Vinyl peresters

Rate and activation parameter data are given in Table 96 for the decomposition of /-butyl vinyl peresters. Data for /-butyl perbenzoate are included for comparison. As one might anticipate, the activation parameters for the vinyl peresters are somewhat similar to those for the perbenzoate. However, the Ail values for the vinyl peresters are consistently lower than the value for the perbenzoate. Resonance stabilization of the benzoyloxy radical has been suggested °. The lower A//  

---

Polymers ndResins. / fZ-Butyl peroxyneopentanoate and other peroxyesters of neopentanoic acid can be used as free-radical initiators for the polymeri2ation of vinyl chloride [75-01-4] (38) or of ethylene [74-85-1]. These peresters have also been used in the preparation of ethylene—vinyl acetate copolymers [24937-78-8] (39), modified polyester granules (40), graft polymers of arninoalkyl acrylates with vinyl chloride resins (41), and copolymers of A/-vinyl-pyrrohdinone [88-12-0] and vinyl acetate [108-05-4] (42). They can also be used as curing agents for unsaturated polyesters (43). 

Azoperoxydic initiators are particularly important due to their capacity to decompose sequentially into free radicals and to initiate the polymerization of vinylic monomers. The azo group is thermally decomposed first to initiate a vinyl monomer and to synthesize the polymeric initiator with perester groups at the ends of polymer chain (active polymer) [31,32]. 

The rates of radical-forming thermal decomposition of four families of free radical initiators can be predicted from a sum of transition state and reactant state effects. The four families of initiators are trarw-symmetric bisalkyl diazenes,trans-phenyl, alkyl diazenes, peresters and hydrocarbons (carbon-carbon bond homolysis). Transition state effects are calculated by the HMD pi- delocalization energies of the alkyl radicals formed in the reactions. Reactant state effects are estimated from standard steric parameters. For each family of initiators, linear energy relationships have been created for calculating the rates at which members of the family decompose at given temperatures. These numerical relationships should be useful for predicting rates of decomposition for potential new initiators for the free radical polymerization of vinyl monomers under extraordinary conditions. 

For example polymethyl acrylate was treated with phosphorus penta-chloride to form copolymers containing 26.6 and 37.8% acid chloride units these copolymers, by treatment with tert-butyl hydroperoxide, yield 4.9 to 6% perester containing polymers which were used for grafting styrene, vinyl acetate, acrylonitrile (177). 

Cobalt octoate/dimethyl aniline liquid mixture in phthalate Special for bisphenol A or vinyl esters with ketone peroxides or peresters short gel/cure times 10-100 C a bed EG... 

Martin and his co-workers have provided a firm experimental foundation for anchimeric assistance in the homolytic decomposition of per-benzoate derivatives (Table 6). A single o-phenylthio group was found to increase the rate of decomposition of f-butyl perbenzoate by a factor of ca. 45 thousand. The effect is not steric since an o-r-butyl group hardly affects the rate of perester decomposition [compare (95) versus (99), Table 6]. A noticeable but weak effect is observed with the homologous sulfide (96). In addition to sulfur, anchimeric assistance by iodine and vinyl groups in (97) and (98), respectively, was observed. The bridged canonical species... 

The world s most popular method of PVC polymerization is the suspension method. Around 80% of PVC is produced this way. The difference in this method is that it uses initiators soluble in the monomer. They are dialkyl and diacyl peroxides, ketone peroxides, peroxo-dicarbonates, peroxo-ketals, alkyl peresters or azo compoimds. Seldom is the role of emulsifiers played by alkalies or buffers in order to improve the plasticizer adsorption in PVC. In this process, in order to obtain proper porosity and particle granulation, so-called suspension stabilizers are used, which are derivatives of meth-ylhydroxypropyl cellulose, karboxymethyl cellulose and poly(vinyl alcohols). PVC obtained this way is of high purity. Its molecular mass depends on the temperature of polymerization. Other parameters depend on the interfacial tension at the water-monomer interface. 

Use of the slug-wise addition of peresters in the emulsion polymerization of vinyl chloride [264]. 

Other examples of polymers containing peroxidic groups are noted in ref. 36. A recent example containing 2 kinds of perester groups and a vinyl group in shown in figure 4 ( ). ... 

In case of perester-stannous carboxylate redox system [192,193] with or without a complexing agent for vinyl chloride polymerization, the polymerization recipe was the same as described earlier for the SnCl2 as reduc-tant. In each case, 10 g of VCM was taken in the experiment for polymerization at 50 C, The conversion was increased in the presence of complexing agents. Some of the results are presented in Table 16. 

Table 16 Vinyl Chloride Polymerization at 50°C with Perester-Stannous Carboxylate Redox System with or Without Complexing Agent...

Vinyl pyridine-grafted polyolefins [229] having improved dyeability were prepared with >0.02 wt% based on the monomer of a perester catalyst and >0.1 wt% based on the monomer of a reducing agent promoter selected from lower-valent salts of multivalent metals, hydrosulfite, or alkali metal formaldehyde sulfoxylate. Thus, the polypropylene-styrene-vinylpyridine-graft copolymer prepared in the presence of 1 wt% sodium hydrosulfite and 0.5 wt% tert-huiyl 2-ethyl perhexanoate at 90 C was melt-spun into fibers... 

---