Amorphous polymers molar mass

In the rheology and processing of polymers the kinetic aspects of the glass transition are of particular interest since the achievement of thermodynamic equilibrium in the amorphous, high-molar-mass polymer is beyond the time frame of the dynamic environment of processing. One way of viewing the glass transition (Stachurski, 1987) is to consider the... 

The quality of the polymer, its photo-oxidation and thermo-oxidation history expressed in concentration of hydroperoxides, carbonyl groups or of other oxidized structures and terminal groups. The rate of an oxidative attack may then be related to the average molar mass and to its distribution, and to the ratio of amorphous/crystalline structures. Polymers cannot be simply ordered according to the intensity of light emission at a given temperature. The chemiluminescence-time patterns are related with the rate of sample oxidation, but they may differ from one to the next polymer. 

Figure 9 demonstrates the fact that the chemiluminescence process occurs predominantly in the amorphous phase of the polymer. Low molar mass dicaproyl hexamethylene diamide is a fully crystalline compound the chemiluminescence signal under isothermal conditions below the melting point (136°C) at 130°C is very low, but it becomes rather strong after the crystallites of... 

The polymers are easily soluble in polar solvents like TFIF, DMAc, and DMSO, indicating that the solubility is enhanced by the large number of polar end groups and the branched structure. It is fully amorphous with a glass transition temperature between 90 and 110 C,depending on molar mass. 

It has been noted that C02 behaves very much like a hydrocarbon solvent with regards to its ability to dissolve small molecules consequently, many monomers exhibit a high solubility within C02. On the other hand, most high-molar-mass polymers are scarcely soluble in C02, and the only polymers that show good solubility under relatively mild conditions (T < 373 K, P < 35 MPa) are amorphous fluoropolymers, silicones, and polyether polycarbonate copolymers. 

This can be demonstrated easiest in the log E - T diagram. The amorphous polymer follows curve a in Figure 4.19 two cases have been indicated (i and d2, for a lower and a higher molar mass, respectively. 

In Chapter 6 we talked about the ability of solvent molecules to interact with and surround amorphous polymer chains, leading to the formation of polymer solutions. A closely related phenomenon utilizes a low-molar mass compound to penetrate a polymer and reduce the forces of attraction between chains. Such a compound is called a plasticizer. It must be compatible with the polymer and is almost always nonvolatile. Solvent molecules actually plasticize a polymer sample before forming a solution. However most solvents are not good permanent plasticizers because they diffuse to the surface and evaporate. 

We have a specific interest in the self-assembled structures formed by poly(ferrocenylsilane) block copolymers, such as poly(ferrocenyldimethylsilane-Z -dimethyl-siloxane) (PFS-PDMS) and (ferrocenyldimethylsilane-Z>-isoprene) (PFS-PI). The PFS block contains an iron atom in the main chain repeat unit. These polymers are particularly promising for novel applications, since they can be used as charge-transport materials and, by pyrolysis, as precursors to ferromagnetic ceramics [4-6], Moreover, they can by synthesized with a very narrow molar mass distribution, with excellent control over chain length and composition [7], An important feature of PFS is that the polymers bearing two methyl groups on the silane unit are crystalline, whereas polymers with two different substituents on each silane (methyl, ethyl methyl, phenyl) are atactic and remain amorphous. This feature of the polymer composition has a strong influence on the type of self assembled structures that these poly-... 

The generic name hydrocarbon resins designates several families of low molar mass polymers (M from 600 to 104) obtained by polymerization of petroleum, coal tar, and turpentine distillates [80-82], In most cases, these products are obtained by cationic polymerization of mixtures either of aliphatic and/or aromatic mono and diolefins present in the more or less enriched Cs and C9 feedstreams, or of pure aromatic monomers generally of the styrene type. They are complex mixtures of polymers ranging from viscous liquids and tacky fluids to hard, brittle thermoplastics, and are used as additives in adhesives, printing inks, rubbers, coatings, etc. [80-82], They are obviously amorphous and are characterized by their softening point (0 to —150° C), determined by standardized methods (i.e.,... 

The entanglement molar mass Me for PE is 1.7 kg.mof. The ratio M c/Mg ranges thus between 23 and 59 versus 5 for low crystalline or amorphous polymers. This means that embrittlement occurs while the... 

Within this framework, one can imagine a two dimensional ductile-brittle transition criterion which would be composed of two perpendicular boundaries in the graph la-Mw (Fig. 7). The vertical boundary would correspond to a critical molar mass M c- In polymers of low crystallinity or fully amorphous, M c would be sharply linked to the entanglement molar mass M c 5Me. In polymers of medium to high crystallinity, M c would be the molar mass below which it is impossible to have values higher than lac- The horizontal boundary would correspond to U = lac-... 

Before these results were published, polymer physicists and chemists mainly investigated only two phase-states, amorphous and crystalline. At the present time, along with these two states, the third phase-state of condensed systems, i.e. the liquid crystalline state, became very important. Here the situation turned out to be the same as in the case of low molar mass liquid crystals. In spite of the fact that historically the low molar mass substances in liquid crystalline state had been known for about a century, the intensive study of their properties began only after they had found an important practical application owing to a sharp change in optical properties of liquid crystals in electromagnetic fields (for visual displays) and as sensitive temperature indicators (in medicine). 

Dispersions of low molar mass LCs in amorphous polymers (PDLC) represent a new class of electro-optical materials. PDLC-based devices operate on the principle of electrically modulating the difference between the refractive indices of the LC and the polymer to control the scattering of light. This subject is reviewed in the chapter by West et al. A new development in this field is to use blends of an LC with an LCP to increase the angle of view of the device. 

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