Block Copolymer as a Compatibilizer

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,... 

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. 

These polymers show lower water uptake than the analogous sulfonated poly(arylene ether sulfone) materials, possibly suggesting some interaction between the aromatic nitrile and sulfonic acid. The phosphine oxide functional moiety could also be used as a compatibilizer with other materials. Sulfonated poly(arylene ether phosphine oxide sulfone) terpoly-mers have been prepared both with sulfonated triphenyl phosphine oxide and with triphenyl phosphine oxide with 3,3 -disulfonate-4,4 —dichlorodiphenyl sulfone as the sulfonic acid bearing monomer. Block copolymers containing phosphine oxide appear to avoid the ether—ether interchange that results when non—phosphine oxide blocks are utilized, and this is being further pursued. ... 

Chemically unlike polymers are incompatible, and it sometimes happens that the reaction medium is heterogeneous at the beginning. However, once some block copolymer is formed it acts as a "compatibilizer" and the reaction medium gradually becomes homogeneous. Many examples of such reactions could be quoted. A recent one is the hydrosilylation reaction carried out between a polystyrene fitted at a chain end with vinylsilane groups, and an a,u-dihydrogenopolydimethylsiloxane. This process is carried out at high concentration and it yields polystyrene-polydimethylsiloxane-polystyrene block copolymers. 2... 

To prepare the graft copolymer, a PO (MW = 50 to 1,000 kg/mol) was either dissolved or swollen in an inert hydrocarbon, monomers (>80 wt% of a methacrylic ester, CH2=C(CH3)COOR) and an initiator was added to the heated mixture while stirring. As a result, acrylic branches of a relatively high molecular weight (MW = 20 to 200 kg/mol) were grafted onto the PO macromolecules. The graft copolymer could be used as a compatibilizer-cwm-impact modifier in a variety of polymers selected from between PO, acrylic polymers, SAN, EVAc, PA, PEST, PC, POM, PAr, PVC, ABS, PVDC, cellulosics, polyester-polyether block copolymers, PEA, PEEK, PEI, PES, CPVC, PVDF, PPE, PPS, PSF, TPU, PAI, PCL, polyglutarimide, blends of PEST with PC or PVC [Ilendra et al., 1992, 1993]. 

The efficiency of a block copolymer is fimited by the formation of micelles in bulk phases and by the kinetic factors. Consequently, the block copolymer used as a compatibilizer should be designed by taking thermodynamic and kinetic parameters into account to achieve the desired effects. Thus the stmcture and transitions in copolymers and homopolymer/copolymer systems is of great interest. 

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. 

The block or graft copolymer used as a compatibilizing agent must have the ability to separate into their respective phase and not be miscible as a whole molecule in one phase. The best choice of block or graft copolymers would be to choose polymers identical to the blended polymers, e.g., poly(A-fo-B) or poly(A-g-B) copolymers for blending poly(A) and poly(B). Another alternative is to use poly(C-fo-D) or... 

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... 

Various compatibilizers and additives have been investigated to improve the interfacial interactions of these blends. Wang et al. [208] used methylenediphenyl diisocyanate (MDI) to improve the interface and studied a blend of 55/45 (%w/w) mixture of PLA and dried wheat starch in an intensive mixer with or without a low level of MDI. Blends with MDI had enhanced mechanical properties that could be explained by the in situ formation of a block copolymer acting as a compatibilizer. SEMs showed reduced interfacial tension between the two phases. The presence of MDI also enhanced the mechanical properties of the blend at temperatures above Tg. Water uptake by the PLA/starch blends with and without MDI did not differ. 

S. P. Economopoulos, C. L. Chochos, V. G. Gregoriou, J. K. Kalhtsis, S. Barrau, G. Hadziioaimou, Novel Brush-Type Copolymers Bearing Thiophene Backbone and Side Chain Quinoline Blocks. Synthesis and Their Use as a Compatibilizer in Thiophene-Quinoline Polymer Blends. Macromolecules 2007,40,921-927. 

For immiscible polymer blends, using a third component as a compatibilizer is a common and effective method [39]. Many block or graft copolymers with functional groups offering specific interaction and/or chemical reaction with component polymers have been used as compatibilizers. They may be added... 

PP blends with 5-20 wt% LDPE and 1-15 wt% EPR showed excellent transparency and mechanical properties. Similarly, in Daicel patent PP was blended with 15-85 wt% ABS and 0.5 wt% CPE (or low-molecular-weight PS) as a compatibilizer ( ). EPR patented blaids of 10-60 wt% PP with EPR block copolymer and a pooxide-containing polyolefin copolymer to give a masterbatch that subsequently was blended with 60 wt% EPDM and to give elastomeric alloy with excellent mechanical properties... 

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. 

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