SAN polymers

If a linear mbber is used as a feedstock for the mass process (85), the mbber becomes insoluble in the mixture of monomers and SAN polymer which is formed in the reactors, and discrete mbber particles are formed. This is referred to as phase inversion since the continuous phase shifts from mbber to SAN. Grafting of some of the SAN onto the mbber particles occurs as in the emulsion process. Typically, the mass-produced mbber particles are larger (0.5 to 5 llm) than those of emulsion-based ABS (0.1 to 1 llm) and contain much larger internal occlusions of SAN polymer. The reaction recipe can include polymerization initiators, chain-transfer agents, and other additives. Diluents are sometimes used to reduce the viscosity of the monomer and polymer mixture to faciUtate processing at high conversion. The product from the reactor system is devolatilized to remove the unreacted monomers and is then pelletized. Equipment used for devolatilization includes single- and twin-screw extmders, and flash and thin film evaporators. Unreacted monomers are recovered for recycle to the reactors to improve the process yield. 

Copolymers of acrylonitrile and vinylidene chloride have been used for many years to produce films of low gas permeability, often as a coating on another material. Styrene-acrylonitrile with styrene as the predominant free monomer (SAN polymers) has also been available for a long time. In the 1970s materials were produced which aimed to provide a compromise between the very low gas permeability of poly(vinylidene chloride) and poly(acrylonitrile) with the processability of polystyrene or SAN polymers (discussed more fully in Chapter 16). These became known as nitrile resins. 

Polystyrene will in the coming years have to show that it can master this situation by further process rationalization and the development of even more sophisticated products. In spite of unfavorable cost trends, polystyrene has up to now continued its march. Production and sales have risen steadily - except for a brief decline in 1975 - and for 1980 we are expecting, in spite of the second price explosion in 1979, a doubling of 1970 sales in the western world to 4.2 million tons. If the estimated 1980 consumption of ABS/SAN polymers and EPS is added to this figure, an amount of 6.1 million tons of styrene polymers is obtained. 

First industrial-scale manufacture of SAN polymers in Ludwigshafen (emulsion process). 

Radical copolymerization of styrene with lCM-0% acrylonitrile yields styrene-acrylonitrile (SAN) polymers. Acrylonitrile, by increasing the intermolecular forces, imparts solvent resistance, improved tensile strength, and raises the upper use temperature of polystyrene although impact resistance is only slightly improved. SAN finds applications in houseware... 

SAN polymers have a natural tendency to assume a yellowish cast when conventionally manufactured (17). This arises from the residual oxygen in the monomer feed. However, when the level of oxygen is below 2 ppm then this problem can be controlled. 

Properties of a SAN resin are shown in Table 10.4. SAN polymers are appreciated because of their excellent transparency and good... 

SAN polymers exhibit high stiffness, dimensional stability and resistance to fluctuating temperatures. 

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. 

The same techniques were used in the present work to study the effects of orientation and rubber content upon the creep behavior of rubber-toughened SAN polymers at room temperature. As in previous work, the tests were conducted at low strain rates and were terminated at longitudinal strains between 5 and 6%. 

Acrylonitrile-styrene-acrylate (ASA) polymers share obvious similarities with ABS but ASA was only developed in the 1960s. ASA polymers are essentially SAN polymers impact modified with an acrylate rubber. The earliest attempt to make ASA was by Herbig and Salyer of Monsanto [23] using butyl acrylate as the rubber phase. This work was then refined by Otto [24] and Siebel [25], both of BASF, who copolymerized butyl acrylate with butadiene to prepare the rubber phase. 

Effects of Acrylonitrile Content and Molecular Weight mi Mechanical and Relaxation Behavior of SAN Polymers... 

Figure 6. The spectrum reflected from a nano-layered SAN polymer with an average layer thickness of (A) 87 nm and (B) 31 nm.

Copolymers of acrylonitrile with other monomers are widely used. Copolymers of vi-nylidene chloride and acrylonitrile find application in low-gas-permeabUity films. St5rrene-acrylonitrile (SAN polymers) copolymers have also been used in packaging applications. Although the gas permeability of the copolymers is higher than for pure polyacrylonitrile, the acrylonitrile copolymers have lower gas permeability than many other packaging films. A number of acrylonitrile copolymers were developed for beverage containers, but the requirement for very low levels of residual acrylonitrile monomer in this application led to many products being removed from the market. One copolymer currently avail-... 

Rubtxr Soluble in SAN Polymer AN, Styi-enc, iiolvent Insoluble... 

ABS resins are composed mainly of styrene (over 50 %) and varying amounts of acrylonitrile comonomer in the SAN polymer backbone and polybutadiene as a chemically grafted rubber dispersion. While the styrene units provide the rigidity and ease of processability, the acrylonitrile units contribute to the chemical resistance and heat stability. The polybutadiene rubber particles in ABS provide the toughness and impact strength. StmcturaUy, ABS itself is a two-phase polymer blend system with the dispersed polybutadiene rubber phase (0.1-1 pm) embedded in a continuous matrix of SAN copolymer. Thus, the composition of ABS resins can vary widely, allowing the production of several grades tailored for different end-use applications. 

Preferential absorption of OSO4 has been shown [115] to reveal spherulites in semicrystalline PET. Stefan and Williams [116] work on ABS-poly-carbonate blends also showed contrast by selective absorption. The dark SAN polymer, in this latter study, contains the osmium stained rubber particles while the polycarbonate was not stained. Niimoni et al. [117] found that there is often enough phase contrast in stained copolymers which have different degrees of unsaturation or functional groups like -OH, -0-, or as they each vary in reactivity with the stain. A specially constructed pressure bomb was developed by Edwards and Phillips [118] in order to terminate crystallization and fix polymers with OSO4 at elevated pressure. This method has permitted determination of lamellar growth rates and the observation of developments in crystalline morphology. 

SANS. Polymer solutions containing the uncrosslinked polymer at the same concentration as the swollen network were also studied. Fig 1 shows the SANS data for a unimodal PDMS network (Mjq 22,500) swollen in C0Dg and the corresponding solution. In all cases the scattering from the networks is greater than that from the solutions. Fig 2 shows the excess scatter-ing from the various swollen bimodal PDMS networks. 

A typical example of reactive functionalisation is a method for improving the compatibility of polyamide-12 (PA-12) and SAN as described by Yukioka and co-workers. It is known that the mixture of PA-12 and SAN polymers is a typical example of an immiscible polymer system. Therefore, this difficulty could be solved by the addition of PS-co-MA, because the anhydride group of this polymer could react with the terminal amino group of PA. Consequently, the melting point of the functionalised PA significantly decreased (about 25%), which resulted in better miscibility of the SAN polymer [68]. 

The higher than expected rA value for commercial SAN polymers made using continuous bulk polymerization at 150-160 °C is puzzling. The discoloration resistance of commercial SAN resins could likely be improved if the cause of the high rA could be found and the copolymerization process operated to increase the alternation tendency of the copolymerization. 

---