Лако-красочные материалы — производство

It is possible by calculation to predict the Tg of a copolymer given the copolymer composition and the Tg of the homopolymers of the acrylic monomers used. J______ Wmi Wm2 Tg " Tgmi Tgm2 Wmi is the weight fraction of monomer 1 in the copolymer WfTi2 is the weight fraction of monomer 2 in the […]

The “glass transition temperature” (Tg) of a polymer is a 2nd order transition, involving a change in the solid polymer, from a flexible state to a rigid state. There are a number of transitions, depending upon the complexity of the molecular structure, for example the temperature at which rotation stops for a styrene unit about […]

This is done experimentally using polymers of known molecular weight fractions to cover as wide a range as possible. The intrinsic viscosity is determined for each fraction and a graph of Log10 [Intrinsic Viscosity] against Log10 [Molecular Weight] is plotted as illustrated below: If a = 1 then Mv = Mw Ifa = -1 then […]

Viscosity is defined as the property which determines the resistance to motion when a sheering force is exerted on the fluid under laminar flow conditions. If denotes the dynamic viscosity of a polymer solution of concentration C, and i)0is the intrinsic viscosity of the solvent of the same temperature, then: _ — Лг Ло where: […]

The effect of molecular weight on the solution viscosity of a surface coating determines the non-volatile (solids) content of the surface coating. As the molecular weight increases, additional solvent will be required, to maintain the viscosity at a level suitable for application. This is illustrated in Figure 1-61. In general the resistance properties of a […]

The term molecular weight, when applied to an acrylic polymer, lacks a single definitive description, since the molecules are not of uniform size. Every polymer sample will contain a range of molecular weights so that when presenting molecular weight data it is necessary to do so in terms of an average molecular weight or molecular […]

A C atom in the backbone chain of an acrylic polymer may have different substituent side groups. Since the structure of the groups on either side may differ, the “chain” C atom itself will be asymmetric. Thus, in acrylic polymers the group — CHX — may exist in one of two forms of steric isomer. […]

The formation of more energetically stable free radicals during propagation can result in orientation of the monomer molecule since the more stable free radical will normally be formed on the substituted side of the C=C bond, where resonance stabilisation is more likely. In the case of ionic polymerisation, electrostatic interaction has a major influence, and […]

These may develop between the growing polymer and a polarised molecule that approaches the polymer chain. They can directly influence the molecular alignment prior to reaction. (i) Steric Hindrance The presence of bulky substituent atoms on the more heavily substituted side of the C=C bond may preclude that side of the molecule from attack by […]

The mechanical, physical and chemical properties conferred on the polymer by the monomers utilised are discussed in detail under the relevant headings in the sections of this book dealing with applications and uses. However, it is pertinent to discuss here, in more general terms, the effect of molecular structure on the chemical and physical behaviour […]