Linear high-crystalline polymer

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). 

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,... 

Linear poly(ethylene) (such as Marlex 50), poly(oxymethylene) (such as Delrin), or other highly crystalline polymer. 

Now that methods have been developed for synthesizing linear and isotactic polymers, the possibility of creating highly crystalline polymers exists. Coupled with more reliable methods of estimating the extent of crystallinity, polymers can now be better characterized than formerly, thus making more significant low temperature specific heat measure-... 

The linear polyethylene produced by the Ziegler-Natta process (called high-density polyethylene) is a highly crystalline polymer with 4000-7000 ethylene units per chain and molecular weights in the range 100,000-... 

With a linear molecular structure of repeating -CF2-CF2-units, PTFE is a highly crystalline polymer with a melting point of 327°C. Density is 2.13-2.19 g/cm. ... 

A eommon feature in such arrangements is the presence of a ID H-bonded ribbons. This particular organisation resembles the photopolymerisation of diolefins named four-center type polymerisations, where each reactive double bonds can independently react, leading to crystalline linear high organic polymer (Scheme 20). 

Parylene is the generic name for members of a series of polymers. The basic member of the series, called Parylene N, is poly(p 2ra-xylylene), a completely linear, highly crystalline material. The structures of four Parylene types are shown in Figure 10.155. 

A group of polymers consisting of isotactic, stereoregular, highly crystalline polymers based on butene-1. Their properties are similar to those of polypropylene and linear polyethylene, with superior toughness, creep resistance, and flexibility. 

Crystallinity can vary widely in semicrystalline polymers. Three rough classes of polymers can be identified, which have high crystallinity (over 50%), medium crystallinity (between 20 and 50%), and low crystallinity (below 20%). High crystallinity polymers are seen in linear PE, iPP, PEO, etc medium... 

Figure 5.25. Suppression of relaxation at Tg in a highly crystalline polymer for a series of polyethylenes with different amounts of short-chain branching as crystallinity increases, the intensity of the P-loss peak diminishes. HOPE = high-density polyetnylene (PE), LLDPE is linear low-density PE, LDPE is low-density PE, ULDPE is ultra low-density PE, and TAFTMER is a specially synthesized low-low density PE. [From Sha et al. (1990) reprinted with permission of the North American Thermal Analysis Society.]...

VIII. To illustrate a highly crystalline polymer a linear polyethylene with a density of 0.965 g/ml at room temperature, corresponding to a high degree of crystallinity. Stress relaxation data of Faucher in simple extension were employed. 

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