Graft-type

Watanabe J, Eriguchi T, Ishihara K (2002) Stereocomplex formation by enantiomeric poly (lactic acid) graft-type phospholipid polymers for tissue engineering. Biomacromolecules 3 1109-1114... 

The reactions of 1,2-thiazine 1,1-dioxides with electrophiles can often lead to a mixture of products due to competing addition at C-4 and C-6. A selective Friedel-Grafts-type acylation of the C-6 position of the 1,2-thiazine 1,1-dioxo ring was observed in reaction of 3,5-dimethyl-1,2-thiazine 1,1-dioxide 71 with anhydrides, such as acetic anhydride, furnishing compound 45 (Equation 18) <1999JPR37>. 

Reactive POs having reactive functional groups are considered to be the most conventional way to produce various polymer hybrids, most of which were graft type copolymers. Typically, it is well-known that the maleic anhydride modified POs are useful as a reactive PO to prepare the polymer hybrid [114]. 

Dispersion polymerization differs from emulsion polymerization in that the reaction mixture, consisting of monomer, initiator, and solvent (aqueous or nonaque-ous), is usually homogeneous. As polymerization proceeds, polymer separates out and the reaction continues in a heterogeneous manner. A polymeric surfactant of the block or graft type (referred to as protective colloid ) is added to stabilize the particles once formed. 

The most common polymeric silicone surfactants are based on polyoxyalkylene groups. The structures of graft-type (rake-type) and ABA structures are illustrated in Figures 6.17 and 6.18. It should be noted that there are many possible variants of these basic structures. The actual structure of graft-type silicone copolymers is a random copolymer of m and n rather than the blocky structure suggested by the diagram. 

Figure 6.1 7 Structure of a graft-type silicone-polyoxyethylene copolymer, MD (D EOxOH)mM.

Anseth, J.W., Bialek, A., Hill, R.M. and Fuller, G.G. (2003) Interfacial rheology of graft-type polymeric siloxane surfactants. Langmuir, 19(16), 6349-56. 

Bis(2,3-dibromopropyl) fumarate has been used as a fourth monomer in nitrile rubber- and graft-type ABS materials giving flame-resistant polymers. At least 10% bromine incorporation is required to pass the Underwriters Laboratories Subject 94 test. The graft-type materials fail at 7-10% bromine only because of dripping. Both types pass the ASTM D-635 test with 7% or more bromine. For the impact strength to be equivalent to that of conventional ABS, the fourth monomer must be present in both the rubber and resin phases. Thermal stability is marginal but can be improved with typical PVC stabilizers. 

Use of bis(2,3-dibromopropyl) fumarate as a fourth monomer in either nitrile rubber- or graft-type ABS materials gives flame-resistant polymers. With either type, better impact strength is obtained when the fourth monomer is present in both the rubber and resin phases. The compositions are more thermally stable than poly (vinyl chloride) and can be stabilized by typical PVC stabilizers. 

Styrene and butadiene also form copolymers known as high impact polystyrene, or rubber-modified polystyrene, when the content of butadiene is 10%. This type of material has excellent mechanical properties, and it is widely used in practice for the manufacturing of numerous objects, including parts for household appliances, furniture, etc. Rubber-modified polystyrene is commonly used as wood replacement and also for packaging. The synthesis of this material typically is done by dissolving polybutadiene in styrene monomer, followed by free radical polymerization achieved using a peroxide catalyst. This procedure leads to block or graft type copolymers. 

Historical Review—A Pathway to Discovery Synthesis—A Survey of Methods Nongrafted Types Grafted Types Derivatization... 

Grafted Types. Graft polymers have been synthesized by a variety of approaches including all of those mentioned earlier (anionic, cationic, radical, etc.). Four of these approaches will be described in this chapter. However, the reader should recognize that many chemical paths to grafting are available, albeit many of these suffer from the complexity of products produced and overall inefficiency of the grafting method. 

Herein are described the preparations of the charge-transfer-type intercalation compound FeOCl (pyridine derivative), of grafted-type intercalation compounds FeO(OCH3) and Fe0(02C2H4)1/2 and of some organic intercalates of HTiNbOs. 

If a polymer molecule is composed of more than the minimum number of repeat units (one, in the case of an addition polymer), it is termed a copolymer. Copolymers may be of a statistical (raruhm), block or graft type ... 

Figure 3.2. Electron photomicrograph (transmission) of an ultrathin section of a graft-type high-impact polystyrene made by a bulk polymerization process. Note the cellular structure within the polybutadiene phase, where polystyrene forms a discontinuous phase. Large, white areas correspond to the continuous matrix of polystyrene homopolymer. (From Huelck and Covitch, 1971.)...

Figure 3.3. Electron micrograph (replica) of a graft-type high-impact polystyrene with polybutadiene as the rubbery component (Keskkula and Traylor, 1967). In the absence of agitation, phase inversion does not occur, and an interwoven cellular structure results, with polybutadiene remaining as the continuous phase. The specimen was prepared for electron microscopy by exposing a polished surface to isopropanol vapor, which preferentially swells the polystyrene phase a double replication technique was then used. The reader should compare the results obtained by this technique to results obtained using thin-section transmission techniques (see, for example. Figure 3.2).

The phenomenon of the phase inversion itself has been investigated by Molau (1965), who studied the graft-type polyblending of styrene with... 

Discussion of the detailed structure of the graft-type polyblend latex particle requires amplification. In the formation of the ABS type G resin, part of the AS copolymer forms a shell around the seed latex (Kato, 1968), as shown in Figure 3.6. As with other types of graft copolymers, some monomer dissolves within the seed latex. Upon polymerization, the second monomer mix phase-separates to yield the complex inner morphology observed. After coagulation, the glassy AS polymer forms the matrix, while the portion occluded within the latex particles remains within the rubber phase (Figure 3.7). 

The importance of graft-type bonding and the finer, more complex morphology developed in graft copolymers should be emphasized. Table 3.2... 

One might speculate that the crack growth through the rubber portion could be used to help explain the greater toughness of graft-type polyblends in... 

At constant content of rubber, the greater toughness of graft-type ABS materials over their HiPS analogs may also be partially attributed to the smaller rubber phase domains in the former, which limit the size of the crazes formed. 

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