Styrene monomer, determination

Table 2.12 shows results obtained for styrene monomer determinations carried out on two samples of pigmented polystyrene by the direct ultraviolet method and by the distillation... 

The free styrene monomer is restrained within the gel and further reaction with fumarate groups is determined by the spacial arrangement the styrene polymerizes in homopolymer blocks as it intercepts fumarate reaction sites. As individual micelles expand and deplete available fumarate sites in the short polymer chains, the remaining styrene forms homopolymer blocks that terminate at the boundaries between overlapping micelles (Fig. 4). 

A 3,500-gal reaetor with styrene monomer undergoes adiabatie polymerization after being heated inadvertently to 70°C. The maximum allowable working pressure (MAWP) of the reaetor is 5 bar absolute. Determine the relief vent diameter required. Assume a set pressure of 4.5 bara and a maximum pressure of 5.4 bara. Other data and physieal properties are given as follows [12] ... 

Steric factors appear to be dominant in determining AHv and ASP. The resonance energy lost in converting monomer to polymer is of secondary importance for most common monomers. It is thought to account for A//, for VAc and VC being lower than for acrylic and styrenic monomers. 

HS-GC methods have equally been used for chromatographic analysis of residual volatile substances in PS [219]. In particular, various methods have been described for the determination of styrene monomer in PS by solution headspace analysis [204,220]. Residual styrene monomer in PS granules can be determined in about 100 min in DMF solution using n-butylbenzene as an internal standard for this monomer solid headspace sampling is considerably less suitable as over 20 h are required to reach equilibrium [204]. Shanks [221] has determined residual styrene and butadiene in polymers with an analytical sensitivity of 0.05 to 5 ppm by SHS analysis of polymer solutions. The method development for determination of residual styrene monomer in PS samples and of residual solvent (toluene) in a printed laminated plastic film by HS-GC was illustrated [207], Less volatile monomers such as styrene (b.p. 145 °C) and 2-ethylhexyl acrylate (b.p. 214 °C) may not be determined using headspace techniques with the same sensitivities realised for more volatile monomers. Steichen [216] has reported a 600-fold increase in headspace sensitivity for the analysis of residual 2-ethylhexyl acrylate by adding water to the solution in dimethylacetamide. 

The Curie Point flash evaporation-pyrolysis gas chromatography-mass spectrometric method [32] described in section 2.2.1.2 for the analysis of aliphatic hydrocarbons in soil has also been applied to the determination of polystyrenes in soil via identification and determination of their unzipping pyrolysis products, such as styrene monomer, a-methyl styrene, 3-methyl styrene, 4-methyl styrene, a-3 dimethyl styrene, 3-ethylstyrene, a-4 dimethyl styrene, 3.5 dimethyl-styrene, a-2 or 2,5 or 2.4 dimethyl styrene also various phenyl ethers. 

The possibility of using graft polymerization of styrene on to allylated wood to provide covalent bonding between surfaces was also investigated (Ohkoshi, 1991). In this case, a free-radical initiator (BPO) was present in the styrene monomer that was used to impregnate the allylated wood, prior to hot-pressing. Bond strength was determined by... 

ISO 1622-1 1994 Plastics - Polystyrene (PS) moulding and extrusion materials - Part 1 Designation system and basis for specifications ISO 1622-2 1995 Plastics - Polystyrene (PS) moulding and extrusion materials - Part 2 Preparation of test specimens and determination of properties ISO 2561 1974 Plastics - Determination of residual styrene monomer in polystyrene by gas chromatography... 

Another major use of butadiene polymer is in the manufacture of HIPS. Most HIPS has about 4%i-12%i polybutadiene in it so that HIPS is mainly a PS-intense material. Here, the polybutadiene polymer is dissolved in a liquid along with styrene monomer. The polymerization process is unusual in that both a matrix composition of PS and polybutadiene is formed as well as a graft between the growing PS onto the polybutadiene is formed. The grafting provides the needed compatibility between the matrix phase and the rubber phase. The grafting is also important in determining the structure and size of rubber particles that... 

