Random Copolymers of Polystyrene

We can readily copolymerize styrene with a variety of comonomers. Commercially, the t vo most important random styrene copolymers are styrene co-acrylonitrile and styrene cobutadiene, the general chemical structures of which are shown in Fig. 21.3, 

By incorporating acrylonitrile into polystyrene we can depress the copolymer s glass transition temperature below that of pure polystyrene. When sufficient acrylonitrile is present, the copolymer s glass transition temperature falls below room temperature. The resulting copolymer is tough at room temperature and at higher temperatures. 

Styrene co-butadiene is a rubbery amorphous polymer with a glass transition temperature well below room temperature. Polystyrene co-butadiene is an important component of several commercial families of plastic that contain polystyrene blocks. 

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Walton et al. went on to study the orientation of block copolymers as a function of interaction with blocks when walls are preferential for one of the blocks, parallel orientation forms.In the case of symmetric wetting of preferential walls, unfrustrated spacing occurs for wall spacing h,h = ndg, which is the bulk spatial period do multiplied by the number of layers n. Alternatively, for asymmetric preferential walls (the walls attract opposite blocks), the unfmstrated system forms when the plate spacing corresponds with h = n + Vi)do-This behavior was confirmed experimentally with PS-b-PMMA sandwiched between two walls treated with random copolymers of polystyrene-ran-poly(methyl methacrylate) (PS-r-PMMA) with varying composition and thus varying block interaction. ... 

The glass-transition temperature in amorphous polymers is also sensitive to copolymerization. Generally, T of a random copolymer falls between the glass-transition temperatures of the respective homopolymers. For example, T for solution-polymerized polybutadiene is —that for solution-polymerized polystyrene is -HlOO°C. A commercial solution random copolymer of butadiene and styrene (Firestone s Stereon) shows an intermediate T of —(48). The glass-transition temperature of the random copolymer can sometimes be related simply as follows ... 

The toughness of interfaces between immiscible amorphous polymers without any coupling agent has been the subject of a number of recent studies [15-18]. The width of a polymer/polymer interface is known to be controlled by the Flory-Huggins interaction parameter x between the two polymers. The value of x between a random copolymer and a homopolymer can be adjusted by changing the copolymer composition, so the main experimental protocol has been to measure the interface toughness between a copolymer and a homopolymer as a function of copolymer composition. In addition, the interface width has been measured by neutron reflection. Four different experimental systems have been used, all containing styrene. Schnell et al. studied PS joined to random copolymers of styrene with bromostyrene and styrene with paramethyl styrene [17,18]. Benkoski et al. joined polystyrene to a random copolymer of styrene with vinyl pyridine (PS/PS-r-PVP) [16], whilst Brown joined PMMA to a random copolymer of styrene with methacrylate (PMMA/PS-r-PMMA) [15]. The results of the latter study are shown in Fig. 9. 

The same procedure can be employed to make well defined comb-like polymers Living polystyrene can be grafted onto a partially chloromethylated polystyrene89 146), or onto a random copolymer of styrene and methyl methacrylate containing less than 10% of the latter monomer I48). 

In the absence of polymer the sediment volume of silica depends on the non-solvent fraction of the medium as shown in Figure 6. The sediment volume assessment of steric stabilization behavior of the copolymers is illustrated in Figures 7a to 7c. At low styrene contents, both the random and block copolymers show a steady increase in sediment volume as the non-solvent content is raised up to the phase separation value. With polystyrene and random copolymers of high styrene content, the sediment volume stays largely constant with alteration in the non-solvent fraction until the theta-point is approached and then continues to become larger as the limit of solubility is reached. In Figure 7b only the data points of RC 86 are shown, RC 94 giving almost identical values. 

SBR is a random copolymer of styrene and butadiene, and it has, therefore, a Tg between that of poly-butadiene (-90 °C) and polystyrene (+95 °C). Its position depends on the S/B ratio, which is chosen in such a way that the polymer can function optimally as a technical rubber for tyres. 

