Amorphous elastomers, synthesis

The true value of the chloropolymer (I) lies in its use as an intermediate for the synthesis of a wide variety of polytorgano-phosphazenes) as shown in Figure 1. The nature and size of the substituent attached to the phosphorus plays a dominant roll in determining the properties of the polyphosphazene. Homopolymers prepared from I, in which the R groups are the same or, if different, similar in molecular size, tend to be semi-crystalline thermoplastics. If two or more different substituents are introduced, the resulting polymers are generally amorphous elastomers. (See Figure 1.)... 

Properties. One of the characteristic properties of the polyphosphazene backbone is high chain dexibility which allows mobility of the chains even at quite low temperatures. Glass-transition temperatures down to —105° C are known with some alkoxy substituents. Symmetrically substituted alkoxy and aryloxy polymers often exhibit melting transitions if the substituents allow packing of the chains, but mixed-substituent polymers are amorphous. Thus the mixed substitution pattern is deUberately used for the synthesis of various phosphazene elastomers. On the other hand, as with many other flexible-chain polymers, glass-transition temperatures above 100°C can be obtained with bulky substituents on the phosphazene backbone. 

Plastomer, a nomenclature constructed from the synthesis of the words plastic and elastomer, illustrates a family of polymers, which are softer (lower hexural modulus) than the common engineering thermoplastics such as polyamides (PA), polypropylenes (PP), or polystyrenes (PS). The common, current usage of this term is reshicted by two limitahons. First, plastomers are polyolehns where the inherent crystallinity of a homopolymer of the predominant incorporated monomer (polyethylene or isotactic polypropylene [iPP]) is reduced by the incorporahon of a minority of another monomer (e.g., octene in the case of polyethylene, ethylene for iPP), which leads to amorphous segments along the polymer chain. The minor commoner is selected to distort... 

A variety of specialty polyolefins and polyolefin alloys can now be made directly in the reactor taking advantage f the new technology. Examples are the catalloy materials from Himont, which are polyolefin alloys made by synthesis and not by the conventional route of compounding. Hivalloy is a polypropylene/polystyrene alloy made by synthesis and combines the properties of both crystalline and amorphous engineering polymers. Such materials could challenge the established positions of several thermoplastic elastomers. 

The sol-gel synthesis of hybrid materials involves the occurrence of hydrolysis and condensation reactions in the presence of an organic polymer. Obviously, the selection of suitable polymer is of fundamental importance for the synthesis of the hybrid materials, as it should exhibit good miscibility with typical sol-gel precursors. The presence of suitable functional groups can facilitate the linkage between the polymer and the inorganic component. Also, the nature of the polymeric matrix is important because different properties of the matrix and, consequently, of the resulting nanohybrid material can be addressed for instance, the polymeric marix can be an elastomer (as in the case of polydimethylsiloxane) or thermoplastic (e.g., polytetrahydrofuran), amorphous, or (partially) crystalline [81]. 

Because of its rapid crystallization, PBT is very suitable for use as crystallizable segment in multiblock copolymers, which belong to the class of thermoplastic polyester elastomers (TPEEs). PBT-based block copolymers have been synthesized and studied in detail in the last thirty years. The commercial PBT block copolymers mostly possess a polyether, e.g. poly(tetramethylene oxide) (PTMO), or aliphatic polyester amorphous phase. Thermoplastic poly(ester-ether) elastomers, based on PBT and PTMO were developed by DuPont, and commercially introduced on the market in 1972, under the trade name Hytrel . Extensive investigations on the synthesis of block copolymers based on PBT rigid (hard) segments and various new... 

Polyurethane elastomers based on ADMH. All samples of the polyurethane elastomers studied (for synthesis see Section 2.6.1) are amorphous, since the poly(tetramethylene oxide) used in their synthesis loses its recrystallization ability within the urethane-containing polymers. For this reason, the areas of heterogeneity existing in the bulk of polyurethane elastomers are domains of hard blocks. As it follows from the small-angle X-ray scattering (SAXS) data (Table 5), sample PU(H) 1/1, which is characterized by structural heterogeneity. 

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