Properties Of Polymer Networks Research Articles

Numerical studies of polymer networks and gels

The elastic and relaxational properties of polymer networks are strongly influenced by quenched disorder, introduced by the crosslinks in the systems. By extensive computer simulations of appropriately tailored model systems these effects can systematically be investigated.

Monte Carlo Simulations on Polymer Network Deformation

We present a new methodology for the investigation of elastic properties of polymer networks. The calculation of the stress-strain relation in simple extension is performed in the framework of a highly flexible lattice Monte Carlo algorithm. The essential features of a network, namely, excluded volume of effective monomers, conservation of topology, noncrossability, and finite extensibility of the network strands, are rigorously accounted for during the dynamics. Analysis of the structure revealed pronounced nonaffine and inhomogeneous deformation behavior.

Formation, structure and properties of polymer networks

AbstractThe systematic study of intramolecular reaction and gel points together with measurements of moduli of trifunctional and tetrafunctional end‐linked networks show that gel points are always delayed and network imperfections always result from the intramolecular reaction which must occur when such networks are formed. The quantitative interpretation and prediction of gel points and moduli directly from reactant structures and reaction conditions are discussed.

Coupling of liquid crystalline and polymer network properties in LC-elastomers

Abstract Electromechanical and electro-optical properties which result from an interplay of ferroelectricity and elasticity in slightly crosslinked ferroelectric liquid crystalline elastomers are studied in the vicinity of the smectic C-smectic A phase transition. In the chiral smectic C phase, the formation of the network during the crosslinking procedure stabilizes the polar orientation which is present. On heating the smectic C network into the chiral smectic A phase, an induced tilt is observed (mechanoclinic effect). The internal mechanical stress induced by the network formation appears to act like an external electric bias-voltage. The results are discussed in terms of a simple Landau model.

Elastic Properties of Polymer Networks

Many fundamental questions for the understanding of polymer melts and networks are more suitably addressed by current computer simulations than by experiments. The reason is that simulations have simultaneous access to the microscopic structure and the macroscopic behavior of well-defined model systems. The coarse-grained models used often bear little relation to actual chemical species. This is justified by the experimentally established universality of polymer dynamics and no limitation for the test and development of theories which are directed at these universal aspects. The difficulties already encountered on this level will be illustrated for entanglements between polymers which dominate the dynamic in dense systems.

Monte‐carlo modelling of the formation, structure and properties of polymer networks

AbstractA new Monte Carlo (MC) algorithm is reported which enables RAfa +RBfb polymerisations to be simulated. It is based on the random reaction of pairs of groups for intermolecular reaction, with intramolecular reaction weighted according to Gaussian statistics and the size of ring structure being formed. The algorithm counts all the ring structures formed and enables polymerisations to be simulated efficiently up to complete reaction. Gel point and modulus results from trifunctional and tetrafunctional polyurethane‐forming polymerisations are modelled, with particular emphasis on the effects on modulus of network defects at complete reaction. More in keeping with experiment, higher reductions in modulus at complete reaction are predicted using the the present algorithm than using Biosym MC software. However, it is shown that quantitative agreement with experiment cannot be obtained unless relationships defining the entropies of various ring structures are elucidated and more accurate modelling of the chain statistics governing the intramolecular reaction forming ring structures of various sizes is used.

The influence of the molecular weight distribution of network chains on the mechanical properties of polymer networks

End-linked poly(dimethylsiloxane) (PDMS) networks with different molecular weight distributions (MWD) of the primary chains were prepared and investigated by isothermal stress-strain measurements. We found a lowering of the elastic modulus with increasing broadness of the MWD. The observed range of the moduli seems not to be restricted to the region limited by the classical models of rubber elasticity. This result is based on our own experimental investigations and on a reanalysis of data taken from the literature. In the case of nearly monodisperse distributions (M n /M w ≲1) the effect of configurational restrictions of the network strands probably dominates. In the opposite case (M n /M w ≪1), we discuss that spatial clustering of the crosslinks may reduce the effective number of elastically active network junctions.

Drug Delivery Systems: 3B. Role of Polymers in Drug Delivery

At present, polymers represent a class of ubiquitous materials. They are being used for a multitude of purposes and the almost inexhaustible varieties of molecular architecture that macromolecular materials can possess provides the possibility for a myriad of applications. Because of the increased interest being shown in the macromolecules by the pharmaceutical industry for the fabrication of drug delivery systems, numerous polymers have been synthesized and successfully used in drug delivery devices. The necessary conditions for developing the concept of pharmaceutically applicable polymers depend upon delineating a detailed knowledge of the relationship between the structure and properties of polymer networks. A number of polymers have been studied systematically from this point of view and there is every indication that the systems described have the potential to become clinically valuable and therefore marketable drug delivery systems. The potential of these promising polymers is still far from being exhausted and there is a strong possibility that many important developments will be forthcoming in this field in the future. In the current review article, polymers for controlled release have been divided into four major categories: diffusion-controlled systems; chemically controlled systems; solvent-activated systems; and magnetically controlled systems. Polymers as drug carriers also have been divided into various subgroups: soluble, biodegradable, mucoadhesive and other polymeric systems. The latter group includes polymers containing pendant bioactive substituents, matrix systems, heparin-releasing polymers, ionic polymers, oligomers and miscellaneous. At an introductory and fundamental level, an overview of these polymers and the materials science for the design of drug delivery systems will be discussed.

