Copolymerization vinyl acetate

Although they lack commercial importance, many other poly(vinyl acetal)s have been synthesized. These include acetals made from vinyl acetate copolymerized with ethylene (43—46), propjiene (47), isobutjiene (47), acrylonitrile (48), acrolein (49), acrylates (50,47), aHyl ether (51), divinyl ether (52), maleates (53,54), vinyl chloride (55), diaHyl phthalate (56), and starch (graft copolymer) (47). 

Several important classes of polar monomers have so far eluded copolymerization by the Pd(II) system. Vinyl chloride insertion, for example, leads to catalyst deactivation following P-halide elimination to form inert chloride species such as 1.32, as shown by Jordan [90], Similarly, attempted vinyl acetate copolymerization results in deactivation by an analogous acetate elimination process, although the ester chelate intermediate that forms after insertion also effectively shuts down the reaction [90], Therefore, -elimination of polar groups represents a significant and unresolved problem for late transition metal polymerization systems unless access of the metal to it is restricted. 

R. Reed, Moldable Ethylene/Vinyl Acetate Copolymer , USP 4090894 (1978) CA 39, 148908 (1978) [Vinyl acetate copolymerized with ethylene is used as a desensitizer and binder for moldable expl compns of cyclic nitramines such as RDX. From 82 to 98 wt % of binder is used, and various ratios of ethylene to vinyl acetate moieties in the resin are utilized to modify molding and extrusion properties. Prepn of typical compns consists of dissolving the copolymer in benz and addition with stirring to an RDX/w slurry, which is stirred until mixt is complete, followed by filtration and drying. Table 1 presents properties of sample compns with and without the ethylene/vinyl acetate copolymer (EVA). The inventor also states that the EVA, unlike other polymeric binders, endothermically breaks down at high temps and acts as a heat sink for the expl content]... 

Emulsion polymerization reactors are made of stainless steel and are normally equipped with top-entry stirrers and ports for addition of reactants. Control of the reaction exotherm and particle size distribution of the polymer latex is achieved most readily by semibatch (also called semicontinuous) processes, in which some or all of the reactants are fed into the reactor during the course of the polymerization. Examples are given in Chapter 8. In vinyl acetate copolymerizations, a convenient monomer addition rate is such that keeps the vinyl acetate/water azeotrope retluxing. at about 70°C. 

Table III. Reactivity Ratios and Q and e Values for Ethylene-Vinyl Chloride and Ethylene-Vinyl Acetate Copolymerizations...

Some data recently obtained on high pressure ethylene copolymerizations illustrate the quantitative aspects of an ethylene-based Q-e scheme (6). In Figures 3 and 4 copolymer composition curves for the ethylene-vinyl chloride and the ethylene-vinyl acetate copolymerizations are given. The monomer reactivity ratios for these two systems are tabulated in Table III along with Q values and e values for vinyl chloride and vinyl acetate calculated using ethylene as the standard (Q = 1.0 and g = 0). These Q and e values may be compared with those obtained using styrene as the standard. 

A very common copolymer of vinyl chloride is with vinyl acetate. Copolymerization with vinyl acetate improves stability and molding characteristics. The copolymers are also used as fibers and as coatings. Copolymers intended for use in moldings are usually prepared by suspension polymerization. Those intended for coating purposes are prepared by solution, emulsion, and suspension polymerizations. The copolymers used in molding typically contain about 10% poly(vinyl acetate). Copolymers that are prepared for coating purposes can contain from 10-17% poly(vinyl acetate). For coatings, a third comonomer may be included in some resins. This third component may, for instance, be maleic anhydride, in small quantities, like 1%, to improve adhesion to surfaces. 

