3 of the phantom network result. Using a theory developed by Flory, these restricted junction fluctuations can be related to the elastic properties of the network. In particular, they were related to the deviations of the elastic modulus from the phantom chain result. When expressed in terms of the Mooney-Rivilin constants C1 and C2, the Flory theory together with the decuced value of the junction fluctuations obtained from the NMR results gives C2/C1=0.18. Using literature data, this value is in close agreement with the value C2/C1=0.21 obtained from mechanical measurements on almost identical networks. [ABSTRACT FROM AUTHOR]

The curing of bisphenol-A-diglycidylether with diaminodiphenylmethane has been investigated by monitoring the fluorescence decay of relaxing stilbazolium dyes. Because these compounds show a very strong viscosity-dependent fluorescence, it is possible to obtain information about the rotational mobility of the probe within the curing system investigated. The conversion degree of epoxy groups was determined by Raman spectroscopy. Further, the time of gelation was measured by a cycloviscograph (torque measurement). Results obtained by Raman spectroscopy and torque measurements are compared with data obtained by time-resolved fluorescence measurements. The fluorescence lifetimes measured during the curing process increase very fast near the gelation point. Investigations of the uncured system lead to the conclusion that two kinds of diffusion can be studied by using such probes: Stokes diffusion and diffusion into free volume. [ABSTRACT FROM AUTHOR]

Inverse gas chromatography (IGC) was used to observe the curing of non-modified and diol modified systems of epoxy resins on the basis of diglycidyl ether of bisphenol A (DGEBA). This method can be used for determining the gel point, the times of vitrification and curing of the respective system. The activation energy of the crosslinking reaction and the diffusion coefficients of the injected solvent in the curing and cured epoxy resins can be obtained by varying the conditions of gas chromatography. [ABSTRACT FROM AUTHOR]

Semiinterpenetrating polymer networks can be prepared by photopolymerization of epoxy acrylates in thin films of several polymers. The results on the polymerization kinetics give evidence of changes in kinetic relations during the entire polymerization process. Furthermore, the polymers formed at different conversion degrees were investigated using crystal violet as a fluorescence probe. The experimental data obtained by means of the fluorescence technique indicate that the polymerization process most likely takes place in a highly viscous medium. Towards the end, the reaction proceeds in a nearly glassy state until the polymerization is frozen. Results obtained by time-resolved fluorescence spectroscopy and dynamic reaction calorimetry are comparable with the data of the DSC experiments. [ABSTRACT FROM AUTHOR]

Pectins with degree of methylation lower than 50% are able to gel in presence of divalent ions such as calcium. A phase diagram of a sodium pectinate (DM=28%) in wate, pH 7.4, and 20°C was established, evidencing three phases: sol, gel, and syneresis. From rheological experiments, the calcium concentration at the sol-gel transition was determined, [Ca2+]t/[COO−] ≈ 0.168, for a polymer concentration of 5.8 g/l and it was shown that this transition was accurately described by the scalar percolation theory. Under the same conditions, potentiometric studies showed that the binding of calcium ions seemed to be independent from physical state (sol or gel). Furthermore, this calcium binding decreased only slightly with the amount of added calcium, whereas the sodium one decreased sharply in the same time. By following the evolution of the 23Na NMR longitudinal relaxation time, and abrupt increase was found around [Ca2+]t[COO−]=0.182, which was close to the results of the rheological study. [ABSTRACT FROM AUTHOR]

Amylose is known to dissolve in water at temperatures above 130°C. The literature unanimously reports that, provided the polymer content exceeds about 1%, any solution will form a gel upon cooling. The phenomenon is attributed to liquid-liquid phase separation followed by crystallization. In the present work, gels were prepared using carefully controlled thermal histories in sealed glass tubes. The crucial parameter is the dissolution temperature Td, i.e., the maximum temperature at which the solution was heated. If Td<160°C, a gel forms on cooling while amylose crystals precipitate out of solutions heated at higher temperatures. The effect of Td on the final macroscopic state of the system is independent of the polymer concentration (between 1% and 12%), the final temperature (between 2° and 45°C) or the cooling rate (between rapid quenching and 1°/h). Moreover, the thermal history effect was thermoreversible and unrelated to polymer degradation. Gels prepared using different Td were investigated by oscillatory shear measurements. The kinetics of gelation were strongly dependent upon Td, confirming that the thermal history should be carefully controlled in such studies. The observations suggest that amylose gelation involves crystallization and requires the presence of nuclei, whose number is determined by Td. Heating at low temperature (< 160°C) leaves a large number of nuclei in the solution. Upon cooling, a gel forms because the nuclei induce rapid crystallization, with any given chain involved in different crystals. In contrast, dissolution at high Td may yield complete melting of the nuclei, which induces a slower but more complete crystallization on cooling. [ABSTRACT FROM AUTHOR]

