Comb polymers, amorphous

Amorphous comb polymers, with short-chain polyethers attached to a polyphosphazene backbone (Blonsky, Shriver, Austin and Allcock, 1984), Fig. 5.15, or a polysiloxane backbone (Xia, Soltz and Smid, 1984), Fig. 5.16, have been found to be excellent hosts for alkali metal salts. The PN... 

Some of the most useful polyphosphazenes are fluoroalkoxy derivatives and amorphous copolymers (11.27) that are practicable as flame-retardant, hydrocarbon solvent- and oil-resistant elastomers, which have found aerospace and automotive applications. Polymers such as the amorphous comb polymer poly[bis(methoxyethoxyethoxy)phosphazene] (11.28) weakly coordinate Li " ions and are of substantial interest as components of polymeric electrolytes in battery technology. Polyphosphazenes are also of interest as biomedical materials and bioinert, bioactive, membrane-forming and bioerodable materials and hydrogels have been prepared. 

The molecular architecture of a polyphosphazene has a profound influence on properties. For example, linear and tri-star trifluoroethoxy-substituted polymers with the same molecular weight (1.2 x 104 or higher) have strikingly different properties.138 The linear polymers are white, fibrous materials that readily form films and fibers, whereas the tri-arm star polymers are viscous gums. One is crystalline and the other is amorphous. Cyclolinear polymers are usually soluble and flexible. Cyclomatrix polymers are insoluble and rigid. Linear polymers can be crystalline, but graft or comb polymers are usually amorphous. 

Wide angle X-ray diffraction, WAXD, studies on the PHAs from octanoic acid (PHA-OCT), nonanoic acid (PHA-NON), and decanoic acid (PHA-DEC) showed that these polymers had the same features as synthetic comb-like polymers [54]. PHA-OCT is the most crystalline (AHm = 8.3 cal/g) and PHA-HEX (the PHA from hexanoic acid) is amorphous, while PHA-HEP (the PHA from hep-tanoic acid) has a very low degree of crystallinity (AHm= 1.3 cal/g). The degrees of crystallinity of PHA-OCT and PHA-NON were determined to be 20 and 30%,... 

Plastics can be classified according to the physical properties imparted to them by the way in which their individual chains are arranged. Thermoplastic polymers have both ordered crystalline regions and amorphous noncrystalline regions. Thermoplastic polymers are hard at room temperature, but soft enough to be molded when heated, because the individual chains can slip past one another at elevated temperatures. Thermoplastic polymers are the plastics we encounter most often in our daily lives—in combs, toys, switch plates, and telephone casings, for example. They are the plastics that are easily cracked. 

The comb-branched polymers based on the phosphazene backbone, —(—R2P=N-),—, where R is an oligomeric poly(ethylene oxide) side chain capped by —OCH3, are amorphous polymers with very low TgS [12, 13] (Table 3.1). As mentioned earlier, a prominent example of the phosphazene polymers is MEEP. 

An effective way to obtain amorphous polyethers is by grafting low molecular weight PEO to the polymer skeleton and form comb- or star-like structures. Since ionic conduction is closely related to the movement of chain segments, it can be expected that a polymer with an amorphous structure together with low Tg will meet the need for fast ionic conduction at room temperature. There are two common ways to synthesize comb polyethers [1] ... 

Usually, both crystalline and amorphous phases are present in polymer electrolytes. Since only amorphous phases present high conductivity, plasticiser solvents are usually added to enhance the amorphous phase and thus the ionic conductivity. Here, propylene carbonate (PC), EC,y-butyrolactone (y-BL) and their binary mixtures are usually used as plasticiser solvents. Hie stereo structures of the polymer matrix molecules are given in Fig. 12.3, including linear, comb, crossing, star, hyper-branched and comb crosslinking. 

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