Ethylene can be free radically copolymerized with vinyl acetate. Copolymerization with 0%-35% vinyl acetate is carried out in bulk at 1000-2000 bar, that of 35%-100%at 100-400 bar in /-butanol, and that of 60%-100%at 1-200 bar in emulsion. Products with vinyl acetate contents of over 10% give shrinkable films those with up to 30% vinyl acetate give thermoplastic films, and those with over 40% vinyl acetate give clear films. Products of still higher vinyl acetate content are elastomers, fusion, and solvent adhesives or modifiers for PVC. The products can be cross-linked with lauroyl peroxide on the addition of, for example, triallyl cyanurate. Copolymers of ethylene and ethyl acrylate have similar properties. 

Alternating copolymers are the result of the copolymerization of 2-vinylpyridine with butylvinyl ether in the presence of acetic acid [(a) acetic acid =1 1.3] [610]. Other examples for alternating copolymers are (la)/vinyl acetate copolymerized in the presence of acetic acid [611] and (c)/acrylonitrile as well as (c)/acrylic amide, using K2S2O8 as complexing initiator [612]. 

MA-thiopene copolymerization, 361, 387 MA-vinyl acetate copolymerization, 333, 405 MA-yV-vinylcaprolactam copolymerization, 336 MA-vinyl ether copolymerizations, 320, 321, 386, 404, 405... 

MA copolymerization, 294 vinyl acetate copolymerization, 294 Lauryl methacrylate, MA copolymerization, 296, 537... 

High molecular weight and essentially linear polymers, controlled particle size in the case of emulsions, and even polymers with spatially regulated structures are available. Vinyl acetate copolymerizes with many other vinyl monomers. Acrylate esters vinyl chloride and vi-nylidene chloride dibutyl and other dialkyl maleates and fiimarates crotonic, acrylic, methacrylic and itaconic acids vinyl pyrroli-done and ethylene are commercially important comonomers. A monomer that does not combine with vinyl acetate alone may be combined by use of a third monomer. Grafting can be used with monomers such as styrene that do not copolymerize with vinyl acetate. 

Note that this inquiry into copolymer propagation rates also increases our understanding of the differences in free-radical homopolymerization rates. It will be recalled that in Sec. 6.1 a discussion of this aspect of homopolymerization was deferred until copolymerization was introduced. The trends under consideration enable us to make some sense out of the rate constants for propagation in free-radical homopolymerization as well. For example, in Table 6.4 we see that kp values at 60°C for vinyl acetate and styrene are 2300 and 165 liter mol sec respectively. The relative magnitude of these constants can be understod in terms of the sequence above. 

The combination of durability and clarity and the ability to tailor molecules relatively easily to specific applications have made acryflc esters prime candidates for numerous and diverse applications. At normal temperatures the polyacrylates are soft polymers and therefore tend to find use in applications that require flexibility or extensibility. However, the ease of copolymerizing the softer acrylates with the harder methacrylates, styrene, acrylonitrile, and vinyl acetate, allows the manufacture of products that range from soft mbbers to hard nonfilm-forming polymers. 

Hydrocarbon resins (qv) are prepared by copolymerization of vinyltoluene, styrene, and a-methylstyrene in the presence of a Eriedel-Crafts catalyst (AlCl ). These resins are compatible with wax and ethylene—vinyl acetate copolymer (197). 

In order to increase the solubiUty parameter of CPD-based resins, vinyl aromatic compounds, as well as other polar monomers, have been copolymerized with CPD. Indene and styrene are two common aromatic streams used to modify cyclodiene-based resins. They may be used as pure monomers or contained in aromatic steam cracked petroleum fractions. Addition of indene at the expense of DCPD in a thermal polymerization has been found to lower the yield and softening point of the resin (55). CompatibiUty of a resin with ethylene—vinyl acetate (EVA) copolymers, which are used in hot melt adhesive appHcations, may be improved by the copolymerization of aromatic monomers with CPD. As with other thermally polymerized CPD-based resins, aromatic modified thermal resins may be hydrogenated. 

Gross-Linking. A variety of PE resins, after their synthesis, can be modified by cross-linking with peroxides, hydrolysis of silane-grafted polymers, ionic bonding of chain carboxyl groups (ionomers), chlorination, graft copolymerization, hydrolysis of vinyl acetate copolymers, and other reactions. 

