Unusual properties poly

Among the many unusual properties that the arborescent architecture leads to, most notable is the discovery that block copolymers with a high MW dendritic (arborescent) polyisobutylene core and poly(para-methylstyrene) end blocks can manifest themselves either as a rubber, or as a plastic, depending on their environment (Figures 7.16 and 7.17). The behavior is thermally irreversible. 

Some Additional Unusual Properties of Poly(dimethylsiloxane)... 

Other Transient Interactions. The PVA/borax example dealt with the effects of surface exposure of a two-component polymer system to a wetting liquid. We discovered a practical example of this class of phenomena in a plasticized poly (vinyl chloride) (PVC) system. A peculiar plasticizer (tetraethyl methylene bisphosphonate) for PVC has been found (6) which has the unusual property of exuding out of PVC immediately upon exposure to high humidity. The plasticizer quickly re-enters the resin when the humidity is reduced. A film of 60% resin and 40% plasticizer was solvent cast from tetrahydrofuran onto an impedometer bar and was subjected to sudden high humidity exposure. 

Three-center (bifurcated) hydrogen bonding between adjacent base pairs explains unusual properties of poly(dA) poly(dT). The stability of the B-form of this duplex (and of its ribo analog) formed by two homopolymers might be a consequence of the extreme propeller twist (Box 20.1) reported for the central portions (the A-tracts) of the double helical dodecamer d(CGCAAAAAAGCG) [702] and d(CGCAAATTTGCG) [703]. In both crystal structures the DNA molecules show the same unusual three-center bonds linking adjacent base pairs. 

Poly (e-caprolactone), poly lactides, and polyglycolides have quite unusual properties of biodegradability and biocompatibility. The majority of polymers used in the biomedical field to develop implants, sutures, and controlled drug-delivery systems are the aforesaid resorbable polyesters produced by ring-opening polymerization of cyclic (di)esters. 

Poly(2,6-dimethyl-l,4-phenylene oxide)—which, thankfiilfy, b referred to as PPO—has the unusual property of being complete miscible with another homopolymer, in thb case polystyrene. Thb enables it to be toughened by alloying with HIPS. The structure of PPO b... 

Poly(6-amino-2,4-hexadienoic acid), for example, represents an amphoteric polyelectrolyte with unusual properties in solution. It can be used as a complexing agent for transition metal ions with a selectivity for divalent ions, such as Cu , Co , or Ni. ... 

In addition, the phosphorus-nitrogen backbone inherently possesses a unique range of unusual properties. For example, it is extremely flexible which in turn can give rise to low glass-transition temperatures, particularly in the case of poly(alkoxyphosphazenes) such as the n-butoxy derivative (Tg = -105°C) (1,4). Furthermore, the backbone is thermally and oxidatively stable, as well as optically transparent from 220 nm to the near infrared region, which makes it resistant to breakdown in many harsh environments, as evidenced by the flame-retardant properties of many polyphosphazenes. 

Thus, it was not until 1990 that the group of Kaminsky and Arndt-Rosenau took a more detailed look at the homopolymerization of norbornene and the structures of the resulting polymers. Driven by the growing interest in copolymers with high norbornene contents and high glass transition (Tg) temperatures, as well as the unusual properties of PNBs, Arndt-Rosenau et al. used the hydrooligomerization technique to produce saturated model norbornene dimers and trimers with metallocene catalysts known to produce atactic, isotactic, and syndiotactic poly(a-olefins) (1-3, Table 16.1). 

The previous paper in this series described the preparation and properties of highly aromatic polyesters that have turbid melts, have melt viscosities highly dependent upon composition and shear rate, and that give unusually anisotropic molded articles. Because these unusual properties are reminiscent of the behavior of nonpolymeric nematic liquid crystalline materials, further work has been done to synthesize and characterize polymers containing other moieties known to lead to liquid crystallinity in nonpolymeric materials. The copolyesters produced were derived by the acidolysis reaction previously described from poly-(ethylene terephthalate) (PET) and a variety of dicarboxylic acids and acetylated difunctional phenols. Some of the copolymer compositions were varied to determine the limits of composition that give the turbid melts characteristic of liquid crystallinity, but which can be melted before decomposition. This paper describes the preparation and the physical and magnetic properties of these polymers. 

Some Unusual Properties of Poly(Dimethylsiloxane). Atypically low values are exhibited for the characteristic pressure (47) (a corrected internal pressure,... 

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