Elastomeric properties, polymers

If a modest number of cross-links between the polymer backbone are introduced, the polymer Hquid crystal takes on elastomeric properties. The useflilness of these materials probably Hes in the coupling of mechanical and optical effects. 

Copolymers of S-caprolactone and L-lactide are elastomeric when prepared from 25% S-caprolactone and 75% L-lactide, and rigid when prepared from 10% S-caprolactone and 90% L-lactide (47). Blends of poly-DL-lactide and polycaprolactone polymers are another way to achieve unique elastomeric properties. Copolymers of S-caprolactone and glycoHde have been evaluated in fiber form as potential absorbable sutures. Strong, flexible monofilaments have been produced which maintain 11—37% of initial tensile strength after two weeks in vivo (48). 

The properties of elastomeric materials are also greatly iafluenced by the presence of strong interchain, ie, iatermolecular, forces which can result ia the formation of crystalline domains. Thus the elastomeric properties are those of an amorphous material having weak interchain iateractions and hence no crystallisation. At the other extreme of polymer properties are fiber-forming polymers, such as nylon, which when properly oriented lead to the formation of permanent, crystalline fibers. In between these two extremes is a whole range of polymers, from purely amorphous elastomers to partially crystalline plastics, such as polyethylene, polypropylene, polycarbonates, etc. 

Fluoiocaibon elastomeis aie synthetic, noncrystaUine polymers that exhibit elastomeric properties when cross-linked. They are designed for demanding service appHcations in hostile environments characterized by broad temperature ranges and/or contact with chemicals, oils, or fuels. 

Applications of NBR adhesives are based on the excellent elastomeric properties of the polymer coupled with its polarity, which provides good solvent resistance... 

Incorporation of flexible siloxane spacers into side chain or main chain liquid crystalline polymers have been shown to drastically reduce the transition temperatures 255,267,271,272,277) anc[ aiso increase the response time of the resultant systems to the applied thermal, optical or electrical fields 350-353>. In addition, siloxanes also provided elastomeric properties and improved the processibility (solution or melt) of the resulting liquid crystalline copolymers. 

Polymers containing each of these configurations are known, the most common being the cis- A and the 1,4-isomers. The first of these, poly(c/ -l,4-isoprene), is the macromolecular constituent of natural rubber the second is the material known as gutta percha. The latter, unlike natural rubber, has no elastomeric properties, but has a leathery texture. It has been used for diverse applications such as golf-ball covers and as an insulating material for the trans-Atlantic cables of the late nineteenth century. 

Jha A. and Bhowmick A.K., Thermoplastic elastomeric blends of poly(ethyleneterephthalate) and carylate rubber 1. Influence of interaction on thermal, dynamic mechanical and tensile properties. Polymer, 38, 4337, 1997. 

Thermoplastic elastomeric compositions from reclaimed NR and scrap LDPE with 50 50 mbber/plastic ratio shows good processability, ultimate elongation, and set properties. Polymer blends of reclaimed mbber and LDPE exhibit higher viscosity over the range of shear rate at various temperatures compared to virgin NR-LDPE blends due to the influence of filler present in the reclaimed mbber (Eigure 38.7) [109]. 

Composition of the terpolymers as expressed in mole%, of course, must be kept in the range that yields good elastomeric properties. E-E polymers of higher ethylene content naturally result in higher tensile strength as a consequnece of formation of partial crystallinity due to short ethylene blocks (f ). of EEDMs studied in this work all abide by the usual EEDM requirements. ... 

The use temperature of an elastomer is determined by the range between the T and the Tm. These new OBCs have increased the use temperature range of olefin-based elastomers by > 40 °C, enabling the introduction of these polymers to many new markets and applications where a simple olefin-based solution was previously unavailable. This performance translates to better high temperature elastomeric properties for the OBCs. For example, the 70 °C compression set of an OBC is much lower than that of a comparable ethylene/LAO random copolymer and is closer to that of f-PVC, TPU, or TPV materials [47] (Fig. 23). 

The phenyl modified polymers possess the optimum combination of high temperature and elastomeric properties and were used in the study of formulation parameters These variables can have an important effect on the thermal stability and property profile of vulcanized systems For example, the use of reinforcing silicas, peroxide content, and oxidative stabilizers have been shown to be important ( 3, 10, in However, polymer-silica interactions had the most pronounced effect on retaining properties during high temperature aging studies ... 

A new class of elastomers uses block copolymers, which contain segments of different monomers. These form crystalline and noncrystalline regions in the polymer, and these polymers have elastomeric properties, as well as high fracture toughness. 

This study is investigating the possibility of obtaining a silicone polymer having good radiation resistance, with retention of elastomeric properties. The main area of interest is the resistance to radiation of blends and block copolymers in which an aromatic component can form a separate microphase... 

Certain polymers can be crystallized by mechanical stress. Namely, the stress induced elongation decreases the entropy of the chains. For this reason, an additional decrease in entropy, which is required for crystallization is comparatively small. Strain induced crystallization phenomena are of great practical importance since the elastomeric properties can be tailored in some way. In particular, PIB readily undergoes strain induced crystallization already close to room temperature. 

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