Chemical Resistance of Styrene Polymers

Ta b I e A. 1 3 Chemical resistance of polystyrene (PS) and impact resistant-modified polystyrene (SB), possible aftertaste caused by styrene monomer residues [32] 

The evaluations summarized in Table A.14 were conducted at 20 °C und 50 °C for almost all chemicals. Only differing results are listed separately. When identical results were reported for 20 °C and 50 °C, good resistance was listed for 50 °C and lack of resistance was listed for 20 °C [832], 

A = Excellent resistance minimal changes in weight, dimensions and properties, no irreversible damage caused by medium (empirical data) 

B = Limited resistance distinct changes in properties, irreversible damage at longer exposure 

C = No resistance strong attack after a short period of time and/or stress cracking, irreversible damage 

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Data about the chemical resistance of styrene polymers in general have been compiled (24). A few data concerning SAN polymers are collected in Table 10.5. 

Table A.14 Chemical resistance of styrene polymers sol. = aqueous solution [832]...

For electrostatic and steric stabilization, the particles can be viewed effectively as colloids consisting of a soft and deformable corona surrounding a rigid core. Colloidal particles with bulk elastomeric properties are also available. These particles, which are generally of submicron size, are developed and used as reinforcement additives to improve the Impact resistance of various polymer matrices [28-30]. The rubber of choice is often a styrene/butadiene copolymer. The presence of chemical groups at the matrix-filler interface leads to improved adhesion between them. Typically, the addition of about 30% by volume of these elastomeric particles increases the impact strength of a brittle glassy polymer like polystyrene by up to a factor of 10. For some applications, particles with more complex architecture have been... 

The chemical resistance of an organic material depends to a very large extent on the molecular weight of the polymer concerned. When optimally cured, po-ly(ester-imide) wire enamels are resistant to the styrene used in impregnating and trickle resins. Optimum curing is dependent, when all the other parameters of the enameling machine are held constant, on the enameling speed of the wire. 

Acrylonitrile-butadiene-styrene (ABS) copolymers are produced by three monomers acrylonitrile, butadiene, and styrene. The desired physical and chemical properties of ABS polymers with a wide range of functional characteristics can be controlled by changing the ratio of these monomers. They are resistant... 

Polyester laminating resins usually consist of an unsaturated ester polymer dissolved in a monomer such as styrene. One of the chief virtues of these resins is the excellent chemical resistance of the laminates. Hence, they are used for corrosion resistant tanks, exhaust ducts, scrabbers, and plating equipment. These materials resist acids and bases for long periods at 94°C. They are attacked by most chlorinated solvents. A closely related polymer family, the vinyl esters, has even more superior chemical resistance and some processing advantages. 

The principal monomer of nitrile resins is acrylonitrile (see Polyacrylonitrile ), which constitutes about 70% by weight of the polymer and provides the polymer with good gas barrier and chemical resistance properties. The remainder of the polymer is 20 to 30% methylacrylate (or styrene), with 0 to 10% butadiene to serve as an impact-modifying termonomer. 

Styrene Copolymers. Acrylonitrile, butadiene, a-methylstyrene, acryUc acid, and maleic anhydride have been copolymerized with styrene to yield commercially significant copolymers. Acrylonitrile copolymer with styrene (SAN), the largest-volume styrenic copolymer, is used in appHcations requiring increased strength and chemical resistance over PS. Most of these polymers have been prepared at the cross-over or azeotropic composition, which is ca 24 wt % acrylonitrile (see Acrylonithile polya rs Copolyp rs). 

In Chapters 3 and 11 reference was made to thermoplastic elastomers of the triblock type. The most well known consist of a block of butadiene units joined at each end to a block of styrene units. At room temperature the styrene blocks congregate into glassy domains which act effectively to link the butadiene segments into a rubbery network. Above the Tg of the polystyrene these domains disappear and the polymer begins to flow like a thermoplastic. Because of the relatively low Tg of the short polystyrene blocks such rubbers have very limited heat resistance. Whilst in principle it may be possible to use end-blocks with a higher Tg an alternative approach is to use a block copolymer in which one of the blocks is capable of crystallisation and with a well above room temperature. Using what may be considered to be an extension of the chemical technology of poly(ethylene terephthalate) this approach has led to the availability of thermoplastic polyester elastomers (Hytrel—Du Pont Amitel—Akzo). 

Modified alkyd resins In this group one finds styrenated alkyds, vinyl toluenated alkyds, oil-modified vinyl resins, acrylic alkyds, silicone alkyds and polyurethane alkyds. The modifying component usually has a number of effects. It always increases the molecular weight of the alkyd polymer, and may impart hardness, durability, or chemical resistance. It also affects the solubility of the polymer in solvents. 

As already shown, it is technically possible to incorporate additive functional groups within the structure of a polymer itself, thus dispensing with easily extractable small-molecular additives. However, the various attempts of incorporation of additive functionalities into the polymer chain, by copolymerisation or free radical initiated grafting, have not yet led to widespread practical use, mainly for economical reasons. Many macromolecular stabiliser-functionalised systems and reactive stabiliser-functionalised monomers have been described (cf. ref. [576]). Examples are bound-in chromophores, e.g. the benzotriazole moiety incorporated into polymers [577,578], but also copolymerisation with special monomers containing an inhibitor structural unit, leading to the incorporation of the antioxidant into the polymer chain. Copolymers of styrene and benzophenone-type UV stabilisers have been described [579]. Chemical combination of an antioxidant with the polymer leads to a high degree of resistance to (oil) extraction. 

The hydrogenation of unsaturated polymers and copolymers in the presence of a catalyst offers a potentially useful method for improving and optimizing the mechanical and chemical resistance properties of diene type polymers and copolymers. Several studies have been published describing results of physical and chemical testing of saturated diene polymers such as polybutadiene and nitrile-butadiene rubber (1-5). These reports indicate that one of the ways to overcome the weaknesses of diene polymers, especially nitrile-butadiene rubber vulcanizate, is by the hydrogenation of carbon-carbon double bonds without the transformation of other functional unsaturation such as nitrile or styrene. 

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