Polymer information networks

Chemical Abstracts Service (CAS) is also an authority on polymer nomenclature. CAS publishes Chemical Abstracts, which is available both in printed format and electronically via STN International, Scientific and Technical Information Network. The Chemical Abstracts Registry file provides many examples of CAS polymer nomenclature principles, which are published as Section 222 of Appendix IV in every edition of the CA Index Guide (33). 

Searchers who choose to search a publicly available file such as the CAS Registry File must learn the rules imposed on them by CAS (2). The CAS Registry File is remotely searchable via the Scientific and Technical Information Network (STN) in Columbus, Ohio. Anyone with an STN accoimt and a computer equipped with the necessary hardware and software may access this file. As of September 2002, the Registry file contains names, structures, or both for over 42 million substances, of which nearly 934,000 are polymers. 

Figure 2. Schematic of the information network approach to designing a tissue engineering scaffold by modifying polymer materials with peptides to achieve a desired response.

Recently, a new approach called artificial neural networks (ANNs) is assisting engineers and scientists in their assessment of fuzzy information, Polymer scientists often face a situation where the rules governing the particular system are unknown or difficult to use. It also frequently becomes an arduous task to develop functional forms/empirical equations to describe a phenomena. Most of these complexities can be overcome with an ANN approach because of its ability to build an internal model based solely on the exposure in a training environment. Fault tolerance of ANNs has been found to be very advantageous in physical property predictions of polymers. This chapter presents a few such cases where the authors have successfully implemented an ANN-based approach for purpose of empirical modeling. These are not exhaustive by any means. 

The presented results and the additional information taken from various references indicate the direct relevance of the size of the network strands for the crack opening displacement and consequently for the toughness of the polymer. In polymers under load, the molecular chains at the tip of the crack break after the deformation zone ahead of the crack has grown to a critical width 5C, that is the crack opening displacement. This value 5C is proportional to the length of the molecular strands of the network and is linked in this way to the molecular structure of the polymer. However, the molecular mechanism for chain breakage in the deformation zone is not known at present. 

In POLYM the output data of KINREL are used with compositional information to calculate the number and mass average molecular masses (Rn and Rm, respectively) and number and end-group average functionalities (fp and fg> respectively) in the pre-gel region in all stages. In addition, the network characteristics such as sol fraction, mj, and the number of elastically active network chains per monomer (5), Ng, are calculated in the post-gel regime of stage 3. 

If we were to have an isolated polymer chain with a single nuclear spin attached to each segment (the marked chain) crosslinked into an unmarked network, the second moment of the NMR line of that spin species would carry information relating to the separation of chain segments, and to their relative orientation with respect to the field direction. If the network were to be subjected to a bulk deformation, these geometrical parameters would be altered, and hence we would expect a corresponding change in the value of the experimentally measured... 

These moment studies have been performed on polymer systems such as polyethylene (or on penetrants in polymer systems) in which the interacting spins (protons or fluorines) reside on the same or on adjacent atoms. This allows essentially no freedom of variation in the internuclear vectors upon deformation of the network. The primary informational content therefore relates to independent segmental orientation distributions. By placing single spins on alternate segments, there should be much greater sensitivity to changes in the chain extension upon bulk deformation. 

Adsorption of nonionic and anionic polyacrylamides on kaolinite clay is studied together with various flocculation properties (settling rate, sediment volume, supernatant clarity and suspension viscosity) under controlled conditions of pH, ionic strength and agitation. Adsorption and flocculation data obtained simultaneously for selected systems were correlated to obtain information on the dependence of flocculation on the surface coverage. Interestingly, optimum polymer concentration and type vary depending upon the flocculation response that is monitored. This is discussed in terms of the different properties of the floes and the floe network that control different flocculation responses. Flocculation itself is examined as the cumulative result of many subprocesses that can depend differently on system properties. 

The information available on aqueous polymer blends is qualitative in nature because of the lack of a suitable theory to interpret the experimental observations. Mixed gels can be comprised of an interpenetrating network, a coupled network (as discussed above), or a phase-separated network [2]. The latter is the most common as the blends have a tendency to form two phases during gelation. In such cases the miscibility and thermodynamic stability have to be empirically investigated and proper conditions for miscible blends identified. This involves a phase diagram study as is described in [3]. 

We have found that combined solid-state NMR spectroscopy and DPC results can be used to calculate reaction enthalpies which are in close agreement with Moore (15). Furthermore, we find that the degree of conversion can be significantly affected by post reaction thermal processing. We conclude that the single pulse solid-state NMR spectroscopy can provide reliable, reproducible, and quantitative information about these highly crosslinked, insoluble, polymer networks. 

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