Vinylic Monomers, Hydroquinone

The reactive vinyl monomers usually are stabilized against polymerization, while in storage, by addition of 0.1 to 1% of an inhibitor. 1,4-Benzenediol (hydroquinone), 2,6-di-terf-butyl-4-methylbenzenol, and 4- ert-butyl-l,2-ben-zenediol are used for this purpose. These substances are especially effective at scavenging RO- radicals, which are formed by oxidation of the monomer with atmospheric oxygen. 

Low concentrations of S02 and TBHP were used to initiate the polymerization of MMA and other vinyl monomers. DPPH and hydroquinone do not inhibit this MMA polymerization. End-group analysis indicates the incorporation of sulfonate and hydroxyl end groups in the polymers, and copolymerization results (MMA-isoprene and MMA-acrylic acid) with this S02-TBHP initiator system and AIBN are in good agreement. The over-all polymerization appears to be primarily radical in nature. Inert solvents (benzene, toluene, and xylene) enhance the rate of polymerization of MMA but not of other vinyl monomers (AN, Sty, V A, EM A, MA, etc.). An initiation mechanism involving monomer and solvent appears to be predominant in the case of MMA, while with other monomers an initiation reaction involving only the monomer is predominant. 

Nyloprint, of BASF is a solid type of photosensitizer compound coated plate, around 1967. The solid photopolymerizing material is a combination of an alcohol-soluble polyamide (such as a polyamide copolymer of hexamethylene diammonium adipate and e-caprolactam), a vinyl monomer (such as bis-acrylamide, hexamethylene bis-acrylamide, triethylene glycol diacrylate, etc.), a photo-initiator such as benzoin methyl ether, and an inhibitor (such as hydroquinone) and maleic anhydride to function as a... 

The determination of hydroquinone in vinylic monomers and polymers, can be carried out in a methanol-benzene (1 1) mixture containing OT M ammonium acetate as a supporting electrolyte. Monomers can be mixed with the solvent in a 1 1 ratio and 0-00004 per cent of hydroquinone can be detected. In polymers, the solubility of which is about 0-2 g in 100 ml. of solvent, 0-03 per cent of hydroquinone is the lowest level. The method has been applied to methacrylates, vinylacetate, acrylonitrile, styrene and divinyl-benzene. For monomeric acids, such as methacrylic, the acid is first neutralized to phenolphthalein, and the anodic wave of hydroquinone is recorded in a phosphate-borate pH 7-0 buffer. 

Hydroquinone -kwi-lnon n [ISV] (ca. 1872) (p-dihydroxybenzene, hydroquinol, p-hydroxyphenol, qui-nol) C6H4(0H)2. a white crystalline material derived from aniline, used, as are many of its derivatives, as an inhibitor of free-radical polymerization in unsaturated polyester resins and in monomers such as vinyl acetate. Hydroquinone is almost colorless and can retain its inhibitory action even in the presence of oxygen. (Odian GC (2004) Principles of polymerization. Wiley, New York)... 

In another study, uniform composite polymethyl-methacrylate/polystyrene (PMMA/PS) composite particles in the size range of 1-10 fim were prepared by the seeded emulsion polymerization of styrene [121]. The PMMA seed particles were initially prepared by the dispersion polymerization of MMA by using AIBN as the initiator. In this polymerization, poly(7V-vinyl pyrolli-done) and methyl tricaprylyl ammonium chloride were used as the stabilizer and the costabilizer, respectively, in the methanol medium. Seed particles were swollen with styrene monomer in a medium comprised of seed particles, styrene, water, poly(7V-vinyl pyrollidone), Polywet KX-3 and aeorosol MA emulsifiers, sodium bicarbonate, hydroquinone inhibitor, and azobis(2-methylbu-... 

Vinyl acetate is normally inhibited with hydroquinone to prevent polymerisation. A combination of too low a level of inhibitor and warm, moist storage conditions may lead to spontaneous polymerisation. This process involves autoxidation of acetaldehyde (a normal impurity produced by hy droly sis of the monomer) to a peroxide which initiates exothermic polymerisation as it decomposes. In bulk, this may accelerate to a dangerous extent. Other peroxides or radical sources will initiate the exothermic polymerisation. 

For example, Melville [26] studied the ultrasonically induced polymerisation of monomers such as styrene, methyl methacrylate and vinyl acetate in the presence and absence of polymethyl methacrylate and found that the polymerisation rates ( 1 % conversion/h) were not substantially increased by the presence of polymer. He concluded, in contrast to Driscoll, that the degradation of polymer was not the major source of radical production. Using hydroquinone as an inhibitor, he was able to deduce, from retardation times, that the rate of radical production was 2 X 10 mol dm s. A typical value for radical production using as an example the thermal initiation of AZBN (10 mol dm ) at 60 °C is 2 x 10" mol dm s" ... 

Vinyl acetate monomer, supplied by Celanese Chemical Company with 3-5 ppm hydroquinone, was distilled under nitrogen through a 5-ft packed column with reflux at 1 atm. The distilled monomer contained less than 0.5 ppm HDQ. Ammonium persulfate (certified grade) was used as the initiator cuid sodium lauryl sulfate (laboratory grade) was the surfactant. The emulsions were buffered with sodium acetate (certified grade) and acetic acid (reagent grade). 

Some reagents react with the initiating radical to give unreactive substances, a process known as inhibition. A common inhibitor for vinyl polymerisations is hydroquinone, which reacts by the transfer of two hydrogen radicals to the initiator radicals (Fig. 2.4). This gives quinone and unreactive initiator and has the net effect of causing a lag time in the polymerisation and a decrease in the initiator concentration. Monomers are often stored in the presence of inhibitor in order to prevent polymerisation. The amount and type of inhibitor may vary depending on the monomer batch and the manufacturer. For inter-laboratory comparisons of materials to be possible, it is therefore important to remove the inhibitor and purify the monomers prior to use [13]. 

VINYL ACETATE or VINYL ACETATE HQ or VINYL ACETATE MONOMER (108-05-4) C4HSO2 Forms explosive mixture with air [explosion limits in air (vol %) 2.6 to 13.4 fiashpoint 18°F/-7°C autoignition temp 756°F/402°C Fire Rating 3]. Polymerizes readily if not inhibited elevated temperatures and the influence of light, air, oxygen, water, or peroxides initiates violent reaction. Must be stabilized (hydroquinone or diphenylamine has been recommended) to prevent polymerization. Violent reaction with strong oxidizers, non-oxidizing mineral acids, 2-aminoethanol, butyl acrylate ... 

VINYL NEODECANO ATE (51000-52-3) CijHjjOj Combustible, polymerizable liquid (flash point >175°F/>79°C). Inhibitor (monomethyl ether of hydroquinone or copper is recommended) must be present in adequate concentrations to avoid explosive polymerization. Inconq)atible with acids, 2-aminoethanol, ammonia, aliphatic amines, alkanolamines, ethylene diamine, ethyleneimine, ozone. The monomer is usually supplied in bulk or resin-lined drums and may be stored in tin- or stainless steel-lined dmms. Storage in plastic or other vessels is not recommended. The uninhibited... 

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