Physical properties of polymeric materials

Many of the published reports of the application of isotopic methods in polymer chemistry have been concerned with reactions occurring during the growth of polymers by radical mechanisms. These methods, of course, are not confined either to the study of radical reactions or even to the examination of problems connected with the process of polymerization. They can be applied equally well to studies of reactions proceeding by non-radical mechanisms and to examination of certain of the chemical and physical properties of polymeric materials. 

Radiation grafting [83, 84, 85, 86, 87, 88, 89] is a very versatile and widely used technique by which surface properties of almost all polymers can be tailored through the choice of different functional monomers. It covers potential applications of industrial interest and particularly for achieving desired chemical and physical properties of polymeric materials. In this method, the most commonly used radiation sources are high-energy electrons, y-radiation, X-rays, U.V.-Vis radiation and, more recently, pulsed laser [90], infrared [91], microwave [92] and ultrasonic radiation [93]. Grafting is performed either by pre-irradiation or simultaneous irradiation techniques [94, 95]. In the former technique, free radicals are trapped in the inert atmosphere in the polymer matrix and later on the monomer is introduced into... 

Most of the unique properties exhibited by polymers are a result of the quasi-unlimited number of spatial arrangements that long chains can assume [123], The knowledge of the energetic effects accompanying the changes from one configuration to another, in correlation with the structural characteristics of the chains, is paramount to interpret and predict the physical properties of polymeric materials [124],... 

Sorption of Water in Newborn Rat Stratum Corneum. The physical properties of polymeric materials are markedly dependent on the interaction of the chain network with low molecular weight compounds (plasticizers). Similarly, stratum corneum interactions with water sig-... 

NMR is not, of course, the only analytical technique used to establish the composition and microstructure of polymeric materials. Others include >66 ultraviolet-visible spectroscopy (UV-Vis), Raman spectroscopy, and infrared (IR) spectroscopy. IR and Raman spectroscopy are particularly useful, when by virtue of cross-linking (see. e.g. Chapter 9), or the presence of rigid aromatic units (see Chapter 4). the material neither melts nor dissolves in any solvent suitable for NMR. The development of microscopy based on these spectroscopic methods now makes such analysis relatively simple (see below). Space precludes a detailed account of these and many other techniques familiar to the organic chemist. Instead we focus for the remainder of the chapter on some of the techniques used to characterize the physical properties of polymeric materials. 

The development of archaeology brings us lots of sanq>les from ancient times. Pol3mieric samples, such as fibers, are included in the artifacts. These samples are very useful in an understanding of the prevailing culture at the time when the samples were produced. However, there are some limitations to such studies. A typical limitation pertains to physical properties of polymeric materials. The passage of time may induce degradation of the polymer. The... 

Table I. Physical Properties of Polymeric Materials Important to Structural Adhesives...

Because degradation is so complex, it is very difficult to specify exact measures for stabilization of polymer structures. Each case has to be looked at separately and one must be aware of all the potential degradation routes. In order to show how chemical changes can bring about deterioration in the physical properties of a polymer, we will first briefly review the molecular basis for the useful physical properties of polymeric materials and show how the physical properties of a polymer may change over time even without chemical reactions. 

Concurrent with the formation of the new division, the first meeting was held in Chicago with Topics of Free Radicals in Polymerization, Polymer Solutions and Reactions of Macromolecules being treated in the first symposia. One year later, with a membership of klk and dues of 2.00, full divisional status was granted. As stated in by-law. Art. 1, Sec. 2., the purpose of the Division is, "to advance knowledge and understanding of the processes of polymerization and of the chemical constitution and chemical and physical properties of polymeric materials and to promote basic research in these fields."... 

The physical properties of polymeric materials depend on the polymerization mechanism involved in the synthetic process due to the difference in molecular masses. 

Irradiation effects in organic polymers result from the cleavage of chemical bonds and the subsequent reactions of intermediates generated thereby. These reactions lead to significant alterations in the physical properties of polymeric materials, and this topic has been covered in numerous books and articles [12,38-54]. As far as linear chain polymers are concerned, any changes in physical properties are due mainly to the formation of permanent main-chain scissions and intermolecular crosslinks. A general free-radical-based mechanism related to these processes is presented in Scheme 5.11. 

To some extent, the physical properties of polymeric materials are influenced by the degree of crystallinity. Crystalline polymers are usually stronger and more resistant to dissolution and softening by heat. Some of these properties are discussed in subsequent chapters. 

RH and temperature greatly affect the physical properties of polymeric materials. 

Electrochemical polymeriza tion of heterocycles is useful in the preparation of conducting composite materials. One technique employed involves the electro-polymerization of pyrrole into a swollen polymer previously deposited on the electrode surface (148—153). This method allows variation of the physical properties of the material by control of the amount of conducting polymer incorporated into the matrix film. If the matrix polymer is an ionomer such as Nation (154—158) it contributes the dopant ion for the oxidized conducting polymer and acts as an effective medium for ion transport during electrochemical switching of the material. 

Some relevant effects of the polymorphism on the properties of polymeric materials are shown in the final section. In particular, it is shown that, while the occurrence of transitions between polymorphic forms can be detrimental for some systems, a precise knowledge of the polymorphic behavior and of the physical properties of the single forms can be used advantageously to improve the in use properties as well as the processing conditions of some polymeric materials,... 

It is known that the structures present in a polymer reflect the processing variables and that they greatly influence the physical and mechanical properties. Thus, the properties of polymeric materials are influenced by their chemical composition, process history, and the resulting morphology. Morphological study usually requires two preparatory steps prior to the study itself selection of instrumental techniques and development of specimen preparation techniques. Structural observations must be correlated with the properties of the material in order to develop an understanding and applications of the material. Figure 22.1 illustrates the types of optical microscope (OM) techniques commonly used to examine polymer specimens [2]. 

Mercaptopropylene sulfide has been used to modify the physical and chemical properties of polymeric materials.88... 

IV. CHEMISTRY AND PHYSICAL PROPERTIES OF POLYMERIC AND MOLECULAR PR MATERIALS... 

Thermal analysis is an important technique for determining the physical and chemical properties of polymeric materials. It may be defined as a set of methods used to measure the physical or chemical changes of substances as a function of temperature. Some common thermal analysis techniques are given in Table 4.8.1. 

The poly (HEM A) sheets were prepared by B. Ratner using a special technique he developed. The HEMA solutions were poured between glass plates, and polymerization was chemically initiated. The chemical and physical properties of this material are very similar to those of radiation-grafted poly (HEMA) insofar as protein adsorption is concerned. Heterogeneous or homogeneous poly (HEMA) films were made by polymerization in solvents in which the poly (HEMA) is insoluble or soluble, respectively the result is a white opaque material in the first case and a transparent material in the second case. The resulting films were washed free of excess monomer and then soaked in the buffer to be used in the fibrinogen adsorption experiment for 10 days at 37 °C prior to the actual experiment. 

---