Elastomeric properties poly

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 structure-property relationship of graft copolymers based on an elastomeric backbone poly(ethyl acry-late)-g-polystyrene was studied by Peiffer and Rabeony [321. The copolymer was prepared by the free radical polymerization technique and, it was found that the improvement in properties depends upon factors such as the number of grafts/chain, graft molecular weight, etc. It was shown that mutually grafted copolymers produce a variety of compatibilized ternary component blends. 

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. 

The elastomeric properties of poly(dichlorophosphazene) have been the subject of various investigations over the years. 

Another approach was attempted by Seppala and Kylma who reported the synthesis of poly(ester-urethane)s by condensation of hydroxyl terminated tel-echelic poly(CL-co-LA) oligomers with 1,6-hexamethylene diisocyanate (Scheme 33) [94]. The diisocyanate acts as chain extender producing an increase in molecular weight of the preformed oligomers. The authors claim that some of the copolymers present elastomeric properties. Using a similar method. Storey described the synthesis of polyurethane networks based on D,L-LA, GA, eCL,... 

These copolymers were made by anionically polymerizing 1,3-butadiene with n-Buli followed by the addition of isoprene to the live cement. The molecular weight was varied in the 1,H poly(bd) block to produce the maximum physical properties. The content of the Bd/isoprene in the copolymer was varied 30/70. Similarly, (Table VI) the molecular weight of the diblock was kept constant at 60 AO Bd isoprene ratio, while the molecular weight of the individual block was varied. In Tables V and VI the physical properties of the di block of the conjugated diene rubber showed elastomeric properties typical of that of the uncrossed elastomer. 

The materials obtained are extremely stable,43 because the electron pair of the phosphine structure has been donated to an oxygen atom. A final series of chains of this type are the poly(phosphorylamides). An example, the poly(phosphoryldimethylamide) chain, is shown in 6.48. These polymers have interesting elastomeric properties, but presumably are hydrolytically sensitive.42... 

Generally, the poly(alkyl acrylate) core is slightly crosslinked to exhibit the needed elastomeric properties. Grafted chains, tethered to the acrylate rubber surface, serve as chemically bonded compatibilizers between the rubber particles and the PSAN matrix (Figure 16.2). 

Further exploration [57] into the variation in properties available in the fully saturated poly(styrene-bl-butadiene-bl-styrene) materials focused on modifying the vinyl content in the polybutadiene block. Exploring practical elastomeric properties such as rebound and modulus, this work showed plainly that the level of vinyl in the polybutadiene block dominated the room temperature elastomeric properties of the block copolymer with a preferred level of about 40mol% percent 1,2-microstructure. 

By this procedure it is possible to synthesize [150] block copolymers, having thermoplastic elastomeric properties, with a micro-domain morphology and glass transition temperatures of -120 and 105 °C, corresponding to polysiloxane and poly(MMA) blocks, respectively. 

In the early 1950 s, B.F. Goodrich introduced the first commercial elastomer based on ionic interactions, a poly(butadiene-co-acry-lon1trile-co-acrylic acid). Typically less than 6% of carboxylic monomer 1s employed in order to preserve the elastomeric properties inherent in these systems. When neutralized to the zinc salt, these elastomers display enhanced tensile properties and improved adhesion compared to conventional copolymers. This enhancement of properties can be directly attributed to ionic associations between the metal carboxylate groups. 

Butyl rubber consists mostly of isobutylene (95-98%) and about 2-5% isoprene units. 1 The isoprene unit is halogenated by either chlorine or bromine to obtain the corresponding halobutyl rubbers. Despite the superior elastomeric properties of halobutyl, the elastomer can easily undergo dehydrohalogenation leading to crosslinfang, and the isoprene unsaturation is subject to ozone cracking. To remedy these problems and to improve the halobutyl properties, a new class of elastomer poly(isobutylene-co-p-methylstyrene) [poly (IB-PMS)] was developed. Unlike butyl rubber, it contains no double bonds and therefore cannot be crosslinked unless otherwise functionalized. The chemical structures of butyl rubber and poly (IB-PMS) copolymers are shown below. 

The early synthetic rubbers were diene polymers such as poly butadiene. Diene elastomers possess a considerable degree of unsaturation, some of which provide the sites required for the light amount of cross-linking structurally necessary for elastomeric properties. The residual double bonds make diene elastomers vulnerable to oxidative and ozone attack. To overcome this problem, saturated elastomers like butyl rubber and ethylene-propylene rubber (EPR) were developed. These rubbers were, unfortunately, not readily vulcanized by conventional means. To enhance cure, it was therefore necessary to... 

MAJOR APPLICATIONS Poly(vdf-hfp) is a synthetic, noncrystalline polymer that exhibits elastomeric properties when cross-linked. Known to be chemically inert, it is designed for demanding service applications in hostile environments and commonly used as a sealmt in hot and corrosive environments. 

Mark and Semiyen, in a series of papers, have studied the mechanism and the effect of trapping cyclics in end-linked elatomeric networks [100-103], Sharp fractions of cyclics of polyfdimethylsiloxane) (PDMS), varying in size from 31 to 517 skeletal atoms, were mixed with linear chains for different periods of time and the linear chains were then end-linked using a tetrafunctional silane. The untrapped cyclics were extracted to determine the amount trapped. It was found that while cyclics with less than 38 skeletal atoms were not at all trapped, for n>38, the percentage of cycUcs trapped increased with size, with 94% trapped in the case of the cychc with 517 skeletal atoms. In effect, the system of trapped cycUcs in the end linked PDMS network is a polymeric catenane. It is thus possible to control the elastomeric properties of the network by incorporating the appropriate sized cyclics. This study has been extended to cyclic PDMS in poly(2,6-dimethyl-l,4-phenylene oxide) [104,105] and cyclic polyesters in PDMS [106]. 

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