Linear crystalline polymers

Saegusa et al. invented a new method of preparing linear polyEI67). This method involves the izomerization polymerization of cyclic iminoethers (cf. Chap. 12), followed by alkaline hydrolysis, leading to perfectly linear crystalline polymers. Using oxazoline (x = 2) and oxazine (x = 3), polyEI and poly(trimethyleneamine) were prepared ... 

Biphasic systems linear crystalline polymers and their properties... 

Linear crystalline polymers always contain a fraction of amorphous material. For this reason they are usually considered biphasic systems. They show the typical transitions of amorphous polymers (glass and secondary) but also the common transitions of crystalline polymers (polymorphic, order-disorder, melting). Mechanical and physical properties of this category of polymers depend on morphology and amorphous/crystalline ratio, but also on the molecular mobility of the amorphous phase. 

Second, in the early 1950s, Hogan and Bank at Phillips Petroleum Company, discovered (3,4) that ethylene could be catalyticaHy polymerized into a sohd plastic under more moderate conditions at a pressure of 3—4 MPa (435—580 psi) and temperature of 70—100°C, with a catalyst containing chromium oxide supported on siUca (Phillips catalysts). PE resins prepared with these catalysts are linear, highly crystalline polymers of a much higher density of 0.960—0.970 g/cnr (as opposed to 0.920—0.930 g/cnf for LDPE). These resins, or HDPE, are currentiy produced on a large scale, (see Olefin polymers, HIGH DENSITY POLYETHYLENE). 

If a polymer molecule has a sufficiently regular structure it may be capable of some degree of crystallisation. The factors affecting regularity will be discussed in the next chapter but it may be said that crystallisation is limited to certain linear or slightly branched polymers with a high structural regularity. Well-known examples of crystalline polymers are polyethylene, acetal resins and polytetrafluoroethylene. 

Orientation in linear amorphous polymers Crystalline Polymers... 

Asymmetrical Peaks are rarely found in WAXS from polymers, but they are ubiquitous in the MAXS of liquid crystalline polymers. For asymmetrical peaks in isotropic patterns it is best to determine the peak position from the maximum of the peak, if peak asymmetry is a result of linear or planar disorder. Linear disorder means that the crystals are more or less one-dimensional (a tower of unit cells). Planar disorder means that the crystallites are made from only very few layers of unit cells (cf. Guinier [6] Chap. 7). 

For elastomers, factorizability holds out to large strains (57,58). For glassy and crystalline polymers the data confirm what would be expected from stress relaxation—beyond the linear range the creep depends on the stress level. In some cases, factorizability holds over only limited ranges of stress or time scale. One way of describing this nonlinear behavior in uniaxial tensile creep, especially for high modulus/low creep polymers, is by a power... 

The isotactic polypropylene is an essentially linear, highly crystalline polymer. The density of polypropylene is 0.905. It has high tensile strength, stiffness and hardness due to its high crystalline character. 

Based on the original commercial processes from the 1940s, this route runs at pressures as high as 50,000 psi and temperatures of 400—650 F. The process has its limitations since free radical peroxide-base catalysts cannot yield linear, highly crystalline polymers. They create branched chains. Today the process is used for LDPE,... 

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