Other Reactive Double Bonds

Although acrylic and styrenic bonds are the most common double bonds of the macromonomers, some authors were interested in introducing unusual vinyl groups. Table 21 gathers some macromonomer structures bearing such peculiar reactive double bonds. 

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While the oxidation of ketones by peracids (Baeyer-Villiger reaction) has been used in steroids mainly for ring cleavage, it has occasionally been applied to 20-ketopregnanes for conversion to 17-acetoxy- or hydroxyandros-tanes. The synthetic utility of this method is limited since reactive double bonds and other ketones are incompatible with the reagent. 

Photodimerization of cinnamic acids and its derivatives generally proceeds with high efficiency in the crystal (176), but very inefficiently in fluid phases (177). This low efficiency in the latter phases is apparently due to the rapid deactivation of excited monomers in such phases. However, in systems in which pairs of molecules are constrained so that potentially reactive double bonds are close to one another, the reaction may proceed in reasonable yield even in fluid and disordered states. The major practical application has been for production of photoresists, that is, insoluble photoformed polymers used for image-transfer systems (printed circuits, lithography, etc.) (178). Another application, of more interest here, is the use that has been made of mono- and dicinnamates for asymmetric synthesis (179), in studies of molecular association (180), and in the mapping of the geometry of complex molecules in fluid phases (181). In all of these it is tacitly assumed that there is quasi-topochemical control in other words, that the stereochemistry of the cyclobutane dimer is related to the prereaction geometry of the monomers in the same way as for the solid-state processes. 

A great number of olefinic compounds are known to photodimerize in the crystalline state (1,2). Formation of a-truxillic and / -truxinic acids from two types of cinnamic acid crystals was interpreted by Bernstein and Quimby in 1943 to be a crystal lattice controlled reaction (5). In 1964 their hypothesis on cinnamic acid crystals was visualized by Schmidt and co-workers, who correlated the crystal structure of several olefin derivatives with photoreactivity and configuration of the products (4). In these olefinic crystals the potentially reactive double bonds are oriented in parallel to each other and are separated by approximately 4 A, favorable for [2+2] cycloaddition with minimal atomic and molecular motion. In general, the environment of olefinic double bonds in these crystals conforms to one of three principal types (a) the -type crystal, in which the double bonds of neighboring molecules make contact at a distance of -3.7 A across a center of symmetry to give a centrosymmetric dimer (1-dimer) (b) the / -type crystal, characterized by a lattice having one axial length of... 

In spite of the unfavorable topochemical arrangement (the reactive double bonds are rotated by 65° with respect to each other and the center-to-center double-bond distance is 3.83 A, see Figure 22), photodimerization occurs in crystals of 19 to give the syn head-tail isomer. On the other hand, 20 which also has nonideal topological arrangement of double bonds in the crystalline state (the distance between the centers of adjacent double bonds is 3.93 A the double bonds are rotated and make an angle of 28° when projected down the... 

The stereochemistry of photodimerization in the solid state and solution has been reported for several halogenated derivatives of t-1 (Table 2) (59-62). Solid state photodimerization of stilbenes, like other alkenes, is subject to topochem-ical control viz, the two reactive double bonds must be parallel and separated by < 4.2 A (63). The photostability of t-1 in the solid state (39b,59) is consistent with its reported crystal packing (64). The halogenated stilbenes 15-20 serve to illustrate the variety of stereochemical outcomes observed for solution and solid state dimerization (eq. 11). 

Other cases have been reported in which the reactive double bonds are skewed to each other and yet react topochemically upon irradiation. In the crystals of 2,5-dibenzylenecyclopentanone [84] and 1,4-dicinnamoylbenezene [67], the reactive bonds are rotated with respect to one another by 56° and 28.5°, respectively, but both are photoreactive. Similarly, the reactive bonds in propyl-4-[2-(4-pyriduyl)] cinnamate [85] are arranged skew to each other with a rotation angle of 74°. 