Fig. 1 Chemical formulas of the polymers used a carboxy-terminated polystyrene PS-COOH b random carboxy-terminated copolymer of polystyrene and 2,3,4,5,6-pentafluoropolystyrene FPS-COOH c 3-glycidoxypropyl trimethoxysilane (GPS) d tridecafluoro-1,1,2,2-tetrahydrooctyl) dimethylchlorosilane FSI...

Lee and Char [93] studied the reinforcement of the interface between an amorphous polyamide (PA) and polystyrene with the addition of thin layers of a random copolymer of styrene-maleic anhydride (with 8% MA) sandwiched at the interface. After annealing above the Tg of PS, they found significantly higher values of Qc for samples prepared with thinner layers of SMA than for the thicker ones. They initially rationalized their results by invoking the competition between the reaction rate at the interface and the diffusion rate of the SMA away from the interface. For very thick layers, and therefore also for pure SMA, the reaction rate was much faster than the diffusion rate away from the interface and favored therefore a multiple stitching architecture, as shown schematically in Fig. 50. Such an interfacial molecular structure does not favor good entanglements with the homopolymer and is mechanically weak. 

The radical nature of nitroxide-mediated processes also allows novel types of block copolymers to be prepared in which copolymers, not homopolymer, are employed as one of the blocks. One of the simplest examples incorporate random copolymers124 and the novelty of these structures is based on the inability to prepare random copolymers by living anionic or cationic procedures. This is in direct contrast to the facile synthesis of well-defined random copolymers by nitroxide-mediated systems. While similar in concept, random block copolymers are more like traditional block copolymers than random copolymers in that there are two discrete blocks, the main difference being one or more of these blocks is composed of a random copolymer segment. For example, homopolystyrene starting blocks can be used to initiate the copolymerization of styrene and 4-vi-nylpyridine to give a block copolymer consisting of a polystyrene block and a random copolymer of styrene and 4-vinylpyridine as the second block.166... 

Detailed examples of the use of the key correlations to calculate the properties of specific polymers (polystyrene, and random copolymers of styrene and oxytrimethylene), will be provided in Chapter 18. Chapter 18 therefore complements chapters 3 to 16, where each physical property was considered individually, and calculated for many different polymers. 

It is instructive to calculate the key properties of specific polymers by using the correlation scheme developed in this book, to complement the earlier chapters where individual properties were calculated for large sets of polymers. Polystyrene, and random copolymers of styrene and oxytrimethylene, will be used as examples. Only the correlations which provide the preferred embodiment of our work will be used. In previous chapters, information provided by available group contributions and by related experimental data were incorporated in calculationss of "best estimates" of some properties. In this chapter, the properties will be calculated by using the new correlations consistently to estimate all parameters in intermediate steps of the calculations. Some values predicted below therefore differ from results listed in previous chapters. The steps involved in calculations of the properties will be listed. See earlier chapters for comparisons of the results with experimental data and with results of calculations using group contributions. 

Franta et al. (115) synthesized graft copolymers by initiation of THF polymerization from chlororaethylated polystyrene, partially brominated 1,4-polybutadiene, and a random copolymer of styrene and methacryloyl chloride in the presence of AgSbFg. 

A random copolymer of styrene and acrylonitrile exhibited a 20 C higher use temperature than that of polystyrene a random copolymer of styrene with butyl acrylate was more flexible than the styrene homopolymer. 

Fig. 8a. Scaling behavior of qm(t) vs the rescaled time f = tD q (0) = 2X(0) [XsM>o) — 3 for the polymer mixture as shown in Fig. 6a and a quench to T = 25 °C. Different symbols refer to different sample geometries. The solid curve is a fit to a formula ohtained by Furukawa [168] corresponding data for polyvinylmethylether (PVME)-polystyrene (PS), dash-dotted [158] and cyclohexane/meth-anol, dashed curve [169], are included. From Bates and Wiltzius [36]. b Coarsening behavior of mixtures of SBR (a random copolymer of styrene and polybutadiene) and polyisoprene (PI) at various compositions, at T = 60 °C. a shows qm(t) and b. corresponding intensity I (t), in arbitrary units, while arrows indicate the times where pinning (t,) or crossover (t ) from intermediate to late stages occurs. From Hashimoto et al. [173]...

