RESIDUAL UNSATURATION

The and e values of the aHyl group in DAP have been estimated as 0.029 and 0.04, respectively, suggesting that DAP acts as a fairly typical unconjugated, bifunctional monomer (42). Cyclization affects copolymerization, since cyclized radicals are less reactive in chain propagation. Thus DAP is less reactive in copolymerization than DAIP or DATP where cyclization is stericaHy hindered. Particular comonomers affect cyclization, chain transfer, and residual unsaturation in the copolymer products. DiaHyl tetrachloro- and tetrabromophthalates are low in reactivity. 

This combination of monomers is unique in that the two are very different chemically, and in thek character in a polymer. Polybutadiene homopolymer has a low glass-transition temperature, remaining mbbery as low as —85° C, and is a very nonpolar substance with Htde resistance to hydrocarbon fluids such as oil or gasoline. Polyacrylonitrile, on the other hand, has a glass temperature of about 110°C, and is very polar and resistant to hydrocarbon fluids (see Acrylonitrile polymers). As a result, copolymerization of the two monomers at different ratios provides a wide choice of combinations of properties. In addition to providing the mbbery nature to the copolymer, butadiene also provides residual unsaturation, both in the main chain in the case of 1,4, or in a side chain in the case of 1,2 polymerization. This residual unsaturation is useful as a cure site for vulcanization by sulfur or by peroxides, but is also a weak point for chemical attack, such as oxidation, especially at elevated temperatures. As a result, all commercial NBR products contain small amounts ( 0.5-2.5%) of antioxidant to protect the polymer during its manufacture, storage, and use. 

EPDM terpolymer of ethylene, propylene and a diene with the residual unsaturated... 

Ozone adds readily to unsaturated organie eompounds and ean eause unwanted eross-linking in rubbers and other polymers with residual unsaturation, thereby leading to brittleness and fraeture. Addition to alkenes yields ozonides whieh ean be reduetively eleaved by Zn/H20 (or I /MeOH, ete.) to yield aldehydes or ketones. This smooth reaetion, diseovered by C. D. Harries in 1903, has long been used to determine the position of double bonds in organie moleeules, e.g. ... 

Compared with tar, which has a relatively short lifetime in the marine environment, the residence times of plastic, glass and non-corrodible metallic debris are indefinite. Most plastic articles are fabricated from polyethylene, polystyrene or polyvinyl chloride. With molecular weights ranging to over 500,000, the only chemical reactivity of these polymers is derived from any residual unsaturation and, therefore, they are essentially inert chemically and photochemically. Further, since indigenous microflora lack the enzyme systems necessary to degrade most of these polymers, articles manufactured from them are highly resistant or virtually immune to biodegradation. That is, the properties that render plastics so durable... 

The reactivity of microgels resides in terminal carboxyl acid groups and in residual unsaturated dicarboxylic acid groups of the EUP-component. Due to sterical hindrance, presence of less reactive maleic acid units and deactivation of termi-... 

Fig. 32. Relation between the residual unsaturation ( ) IR-spectroscopy, (O) hydrolytic degradation resp. the titratable acid groups of microgels (a) and their EUP-content [132]. EUP(MA+HD),Mn 1640, c/t 67/33, EUP/S varied, W/M 20.

Non-reacted vinyl groups of these crosslinked polymers may be expressed by the residual unsaturation (RU). The RU is a measure for both the reactivity of the monomer and the structure of the crosslinked polymer. The RU may be determined by spectroscopic or chemical methods. For the spectroscopic determination a model compound of low molar mass is required as a reference for the standardization [217, 231, 254]. For the chemical determination a reagent of low molar mass is added to the pendant vinyl groups. Then the RU is obtained either by elemental analysis or by back-titration of the non-reacted reagent [231, 283-285]. 

An increase of the light-intensity leads not only to a faster cure but also to a more complete polymerization 19. For instance, the amount of residual unsaturation of the UV-cured acrylate polymer was shown to drop from 15 to 5% when the light intensity was increased from to 3 to 100 mW cm-2. This trend can be explained by two factors (i), an increase of the sample temperature which provides more molecular mobility and (ii), a longer time lag between conversion and shrinkage... 

The product obtained in the polymerization of 4-methyl-l,6-heptadiene contains no residual unsaturation. What is its chemical structure ... 

