Polypropylene resins atactic

When the insertion of propylene molecules in the growing chain is such that all methyl branches are on the same hand, the regularity of the chain allows it to crystallize this is the isotactic polypropylene (iPP), synthesized by Natta [8, 9] and the most commercial type obtained by the Ziegler-Natta stereoregular polymerization process. When the monomer insertion is consistently in the opposite hand to previous monomer insertion, the polymer obtained is syndiotactic polypropylene (sPP), which achieves lower crystallinity and today has less commercial interest. The random stereo incorporation of monomer units results in an amorphous resin, atactic polypropylene (aPP). 

Atactic polypropylene (APP) is tacky as produced and is not easily formulated. It is used essentially as a neat resin or extended with a small amount of wax or a polymer to add hot tack. Atactic polypropylene used to be a byproduct in the production of crystalline polypropylene, but with the development of new, more efficient catalysts, less atactic polypropylene is produced. As a result, at least two companies are now producing APP directly. This means that a greater number of precise products are available however, pricewise they will have to bear the full cost of production. It is therefore anticipated that atactic polypropylene resins will be developed mainly for specific applications having higher value-added performance. 

Polypropylene, Polypropylene and its copolymers account for about 13 percent of U.S. resin sales. Its manufacture and properties have much in common with HDPE. Unlike polyethylene, however, isotactic, syndiotactic. Nomenclature ). Atactic polypropylene, and atactic configurations are possible as a consequence of the pendant methyl group (see above, under Polymer Structure and... 

For many years atactic polypropylene was an unwanted by-product but today it finds use in a number of markets and is specially made for these purposes rather than being a by-product. In Europe the main use has been in conjuction with bitumen as coating compounds for roofing materials, for sealing strips where it confers improved aging properties and in road construction where it improves the stability of asphalt surfaces. Less important in Europe but more important in USA is its use for paper laminating for which low-viscosity polymers are used, often in conjunction with other resins. Limestone/atactic... 

ABA ABS ABS-PC ABS-PVC ACM ACS AES AMMA AN APET APP ASA BR BS CA CAB CAP CN CP CPE CPET CPP CPVC CR CTA DAM DAP DMT ECTFE EEA EMA EMAA EMAC EMPP EnBA EP EPM ESI EVA(C) EVOH FEP HDI HDPE HIPS HMDI IPI LDPE LLDPE MBS Acrylonitrile-butadiene-acrylate Acrylonitrile-butadiene-styrene copolymer Acrylonitrile-butadiene-styrene-polycarbonate alloy Acrylonitrile-butadiene-styrene-poly(vinyl chloride) alloy Acrylic acid ester rubber Acrylonitrile-chlorinated pe-styrene Acrylonitrile-ethylene-propylene-styrene Acrylonitrile-methyl methacrylate Acrylonitrile Amorphous polyethylene terephthalate Atactic polypropylene Acrylic-styrene-acrylonitrile Butadiene rubber Butadiene styrene rubber Cellulose acetate Cellulose acetate-butyrate Cellulose acetate-propionate Cellulose nitrate Cellulose propionate Chlorinated polyethylene Crystalline polyethylene terephthalate Cast polypropylene Chlorinated polyvinyl chloride Chloroprene rubber Cellulose triacetate Diallyl maleate Diallyl phthalate Terephthalic acid, dimethyl ester Ethylene-chlorotrifluoroethylene copolymer Ethylene-ethyl acrylate Ethylene-methyl acrylate Ethylene methacrylic acid Ethylene-methyl acrylate copolymer Elastomer modified polypropylene Ethylene normal butyl acrylate Epoxy resin, also ethylene-propylene Ethylene-propylene rubber Ethylene-styrene copolymers Polyethylene-vinyl acetate Polyethylene-vinyl alcohol copolymers Fluorinated ethylene-propylene copolymers Hexamethylene diisocyanate High-density polyethylene High-impact polystyrene Diisocyanato dicyclohexylmethane Isophorone diisocyanate Low-density polyethylene Linear low-density polyethylene Methacrylate-butadiene-styrene... 

A sample of commercial atactic polypropylene (Montecatini resin) was purified by extraction with hot toluene followed by precipitation from the toluene solution with methanol to remove isotactic PP contamination. The purified material showed no detectable crystalline melting endotherm by DSC (< 0.5% crystalline content). However, IR indicated the presence of some stereoblock material. The atactic PP was cast into thin films ( 50 pm) on glass from heptane solution, vacuum dried and peeled from the glass with a sharp blade. 

Early pressure-sensitive hot-melt adhesives used ethylene-vinyl acetate copolymers as elastomers, but they are seldom used now. Atactic polypropylene is sometimes used on its own or in admixtures. More recently, vinyl ethers and acrylic resins have become available and will probably play an increasingly important role as the technology is developed, especially on polar surfaces. 

Atactic (amorphous) polypropylene can be directly synthesized as well. Resins in low- to moderate-molecular weight resins ate commercially available (Eastman Chemical Company) for hot-melt adhesive and other applications. 

Fig. 2.10 The binary interaction parameters for two PIB resins (M = 81.6 and 114 kg/mol) with either ethylene-butene copolymers (of different and composition) or with an atactic head-to-head polypropylene (HHPP), based on SANS data (Krishnamoorti et al. 1995)...

The chemical composition distribution of polyolefins is measured (indirectly) by either temperature rising elution fractionation (Tref) or crystallization analysis fractionation (Crystaf). These two techniques provide similar information on the chemical composition distribution of polyolefins and can be used interchangeably in the vast majority of cases. Both methods are based on the fact that the crys-tallizability of HOPE and LLDPE depends strongly on the fraction of a-olefin comonomer incorporated into the polymer chains, that is, chains with an increased a-olefin fraction have a decreased ciystallizability. A similar statement can be made for polypropylene and other polyolefin resins that are made with prochiral monomers resins with high stereoregularity and regioregularity have higher crystalliz-abilities than atactic resins. 

Many processes have been developed for the polymerization of olefins. They differ in both the physical state of the reactor media and in the mechanical operation of the unit. The choice of process is determined by economics, feedstock availability, catalyst, and the desired range of products to be produced. Significant improvements in catalyst design over the past years have led to improvements in process design and simplification. Modem supported catalysts are able to produce polymer with high yields and stereospecificity (for polypropylene) such that the removal of catalyst residue and atactic polymer from the resin is no longer required, see Table 2.7. 

Atactic polypropylene still finds use in paper laminates and reinforced tape, but these markets are considered mature. Some research work is currently underway to produce polypropylene copolymers which will exhibit unusual properties. New polyamide and polyester resins, as well as more complex polymers, as poly amide-poly ethers or poly ester-poly ethers, are also under development. 

Specific Heat Capacity. Representative values of specific heat capacity are shown in Tables 3 and 6. The range of values is only about 850 to 2400 J/(kgK) or barely a factor of three. As a general rule, differences are usually associated with the molecular composition of the polymer and less with molecular architecture, although crystallinity may be important. For example, a comparison of three forms of polyethylene (Table 6) reveals little difference in heat capacity the high density, and hence more crystalline, form has a somewhat lower value. Similarly, no differences are observed between two grades of phenol-formaldehyde resin, or between them and phenol-furfural resin. However, in comparing isotactic and atactic (amorphous) polypropylene shown in Table 3 with values of 1790 and 2350 J/(kg K), respectively, a fairly substantial difference is observed the more ordered, denser isotactic form has the lower heat capacity, as is to be expected. However, comparable values of isotactic and atactic polystyrene have been reported to be 1264 and 1227 J/(kg-K), respectively (65) here the difference is small. 

---