Influence of crosslinking density on the properties of polymer networks

The density, refractive index, glass-transition temperature, and the equilibrium modulus of elasticity have been calculated for polymer networks differing in their chemical nature and having different amounts of repeat-units in the fragment between crosslinks. The networks studied were based on PE, on the copolymer of styrene with divinylbenzene and sulphur vulcanized polyisoprene. When the number of repeat-units in the fragment is reduced to five or less, a marked change in the above listed physical characteristics was observed for all the systems under review. This change is attributed to a transition from sparse networks to dense ones.

Drug Delivery Systems: 3A. Role of Polymers in Drug Delivery

At present, polymers represent a class of ubiquitous materials. They are being used for a multitude of purposes and the almost inexhaustible varieties of molecular architecture that macromolecular materials can possess provides the possibility for a myriad of applications. Because of the increased interest being shown in the macromolecules by the pharmaceutical industry for the fabrication of drug delivery systems, numerous polymers have been synthesized and successfully used in drug delivery devices. The necessary conditions for developing the concept of pharmaceutically applicable polymers depend upon delineating a detailed knowledge of the relationship between the structure and properties of polymer networks. A number of polymers have been studied systematically from this point of view and there is every indication that the systems described have the potential to become clinically valuable and therefore marketable drug delivery systems. The potential of these promising polymers is still far from being exhausted and there is a strong possibility that many important developments will be forthcoming in this field in the future. In the current review article, polymers for controlled release have been divided into four major categories: diffusion-controlled systems; chemically controlled systems; solvent-activated systems; and magnetically controlled systems. Polymers as drug carriers also have been divided into various subgroups: soluble, biodegradable, mucoadhesive and other polymeric systems. The latter group includes polymers containing pendant bioactive substituents, matrix systems, heparin-releasing polymers, ionic polymers, oligomers and miscellaneous. At an introductory and fundamental level, an overview of these polymers and the materials science for the design of drug delivery systems will be discussed.

In‐situ photopolymerization of oriented liquid‐crystalline acrylates, 4. Influence of a lateral methyl substituent on monomer and oriented polymer network properties of a mesogenic diacrylate

AbstractMesomorphism and the molecular orientation of 1,4‐phenylene bis{4‐(6‐(acryloyloxy)hexyloxy)benzoate} (1) and its derivative with a methyl‐substituent in the central phenylene group (2) are studied. The methyl group affects the transition temperatures and the thermodynamic parameters, but not the order parameter of the monomers. The photoinitiated polymerization of the diacrylate monomers in their uniaxially oriented state leads to highly oriented and densely crosslinked polymer networks. The order parameter of these networks depends on the polymerization temperature, but becomes nearly temperature‐independent after polymerization. The presence of the methyl group leads to a significant lower degree of order in the polymeric state. In addition, data are presented on the monomeric viscosity of 2 and on the tensile moduli, glass transitions and refractive indices of the oriented polymer networks. In order to extend the mesomorphous temperature range, mixtures of 1 and 2 are also investigated.

Deformation-dependent properties of polymer networks constructed by addition of crosslinks under strain

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDeformation-dependent properties of polymer networks constructed by addition of crosslinks under strainL. G. Baxandall and S. F. EdwardsCite this: Macromolecules 1988, 21, 6, 1763–1772Publication Date (Print):June 1, 1988Publication History Published online1 May 2002Published inissue 1 June 1988https://doi.org/10.1021/ma00184a039RIGHTS & PERMISSIONSArticle Views120Altmetric-Citations19LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (967 KB) Get e-Alerts Get e-Alerts

Polydisperse polymer networks : elasticity, orientational properties, and small angle neutron scattering

The properties of polymer networks may be expected to depend upon the distribution, f(S), of chain lengths between crosslinks. We develop a formalism for treating phantom networks which allows the explicit inclusion of an arbitrary f(S) distribution. In bimodal networks we investigate chain orientation in the strained network by calculating and for the long and the short chains separately. The responses of the two species differ markedly from each other, although it is found that the overall network birefringence is dependent only on the mean chain length. Similarly, although the typical degree of extension of the chains upon straining the network differs widely between the species, the network modulus is formally independent of f( S). We investigate scattering from a long labelled chain crosslinked in a network at many randomly-positioned points, and explicitly account for the Poisson distribution of lengths between crosslinks. The scattering function is calculated exactly if the simplification of affine deformation of the junction points is made, and if the junctions are allowed to fluctuate freely, then an approximate solution is possible. The former model (Polydisperse Junction Affine model) agrees much better with the experimental data than the existing theories, both as regards the shape of the Kratky plot and the iso-intensity contours. There remain, however, features of the data which cannot be reproduced by any of the models considered. It is shown by the calculation of limit curves that these differences can only be accounted for by a treatment which goes beyond the idea of phantom chains.

