Grafting from polybutadiene

Graft copolymers are also used as compatibilizers to tie together different phases. HIPS contains PS grafted onto polybutadiene backbones. This allows stress or strain to be transferred from the PS to the polybutadiene phase transferring energy that might break the brittle PS to the more flexible polybutadiene phase. That is why HIPS is stronger than PS itself. 

Grafting from, exploits the active sites, which exist or can easily be generated on a polymer. Halogenated polymers are most frequently used for this purpose poly(vinyl) chloride), polychloroprene, chlorinated EPDM, chlorobutyl rubber, bromobutyl rubber, chlorinated polybutadiene, chlorinated butadiene-styrene copolymers etc.145). 

The diameter of the polybutadiene latex particles used in ABS synthesis usually ranges from 0.1 ju to lju, and the polymer is always crosslinked within the particles. Consequently, after grafting, every polybutadiene particle becomes a particle of grafted and crosslinked polymer which is much heavier than the linear copolymer molecules. 

SMA PC blend. This blend (Arloy , Arco) contained SMA grafted with polybutadiene as the impact modifier. The properties of SMA/PC blend were similar to ABS/PC blend with slightly higher heat distortion temperatures (107 to 117°C) but comparable impact strength (> 500 J/m). However, it was discontinued from the market due to unfavorable economics relative to ABS/PC blend. The partial miscibility between the styrene-maleic anhydride and polycarbonate accounts for the adequate compatibility of this blend as evidenced by the high level of tensile and impact strengths. 

As shown above (Section 8.4), the IPN s prepared from polybutadiene/ polystyrene combinations are much tougher than the corresponding graft copolymers (Curtius et a/., 1972). More recently, the mechanical behavior of the IPN s and semi-IPN s was compared (Donatelli et u/., 1974ft) (see Figure 8.27). While all materials exhibited a yield point, the (full) IPN exhibited slightly better mechanical properties than the semi-IPN of the first kind, and much better properties than the semi-IPN of the second kind. The IPN s exhibited Charpy impact strengths of 5-6 ft-lb/in. of notch. 

Figure 3.5 Experimentally determined fractions of methyl methacrylate in the droplet phase as a function of the fraction of methyl methacrylate in different latex particles. Methyl methacrylate and styrene in polybutadiene (open circles), SMMA-free (open squares), SMMA-graft (open triangles) from polybutadiene-graft-poly(styrene-co-methyl methacrylate) latex particles, while the closed squares represent a poly(styrene-co-methyl methacrylate) latex swollen with styrene and methyl methacrylate. The solid line gives the theoretical prediction according to Equation 3.13.

The addition of diethylaluminum chloride onto the pendant unsaturations of 1,2-units in polybutadiene has been studied by Greber and others. " The aluminated polymer can be reacted with ethylene in the presence of a transition metal compound (TiClj), to yield polyethylene grafts (Scheme 11). A similar method has been used to grow polyacetylene grafts from a polybutadiene... 

Remember from Sec. 1.3 that graft copolymers have polymeric side chains which differ in the nature of the repeat unit from the backbone. These can be prepared by introducing a prepolymerized sample of the backbone polymer into a reactive mixture—i.e., one containing a source of free radicals—of the side-chain monomer. As an example, consider introducing polybutadiene into a reactive mixture of styrene ... 

Figure 9.17 Plot of log [i ]M versus retention volume for various polymers, showing how different systems are represented by a single calibration curve when data are represented in this manner. The polymers used include linear and branched polystyrene, poly(methyl methacrylate), poly(vinyl chloride), poly(phenyl siloxane), polybutadiene, and branched, block, and graft copolymers of styrene and methyl methacrylate. [From Z. Grubisec, P. Rempp, and H. Benoit, Polym. Lett. 5 753 (1967), used with permission of Wiley.]...

Thermal Oxidative Stability. ABS undergoes autoxidation and the kinetic features of the oxygen consumption reaction are consistent with an autocatalytic free-radical chain mechanism. Comparisons of the rate of oxidation of ABS with that of polybutadiene and styrene—acrylonitrile copolymer indicate that the polybutadiene component is significantly more sensitive to oxidation than the thermoplastic component (31—33). Oxidation of polybutadiene under these conditions results in embrittlement of the mbber because of cross-linking such embrittlement of the elastomer in ABS results in the loss of impact resistance. Studies have also indicated that oxidation causes detachment of the grafted styrene—acrylonitrile copolymer from the elastomer which contributes to impact deterioration (34). 

Interfacial polycondensation between a diacid chloride and hexamethylenediamine in the presence of small amounts of ACPC also yield polymeric azoamid, which is a macroazo initiator.[27] In this manner, azodicarbox-ylate-functional polystyrene [28], macroazonitriles from 4,4 -azobis(4-cyano-n-pentanoyl) with diisocyanate of polyalkylene oxide [29], polymeric azo initiators with pendent azo groups [3] and polybutadiene macroazoinitiator [30] are macroazoinitiators that prepare block and graft copolymers. 

Grafting reactions onto a polymer backbone with a polymeric initiator have recently been reported by Hazer [56-60]. Active polystyrene [56], active polymethyl methacrylate [57], or macroazoinitiator [58,59] was mixed with a biopolyester polyhydroxynonanaate [60] (PHN) or polybutadiene to be carried out by thermal grafting reactions. The grafting reactions of PHN with polymer radicals may proceed by H-abstraction from the tertier carbon atom in the same manner as free radical modification reactions of polypropylene or polyhy-droxybutyratevalerate [61,62]. 

Grafting reactions of polybutadiene with macrazo-inimers or polyazoesters produced polyethylene gly-col-polybutadiene crossHnked graft copolymers. Macroradicals thermally formed from macroazoinimers or polyazoesters attack 1,2-linked vinyl pendant groups of polybutadiene ... 

Table 9.3 Structural characteristics of arborescent graft polybutadienes (adapted from ref. 15)...

Figure 2. Morphology of various cross-polybutadiene-in/er-cross-polystyrene sequential IPNs and graft copolymers via transmission electron microscopy. The double bonds in the polybutadiene phase are stained dark with osmium tetroxide. (Reproduced from ref. 15. Copyright 1976 American Chemical Society.)...

E4 polystyrene-Z)/ocA -[l,4-polybutadiene-grq/Z -poly(styrene-co-acrylonitrile)] (copolymer from styrene and acrylonitrile grafted to a 1,4-polybutadiene-polystyrene two-block copolymer at unspecified sites of some of the but-2-ene-... 

Step 2—Polybutadiene rubber is further polymerized, but in the presence of styrene and acrylonitrile monomers. This is done in low-pressure reactors under a nitrogen atmosphere. In this operation, the monomers are grafted onto the rubber backbone through the residual unsaturation remaining from the first step. 

Thus, the thermal stabilization of PVC which resulted from the heterogeneous grafting of as little as 3-5% cis-1,4-polybutadiene was more than a simple additive effect and indicates a synergistic interaction. This was demonstrated further by dissolving up to 10% cis-1,4-polybuta-diene in a chlorobenzene suspension or solution of PVC and isolating the polymer blend by precipitation with methanol. Films pressed from the polymer blend were generally deeply colored and contained incompatible, probably gelled or crosslinked, areas. 

Figure 1. Evolution of hydrogen chloride at 180° C (nitrogen as carrier gas) from suspension PVC (1), suspension FVC + stabilizer (2), ds-l,4-polybuta-diene-PVC (suspension) graft copolymer from monomeric butadiene (Type M) (3), Type M graft copolymer + stabilizer (4), and graft copolymer from cis-1,4-polybutadiene (Type P) (5)...

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