Block Copolymers as Compatibilizers

One approach to compatibilize non-compatible polymers is to include in the blend a block copolymer which contains one chain segment derived from monomers compatible with one blend polymer and another chain segment derived from monomers compatible with the other blend polymer (2). 

Polymer blends made from a poly(carbonate) (PC) resin and poly-(isobutylene) can be compatibilized by including a minor amount of a poly(carbonate-isobutylene) block copolymer in the blend composition (38). Further, block copolymers of poly(isobutylene) and poly-(dimethylsiloxane) and suggests their use as compatibilizers (39) have been suggested. 

Radicalic polymerized block copolymers containing poly(isobut-ylene) and poly(p-chlorostyrene) have been described as compatibilizers (40). Similarly, copolymers containing poly(isobutylene) and p-ferf-butylstyrene are useful compatibilizers for olefinic elastomers (2). 

Macromonomers of polymeric dicyclopentadiene and polymeric ethylidene norbomene have been prepared and then terpolymerized with ethylene and propylene. This terpolymer exhibits compatibi-lization of ethylene-propylene rubber and butyl rubber (41). 

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Gradient block copolymer in which there is a gradual change of composition at the junction between the two blocks from pure AAAAAAAA type to pure BBBBBBBB type. The tapered block copolymers are reported to be more efficient than pure AB block copolymers as compatibilizers of polymer blends. Tapping cutting threads in the walls of a circular hole. 

Dexco (Exxon/Dow) has developed styrenic block copolymers as compatibilizers. to improve impact strength. Vector SBS (not containing halide salts) gives better heat stability than conventional block copolymers due to absence of residual halides, which can lead to property degradation. It can boost ultimate elongation and impact strength of PS waste. 

VI. Blends of Block Copolymers A. Block Copolymers as Compatibilizers in Polymer Blends... 

Most studies of the behavior of block copolymers as compatibilizing agents consider two opposing effects during deformation a reduction in critical droplet size due to a reduction in the interfhcial tension (droplet breakup) proposed by Taylor, and an increase in droplet size due to increased collision frequency between droplets (droplet coalescence) studied by Smoluchowski. The problem of droplet breakup in a... 

From the foregoing it looks interesting to try to characterize the change ui the interphase bomidary between two immiscible polymers in the presence and in the absence of a compatibilizer by means of microindentation hardness and scanning electron microscopy (SEM). For this purpose, solution blended PS and NR as well as styrene-butadiene-styrene (SBS) block copolymer as compatibilizer were used. 

C. Auschra, R. Stadler, and LG. Voigt-Martin, Poly (styrene-b-methyl methacrylate) block copolymers as compatibilizing agents in blends of poly (styrene-co-acrylonitrile) and poly (2, 9-dimethyl-l, 4-phen-ylene ether) 2. Influence of concentration and molecular weight of symmetric block copolymers. Polymer, 34 2094r-2110,1993. 

Frounchi and Burford [37] studied the effect of styrene block copolymer as a compatibilizer in isotactic PP-ABS blends. It was found hat in PP-rich blends a marginal improvement in mechanical properties was obtained. However, in acrylo nitrile butadiene styrene (ABS) rich blends no improvement was obtained. The effects of four different block copolymers, SBS, SIS,... 

Styrene-based resins, extrusion of, 23 398 Styrene block copolymers, as mixed plastics compatibilizers, 21 454 Styrene-butadiene (SB) block copolymers, 20 324, 23 377, 393 Styrene-butadiene copolymer latex binders, 19 360... 

The effect of compatibilization of grafted or block copolymers as controllers of interphase interaction has been well known (1,28). Marosi and Bertlan (29), for example, described the compatibUizing effect of polybutylene terephthalate-polytetramethylene oxide block copolymers on PA6/HDPE blends. The addition of a block copolymer prevents separation in the blends during processing and increases the impact strength of the material several times. 

In addition, there has been an increasing interest in new synthetic methods for the preparation of well-defined polymers with controlled chain-end functional groups [23], such as telechelic polymers, which are characterized by the presence of reactive functional groups placed at both chain ends. These materials can then be used as precursors in the synthesis of block copolymers, as modifiers of the thermal and mechanical properties of condensation polymers, as precursors in the preparation of polymer networks, and as compatibilizers in polymer blends [24]. 

Much of the work on copolymers as interfacial modifiers has utilized block copolymers as additives. The role of copolymer molecular weight, composition, and other molecular parameters on the ability of a block copolymer to improve the properties of a biphasic blend is well understood. However, block copolymers are expensive and difficult to synthesize. Therefore, their use as interfacial modifiers in commercial applications has been limited. Other copolymer stmctures, including random copolymers, may also act as compatibilizers. However, there exist conflicting results regarding the utility of random copolymers as interfacial modifiers."- w - 5.25... 

Chen HY, et al. Olefin block copolymers as polyolefin blend compatibilizer. ANTEC 2007, conference proceedings. Society of Plastics Engineers 2007. 

Diblock copolymers consist of two blocks of polymer (A and B), covalently bonded together. Besides the technical importance of block copolymers as new materials and as compatibilizing agents in polymer blends, tb are of particular scientific interest Lcibler [1] described the phase transition of copolymers in mean field theory, which gives already the main aspects of this phenomenon. 

Figure 3.6 Fracture surfaces of the PS/PE 95/5 (wt%). (a) Without compatibilizer (b) With 1 wt.% of styrene-butadiene-styrene block copolymer as a compatibilizer. Reproduced with permission from Ref [122] 2012, Elsevier.

Comparing Eqs (3.23) and (3.25), it can be shown that the interface becomes broader in systems with low-molecular-weight components [45]. The experimentally estimated interfacial thicknesses [45-48] were found to be in reasonable agreement with the Helfand-Tagami and Broseta predictions. The distribution of the chain segments for systems containing at the interface a block copolymer as a compatibilizer, was derived by Noolandi [49]. Typical values of the interfacial thickness in different polymer blends are summarized in Table 3.1. 

It is easy to visualize how a block copolymer orients at the interface and binds two immiscible polymer phases together to give a strong interface and good practical compatibility. This is why most compatibilization research has concentrated on block copolymers as physical additives. Unfortunately, most block copolymers are difficult and expensive to synthesize, which is a serious liability in industry. 

The main limitation to the use of preformed block or graft copolymers as compatibilizers has to be found in the non selective localization of these additives at the interface as a result of high melt viscosity and tendency to form micelles in a homopolymer phase [20-22]. 

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