Methacrylate cross-linked

Methacrylate monomers are most effective with derivatives of bisphenol A epoxy dimethacrylates, in which the methacrylate—methacrylate cross-linking reaction proceeds at a much faster pace than with styrene monomer. This proves beneficial in some fabrication processes requiring faster cure, such as pultmsion and resin-transfer mol ding (RTM). 

It is on the basis of Lovrien s ideas concerning the photoregulation of polymer conformation in solution by means of photochromic species that Van der Veen Prins reported a first photomechanochemical model transducer, consisting of water-swollen membranes of poly(2-hydroxyethyl methacrylate) cross-linked with ethylene glycol dimethacrylate (1.1 wt-%) in the presence of a sulfonated bis-azostilbene dye (chry-sophenine G), the ratio chrysophenine/2-hydroxyethyl methacrylate being 1/400. 

Humic and flilvic acids are traditionally extracted from soils and sediment samples as the sodium salts by using sodium hydroxide solution. The material that remains contains the insoluble humin fraction (Figure 3). The alkaline supernatant is acidified to pH 2 with HCl. The humic acid precipitates and the fulvic acid remains in solution with other small molecules such as simple sugars and amino acids. These molecules can be separated by passing the solution through a hydrophobic resin, such as the methacrylate cross-linked polymer, XAD-8. The fulvic acids will sorb to the resin while the more hydrophilic molecules pass through the column. The fulvic acid can be removed with dilute base. 

Sequential IPNs are started with one polymer that is already cross-linked. It is swollen, and a monomer along with an initiator and a cross-linking agent are added and polymerized in place. A typical example (37) is an elastomer such as butadiene or ethyl acrylate cross-linked with divinylbenzene as the first polymer. The monomer that is polymerized in the swollen polymer is styrene or methyl methacrylate cross-linked with divinylbenzene or tetraethylene glycol dimethacrylate. The initiator is potassium for butadiene, and benzoin for the other monomers. 

Rasmussen found that copolymers comprising cross-Unked networks of meth-acrylic acid and 2-hydroxy methacrylate, cross-linked with cross-linking agents such as ethylene glycol dimethacrylate and 1,1,1-trimethylolpropane trimethacrylate had tensile strengths well above the tensile strengths of polyacrylamide type materials (Table 4.1) [6]. 

Cross-linking by addition polymerization is also used to a considerable extent. Unsaturated polyesters are cross-linked by copolymerization with styrene or methyl methacrylate. Cross-linking soft, natural rubber with sulfur gives the normally used hard, vulcanized rubber. Ethylene-propylene rubbers can be cross-linked with peroxides. The cross-linking of elastomers is also called vulcanization, since the classic cross-linking of natural rubber, cis-l,4-poly(isoprene), uses heat and sulfur, which were the elements assigned to the god Vulcan (see also Chapter 37). 

EC member states have voted that there should be no further restriction on the marketing and use of cadmium pigments for plastics. The International Cadmium Association (ICA) believes that this should now be safeguarded for the next three years, when a more far-reaching report on cadmium and cadmium oxide is expected. A Directive (91/338/EEC) was adopted by the EC to harmonize restrictions on the use of cadmium-based pigments that had been introduced by different countries. It does not ban the use of these materials but limits their use. For example, cadmium-based pigments may not be used in plastics materials where there are other satisfactory substitutes. Polypropylene and polystyrene are specifically listed as polymers where non-cadmium pigments must be used where possible. Other polymers where there is a restriction include thermoplastic polyesters, poly(methyl methacrylate), cross-linked polyethylene and melamine, urea, and polyester resins. 

Copolymer. 4-(iV -2-methyacroyolxyelhyl-N-methyl-amino-4 -nitrostilbene and methyl methacrylate. Cross-linked polymer polyurethane polymer containing Disperse Red 19 chromophores. 

It is only relatively recently that the technology has been developed to produce particulate materials that meet the requirements of HPIEC of peptides and proteins. Table 11 lists these requirements. Historically the first of these substrates was silica, followed by polystyrene highly cross-linked with divinylbenzene, then hydroxylated polyether, poly methacrylates, cross-linked with glycerol and glycols, alumina and most recently, a polyester—polyamine co-polymer. 

Figure 4 The dynamic storage modulus, of polyurethane (linear) and poly(ester-styrene-methyl methacrylate) (cross-linked) semi-II SIN S. The midrange compositions have very broad glass transitions, indicative of a microheterogeneous...

The use of hydroxyethyl (also hydroxypropyl) methacrylate as a monomer permits the introduction of reactive hydroxyl groups into the copolymers. This offers the possibility for subsequent cross-linking with an HO-reactive difunctional agent (diisocyanate, diepoxide, or melamine-formaldehyde resin). Hydroxyl groups promote adhesion to polar substrates. 

