1,2-Dimethylbutadiene, polymerization

Nafion-H (144), a perfluorinated resin-sulfonic acid, is an efficient Bronsted-acid catalyst which has two advantages it requires only catalytic amounts since it forms reversible complexes, and it avoids the destruction and separation of the catalyst upon completion of the reaction [94], Thus in the presence of Nafion-H, 1,4-benzoquinone and isoprene give the Diels-Alder adduct in 80% yield at 25 °C, and 1,3-cyclohexadiene reacts with acrolein at 25 °C affording 88 % of cycloadduct after 40 h, while the uncatalyzed reactions give very low yields after boiling for 1 h or at 100 °C for 3.5 h respectively [95], Other examples are given in Table 4.24. In the acid-catalyzed reactions that use highly reactive dienes such as isoprene and 2,3-dimethylbutadiene, polymerization of alkenes usually occurs with Nafion-H, no polymerization was observed. 

Inclusion polymerization in PHTP has a wider range of feasibility butadiene and 2,3-dimethylbutadiene polymerize in PHTP, whereas butadiene polymerizes only in urea, and 2,3-dimethylbutadiene polymerizes only in thiourea. 

Polymeric dimethylbutadiene peroxide Polymeric peroxides of methacrylic acid esters and styrene... 

Dimethylbutadiene Peroxide, Polymeric. See Vol 5 D1329-R to D1330-L Hexamethylenetetramine Triperoxide and Hexa-methylenetriamine Triperoxide. See Vol 7, H83-L... 

Dimethyl peroxide Diethyl peroxide Di-t-butyl-di-peroxyphthalate Difuroyl peroxide Dibenzoyl peroxide Dimeric ethylidene peroxide Dimeric acetone peroxide Dimeric cyclohexanone peroxide Diozonide of phorone Dimethyl ketone peroxide Ethyl hydroperoxide Ethylene ozonide Hydroxymethyl methyl peroxide Hydroxymethyl hydroperoxide 1-Hydroxyethyl ethyl peroxide 1 -Hydroperoxy-1 -acetoxycyclodecan-6-one Isopropyl percarbonate Isopropyl hydroperoxide Methyl ethyl ketone peroxide Methyl hydroperoxide Methyl ethyl peroxide Monoperoxy succinic acid Nonanoyl peroxide (75% hydrocarbon solution) 1-Naphthoyl peroxide Oxalic acid ester of t-butyl hydroperoxide Ozonide of maleic anhydride Phenylhydrazone hydroperoxide Polymeric butadiene peroxide Polymeric isoprene peroxide Polymeric dimethylbutadiene peroxide Polymeric peroxides of methacrylic acid esters and styrene... 

At least 90 percent of free-radical-polymerized 2,3-dimethylbutadiene consists of 1,4 units according to ozone degradation experiments. Successive substitution of the methyl groups on carbons 2 and 3 of butadiene is seen to increase the proportion of 1,4 units formed. In polychloroprene no less than 97 percent of the structure consists of 1,4 Cl... 

In the free radical polymerization of 1,3-dienes, 1,4 addition dominates 1,2 addition. The proportion of 1,2 (and 3,4 )units decreases in passing from butadiene to its methyl and chlorine substitution products isoprene, 2,3-dimethylbutadiene and chloroprene. The trans configuration of the 1,4 unit from butadiene is formed preferentially, the proportion of trans increasing rapidly with lowering of the polymerization temperature. 

A line of research that has aroused much interest in recent years is the study of head-to-head, tail-to-tail polymers (96-98). Their direct synthesis has little likelihood of being successffil as head-to-tail sequences usually predominate in vinyl polymerization. One possibility for their preparation is through the chemical modification of suitable preformed polymers. In the case of the head-to-head, tail-to-tail polypropylene, different stereoisomeric forms have been isolated, depending on the method of preparation. In the general scheme, the precursor is an unsaturated polymer obtained by polymerization of the disubsti-tuted butadiene (2,3-dimethylbutadiene or 2,4-hexadiene) then, by chemical or catalytic reduction, this polymer is converted into the desired polypropylene, whose stmcture can then be examined by NMR spectra. Head-to-head, tail-to-... 

More recently ERUSSALIMSKY et al (15) investigated the polymerization of 2,3-dimethylbutadiene induced by oligo-2,3 dimethyl-butadienyllithium/TMEDA. Contrary to butadiene and isoprene, catalytic amounts of TMEDA decrease the propagation rate of dime- thylbutadiene. 