Analytical Procedures. Figures for conversion are based on a method in which the graft copolymer was dissolved in o-dichlorobenzene and residual styrene monomer was determined by ultraviolet spectrophotometry. 

Studies of the migration of styrene monomer from HIPS and likewise from PS foams via the gas phase has been determined in a sealed system. The results show that the amount of styrene migrating from the polymers is proportional to the square root of the time of exposure (34-36). 

Epoxy vinyl ester resins are a special class of unsaturated resin. This resin is made by capping an epoxy resin with methacrylic acid and then dissolving in styrene monomer to the desired viscosity. This gives mechanical properties similar to epoxy resins, but the processibility (low viscosity allowing for resin infusion processes) of an unsaturated polyester resin. As with unsaturated vinyl esters, the most common fire retardant vinyl ester resin is based on a resin made from a halogenated system, tetrabromobisphenol A. The level of bromine in the resin and the presence of antimony will determine the fire performance of the resin. These resins are normally used for corrosion resistant equipment or when fire performance and high mechanical properties are required. It is very difficult to get a low smoke value with a brominated vinyl ester resin again due to the fact that bromine... 

The initial concentration of styrene in the polymer (P), cp,o (mg kg-1), is known either from the manufacturer of the material or has been determined by analysis of the material. In the absence of initial styrene monomer concentration data one could assume as a worst case a level of 1000 mg/kg which is the highest level usually seen in commercial PS materials. Usually the level found in the material is 500 mg/kg or less which is the industry standard for food grade polystyrene. 

ISO 2561-1974 Plastic Materials - Determination of residual styrene monomer in polystyrene by gas chromatography. ISO, Geneva, Switzerland. 

Table 13 tabulates the rate constants of propagation of styrene monomers calculated from UV data assuming that e = 10,000 mol 1L cm 1 for growing styrene and a-methylstyrene carbenium ions, and e = 28,000 mol- L em-1 for carbenium ions based on /i-methoxystyrene derivatives. The former extinction coefficient was determined in superacid media assuming quantitative formation of carbenium ions, and is probably... 

In a study recently carried out in Hong Kong on disposable plastic containers for take-away meals the migration of styrene oligomers, heavy metals and the overall migration from plastic containers and, where present, their lids were determined into food simulants under different test conditions. Results showed that all the disposable plastic container samples met the safety standards for heavy metals and residual styrene monomers. Hence, with the proper use of disposable plastic containers, they would be unlikely to cause a food... 

While the majority of SBC products possess discrete styrene and diene blocks, some discussion of the copolymerization of styrene and diene monomers is warranted. While the rate of homopolymerization of styrene in hydrocarbon solvents is known to be substantially faster that of butadiene, when a mixture of butadiene and styrene is polymerized the butadiene is consumed first [21]. Once the cross-propagation rates were determined (k and in Figure 21.1) the cause of this counterintuitive result became apparent [22]. The rate of addition of butadiene to a growing polystyryllithium chain (ksd) was found to be fairly fast, faster in fact than the rate of addition of another styrene monomer. On the other hand, the rate of addition of styrene to a growing polybutadienyllithium chain (k s) was found to be rather slow, comparable to the rate of butadiene homopolymerization. Thus, until the concentration of butadiene becomes low, whenever a chain adds styrene it is converted back to a butadienyllithium chain before it can add more styrene. Similar results were found for the copolymerization of styrene and isoprene. Monomer reactivity ratios have been measured under a variety of conditions [23]. Values for rs are typically <0.2, while values for dienes (rd) typically range from 7 to 15. Since... 

With some solid samples, even the previous modifications fail and no apparent equilibrium is reached. Such is the case with coarse or bulky materials (e.g. large granules or solid pieces). Occasionally, the situation can be effectively improved by milling granules while cooling with dry ice, as in the determination of residual styrene monomer in large polystyrene granules [45]. 

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