Polymers bulk properties

Treatment of polymer surfaces to improve their wetting, water repulsion, and adhesive properties is now a standard procedure. The treatment is designed to change the chemistry of the outermost groups in the polymer chain without affecting bulk polymer properties. Any study of the effects of treatment therefore requires a technique that is specific mostly to the outer atomic layers this is why SSIMS is extensively used in this area. 

Network properties and microscopic structures of various epoxy resins cross-linked by phenolic novolacs were investigated by Suzuki et al.97 Positron annihilation spectroscopy (PAS) was utilized to characterize intermolecular spacing of networks and the results were compared to bulk polymer properties. The lifetimes (t3) and intensities (/3) of the active species (positronium ions) correspond to volume and number of holes which constitute the free volume in the network. Networks cured with flexible epoxies had more holes throughout the temperature range, and the space increased with temperature increases. Glass transition temperatures and thermal expansion coefficients (a) were calculated from plots of t3 versus temperature. The Tgs and thermal expansion coefficients obtained from PAS were lower titan those obtained from thermomechanical analysis. These differences were attributed to micro-Brownian motions determined by PAS versus macroscopic polymer properties determined by thermomechanical analysis. 

In some cases, polymers may be compounded from simpler starting compounds formed with two or more of the raw materials. These are identified as master batches and are often prepared when bulk addition to a single stage process would cause them to separate or to alter the bulk polymer properties during mixing to the point where mixing would be inefficient. 

Nowadays a promising way to control the bulk polymer properties, such as conductivity, processability, thermal, and mechanical stabihties, is through the organization of the polymeric chains on the nanometer scale [7-9]. The first approach used to achieve this goal was the synthesis of conducting polymers in cavities of porous hosts. Commonly named nanocomposites, these materials have two or more different components on the nanoscale, and can show catalytic, electronic, magnetic, and optical properties better than those of the individual phases. The basic reason for this synergism is still not fully understood, but it is considered that confinement and electrostatic interactions between the components play an important role. 

Although the molar mass of the polymer formed is unaffected by intramolecular chain transfer to polymer, the resulting change in polymer skeletal structure usually has significant consequences for bulk polymer properties. 

Principal monomer classes for the design of bulk polymer properties... 

Thus, intermolecular chain transfer to polymer leads to premature termination of the growth of one propagating chain and the reactivation of a dead chain which then grows a long-chain branch. As a consequence, the molar mass distribution of the polymer broadens. The changes in skeletal structure and molar mass distribution inevitably have major effects upon bulk polymer properties. 

To a large extent the end-use requirements can be satisfied by the bulk polymer properties the other requirements are dictated by surface and colloidal properties. The bulk properties are usually determined by a handful of monomers as shown in Table 6.1. Crosslinking, surface and colloidal properties are governed by functional monomers which are described in Section 6.2.3. 

Bulk polymer properties such as viscosity and elasticity are concerned with averaged responses of an assembly of polymer chains to external stimuli. On the other hand, the self-diffusion coefficient has something to do with the average speed of translation of the centers-of-mass of individual chains. Thus its study should give us a clue to the clarification of the modes of Brownian motion of a single chain on long timescales. This expectation must have been in the mind of polymer workers for many years, but, except in dilute solutions, few measurements of Ds were undertaken until recently, probably on the one hand because of experimental difficulties and on the other because of the lack of an adequate guiding theory. 

Nowadays, ordered inorganic/organic PNs with a finely tuned structure have displaced a lot of traditional composite materials in a variety of applications because the intimate interactions between components can provide enhancement of the bulk polymer properties (i.e., mechanical and barrier properties, thermal stabihty, flame retardancy, and abrasion resistance). The reinforcing nanoparticle/ polymer adhesion is of primarily importance, as it tunes the final properties of the nanocomposite. Polymer/clay nanocomposites (PCNs) meet this demand due to the platelet-type dispersion of the clay filler in the organic matrix [1]. 

As it has been noted above, the main feature of polymers is that they consist of long chain macromolecules. Therefore, it is to be expected that polymer chains structure and their characteristics will be influenced essentially on bulk polymers properties. One of such polymer chain structural factors is availability in it of bulk side groups, which results to bulk polymers brittleness enhancement [40], A side groups effect on plasticity level for heterochain polymers was considered in Ref. [41], where brittleness increase was explained by side groups nonparticipation in local or macroscopic plasticity processes. 

Many bulk polymer properties have been well defined in the recent literature. In addition, theories that offer reasoning for changes in these bulk properties with temperature, pressure, etc. have been developed. Focus has been shifted in the past decade to polymers in thin film geometries. These systems remain obscure to polymer scientists. 

Dielectric analysis of bulk polymer properties has been well documented. Similarly, DEA has often been employed in monitoring polymer reactions.Another, quite common application uses DEA to measure the breadth of a polymer relaxation. This analysis is directly related to the coupling parameter, which quantifies cooperativity. DEA has been used for characterizing thin polymer films. However, the polymer systems that have been studied involve free-standing films that have been sputter coated on both sides. Adding conductive substrates, such as aluminum foil, has also been accomplished, as well as relying on sputter coated, conducting surfaces. 

The implication of these observations is that the polymer architecture has a significant effect on the crystalline nature and this in turn has major implications for bulk polymer properties such as warpage and shrinkage (see later). 

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