Highly Crystalline Polymers from Melts

An example of the viscoelastic behavior of a polymer with a high degree of crystallinity prepared by crystallization from the melt is shown in Figs. 16-5 and 

Whereas reduced variables could be applied to the data of Figs. 16-1 and 16-2 to combine measurements at different temperatures over a considerable range to a close approximation, there were deviations at higher temperatures and/or longer times. A similar effect is found in the data of Fig. 16-6 if the data at higher frequencies are superposed as shown in Fig. 16-7, using empirical ot factors, the data at lower frequencies do not coincide. However, if J is postulated to be the sum of two contributions, J i and J u, with different temperature dependences, and the logarithmic frequency dependence of the former is assumed to be symmetrical as represented by the dashed line in Fig. 16-7, it is found that the second 

Storage compliance of linear pdyethylene crystallized from the melt, measured at 10 different temperatures as shown. Open circles, from forced oscillation half black, from free vibration black, calculate indirectly from creep measurements. (Nakayasu, Markovitz, and Plazek. ) 

It is somewhat arbitrary to select the compliances rather than the moduli for decomposition, without more knowledge of the origin of the viscoelasticity. In fact, a similar analysis on the basis of the moduli E and E has been performed on data for crystalline polyethylene terephthalate by Kawai and associates. The two procedures correspond to assuming that the stress or the strain, respectively, is homogeneous throughout the sample. Actually, depending on the structure and microscopic features of the viscoelastic response, neither may be strictly homogeneous cf. Chapter 14, Section F). 

It is difficult to compare the shapes of the viscoelastic functions for single crystal mats and bulk crystalline polymer from the data of Figs. 16-1, 16-2, 16-S, and 16-6 without extensive recalculation under circumstances where approximation methods give poor precision because the functions vary so slowly with time or frequency cf. equation 40 of Chapter 4). Comparisons of the two types of samples will be shown for isochronal viscoelastic functions in Section B below. 

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Highly Crystalline Polymers from Melts or Cast from Solvents... 

The microstructure and the properties depend on the cis/trans ratio of the ring bonding and on the stereochemistry between the rings. Poly(methylene-l,3-cyclopentane) obtained by cyclopolymerization of 1,5-hexadiene shows four different structures from which the tram isotactic structure is predominant, when using simple biscyclopentadienyl compounds. Higher substituted (pen-tamethyl) zirconocenes yield mainly as-connected polymers which are highly crystalline and have melting points up to 190 °C. 

Syndiotactic polystyrene (sPS) represents an important achievement in olefin polymerization catalysis. Syndiotactic PS is an industrially relevant thermoplastic material produced by Dow Chemical and Idemitsu Kosan Co. under the tradenames Questra and Xarec , respectively. Industrial interest on sPS originates from the remarkable properties exhibited by this highly crystalline polymer. The high melting temperature, 270 °C, the relatively fast crystallization rate (at least much faster than that of iPS), the high heat resistance, the low dielectric constant, the high elastic modulus, and an excellent resistance to chemicals explain the industrial interest for this material. Syndiotactic PS was considered as an innovative new resin option for the automotive, electrical, and electronic markets, appliances such as... 

Polyplvalolactone Is a highly crystalline polymer that exists In three crystalline modifications those have been described by Oosterhoff (17) of Shell Laboratories. The main product that crystallizes from a polyplvalolactone melt Is the crmodlflcatlon. It melts at about 245°C and has a glass transition temperature (Tg) of -10 C. In this form the polymer chains have a helical structure with two monomer units per turn. 

In the mid-sixties it was discovered that highly crystalline polymers such as polypropylene can be extruded under specific conditions of crystallization from the melt to produce remarkably elastic fibers and films Owing to their unusual... 

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