Crosslinkable emulsion polymers

Tg values of several important homopolymers are hsted in reference [2], The values were determined on samples of non-crosslinked emulsion polymers. In crosslinked polymers, Tg is shifted to higher temperatures as a result of the restricted chain mobility. A number of approximations for calculating the Tg of copolymers have been proposed in the literature [26], The Gordon-Taylor equation usually produces reliable results ... 

Distinctly different approaches to avoid these problems and still achieve high viscosities were conceived and applied. The different approaches can be categorized as 1) preparation of emulsions or foams and 2) addition of crosslinkers to the polymer. Two separate processes which utilized crosslinking of polymer gelling agents were pursued. These are the use of secondary (or delayed) gelling agents and the use of metallic crosslinkers added on-site. 

Figure 6.4 The preparation of nanostructured materials in solution evolves from (a) the classic examples of suspension, dispersion, or emulsion polymerization, to the methods that include the covalent crosslinking of select domains within supramolecular polymer assemblies (b) core crosslinking of polymer micelles (c) shell crosslinking of polymer micelles (SCKs) (d) nanocages from core-eroded SCKs (e) shaved hollow nanospheres from outer shell/core-eroded vesicles.

By far the most studied PolyHIPE system is the styrene/divinylbenzene (DVB) material. This was the main subject of Barby and Haq s patent to Unilever in 1982 [128], HIPEs of an aqueous phase in a mixture of styrene, DVB and nonionic surfactant were prepared. Both water-soluble (e.g. potassium persulphate) and oil-soluble (2,2 -azo-bis-isobutyronitrile, AIBN) initiators were employed, and polymerisation was carried out by heating the emulsion in a sealed plastic container, typically for 24 hours at 50°C. This yielded a solid, crosslinked, monolithic polymer material, with the aqueous dispersed phase retained inside the porous microstructure. On exhaustive extraction of the material in a Soxhlet with a lower alcohol, followed by drying in vacuo, a low-density polystyrene foam was produced, with a permanent, macroporous, open-cellular structure of very high porosity (Fig. 11). 

Acrylic Monomers. The physical properties of a polymer are dependent upon the monomers used in the polymerization. Impurities contained in the monomers also affect the physical properties. Acrylosilane resins and crosslinkable emulsions can be prepared using 3-(Diethoxymethylsilyl) propyl methacrylate (I) (H)). Free-radical polymerization using (I) will yield a resin... 

The physical or chemical crosslinking of polymers can be also realized in water-in-oil (W/O) emulsion systems. In this case, aqueous droplets of prepolymers are stabilized by oil-soluble surfactants in a continuous oil phase. Hyaluronan-based microgels were prepared by crosslinking of carboxylic units of hyaluronan with adipic dihydrazide in aqueous droplets [19]. Chitosan-based microgels were prepared by crosslinking of chitosan chains with glutaraldehyde in aqueous droplets [20-25],... 

An emulsion polymer-isocyanate adhesive, a crosslinked polyvinyl acetate adhesive, a resorcinol-formaldehyde adhesive, a phenol-resorcinol-formalde-hyde adhesive, and an acid-catalyzed phenolic-formaldehyde adhesive developed bonds of high shear strength and wood failure at all levels of acetylation in the dry condition. A neoprene contact bond adhesive and a moisture-curing polyurethane hot-melt adhesive performed as well on acetylated wood as untreated wood in tests of dry strength. Only a cold-setting resorcinol-formal-... 

Latex IPNs. Latex IPNs are the third type of IPNs and are manufactured according to the general schematic illustrated in Figure 3. Latex IPN synthesis involves the initial synthesis of a crosslinked seed polymer, usually in the form of an aqueous latex. The seed latex is then swollen with a second monomer/crosslinker/initiator system which is then polymerized "in situ" to form an aqueous IPN emulsion. Materials of this type are best suited to coating applications as illustrated by the development of "Silent Paint" by Sperling et al ( ). However, latex IPNs are limited to water emulsifiable monomer/polymer systems, most of which have fairly low service temperatures, less than 150 C. 

All these emulsion polymers are aqueous based, supplied at 45% solids. The polymers are all self-crosslinking and self-catalyzed to provide maximum durability. 

In the coatings industry, emulsion polymerization, as a synthetic tool for the preparation of acrylic and vinyl polymers, allows the manufticturer access to a wide array of polymeric systems, simply based on the types and ratios of the monomers used [7]. However, coatings derived fi"om these emulsion polymers often are deficient in performance because of lack of an internal crosslinking mechanism. Silanes can remedy this deficiency. 

Emulsion polymers (latexes) are the most commonly used film formers in the coating industry. This is particularly the case with aqueous emulsion paints that are used for home decoration. These aqueous emulsion paints are apphed at room temperature, and the latexes coalesce on the substrate to form a thermoplastic film. Occasionally, functional polymers are used for crosslinking in the coating system. The polymer particles are typically sub micron (0.1-0.5 pm). 

ZinplexlS. [Ultra Additives] Crosslinker for ink, floor polish, emulsion polymers. 

A majority of the acrylic emulsion polymers used in textile and non-woven applications are crosslinked or cured after film formation to provide wet stroigth, solvent resistance and durability to laundering and dry cleaning. As with architectural coatings binders, the principal monomers used are BA, EA and MMA,... 

Figure 1 8 Effects on modulus-temperature behaviour of acrylic emulsion polymers (a) molar mass and crosslinking, (b) cc lymer vs blend of lattices...

Uses Crosslinking agent, hand builder adding durability and resilience to fabrics (cellulosics, synthetics) adds durability to fluorochem. and water repellent finishes crosslinking agent for hydroxyl-contg. emulsion polymers for top coat systems, waterborne wood finishes, nonwoven binders... 

Uses Reactive comonomer for acrylic resins in self-crosslinking emulsions, heat-curing coalings, crosslinked acrylic sheets Manuf/Distrib. Aldrich Fluka Monomer-Polymer Dajac Labs ... 

Cymel 350 Cymel 1125 crosslinking agent, hydroxyl-contg. emulsion polymers topcoats... 

Okubo et al. examined the penetration/release behavior of various solvents in-to/from the interior of micron-sized monodisperse cross-linked polystyrene/poly-divinylbenzene composite particles [63]. The hollow particles were produced by the seeded polymerization utilizing the dynamic swelling method [64], Itou et al. prepared crosslinked hollow polymer particles of submicron size by means of a seeded emulsion polymerization [65]. The morphology of the particles depends on the composition of divinylbenzene and methyl methacrylate. 

Polychloroprene. To 200 g of emulsion were added 2 g of a 50% water solution of sodium dibutyl dithiocarbamate, 8.3 g of zinc oxide dispersion, and 2 g of a butylated bisphenol A dispersion. The mixture was stirred and films were cast, dried, and cured as above, thereby crosslinking the polymer via two mechanisms the usual zinc oxide vulcanization, and a bisalkylation in which the crosslinking takes place at sites where there are tertiary allylic chlorine atoms formed by 1,2 polymerization of chloroprene monomer. 

Silicone. To 125 g of silicone emulsion was added 25 g of stannous octoate emulsion. The mixture was stirred, films cast, dried, and cured as before, thus crosslinking the polymer through formation of siloxane bonds between chains by reaction of stannous octoate with the active hydrogen atoms present. 

The latex IPNs were synthesized by a two-stage emulsion polymerization technique. The first stage consisted of making a seed latex of crosslinked PVC polymer I and then introducing the monomer II mixture of butadiene and acrylonitrile and crosslinker followed by a second polymerization. The recipe for the seed latex was as follows ... 

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