Propylene with Dienes

Although presently lacking industrial importance, alternating copolymers can be made from propylene and butadiene, also from propylene and isoprene. Copolymers of propylene and butadiene form with vanadium- or titanium-based catalysts combined with aluminum. alkyls. The catalysts have to be prepared at very low temperature (-70 C). Also, it was found that a presence of halogen atoms in the catalyst is essential.Carbonyl compounds, such as ketones, esters, and others, are very effective additives. A reaction mechanism based on alternating coordination of propylene and butadiene with the transition metal was proposed by Furukawa.  

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Elastomers. Ethylene—propylene terpolymer (diene monomer) elastomers (EPDM) use a variety of third monomers during polymerization (see Elastomers, ethyiene-propylene-diene rubber). Ethyhdenenorbomene (ENB) is the most important of these monomers and requires dicyclopentadiene as a precursor. ENB is synthesized in a two step preparation, ie, a Diels-Alder reaction of CPD (via cracking of DCPD) with butadiene to yield 5-vinylbicyclo[2.2.1]-hept-2-ene [3048-64-4] (7) where the external double bond is then isomerized catalyticaHy toward the ring yielding 5-ethyhdenebicyclo[2.2.1]-hept-2-ene [16219-75-3] (ENB) (8) (60). 

The isoprene units in the copolymer impart the ability to crosslink the product. Polystyrene is far too rigid to be used as an elastomer but styrene copolymers with 1,3-butadiene (SBR rubber) are quite flexible and rubbery. Polyethylene is a crystalline plastic while ethylene-propylene copolymers and terpolymers of ethylene, propylene and diene (e.g., dicyclopentadiene, hexa-1,4-diene, 2-ethylidenenorborn-5-ene) are elastomers (EPR and EPDM rubbers). Nitrile or NBR rubber is a copolymer of acrylonitrile and 1,3-butadiene. Vinylidene fluoride-chlorotrifluoroethylene and olefin-acrylic ester copolymers and 1,3-butadiene-styrene-vinyl pyridine terpolymer are examples of specialty elastomers. 

With larger amount of propylene a random copolymer known as ethylene-propylene-monomer (EPM) copolymer is formed, which is a useful elastomer with easy processability and improved optical properties.208,449 Copolymerization of ethylene and propylene with a nonconjugated diene [EPDM or ethylene-propylene-diene-monomer copolymer] introduces unsaturation into the polymer structure, allowing the further improvement of physical properties by crosslinking (sulfur vulcanization) 443,450 Only three dienes are employed commercially in EPDM manufacture dicyclopentadiene, 1,4-hexadiene, and the most extensively used 5-ethylidene-2-norbomene. 

A similar phenomenon has been observed in the spectra of some diene-iron tricarbonyl compounds (136). The anisolechromium tricarbonyl complex shows loss of 2 H from the [M - 3 CO]+ ion, giving C7H6OCr+, which could have the tropone structure (XIV) while the analogous iso-propoxy complex loses propylene with the probable rearrangement to give... 

An EPDM rubber is produced by the terpolymerisation of ethylene and propylene with a small amount (typically of the order of 5%) of an unconjugated di-olefin. The di-olefins used, include dicyclopentadiene, 1,4-hexadiene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene and methyl tetrahydroindene, 1,5 cyclo octadiene. A number of other dienes [74,75] have been tried. Infrared spectroscopy [35] is used to find out the ter monomer content. The characteristic peaks for the ter monomer are shown in Table 3.4. In view of the relatively low concentrations, it is probable that ter monomer base units are present largely as isolated units in EPDM but the distribution of propylene and methylene sequences is of considerable interest. 

Random ethylene/propylene copolymers are amorphous and represent an interesting class of synthetic elastomers. The introduction of double bonds, useful for sulphur vulcanisation in the copolymer, can be achieved by copolymerisation of ethylene and propylene with non-conjugated dienes containing only one double bond capable of insertion for instance, 1,4-hexadiene, dicy-clopentadiene and 5-ethylidene-2-norbornene (endocyclic double bond)... 

Et(Ind)2ZrCl2/MAO gives copolymers of ethylene or propylene with nonconjugated dienes, such as 2-methyl-1,4-pentadiene, 7-methyl-1,6-octadiene and 1,7-octadiene, (Eq. 23) [103]. rac-Et(Ind)2ZrCl2/MAO also catalyzes copolymerizations of asymmetrically substituted linear dienes, 6-phenyl-1,5-hexadiene, 7-methyl-1,6-octadiene, and R-(+)-5,7-dimethyl- 1,6-octadiene. The copolymerization of R-(+)-5,7-dimethyl-l,6-octadiene with propylene to give the polymer with ca. 15% diene incorporation. The ratio of the diene-derived part is ca. 15% of the polymer [104]. 

Szewczyk, H., Zielasko, A. Determination of propylene in ethylene-propylene copolymers and terpolymers with dienes by infrared spectroscopy. Polimery 13, 415-418 (1968). 