Use of dimethylaminoethyl (also rert-butylaminoethyl) methacrylate as a monomer permits the introduction of pendent amino groups which can serve as sites for secondary cross-linking, provide a way to make the copolymer acid-soluble, and provide anchoring sites for dyes and pigments. 

Tetrahydrofurfuryl acrylate and methacrylate reactive unsaturated monomers, are readily polymerized and easily cross-linked by exposure to heat, peroxide catalysts, or uv radiation. 

Anaerobic stmctural adhesives are typically formulated from acryhc monomers such as methyl methacrylate [80-62-6] C Hg02, and methacrylic acid [79-41-4] (see Acrylic ester polymers). Very often, cross-linking agents such as dimethacrylates are also added. A peroxide, such as cumene... 

In poly(ethylene terephthalate) (14—16) and poly(methyl methacrylate) (17—19), the mechanism of action of phosphoms flame retardants is at least partly attributable to a decrease in the amount of combustible volatiles and a corresponding increase in nonvolatile residue (char). In poly(methyl methacrylate), the phosphoms flame retardant appears to cause an initial cross-linking through anhydride linkages (19). 

Other Polymers. Besides polycarbonates, poly(methyl methacrylate)s, cycfic polyolefins, and uv-curable cross-linked polymers, a host of other polymers have been examined for their suitabiUty as substrate materials for optical data storage, preferably compact disks, in the last years. These polymers have not gained commercial importance polystyrene (PS), poly(vinyl chloride) (PVC), cellulose acetobutyrate (CAB), bis(diallylpolycarbonate) (BDPC), poly(ethylene terephthalate) (PET), styrene—acrylonitrile copolymers (SAN), poly(vinyl acetate) (PVAC), and for substrates with high resistance to heat softening, polysulfones (PSU) and polyimides (PI). 

Fig. 26. Qualitative compatison of substrate materials for optical disks (187) An = birefringence IS = impact strength BM = bending modulus HDT = heat distortion temperature Met = metallizability WA = water absorption Proc = processibility. The materials are bisphenol A—polycarbonate (BPA-PC), copolymer (20 80) of BPA-PC and trimethylcyclohexane—polycarbonate (TMC-PC), poly(methyl methacrylate) (PMMA), uv-curable cross-linked polymer (uv-DM), cycHc polyolefins (CPO), and, for comparison, glass.

Organic peroxides are used in the polymer industry as thermal sources of free radicals. They are used primarily to initiate the polymerisation and copolymerisation of vinyl and diene monomers, eg, ethylene, vinyl chloride, styrene, acryUc acid and esters, methacrylic acid and esters, vinyl acetate, acrylonitrile, and butadiene (see Initiators). They ate also used to cute or cross-link resins, eg, unsaturated polyester—styrene blends, thermoplastics such as polyethylene, elastomers such as ethylene—propylene copolymers and terpolymers and ethylene—vinyl acetate copolymer, and mbbets such as siUcone mbbet and styrene-butadiene mbbet. 

The cross-linking reaction mechanism is also influenced by the presence of other monomers. Methyl methacrylate is often used to improve the uv resistance of styrene-based resins. However, the disparate reaction rates of styrene and methacrylate monomer with the fumarate unsaturation not only preclude the use of more than 8% of the methacrylate monomer due to the significant slowing of the cross-linking reaction but also result in undercured products. 

Poly(methyl methacrylate) and poly(vinyl acetate) precipitate from the resin solution as it cures. This mechanism offsets the contraction in volume as the polyester resin cross-links, resulting in a nonshrinking thermoset. Other polymer additives such as poly(butylene adipate) provide similar shrinkage... 

Interpenetrating networks of DMPPO and polymers such as polystyrene, polybutadiene, poly(urethane acrylate), and poly(methyl methacrylate) have been prepared by cross-linking solutions of DMPPO containing bromomethyl groups with ethylenediamine in the presence of the other polymer (68). 

The DADC monomer has been copolymerized with small amounts of polyfunctional methacryflc or acryflc monomers. For example, 3% triethylene glycol dimethacrylate was used as a flexibiflzing, cross-linking agent with a percarbonate as initiator (26). CR-39 and diethylene glycol diacrylate containing isopropyl percarbonate were irradiated with a mercury lamp to a 92% conversion and then cured at 150°C (27). By a similar two-step process DADC was copolymerized with methyl methacrylate and tetraethylene glycol dimethacrylate (28). 

Monomers such as aUyl methacrylate and diaUyl maleate have appUcations as cross-linking and branching agents selected especiaUy for the different reactivities of their double bonds (90) some physical properties are given in Table 8. These esters are colorless Uquids soluble in most organic Uquids but htde soluble in water DAM and DAF have pungent odors and are skin irritants. 

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