Styrene random copolymers

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

Styrene-Acrylonitrile (SAN) Copolymers. SAN resins are random, amorphous copolymers whose properties vary with molecular weight and copolymer composition. An increase in molecular weight or in acrylonitrile content generally enhances the physical properties of the copolymer but at some loss in ease of processing and with a slight increase in polymer color. 

Pressure sensitive adhesives typically employ a polymer, a tackifier, and an oil or solvent. Environmental concerns are moving the PSA industry toward aqueous systems. Polymers employed in PSA systems are butyl mbber, natural mbber (NR), random styrene—butadiene mbber (SBR), and block copolymers. Terpene and aUphatic resins are widely used in butyl mbber and NR-based systems, whereas PSAs based on SBR may require aromatic or aromatic modified aUphatic resins. 

Fig. 3. Oxygen permeabiUties of block (A) and random ( ) styrene—methacrylonitrile (MAN) copolymers [33961 -16-9] (11). See Table 1 for unit...

Butadiene-Styrene Copolymers from Ba-Mg-Al Catalyst Systems. Figure 13 shows the relationship between copolymer composition and extent of conversion for copolymers of butadiene and styrene (25 wt.7. styrene) prepared in cyclohexane with Ba-Mg-Al and with n-BuLi alone. Copolymerization of butadiene and styrene with barium salts and Mg alkyl-Al alkyl exhibited a larger initial incorporation of styrene than the n-BuLi catalyzed copolymerization. A major portion of styrene placements in these experimental SBR s are more random however, a certain fraction of the styrene sequences are present in small block runs. 

This block copolymer has substantially different physical properties as compared to a random styrene-butadiene copolymer. 

The last property is related to the processing of the rubber in the tire making equipment. By using organo-lithium compound in this case, it was possible to maintain a vinyl content not greater than 18, but to produce a polybutadiene styrene copolymer that has random block styrene and without the use of polar modifiers, which normally will increase the 1,2 content. This copolymer, when compounded in the tread recipe, as shown in the Table XVI, gave properties that are actually equivalent to that of emulsion SBR and in some cases even better. This is particularly true in the properties of the Young modulus index, which showed between -38 to -54 C the Stanley London Skid Resistant, in which the control is 100, shows that 110-115 was obtained. 

Copolymers of styrene include a large group of random, graft, and block copolymers. Those with a high proportion of acrylonitrile used in barrier films as well as others such as methacrylic-butadiene-styrene copolymer (MBS) plastic is used as modifiers in PVC, SAN, ABS, ASA, etc. The styrene-acrylonitrile copolymer (SAN) is the most important when considering volume and number of applications. 

Instead of block copolymers, the use of pseudo-random linear copolymers of an aliphatic a-olefin and a vinyl aromatic monomer has been reported [20], where the styrene content of the polymer must be higher than 40 wt%. Preferred are styrene and ethylene copolymers. These blends may contain, amongst other things, an elastomeric olefinic impact modifier such as homopolymers and copolymers of a-olefins. Presumably the styrene-ethylene copolymer acts as a polymer emulsifier for the olefinic impact modifier. Using 5 wt% of an ethylene-styrene (30 70) copolymer and 20% of an ethylene-octene impact modifier in sPS, a tensile elongation (ASTM D638) of 25 % was obtained. 

Gausepohl et ah [31] investigated the behavior of blends between sPS and random styrene-l,l-diphenylethylene copolymers obtained by anionic synthesis. The blends were miscible for copolymer contents of 1,1-diphenylethylene lower than 15 wt% as indicated by the occurrence of a single Tg (114°C). Tm and crystallization rate were not influenced. 

As a result of the catalyst and process conditions used in their manufacture, the particular copolymers of current major interest are atactic, and contain typically up to about 50 mol% ( 80 wt%) styrene. These materials have been described as pseudo-random , since successive head-to-tail styrene chain insertions have been shown to be absent, even at high levels of styrene incorporation [1,2]. The term ethylene-styrene interpolymer (ESI) is used here to describe the specific ethylene-styrene copolymers produced via INSITE Technology. For convenience, all subsequent comonomer contents are expressed in weight percentages, unless otherwise stated. For example, the code ES70 refers to an interpolymer having 70 wt.% comonomer styrene incorporation. 

This chapter discusses the dynamic mechanical properties of polystyrene, styrene copolymers, rubber-modified polystyrene and rubber-modified styrene copolymers. In polystyrene, the experimental relaxation spectrum and its probable molecular origins are reviewed further the effects on the relaxations caused by polymer structure (e.g. tacticity, molecular weight, substituents and crosslinking) and additives (e.g. plasticizers, antioxidants, UV stabilizers, flame retardants and colorants) are assessed. The main relaxation behaviour of styrene copolymers is presented and some of the effects of random copolymerization on secondary mechanical relaxation processes are illustrated on styrene-co-acrylonitrile and styrene-co-methacrylic acid. Finally, in rubber-modified polystyrene and styrene copolymers, it is shown how dynamic mechanical spectroscopy can help in the characterization of rubber phase morphology through the analysis of its main relaxation loss peak. 

Samples tested were styrene copolymers of methacrylates, acrylates, vinyl acetate, and acrylonitrile, in addition to ethyl methacrylate-butyl methacrylate copolymers. These samples were dissolved in the initial mobile phase and the injection volume was 0.05-0.2 mL. These samples were prepared by solution polymerization at low conversion and have rather narrow CCD. These samples are random (statistical) copolymers. 

Mazzola et al used polyesters for foamed composites (6). Narkis et al (27) described foamed polyester composites made using random glass mat. Saidla et al (28) reported making foamed polyester composites using -inch glass fibers. Vinyl ester/styrene copolymer foams were developed by Olstowski and Perrish (10, 11). Vinyl ester-based hybrid-foam composites were developed by Frisch and Ashida (19). 

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... 

Figure 8. Critical surface energy as a function of oxygen carbon ratio for butadiene styrene copolymers and homopolymers after ozone exposure at 375 ppm for 150 min. Key a, crosslinked butadiene o, random copolymers and 0, block copolymers.

Equation (5-27), also known as the Gordon-Taylor11 equation, has found wide application to random amorphous copolymers. Figure 5-10 shows the experimental results for a series of styrene-butadiene copolymers along with the corresponding Tg s calculated from equation (5-27) with k = 0.34. (See problems at the end of this chapter for additional equations.)... 

Figure 5-10. Composition dependence of Tg for a series of random styrene-butadiene copolymers compared to the predicted curve calculated on the basis of equation (5-27) with k = 0.34. [After M. Gordon and J. S. Taylor, J. Appl. Chem. 2, 493 (1952).]...

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