Vinyl acetate is another monomer used in latex manufacture for architectural coatings. When copolymerized with butyl acrylate, it provides a good balance of cost and performance. The interior flat latex paint market in North America is almost completely dominated by vinyl acetate—acryHc copolymers. Vinyl acetate copolymers are typicaHy more hydrophilic than aH-acryHc polymers and do not have the same ultraviolet light resistance as acryHcs as a result. 

Almost all synthetic binders are prepared by an emulsion polymerization process and are suppHed as latexes which consist of 48—52 wt % polymer dispersed in water (101). The largest-volume binder is styrene—butadiene copolymer [9003-55-8] (SBR) latex. Most SBRlatexes are carboxylated, ie, they contain copolymerized acidic monomers. Other latex binders are based on poly(vinyl acetate) [9003-20-7] and on polymers of acrylate esters. Poly(vinyl alcohol) is a water-soluble, synthetic biader which is prepared by the hydrolysis of poly(viayl acetate) (see Latex technology Vinyl polymers). 

Vinyl resins ie, copolymers of vinyl chloride and vinyl acetate which contain hydroxyl groups from the partial hydrolysis of vinyl acetate and/or carboxyl groups, eg, from copolymerized maleic anhydride, may be formulated with alkyd resins to improve their appHcation properties and adhesion. The blends are primarily used in making marine top-coat paints. 

Fig. 2. Relationship between relative rate and monomer composition in the copolymerization of DAP with vinyl monomers A, styrene or methyl methacrylate B, methyl acrylate or acrylonitrile C, vinyl chloride D, vinyl acetate, and E, ethylene (41).

Tables 7 and 8 give properties of some diaHyl esters. DimethaHyl phthalate [5085-00-7] has been copolymerized with vinyl acetate and benzoyl peroxide, and reactivity ratios have been reported (75).

In studies of the polymerization kinetics of triaUyl citrate [6299-73-6] the cyclization constant was found to be intermediate between that of diaUyl succinate and DAP (86). Copolymerization reactivity ratios with vinyl monomers have been reported (87). At 60°C with benzoyl peroxide as initiator, triaUyl citrate retards polymerization of styrene, acrylonitrile, vinyl choloride, and vinyl acetate. Properties of polyfunctional aUyl esters are given in Table 7 some of these esters have sharp odors and cause skin irritation. 

Small amounts of TAIC together with DAP have been used to cure unsaturated polyesters in glass-reinforced thermo sets (131). It has been used with polyfunctional methacrylate esters in anaerobic adhesives (132). TAIC and vinyl acetate are copolymerized in aqueous suspension, and vinyl alcohol copolymer gels are made from the products (133). Electron cure of poly(ethylene terephthalate) moldings containing TAIC improves heat resistance and transparency (134). 

The simplest monomer, ethylenesulfonic acid, is made by elimination from sodium hydroxyethyl sulfonate and polyphosphoric acid. Ethylenesulfonic acid is readily polymerized alone or can be incorporated as a copolymer using such monomers as acrylamide, aHyl acrylamide, sodium acrylate, acrylonitrile, methylacrylic acid, and vinyl acetate (222). Styrene and isobutene fail to copolymerize with ethylene sulfonic acid. 

Table 4. Copolymerization Parameters of Vinyl Acetate (M ) and Comonomers (M2)...

Issues to be considered in selecting the best stabilizing system are polymeric chain branching which increases with high temperature and the presence of some stabilizers, polydispersity of the particles produced, and grafting copolymerization, which may occur because of the reaction of vinyl acetate with emulsifiers such as poly(vinyl alcohol) (43,44). 

Continuous emulsion copolymerization processes for vinyl acetate and vinyl acetate—ethylene copolymer have been reported (59—64). CycHc variations in the number of particles, conversion, and particle-size distribution have been studied. Control of these variations based on on-line measurements and the use of preformed latex seed particles has been discussed (61,62). 

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