When butadiene and 2,3-dimethylbutadiene are included in the channels of urea and thiourea, respectively, 1,4 addition invariably results to yield polymers with chemical and stereo regularities (Scheme 39). Note that addition in the 1,2 fashion is prevented sterically by the narrow channel. Similarly, high selectivity was obtained when butadiene, vinyl chloride, and styrenes were polymerized in the channels of cyclophosphazenes. Syndiotac-tic polymer alone is obtained from vinyl chloride included in urea channels this is apparently the first example of inclusion polymerization of a vinyl polymer in which control is exerted over the steric configuration of the developing tetrahedral carbon atom (Scheme 39). Highly isotactic polymer is obtained from 1,3-pentadiene when it is included in a perhydrotriphenylene matrix (Scheme 39). Note that addition could occur at either end (i.e., Q to... 

Figure 33. Polymerization of 2,3-dimethylbutadiene in the thiourea channel. Note the relative arrangement of reactive monomers.

Hr he first observations of popcorn (PC) polymer formation go back to the beginning of this century when Kondakow (J) studied the polymerization of dimethylbutadiene. The name popcorn polymers, however, is of much more recent origin. It was first used in the U.S. in 1940, where the similarity of appearance of these materials to a sponge or to cauliflower was replaced by the obviously more popular popcorn. Today, it is possible to prepare polymers of this type having no similarity at all to popcorn, but the name is retained. 

The presence of TMEDA has been reported to cause a decrease in the rate of polymerization of 2,3-dimethylbutadiene 186) but an increase in that of isoprene187). 

This group covers polymeric peroxides of indeterminate structure rather than polyfunctional macromolecules of known structure. These usually arise from autoxidation of susceptible monomers and are of very limited stability or explosive. Polymeric peroxide species described as hazardous include those derived from butadiene (highly explosive) isoprene, dimethylbutadiene (both strongly explosive) 1,5-p-menthadiene, 1,3-cyclohexadiene (both explode at 110°C) methyl methacrylate, vinyl acetate, styrene (all explode above 40°C) diethyl ether (extremely explosive even below 100°C ) and 1,1-diphenylethylene, cyclo-pentadiene (both explode on heating). 

As was found for the polymerization of styrene, CpTiCT/M AO and similar half-sandwich titanocenes are active catalysts for the polymerization of conjugated 1,3 dienes (Table XX) (275). Butadiene, 1,3-pentadiene, 2-methyl-l,3-pentadiene, and 2,3-dimethylbutadiene yield polymers with different cis-1,4, trans-1,4, and 1,2 structures, depending on the polymerization temperature. A change in the stereospecificity as a function of polymerization temperature was observed by Ricci et al. (276). At 20°C, polypen-tadiene with mainly ds-1,4 structures was obtained, whereas at -20°C a crystalline, 1,2- syndiotactic polymer was produced. This temperature effect is attributed to a change in the mode of coordination of the monomer to the metallocene, which is mainly cis-rf at 20°C and trans-rj2 at -20°C. 

As found for the polymerization of styrene, CpTiCl3/MAO and similar half-sandwich titanocenes are active catalysts for the polymerization of conjugated 1,3-dienes (Table 25) [218], Butadiene, 1,3-pentadiene, 2-methyl-l,3-pentadiene and 2,3-dimethylbutadiene yield polymers with different... 

Co(acac)3 is frequently used as a probe for enantioseparation efficiency of col-umns " . A monolytic capillary silica gel column was functionalized with methacrylate residues in two steps, as shown in equation and then it was impregnated with cellulose or amylose (51a, b) which was modified so that 30% of the R groups were the methacrylate group 52 and the rest was identical to R (53). For further stability of the column, the polymeric modifier was immobilized on the silica gel by in situ copolymerization with an olefinic monomer such as 2,3-dimethylbutadiene. Only the column containing cellulose modified as in 51a was able to separate the Co(acac)3 racemic mixture, whereas neither cellulose nor amylose modified as in 51b did, although they were successful in resolving other racemic mixtures ° °. ... 

In thiourea the polymerization of 2,3-dimethylbutadiene and 2.3-di-chlorobutadiene was investigated in detail (77). Both monomers form complexes with thiourea in which they are stacked as shown in Fig. 2. 

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