The proximity and the degree of parallelism of the reacting double bonds are crucial for dimerization. Generally, the reactive double bonds are expected to be within 4.2 A and be parallel to each other. 

Acrylic acid is almost exclusively used directly, or after conversion to an ester, as a monomer. Acrylate esters are produced by normal esterification processes. However, in dealing with acrylic acid, acrolein, or acrylates, unusual care must be taken to minimize losses due to polymerization and other side reactions such as additions of water, acids, or alcohols across the reactive double bond. Polyacrylic acids find use in superabsorbers, dispersants, and water treatment. The polyesters are used in surface coatings, textile fibers, adhesives, and various other applications. 

Patulin was originally considered desirable for its antibacterial properties. However, its toxicity to mammals precluded its use as an antibiotic. Patulin (fig. 4), a metabolite of many species of Penicillium and Aspergillus, has been detected in damaged apples, apple juice and apple cider made from partially decaying apples and in other fruit juices as well as in wheat. A heat-resistant fungus Byssochlamys nivea, frequently found in foods also produces patulin [109]. Due to highly reactive double bonds that readily react with sulfhydryl... 

Divinylbenzene (a crosslinking agent) has two reactive double bonds, which are both used when divinylbenzene inserts itself into two adjacent polymer chains. The chains cannot move past each other because the crosslinks bond adjacent polymer chains together making the polymer more rigid. 

The reactivity of the DSP crystal was thoroughly interpreted in terms of the topochemical concept proposed by Schmidt, in which potentially reactive double bonds are oriented parallel to each other and separated by approximately 3.5-4.2 A. The reaction proceeds with a minimum of atomic and molecular motion (2 ). The reactive double bonds in most of the topochemically polymeric crystals thus far found are related to the center of symmetry (centrosymmetric ct-type crystal) and dimerize to give highly crystalline polymers containing cyclobutanes with a 1,3-trans configuration in the main chain. 

Guideline Two. - Electron-rich double bonds react in preference to more electron-deficient double bonds. You can see that this is partly responsible for Guideline One but the principle extends beyond this. The benzoate ester 138 contains two trans double bonds but one is evidently much more reactive than the other. The double bond on the left is part of an allylic ester and is deactivated by the electron-withdrawing benzoate group. 

Ethylene and propylene monomers combine to form the saturated and stable backbone [4], This saturated backbone will provide excellent heat, oxidation, ozone, and weather aging because no reactive double bonds are in the backbone structure [4], The third monomer (ENB) is added in a controlled manner and provides a site for cross-linking via the double bond. The M in EPDM refers to a saturated backbone. By virtue of the ENB, various amounts of vulcanization can be obtained to acquire the durometer, tear strength and tensile and other properties needed for the sealing or isolation needs of the automobile part. 

Many organotin compounds, and in particular those that contain special substituents and are in some cases difficult to obtain in other ways, can be prepared by addition of organic tin hydrides to compounds containing double or triple carbon-carbon bonds. Tin hydrides containing three organic groups add to reactive double bonds and to acetylenes even on mere heating at 80 to 100° 437 e.g. ... 

The evidence so far points to an aromatic group (benzene) and a reactive double bond, which must be part of some substituent attached to the benzene ring. In other words, the presence of an arene is suggested. An arene is a hydrocarbon that contains both aliphatic and aromatic units. The presence of the benzene ring is confirmed by the fact, that vigorous oxidation of indene yields phthalic... 

In the case of BR or SBR, the efficiency can be much greater than 1.0, especially if all antioxidant materials are removed. A chain reaction is indicated here. It might be explained by steric considerations. In butadiene-based rubbers, double bonds are quite accessible. Radical addition to double bonds could give highly reactive radicals, which would be likely to add to other polymer double bonds. A chain of additions might be more likely in butadiene rubber than in the presence of hindering methyl groups in isoprene rubbers. 

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