Methyl methacrylate melting range

The melt viscosity of a polymer at a given temperature is a measure of the rate at which chains can move relative to each other. This will be controlled by the ease of rotation about the backbone bonds, i.e. the chain flexibility, and on the degree of entanglement. Because of their low chain flexibility, polymers such as polytetrafluoroethylene, the aromatic polyimides, the aromatic polycarbonates and to a less extent poly(vinyl chloride) and poly(methyl methacrylate) are highly viscous in their melting range as compared with polyethylene and polystyrene. 

Mixtures of poly(vinylidene fluoride) with poly (methyl methacrylate) and with poly (ethyl methacrylate) form compatible blends. As evidence of compatibility, single glass transition temperatures are observed for the mixtures, and transparency is observed over a broad range of composition. These criteria, in combination, are acceptable evidence for true molecular intermixing (1, 19). These systems are particularly interesting in view of Bohns (1) review, in which he concludes that a compatible mixture of one crystalline polymer with any other polymer is unlikely except in the remotely possible case of mixed crystal formation. In the present case, the crystalline PVdF is effectively dissolved into the amorphous methacrylate polymer melt, and the dissolved, now amorphous, PVdF behaves as a plasticizer for the glassy methacrylate polymers. 

Both Tg and Tm are important parameters that serve to characterize a given polymer. While Tg sets an upper temperature limit for the use of amorphous thermoplastics like poly(methyl methacrylate) or polystyrene and a lower temperature limit for rubbery behavior of an elastomer-like SBR rubber or 1,4-cw-polybutadiene, Tm or the onset of the melting range determines the upper service temperature for semicrystalline thermoplastics. Between T,n and Tg, these polymers tend to behave as a tough and leathery material. They are generally used at temperatures between Tg and a practical softening temperature that lies above Tg and below Tm-... 

Linear amorphous polymers exist in a number of characteristic physical states depending on the timescale of the measurement and temperature. These are illustrated in Fig. 5.2 in terms of an arbitrary modulus function and are classified as glassy, leathery, rubbery, rubbery flow, and viscous (Tobolsky 1960 Collins et al. 1973). All linear amorphous polymers exhibit these five physical states when they are observed over a wide range of time or temperature. Materials of this type are typical of amorphous thermoplastics, such as polystyrene (PS), poly(methyl methacrylate) (PMMA), or polycarbonate (P(i ) polymers. Polymers that are either crosslinked or crystalline do not exhibit the rubbery flow and viscous liquid responses as illustrated. Crystalline polymers, however, will exhibit a viscous response at temperatures above the melting transition. 

Most interfacial tension measurements have been made by the pendant drop technique. A drop of a polymer melt is formed in another polymer melt. The shape is recorded photographically and the interfacial tension found from drop dimensions, i,e. maximum width and width at a height equal to the maximum width, using tabulated ratios found from numerical solutions of the equations of Bashforth and Adams. The interfacial tension can also be found by a full analysis of the shape of the drop. The method is preferred over alternatives since equilibration is not a serious problem but accurate density measurements are required. Tabulated values of interfacial tensions are available in the literature and range from about ImNm" for polymers similar in polarity such as polyethylene/polypropylene to llmNm" for dissimilar polymers such as polyethylene poly-(methyl methacrylate). 

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