The data on chemical analysis, gel fraction, and TBA experiments have been used to identify chemical and physical transformations during the isothermal cure of three model reactive systems: trimethylolphenol, epoxy, and unsaturated ester, through condensation, addition, and free radical chain polymerization, respectively. For the first two systems cured by stepwise, statistically homogeneous reaction, TBA technique revealed physical gelation identified as 1,1-transition which proceeded and superimposed on chemical gelation and vitrification. In the unsaturated ester cured through heterogeneous (microgel) polymerization, microgelation and vitrification are associated with a space-filling packing of rubbery or glassy microgels, respectively. [ABSTRACT FROM AUTHOR]

Starting from a microscopical master equation for simple kinetic processes on a lattice (diffusion, aggregation, decomposition), an exact field theoretical representation for the gelation process was predicted. As a result of the renormalization group theory, one gets the critical dimension dc=6 and the same universality as in the random percolation for the diffusion limited gelation process and new universality class (also with dc=6) for the reaction limited gelation. [ABSTRACT FROM AUTHOR]

The relaxation behavior of networks, where the entanglement density is comparable with the crosslink density, can be explained by a broad distribution of the lengths of the network chains. A stretched exponential behavior is obtained with a fractional exponent of 1/3. — In the case of lightly corsslinked systems the influence of entanglements on the dynamics of a tagged network chain is investigated. It is assumed that the entanglement dynamics can be viewed as a cooperative stochastic process. A mode coupling ansatz is ued which yields nonuniversal scaling behavior of the characteristic relaxation time of the form: τN=τ0 · Ny, where the exponent γ depends on the averaged entanglement distance. Moreover, the relaxation function can be represented by a stretched exponential function: g(t) ∞ e−(t/GtN)β. The fractional exponent β also depends on the entanglement density. [ABSTRACT FROM AUTHOR]

Generally speaking, the law: G* ∼ G∞εtf(iω/ω*) with ω*=ω0εs+t, describes the viscoelastic properties near the gelation threshold. G* is the complex elastic modulus, ω* is the frequency associated with the longest relaxation time, and ε is the relative distance to the gelation threshold. G∞ and ω0 are linked to the local properties of the viscoelastic medium. At low frequency (ω < ω*), before the threshold, the viscosity diverges as (G∞ω0)ε−s while after the threshold, the elastic modulus emerges as G∞εt. At higher frequency (ω > ω*), before and after the threshold, one expects the complex modulus to be ε independent and to obey the frequency power law: G″=G′tg(πu/2)=G∞(ω/ω0)u, with u=t/(s + t). — Static properties of branched polymers near the gelation threshold are percolation-like, while dynamical properties and, more precisely, the s and t exponents values measured by different authors are very scattered. — We suspect that the frequency which describes local properties of polymers is not a constant ω0, but the frequency ωg associated with the glass transition. The frequency ωg decreases with increasing connectivity, which would lead to ε dependent prefactors of power laws and to non-universal apparent exponents. This could explain the apparent non-universality observed for the rheological properties near the gelation threshold. [ABSTRACT FROM AUTHOR]

Large-strain relaxation in permanent networks (natural rubber, PMMA) is explained by applying thermodynamics of irreversible processes and using the van der Waals network model. The memory function is shown to be strain-invariant. Independent Onsager processes characterized by the relaxation-time distribution are altogether coupled in the same manner to the global level. The macroscopically nonlinear response, including necking in the glass-transition regime is discussed. [ABSTRACT FROM AUTHOR]

