Preparation elastomer

Turner, S. Richard, 1 Two-component (2-K), nonsagging, polyurea structural adhesive, preparation of, 255-256 Two-component (2-K) systems, 238-241 Two-component (2-K) waterborne polyurethane coatings, 206 preparation of, 254-255 Two-shot cast elastomer, preparation of, 249-250... 

Balas, A., Palka, G., Foks, J., and Janik, H., Properties of cast urethane elastomers prepared from poly( e-caprolactone)s,... 

Elastomers Prepared. The three elastomers discussed herein were prepared from PPG, toluene-2,4-diisocyanate (TDI), and either LHT-240 or TIPA. Elastomers prepared by a one-step procedure are designated LHT-240 and TIPA, indicative of the triol used. A third elastomer, designated Tri-NCO, was prepared by first reacting LHT-240 with all of the required TDI for two hours at 50°C to obtain a triisocyanate (or essentially... 

Glass Temperature. The glass temperatures for a substantial number of polyurethane elastomers, similar to those discussed herein, were found (1 ) to increase linearly with the concentration of urethane moieties, [U]. For the present elastomers prepared using LHT-240 and TIPA, [U] should be 1.10 and 1.15 moles/kg, respectively. Their glass temperatures should be about —57°C, indicated by the previous data. 

Figure 4. Equilibrium modulus vs. functionality of prepolymers as ascertained for elastomers prepared with increasing quantities of CTI (cyclohexane triisocyanate)...

Figure 4.8 Prepolymer route for polyurethane elastomer preparation.

Elastomers, prepared by free-radical initiated copolymerization of ethyl acrylate with cellulose to several hundred percent extent of grafting of poly (ethyl acrylate) onto cellulose, exhibited rubber-like behavior and second-order transition temperatures. Cellulose-poly (ethyl acrylate) elastomers had transition temperatures below —35°C, about — 20°C, and below 5°C when measured in ethyl acetate, dry air, and water, respectively (43, 44). 

Raw-gum fluorocarbon elastomers are transparent to translucent with molecular weights from approximately 5000 (e.g., VITON LM with waxy consistency) to over 200,000. The most common range of molecular weights for commercial products is 100,000 to 200,000. Polymers with molecular weights over 200,000 (e.g., Kel-F products) are very tough and difficult to process. Elastomers prepared with vinylidene fluoride as comonomer are soluble in certain ketones and esters, copolymers of IFF and propylene in halogenated solvents perfluorinated elastomers are practically insoluble.16... 

Physical properties are related to ester-segment structure and concentration in thermoplastic polyether-ester elastomers prepared hy melt transesterification of poly(tetra-methylene ether) glycol with various diols and aromatic diesters. Diols used were 1,4-benzenedimethanol, 1,4-cyclo-hexanedimethanol, and the linear, aliphatic a,m-diols from ethylene glycol to 1,10-decane-diol. Esters used were terephthalate, isophthalate, 4,4 -biphenyldicarboxylate, 2,6-naphthalenedicarboxylate, and m-terphenyl-4,4"-dicarboxyl-ate. Ester-segment structure was found to affect many copolymer properties including ease of synthesis, molecular weight obtained, crystallization rate, elastic recovery, and tensile and tear strengths. 

Table 1 Results of elastomers prepared via post-cure methodology...

A similar effect is observed with silicone elastomers prepared with the co-cure method the surfaces are hydrophobic and deficient in PEO, because PDMS and PHMS constituents are directed to the air interface. Interestingly, in this case, however, the silicones partition differently at the surface. ATR-FTIR demonstrated a relative increase in SiH functionality over PDMS when compared to the control. These results can only be explained by preferential migration of SiH polymer to the surface when sequestering PEO in the interior, perhaps as a result of the reduced steric bulk of each monomer unit. The resulting inside out elastomers with a hydrophilic interior and a SiH rich exterior may offer a potential route to asymmetrically structured siloxanes by subsequent reactions with other olefinic groups. 

Table 4.5. Physical properties of polyurethane elastomers prepared from HTPB and 2,4-toluene diisocyanate (TDI) 205)...

A new high-performance elastomer, prepared from tetrafluoroethylene (TFE) and perfluoro(methyl vinyl ether) (PMVE), and characterized by outstanding resistance to chemical attack and excellent thermal stability, was reported recently by Barney et al. (I) of our laboratory. That paper described a rubbery perfluorinated dipolymer that could not be crosslinked using ordinary techniques because of its chemical inertness, and also a terpolymer in which an unspecified third monomer was used to introduce active crosslinking sites. 

Cast Elastomers. Table II shows the elastomers prepared from MDI, PPDI, CHDI and NDI with POTMG,... 

TABLE II - Properties of Elastomers Prepared from Polyester-MDI Prepolymer (Vibrathane 6020) Cured with B.D, EG, HQEE Polacure No. 740M, Polyol 50-1180 and Vibracure 3095. 

TABLE III - Properties of Elastomers Prepared from Polyether-MDI... 

Polymers II a-f were found by X-ray diffraction to be noncrystalline amorphous materials. Similar structured polymers were prepared for free radical vulcanization by the introduction of vinyl crosslinking sites. The polymers were formulated Into high consistency elastomers reinforced with silica and were free radical vulcanized. The properties for only lib and Ild are shown In Table I with a commercial elastomer prepared from polymethyl (3,3,3-tr1flu-oropropyl)s11oxane (LS) shown for comparison. Also included Is an elastomer prepared from the following copolymer (III),... 

These materials have been chosen due to their economic expediency and the valuable combination of physical and chemical, physical and mechanical, and other properties of individual pol5miers-PHB is a brittle thermoplastic PIB an elastomer. Preparation of composite materials based on... 

Figure 6. Schematic representation of LC elastomers prepared from chiral combined main-chain/side-chain copolymers, d] main-chain mesogens Idl side-chain mesogens chiral groups [7],...

All the LC elastomers prepared from combined LC elastomers were soft materi-... 

The only important commercial elastomer prepared by a cationic polymerization is butyl rubber, i.e., a copolymer of isobutene and isoprene. The latter... 

The discovery of living cationic polymerization has provided methods and technology for the synthesis of useful block copolymers, especially those based on elastomeric polyisobutylene (Kennedy and Puskas, 2004). It is noteworthy that isobutylene can only be polymerized by a cationic mechanism. One of the most useful thermoplastic elastomers prepared by cationic polymerization is the polystyrene-f -polyisobutylene-(>-polystyrene (SIBS) triblock copolymer. This polymer imbibed with anti-inflammatory dmgs was one of the first polymers used to coat metal stents as a treatment for blocked arteries (Sipos et al., 2005). The SIBS polymers possess an oxidatively stable, elastomeric polyisobutylene center block and exhibit the critical enabling properties for this application including processing, vascular compatibility, and biostability (Faust, 2012). As illustrated below, SIBS polymers can be prepared by sequential monomer addition using a difunctional initiator with titanium tetrachloride in a mixed solvent (methylene chloride/methylcyclohexane) at low temperature (-70 to -90°C) in the presence of a proton trap (2,6-dt-f-butylpyridine). To prevent formation of coupled products formed by intermolecular alkylation, the polymerization is terminated prior to complete consumption of styrene. These SIBS polymers exhibit tensile properties essentially the same as those of... 

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