From other p<%olefins, photocrossiinking of ethylene propylene da omers, copolymerized with dienes such as dicyclopentadiene, 1.4-hexadiene, and 5-ethylidene... 

Because of their saturated structure, EPM rubbers cannot be vulcanized by using accelerated sulfur systems, and the less convenient vulcanization with free-radical generators (peroxide) is required. In contrast, EPDM rubbers are produced by polymerizing ethylene and propylene with a small amount (3-8%) of a diene monomer, which provides a cross-bnk site for accelerated vulcanization with sulfur. 

A more speeialized reaetion involves the use of a Ziegler eatalyst, formed from vanadium and titanium halides eomplexed with alkyl aluminum compounds, to synthesize alternating copolymers from propylene and dienes, but the meehanism is now different. 

While the third monomer can be a conunon diene, like isoprene, more often it is a bridged ring structure with at least one double bond in the ring. In typical terpolymer rubbers with 60 to 40 ratios of ethylene to propylene, the diene components usually comprise about 3% of the total. Some specialty rubbers, however, may contain 10% of the diene or even more. Reaction conditions are always chosen to obtain 1,2 placement of the diene. Dienes in common use are ethylidine norbomene, methylene norbomene, 1,4-hexadiene, dicyclopentadiene, and cycloocadiene ... 

Special method of vulcanization with peroxide, dependent on transfer reactions, has to be developed. On the other hand, the newer ethylene-propylene elastomers are terpolymers (EPT rubbers) which contain a small percentage of a third component with diene structure, which provides the double bonds necessary for the classic sulfur vulcanization. Such third-component compounds include the following ... 

SBR elastomer with known crosslinking densities was studied in dynamic shear and tensile creep and data collected from -30 to 70 °C used to construct TTS master curves. In addition to a temperature shift factor a vertical shift factor was required from 10 to 30 °C to account for changes in density. Linear viscoelastic properties were observed in accordance with the classical theory of rubber elasticity. Standard vertical shift factors were required in a comparative TTS test with uncrosslinked polybutadiene and poly(ethylene-cu-propylene-co-diene monomer) (EPDM). ... 

Many types of rubber which resist ozone were obtained by copolymerization of ethylene and propylene with asymmetric dienes such as 1,4-hexadiene, dicyclopen-tadiene, or ethylidenenorbornene. The addition to the reaction mixture of a certain amount of diene allows preparation of a very stable polymer, because the formation of a linear polymer requires breaking of one double bond while the other bond is utilized to net the copolymer which takes place during the polymerization process. Vanadium... 

Interfacially active graft or block copolymers of the t5 pe A-B or A-C may compatibilize the immiscible polymers A and B provided that C is also miscible or capable of strong interactions with B. Poly(ethylene-co-propylene) elastomer (EPR) or poly(ethylene-co-propylene-co-diene) (EPDM) is an example of such nonreactive compatibilizer for polyethylene/polypropylene (PE/PP) blends. 

Ziegler Catalysts. For his work in the discovery of a new class of highly active catalysts for polymerization of ethylene, propylene, and dienes, Karl Ziegler shared the 1963 Nobel Prize in Chemistry with Guilio Natta whose contributions were predominantly related to polypropylene. Today, these catalysts together with the Phillips catalyst are responsible for the majority of the world s polyethylene production. Loosely defined, Ziegler catalysts are polyethylene catalysts derived from transition-metal halides and main group metal alkyls (46,50-53). In modem... 

Copolymerizations of ethylene and/or propylene with nonconjugated dienes using various metallocene catalysts are a useful method to synthesize polyolefins with cyclic backbones. 

Synthetic rubbers are produced as commodities. Polybutadiene, polybutylene, polychloroprene and polyepichlorohydrin are examples of elastomeric homopolymers. Copolymeric rubbers comprise poly-(butadiene-co-styrene), poly(butadiene-co-acryloni-trile), poly(ethylene-co-propylene-co-diene), and poly-(epichlorohydrin-co-ethylene oxide). The unsaturated group in the comonomer provides reactive sites for the crosslinking reactions. Copolymers combine resilience with resistance to chemical attack, or resilience in a larger temperature range, and thermoplastic-like properties. There are several studies in the literature describing the preparation of blends and composites of elastomers and conductive polymers. A description of some significant examples is given in this section. 

Like the butyls, there are basically two types of ethylene propylene. One is a fully saturated chemically inert copolymer of ethylene and propylene (EPR). The other, called EPDM, has the ethylene and the propylene, plus diene monomer. EPDM is chemically reactive and capable of sulfur vulcanization. The copolymer, EPR, is cured with a peroxide catalyst. 

In Section 8.2.1 reference was made to the work of Moore and Watson on the vulcanization of natural rubber with t-butyl peroxide and the reactions involved were summarized. It is however to be noted that additional reactions may be possible with other peroxides and other rubbers. In Chapter 12, for example, particular attention is given to the industrially important use of peroxides as curing agents for ethylene-propylene rubbers. At this stage comment will be confined to the most important reactions that may occur with diene rubbers. 

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