The relationship between glass-transition temperature Tg, plateau modulus GN0, microstructure of different polymers (high cis-1,4-BR, NR, butyl rubber and various styrene-butadiene copolymers) and the wet skid resistance (WSR) of the corresponding filled treat compounds were investigated. Additionally, the relation between WSR and rolling resistance of vulcanizates was investigated. Both Tg and GN0 give only a poor correlation to the values of WSR. A good correlation is reached relating the WSR of elastomers to their total viscoelastic behavior in the glass-rubber transition zone. REalistic damping curves of the polymers in this region can be obtained within a bead-spring model of a tree-like entanglement network with a certain number of subchains. It is concluded that the high-frequency dependence of the loss curve is related to the local chain dynamics, whereas the cooperative large scale Rouse-like motion of many entangled strands dominates in the low-frequency region of the loss curve. In the surrounding of the loss maximum act both intra- and intermolecular correlations. [ABSTRACT FROM AUTHOR]

The effects of structural elements on the elastic behavior of networks is discussed. Heterogeneities of fractal nature embedded in networks will effect the elastic behavior and the neutron scattering as long as the fractal regions are not saturated. This saturation depends on the topology (connectivity) via the spectral dimension of the fractal. This has the effect that, if fractals are embedded in the network, their internal crosslinks do not count to the modulus if the fractals are saturated. The phase behavior of crosslinked blends and semi-interpenetrating networks is also discussed. For example, a critical crosslink density of thenetwork is found for which free chains solved in the network (semi IPN) are expelled from the network. [ABSTRACT FROM AUTHOR]

Photon correlation spectroscopy (PCS) and Brillouin spectroscopy (BS) are employed in the study of the local segmental dynamics in a 50/50 interpenetrating polymer network (IPN) of polyurethane (PUR) with poly(methyl methacrylate) (PMMA) in the temperature 140 to 390 K. The faster of the two primary relaxations present, due to the soft PUR component is studied by PCS and it exhibits broad distribution of retardation times. The Brillouin spectra of the present IPN exhibited significant hypersonic attenuation both above and below the glass transition temperature Tg of the PUR. [ABSTRACT FROM AUTHOR]

Networks of diglycidylether of bisphenol A and 4,4′-diaminodiphenylmethane in the presence of imidazole up to 2,5 mole-% and in the absence of an accelerator were investigated. Differences in network density, glass transition temperature, thermal expansion coefficient above Tg, and in the soluble part of the samples were found if an equimolar ratio of epoxy groups to amino hydrogen or an epoxy excess and different accelerator concentrations were used for network syntheses. Imidazole accelerates the conversion of epoxy groups, not only with amino hydrogen, but also with the hydroxyl groups formed. This is the reason for the differences in glass transition temperature, network density, thermal expansion coefficient, and soluble part between the samples investigated. [ABSTRACT FROM AUTHOR]

The thoeretical model of a polymer network with chemical and physical junctions is proposed on the basis of the statistical thermodynamic methods. Expressions for the average physical junction number and chemical potential of solvent in the swelling gel are obtained. Some interesting corollaries of these expressions are the non-linear character of the stess-strain dependence and the phase separation process in swelling gel. [ABSTRACT FROM AUTHOR]

The present work discusses structural properties of randomly crosslinked polymer melts. Using a method based on the burning method for percolation investigations, rubber networks can be characterized by their connectivity. We identify the elastically active crosslinks as well as the active polymer strands. This also reveals the effective length of the elastic strands, which turns out to be larger than the bare average strand length between two consecutive crosslinks within the percolating gel. [ABSTRACT FROM AUTHOR]

Kinetics and extent of equilibrium swelling of gelatin hydrogels formed under different conditions were studied as a function of polymer concentration φ, temperature of sol-gel transition Tg and aging time ta. It is shown that swelling kinetics can be described by the Peters and Candau approach. The extent of equilibrium swelling Qe is related to the conditions of gel formation by equation Qe∼ Φ1 − vta−0.15Tg0.1 where v=0.4. The last result is indicative of the applicability of Flory's classical theory to describe swelling of polymer gels formed by complex protein macromolecules. [ABSTRACT FROM AUTHOR]