All films were touch-dried after one passage through the Mini-Cure (i.e. no oxygen inhibition was noticed). Raman spectra of the resins before and after curing showed no detectable amount of residual unsaturation (i.e. less than 5%). This showed that all acrylate groups are accessible to polymerization and not caged in the hyperbranched structure. 

Structure characterization, residual unsaturation Thermal transitions... 

Hydrogenation To an up-flow tubular reactor packed with a supported Ni catalyst were fed a liquid stream comprised of 3.52 g/min of hydroformylated soy methyl ester and a recycle stream of 16.5 g/min (total liquid hourly space velocity of 3.65 hr ). Hydrogen was fed at 2000 seem, at 159 C and a reactor outlet pressure of 459, yielding the desired conversion of residual unsaturation and aldehydes. 

The copolymerization within a wide range of initial compositions of the monomer mixtures was carried out in DMF solution in the presence of AIBN labeled with C. The residual unsaturation (molar ratio of the unsaturated pendant methacrylate groups to the total methacrylate groups linked with the template chain in the copolymer) is rather low (from 0.01 to 0.08). Also, a number of branching points can be estimated at 1-2 per hundred repeating units. These results confirm the conclusion that propagation occurs... 

Butyl rubber is produced by a process in which isobutylene is copolymerized with a small amount of isoprene using aluminum chloride catalyst at temperatures around — 150° F. (20). The isoprene is used to provide some unsaturation, yielding a product that can be vulcanized (43). Vulcanized Butyl rubber is characterized by high tensile strength and excellent flex resistance furthermore, as a result of its low residual unsaturation (only 1 to 2% of that of natural rubber) it has outstanding resistance to oxidative aging and low air permeability. These properties combine to make it an ideal material for automobile inner tubes (3), and Butyl rubber has continued to be preferred over natural rubber for this application, even when the latter has been available in adequate supply. 

Tphe major objective of this work was to understand better the effect - of heavy metals in autoxidation reactions in view of the importance of trace metals in oils, fats, rubber, plastics, and other materials. Because of our interest in the stability of polyolefins such as polyethylene and polypropylene the major model substance used was 2,6,10,14-tetramethyl-pentadecane. With its four tertiary C—H bonds it is a suitable model for either polypropylene or branched polyethylene. Hexadec-l-ene was also used since its mono-olefinic character could be typical of some residual unsaturation in polyethylene. N-alkylamides served as model substances for polyamides, and a few experiments were also carried out with methyl linoleate. While studying the causes of initiation of the autoxidation of these substances we observed that certain compounds were catalysts at low concentrations but became inhibitors at higher concentrations. The phenomenon was called catalyst-inhibitor conversion. ... 

EPDM - ASTM abbreviation for a terpolymer of ethylene, propylene, and a diene with the residual unsaturated portion of the diene in the side chain. 

Step 2—Polybutadiene rubber is further polymerized, but in the presence of styrene and acrylonitrile monomers. This is done in low-pressure reactors under a nitrogen atmosphere. In this operation, the monomers are grafted onto the rubber backbone through the residual unsaturation remaining from the first step. 

Only two spectroscopic studies on sulfur vulcanisation of EPDM by Fujimoto and coworkers are available [73-74], Using attenuated total reflectance (ATR) IR spectroscopy they showed that during sulfur/TMTD/MBT/ZnO/stearic acid vulcanization, the C=C bands at 3035, 966 and 870 cm 1 of the residual unsaturations of the EPDM third monomers, DCPD, 1,4-hexadiene (HD) and 5-methylidene-2-norbornene (MNB), respectively, decreased in intensity as a function of time at 140 and 150 °C. The relative decrease in intensity was shown to correlate with the increase in crosslink density. In Sections 6.2.2.2 and 6.2.2.3 it will be shown that this decrease of intensity should not be interpreted as a loss of unsaturation during sulfur vulcanisation of EPDM. 

Table 1 shows the experimental results of DAP, including the residual unsaturation and the number-average degree of polymerization P of DAP pre-polymer and the primary chain length Pn(ch)- In Table 2 the results of Rus,o, Pn,o. and Pn(ch),o as extrapolated to zero conversion from the conversion-dependences based on the data of Table 1 are summarized along with those of DAI and DAT polymerizations. 

The residual unsaturation is the degree of unsaturation of the polymer expressed as a percentage of the corresponding pure DAP monomer. 

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