Homopolymers, properties

Most of the experiments reported so far have been performed on linear homopolymer systems. In Chap. 6 we discuss what has been achieved so far beyond such simple materials. We begin with the discussion of neutron spin echo data on miscible polymer blends, where the main issue is the dynamic miscibility . There are two questions Firstly, on what length and time scales and to what extent does a heterogeneous material like a blend exhibit homogeneous dynamics Secondly, how does it relate to the corresponding homopolymer properties ... 

Block copolymerization is one method of mixing chemically different polymers. The block copolymers have received much attention, since the different homopolymer properties are maintained in the block copolymer, and this allows easy modification of the polymer characteristics [63,72,86,87,108]. 

It often occurs that it is desirable to modify the properties of a homopolymer to achieve certain application-specific characteristics that are perhaps not possible by solely manipulating the polymer molecular weight or by chemical modification of the final producf. Perhaps one is interested in achieving properties that are intermediate to two homopolymers. Properties of interest could include crystallinity, flexibility, tensile strength, melting point, glass-transition temperature, and many others. 

In general, the properties of random copolymers that are affected most strongly by chain flexibility and inter molecular forces tend to be a weighted average of those of the respective homopolymers. Properties affected primarily by crystallinity, however, such as melt temperature, tend to be decreased by copolymerization, due to the irregularity that copolymerization produces in the chemical structure of the polymer molecules. This will be discussed further in Section 3.10. 

Chem. Descrip. Ethoxylated trimethylolpropane triacrylate Uses Monomer for aqisolv. developable photopolymers, paper, textiles coalings and other porous substrates Features Very high ethoxylate homologue of Photomer 4149 partially water sol. MFA which cures to a flexible, soft homopolymer Properties High m.w. 

Definition Cryst. isotactic modified homopolymer Properties Pellets insol. in water m.w. 9100 avg. dens. 0.950 m.p. 152 C... 

A different equation results if one assumes that the product of the change in expansivity with the glass transition temperature, AaT, is a constant, known as the empirical Simha-Boyer rule AaT = 0.113. The well-known and simple Fox expression for the glass transition temperature results on insertion of the Simha-Boyer rule into the Gordon-Taylor equation. The Gibbs-Di Marzio and the Fox equations are easily generalized to SVT or pVT equations of state when assuming that the solution can be based on simple additivity of the homopolymer properties. 

Many commercial polymers, including polystyrene, PMMA and LDPE, are synthesized via homogeneous FRP of a single monomer. Homopolymer properties are controlled by average chain length and chain-length distribution as well as, in some cases, structural characteristics such as branching level. 

Table 5.2 Summary of homopolymer properties for poly(a-hydroxy acids)...

Both equations are easily generalized to PVT equations of state assuming that the solution can be based on additivity of the homopolymer properties. The Gordon-Taylor equation, in contrast, is recovered from DM ifL assumes the value Y2wl yiO- - w)] where y represents the number of the respective flexible bonds. Finally, to add effects of specific interactions, the Gordon-Taylor equation has been expanded into a virial equation in terms of the variable u)2c which is the expansivity-corrected mass fraction of equation 41 [m 2c = Lw2 K.w + Lw2) - This is the Schneider equation, S, written as... 

Styrene-acrylonitrile (SAN) is produced by mass, suspension, and emulsion polymerization. The copolymer has better chemical and mar resistance than the homopolymer. Properties vary with the ratio of the monomers in general, an increase in the acrylonitrile content improves toughness and chemical resistance, but also increases color and melt viscosity. SAN is used for cups, handles, housings, and appliance parts. Low-color resins with high light transmittance are now available. Good optical properties make SAN useful for tumblers, serving dishes, canisters, and some disposable medical products. ... 

Definition Cryst. isolactic modified homopolymer Properties Pellets insol. in water m.w. 9100 avg. dens. 0.950 m.p. 152 C Terdcdogy May be harmtul by inh., Ing., or skin absorption irritating to eyes, skin, respiratory s em possible sensitizer Precaution Incompat. with strong oxidizing agents... 

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