Formation and properties of polymer networks

AbstractThe systematic study of intramolecular reaction and gel points together with measurements of moduli of tri‐ and tetra‐functional end‐linked networks show that network imperfections always result from the gel‐gel intramolecular reaction which must occur when such networks are formed. Even in the limit of zero pre‐gel intramolecular reaction, post‐gel intramolecular reaction and network imperfections still persist (law‐of‐mass‐action effect) to give marked reductions in modulus, particularly for trifunctional networks.

Topological aspects of structure and properties of highly crosslinked networks

AbstractStatistical model approach which allows to set the quantitative interrelation between the chemical structure of initial reagents, formation mechanism, topology and in the final analysis mechanical properties of highly crosslinked networks, is considered. The role of network topology in the formation of the main physico‐mechanical properties of polymer network is singled out. The analysis is carried out on the important class of highly crosslinked networks, formed by polyaddition reaction of diepoxides with aromatic diamines.

Effect of cyclization on the topological structure and properties of polymeric networks based on diglycidyl ethers and aromatic amines

The dependence of ring-formation on the structure of diglycidyl ethers in reactions with aromatic amines is discussed. The structure of the network polymer and the conformational tendency to cyclization in the oligomers under consideration are analysed on the basis of a statistical model. An interconnection between the probability of ring-formation and the equilibrium elasticity of the network systems is demonstrated. The tendency towards the formation of ring structures in systems based on diglycidyl ortho-ethers has been established experimentally, a fact which is in agreement with the theoretical calculations.

Elasticity and structure of crosslinked polymers

The subject of this work is to determine the dynamic and static elastic properties of polymer networks and to compare the experimental results with theoretical predictions. It is found that poly(dimethylsiloxane) (PDMS) networks on the one hand and polyisoprene (IR) and natural rubber (NR) networks on the other hand show different behaviour in frequency dependence of the storage modulusG′ is observed in the range 10−3 − 1 Hz, contrary to IR or NR. The reason for this is the absence of entanglements in PDMS. Comparing the measured static moduli with those calculated by rubber elasticity theory, we found that the front factorA· <r 2>/<r 2>0 is near to 0.5 in case of PDMS, but near to I for IR/NR networks. Both parts of the front factor may possibly cause this difference. As the PDMS chains possess a relatively high mobility we can assume that fluctuations of the junction points are less restricted than in IR/NR. This causes a structure factor A smaller than 1 in agreement with Flory's recent theory. According to James and Guth, the network chains tend to contract during the crosslinking process. This will be more likely in the networks of entanglement-free, highly mobile PDMS chains than in IR or NR rubbers. Hence the memory term <r 2>/<r 2>0 is smaller for PDMS than for IR/NR. Both alternative explanations are based on the different mobility of the chains considered. It may be assumed that the front factor is influenced by both effects and not only by the fluctuations of crosslinks.

High elastic properties of polymer networks of inhomogeneous structure

This paper describes the development of a theory of high elastic properties of incompressible polymer networks that have space-fluctuating shear moduli. Equations have been derived and verified by experiments.

Progress in the chemistry of polyreactive oligomers and some trends of its development. II. Specific features of network formation of oligomers and properties of network polymers

Progress in the chemistry of polyreactive oligomers and some trends of its development. II. Specific features of network formation of oligomers and properties of network polymers

Computer simulation of network formation processes, structure and mechanical properties of polymer networks

The possibilities offered by computer simulation for the investigation of polymer networks are discussed. Instantaneous crosslinking can be simulated by fixing the conformation of a set of linear macromolecules. Equilibrium crosslinking requires a complete rearrangement of the conformation after formation of each crosslink. The conformations of the lattice models of polymer networks with certain topologies can be constructed using a Monte Carlo procedure for obtaining the equilibrium configurations of the junction points, and the methods of generating conformations of polymer chains with fixed end-to-end distances. The deformational properties of polymer networks, taking into account the finite length of chains, can be investigated by the use of a model of interacting junction points, quasi-particles. The way of investigating the entanglement effects and the interchain interactions are proposed. Polymer chain mobility may be simulated by the molecular dynamics of the ‘pearl necklace’ model. Destruction processes in polymer networks can be simulated by a Monte Carlo method if the breakage of a strand connecting two junction points is regarded as an elementary event.