Activated Ester Containing Polymers: Opportunities and Challenges for the Design of Functional Macromolecules

The creep compliance of viscoelastic materials such as synthetic polymers is an established metric of the rate at which strain increases for a constant applied stress and can, in principle, be implemented at the nanoscale to compare quantitatively bulk or thin film polymers of different structures or processing histories. Here, we outline the evolution of contact creep compliance analysis and application for both conical and spherical indenter geometries. Through systematic experiments on four amorphous (glassy) polymers, two semi-crystalline polymers and two epoxies, we show that assumptions of linear viscoelasticity are not maintained for any of these polymers when creep compliance is measured via conical indentation at the nanoscale, regardless of the rate of stress application (step or ramp). Further, we show that these assumptions can be maintained to evaluate the contact creep compliance Jc(t) of these bulk polymers, regardless of the rate of stress application, provided that the contact strains are reduced sufficiently through spherical indentation. Finally, we consider the structural and physical properties of these polymers in relation to Jc(t), and demonstrate that Jc(t) correlates positively with molecular weight between entanglements or crosslinks of bulk, glassy polymers.

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Contact creep compliance of viscoelastic materials via nanoindentation

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1993&context=nanopub

Molecular dynamics predictions of thermal and mechanical properties of thermoset polymer EPON862/DETDA

Effect of chemical structure and crosslinking density on the thermo-mechanical properties and toughness of (meth)acrylate shape-memory polymer networks

Combination of Orthogonal Supramolecular Interactions in Polymeric Architectures

Methacrylate Polymers Containing Metal Binding Ligands for Use in Supramolecular Materials: Random Copolymers Containing Terpyridines

This contribution considers to what extent two molecular parameters, the glass transition temperature and the cohesive energy density, relate to the yield behavior of epoxy-based glassy thermosets. Eight different formulations consisting of four aliphatic and four aromatic resins with varying molecular weights between crosslinks were investigated over a broad range of test temperatures. Additionally, one aromatic formulation is studied over a range of stress states and test temperatures. The results indicate that both the glass transition and cohesive energy density are governing parameters that relate to the yield response of these systems. A model is proposed to incorporate these parameters and to predict the yield response as a function of strain rate, temperature, and stress state. The functional form of the results also indicate that the activation energy density (i.e., the activation energy divided by the activation volume) may be the material characteristic that relates to yield of these systems rather than each term individually.

Molecular parameters governing the yield response of epoxy‐based glassy networks

Improvements in physical, mechanical, and thermal properties of an epoxy network are made with the use of a unique class of molecules that reinforce the network at the molecular scale. These molecules are commonly referred to as antiplasticizers or fortifiers. In this contribution, two types of fortifiers are incorporated into the model epoxy network. One, dimethyl methylphosphonate, is a simple additive while the other, diethyl phosphoramidate, contains a reactive amine and is cured as part of the network. The two approaches provide some unique differences in the physical and mechanical properties of the networks. Several mechanisms of fortification are discussed and correlated to the observed properties. In addition, it is shown that the fortifiers improve the rheological characteristics of the epoxy resin and act as fire-retardants in the cured network. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4606–4615, 2006

Comparing reinforcement strategies for epoxy networks using reactive and non-reactive fortifiers

The yield response of nine architecturally different glassy networks is investigated under several stress states, strain rates, and temperatures, and correlations are made among them. Differences in molecular architecture are quantified through two proposed governing parameters; the glass transition temperature, T
 g, capturing network stiffness and the cohesive energy density, E
 c, reflecting network strength. Cohesive energy density is estimated using molecular modeling techniques and supported by solvent swelling experiments. The limits of the correlations made between molecular architecture and yield behavior are further studied with attempts to relate yielding in thermoplastic glasses and heterogeneous networks.

Correlating yield response with molecular architecture in polymer glasses

Earlier research with phosphorus-based molecular fortifiers showed a range of improvements in physical, thermal, and mechanical properties. This contribution introduces sulfur- and carbon-based molecules into a model epoxy network for comparison. Similar improvements inrheological, physical, and select mechanical propertiesare found between the phosphorus and sulfur- and carbon-based fortifiers. Thermal properties are not enhanced with the sulfur and carbon fortifiers. Two of the sulfur compounds phase separate upon cure of the epoxy network and show unique behavior. In addition, infrared spectroscopy is performed to identify possible mechanisms of reinforcement. POLYM. ENG. SCI., 47:1569–1575, 2007. © 2007 Society of Plastics Engineers

Kevin J. Calzia

Papers

Methacrylate Polymers Containing Metal Binding Ligands for Use in Supramolecular Materials: Random Copolymers Containing Terpyridines

Molecular parameters governing the yield response of epoxy‐based glassy networks

Comparing reinforcement strategies for epoxy networks using reactive and non-reactive fortifiers

Correlating yield response with molecular architecture in polymer glasses

Reinforcement of epoxy networks with sulfur‐ and carbon‐based molecular fortifiers