Polypropylene crystalline polymer

Polymerization. Supported catalysts are used extensively in olefin polymerization, primarily to manufacture polyethylene and polypropylene. Because propylene can polymerize in a stereoregular manner to produce an isotactic, or crystalline, polymer as well as an atactic, or amorphous, polymer and ethylene caimot, there are large differences in the catalysts used to manufacture polyethylene and polypropylene (see Olefin polymers). 

Blends of polypropylene (PP) and liquid crystalline polymer (LCP) processed without melting the LCP were compared with conventional melt processed blends. In a first stage, PP was blended with 20 wt% of LCP in a twin-screw extruder with the take-up speed varied to achieve blends with different LCP fiber dimensions. In the second stage, these blends were processed both below and above the Tm of the LCP by extrusion and injection molding. 

Dow ABS Nylon 6/6 Polycarbonate Polyethylene, HDPE, LDPE, LLDPE, ULDPE Polypropylene HPPP, CPPP Polystyrene HIPS, GPPS, Recycled, Advanced Styrenic Resin SAN Polyurethane Elastomers Polyolefin Plastomer PC/ABS Crystalline Polymer ABS/TPU... 

Thin polymer films may also be investigated by TEM and high resolution images are obtained for e.g. thin films of liquid crystalline polymers [64]. Usually thin microtome cuts from bulk samples are investigated, but also epitaxial growth of polyoxymethylene on NaCl [152], chain folding of polyethylene crystals [153], epitaxial crystallization of polypropylene on polystyrene [154] or monomolecular polystyrene particles [155] are observed. The resolution is, however, in most cases not comparable to STM. 

Polypropylene (PP) is a crystalline polymer suitable for low-stress applications up to 225°F (105°C). For piping applications this polymer is not recommended above 212°F (100°C). Polypropylene is shielded, pigmented, or stabilized to protect it from uv light. Polypropylene is often a combination of polyethylene and polypropylene which enhances the ductility of the polymer. 

Nucleating agents are used to improve the clarity of crystalline polymers such as polypropylene. Species such as diparamethyl-dibenzylidene sorbitol are... 

Many industrial semi-crystalline polymer materials like polypropylene, polyamides, or polyesters contain nucleating agents or clarifiers which form needle-shaped aggregates already in the polymer melt. "For this purpose the pattern is desmeared using the measured primary beam. For a less involved treatment it may be sufficient to know the integral width of the primary beam profile in fiber direction. 

Annealing can reduce the creep of crystalline polymers in the same manner as for glassy polymers (89,94,102). For example, the properties of a quenched specimen of low-density polyethylene will still be changing a month after it is made. The creep decreases with time, while the density and modulus increase with time of aging at room temperature. However, for crystalline polymers such as polyethylene and polypropylene, both the annealing temperature and the test temperatures are generally between... 

In a crystalline polymer the chains can be nonparallel for instance, the structure of the y-form of isotactic polypropylene is characterized by the packing of nearly perpendicular chains.141142... 

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. 

P.Y.62 is thermally stable up to 250°C. It has a considerable effect on the shrinkage of HDPE and other partially crystalline polymers. The pigment is an equally suitable colorant for polystyrene and polyurethane and lends color to polypropylene spin dyeing products with minimal application requirements. 

Crystalline polymers exhibit the following basic properties They are opaque as long as the size of the crystallites or spherulites, respectively, lies above the wavelength of light. Their solubility is restricted to few organic solvents at elevated temperature. The following crystalline polymers have attained technical importance as thermoplastic materials polyethylene, polypropylene, aliphatic polyamides, aliphatic/aromatic polyamides, aliphatic/aromatic polyesters, poly-oxymethylene, polytetrafluoroethylene, poly(phenylene sulfide), poly(arylene ether ketone)s. 

In contrast, the curve E2 (isotactic polypropylene) is characteristic for partially crystalline polymers. The modulus is three decades higher than in an elastomer. At the glass transition temperature [T (2) 0 °C] the decay of the E modulus is small it does not drop to the lower level of the molten state before the melting point. 

The structure of crystalline polymers may be significantly modified by the introduction of fillers. All aspects of the structure change on filling, crystallite and spherulite size, as well as crystallinity, are altered as an effect of nucleation [9]. A typical example is the extremely strong nucleation effect of talc in polypropylene [10,11], which is demonstrated also in Fig. 2. Nucleating effect is characterized by the peak temperature of crystallization, which increases significantly on the addition of the filler. Elastomer modified PP blends are shown as a comparison crystallization temperature decreases in this case. Talc also nucleates polyamides. Increasing crystallization temperature leads to an increase in lamella thickness and crystallinity, while the size of the spherulites decreases on... 

The clarity of a translucent crystalline polymer, such as polypropylene (PP), may be improved by biaxial orientation. Monoaxial orientation of a crystalline film produces an anisotropic birefringent film. 

Propylene polymerization processes have undergone a number of revolutionary changes since the first processes for the production of crystalline polypropylene (PP) were commercialized in 1957 by Montecatini in Italy and Hercules in the United States. These first processes were based on Natta s discovery in 1954 that a Ziegler catalyst could be used to produce highly isotactic polypropylene. The stereoregular, crystalline polymers produced by this technology had sufficiently attractive economic and property performance that they became significant commercial thermoplastics in a remarkably short period. 

In this section we will discuss the molecular structure of this polymer based on our results mainly from the solid-state 13C NMR, paying particular attention to the phase structure [24]. This polymer has somewhat different character when compared to the crystalline polymers such as polyethylene and poly(tetrameth-ylene) oxide discussed previously. Isotactic polypropylene has a helical molecular chain conformation as the most stable conformation and its amorphous component is in a glassy state at room temperature, while the most stable molecular chain conformation of the polymers examined in the previous sections is planar zig-zag form and their amorphous phase is in the rubbery state at room temperature. This difference will reflect on their phase structure. 

We studied the structure of bulk-crystallized isotactic polypropylene in the previous section, in this section we will examine the gel structure of syndiotactic polypropylene (sPP) [25]. Many crystalline polymers form a gel from the con-... 

On the other hand, in the solid-state high resolution 13C NMR, elementary line shape of each phase could be plausibly determined using magnetic relaxation phenomenon generally for crystalline polymers. When the amorphous phase is in a glassy state, such as isotactic or syndiotactic polypropylene at room temperature, the determination of the elementary line shapes of the amorphous and crystalline-amorphous interphases was not so easy because of the very broad line width of both the elementary line shapes. However, the line-decomposition analysis could plausibly be carried out referring to that at higher temperatures where the amorphous phase is in the rubbery state. Thus, the component analysis of the spectrum could be performed and the information about each phase structure such as the mass fraction, molecular conformation and mobility could be obtained for various polymers, whose character differs widely. 

Phillips catalysts are active in the polymerisation of propylene and higher a-olefins, yielding tacky polymers with irregular structure and small amounts of crystalline polymers in the case of polypropylene, a small amount of crystalline fraction appeared to constitute the isotactic polymer [236]. 

It should be added that alternating ethylene/2-butene copolymers can exhibit stereoregularity namely the ethylene/cA-2-butene copolymer, which possesses an erythro-diisotactic structure and is a crystalline polymer. It may be interesting to note that from the formal point of view the alternating eryt/zro-diisotactic ethylene/cA-2-butene copolymer, i.e. erythro-diisotactic poly[ethylene- //-(c/.v-2-butene)], can be treated as isotactic head-to-head and tail-to-tail polypropylene. Isomeric trans-2-bu. ene gives atactic amorphous copolymers with ethylene [2,82]. 

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