The UV absorption in the 260 nm region is frequently used to evaluate styrene content in styrene-based polymers (2, 2, 3, 4, 5, 6, 7). Calibration curves for polystyrene solutions are usually based on the assumptions that the UV absorption of the copolymer depends only on the total concentration of phenyl rings, and the same linear relationship between optical density and styrene concentration that is valid for polystyrene holds also for its copolymers. These assumptions are quite often incorrect and have caused sizable errors in the analysis of several statistical copolymers. For example, anomalous patterns of UV spectra are given by random copolymers of styrene and acrylonitrile (8), styrene and butadiene (8), styrene and maleic anhydride (8), and styrene and methyl methacrylate (9, 10, 11). Indeed, the co-monomer unit can exert a marked influence on the position of the band maxima and/or the extinction... 

Glycidyl methacrylate High density polyethylene Isotactic copolymer of styrene and p-methyl styrene Isotactic poly(ethyl methacrylate) Isotactic poly(methyl methacrylate) Isotactic polystyrene Low density polyethylene Linear low density polyethylene Maleic anhydride Poly(4-methyl pentene) Random copolymer of phenyl ether and phenyl ketone... 

Triblock and random polyampholytes based on DMAEM-MMA-MAA were examined for their phase separation behaviour [52]. Triblock polyampholytes have a much broader phase separation region than the random ones. The specific structure of PMAA-fc-PlM4VPCl with the excess of cationic or anionic blocks at the lEP is close to the structure of non-stoichiometric IPC. It is suggested that its nucleus consists of intraionic IPC surrounded by cationic blocks protecting it from precipitation [53]. ABC triblock copolymers of polystyrene-b/ock-poly(2-(or 4)vinylpyridine)-fc/ock-poly(methacrylic acid) were synthesized by living anionic polymerization [53 a]. Interpolymer complexation of the polyvinylpyri-dine and poly(methacrylic acid) blocks in the micellar solution was studied in relation to pH in solution by potentiometric, conductimetric and turbidimetric titration and in bulk by FTIR spectroscopy. 

The first set of experiments that will be considered has examined the ability of random copolymers of styrene and methyl methacrylate to improve the interfacial strength between polystyrene and poly(methyl methacrylate). Using the asymmetric double cantilever beam technique, the researchers have found that a diblock copolymer (50/50 composition, Mw = 282,000) creates an interface with strength of400 J/m2. When utilizing a random copolymer however, it was found that the strongest interface (70% styrene, Mw =... 

Polystyrene/Poly(styrene-co-para-fIuorostyrenc) Systems involving PS and random copolymers of styrene and fluoro-substituted styrenes are among the most... 

Poly(vinyl chloride) (PVC) homopolymer is a stiff, rather brittle plastic with a glass temperature of about 80°C. While somewhat more ductile than polystyrene homopolymer, it is still important to blend PVC with elastomer systems to improve toughness. For example, methyl methacrylate-butadiene-styrene (MBS) elastomers can impart impact resistance and also optical clarity (see Section 3.3). ABS resins (see Section 3.1.2) are also frequently employed for this purpose. Another of the more important mechanical blends of elastomeric with plastic resins is based on poly(vinyl chloride) as the plastic component, and random copolymers of butadiene and acrylonitrile (AN) as the elastomer (Matsuo, 1968). On incorporation of this elastomeric phase, PVC, which is ordinarily a stiff, brittle plastic, can be toughened greatly. A nonpolar homopolymer rubber such as polybutadiene (PB) is incompatible with the polar PVC. Indeed, electron microscopy shows... 

Glass transition temperatures of random copolymers of styrene and txjtadiene as a function of percentage styrene in the copolymer. The glass transitions of the homopolymers are polystyrene 95 C polybutadiene -87°C. The styrene contents of commercial SBR rubbers fall in the range 10 to 40% (after tilers). 

Young s modulus, yield (break) strength, and elongation to yield (break) have been measured for blends of poly (2,6-dimethyl-1, 4-phenylene oxide)(PPO) with polystyrene (PS), poly (p-chloro-styrene) (PpClS), and random copolymers of styrene and 2 -ch loro-styrene)(pels). The significant difference between blend compositions is the compatibility of PPO with each styrene polymer. 

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