Diblock copolymers compatibilizing effect

Sivula K, Ball ZT, Watanabe N, Fr6chet JMJ (2006) Amphiphilic diblock copolymer compatibilizers and their effect on the morphology and performance of polythio-phene fullerene solar cells. Adv Mater 18 206... 

K. Sivula, Z. T. Ball, N. Watanabe, J. M. J. Frechet, Amphiphihc Diblock Copolymer Compatibilizers and Their Effect on the Morphology and Performance of Polythiophene FuUerene Solar Cells. Adv. Mater. 2006, 18, 206-210. 

Xu S, Zhao H, Tang T, Dong L, Huang B. Effect and mechanism in compatibilization of poly(styrene-l)-2-ethyl-2-oxazoline) diblock copolymer in poly(2,6-dimethyl-1,4-phenylene oxide)/poly(ethylene-ran-acrylic acid) blends. Polymer 1999 40 1537-1545. 

The interfacial properties of an amphiphilic block copolymer have also attracted much attention for potential functions as polymer compatibilizers, adhesives, colloid stabilizers, and so on. However, only a few studies have dealt with the monolayers o well - defined amphiphilic block copolymers formed at the air - water interface. Ikada et al. [124] have studied monolayers of poly(vinyl alcohol)- polystyrene graft and block copolymers at the air - water interface. Bringuier et al. [125] have studied a block copolymer of poly (methyl methacrylate) and poly (vinyl-4-pyridinium bromide) in order to demonstrate the charge effect on the surface monolayer- forming properties. Niwa et al. [126] and Yoshikawa et al. [127] have reported that the poly (styrene-co-oxyethylene) diblock copolymer forms a monolayer at the air - water... 

Since they act as surfactants, copolymers are added in only small amounts, typically from a thousandth parts to a few hundredth parts. Theoretically, Leibler [30] showed that only 2% of a diblock copolymer may thermodynamically stabilize an 80%/20% incompatible blend with an optimum morphology (submicronic droplets). However, in practice kinetic control and micelle formation interfere in this best-case scenario. To a some extent, compatibilization increases with copolymer concentration [8,31,32], Beyond a critical concentration (critical micellar concentration cmc) little or no improvement is observed (moreover, for high amounts, the copolymer can act as a plasticizer). Copolymer molecular weight influence is similar to that of the concentration effect. For example, in a PS/PDMS system [8,31,32], when the copolymer molecular weight increases, domain size decreases to a certain extent. Hu et al. [31] correlated their experimental results with theoretical prediction of the Leibler s brush theory [30]. Leibler distinguishes two regimes to characterize the behaviour of the copolymer at the interface... 

One possible way of reducing interfacial tension and improving phase adhesion between PP-based blend phases is to use a selected copolymeric additive that has similar components to the blend, as a compatibilizer in the blend system. Well-chosen diblock copolymers, widely used as compatibilizing agents in PP-based blends, usually enhance interfacial interaction between phases of blends (15, 16), reduce the particle dimensions of the dispersed phase (16, 17), and stabilize phase dispersion against coalescence (16-18) through an emulsification effect, thus improving the mechanical properties (15-19). 

Enhanced interphase interactions, deduced from thermal and dynamic mechanical properties and morphology observed by SEM, demonstrate the efficient compatibilizing effect of iPS-fo-iPP copolymer on iPS-iPP blends. Each sequence of the iPS-fc-iPP diblock copolymer can probably penetrate or easily anchor its homopolymer phase and provide important entanglements, improving the miscibility and interaction between the iPS and iPP phases. This is in good agreement with what is inferred from the mechanical properties of the iPS-fo-iPP-iPS-iPP polyblends. 

In contrast to the situation found for dilute solutions, the behavior of nonlinear block copolymers in the solid state seems to have attracted great attention. Many theoretical publications appeared in recent years, dealing mainly with the phase behavior of star-block, simple graft and comb copolymers. Issues like the nature of the phase diagram and the order-disorder transition have been studied in considerable detail. The compatibilizing effects of complex copolymers, in comparison to simple diblock copolymers, were also investigated. 

Thus, from this data, it appears that both the alternating and diblock copolymers are the most efficient at compatibilizing polymer blends. Unfortunately, these two copolymers are also the most difficult to realize and therefore, this is of little use from a commercial standpoint. It is interesting that the alternating copolymer may rival the diblock copolymer as a compatibilizer and this possibility is currently under investigation in our laboratory. Within the random copolymers (Px = 0.5, 1.0, and 1.5), these results suggest that the blocky structure is much better at interacting with the homopolymers than the alt-ran structure, and thus should be a more effective interfacial modifier. 

The change in volume of the copolymer as the system goes from a miscible to an immiscible state has been utilized as a qualitative measure of its ability to compatibilize a biphasic blend. This can be quantified by using the difference between the volume of the copolymer in the miscible system and the volume of the copolymer in the phase separated system at its deepest quench as a measure of the effectiveness of the copolymer as a compatibilizer. This value is plotted vs. the sequence distribution, Px in Figure 2. This data quantifies the trend that is described above the alternating and diblock copolymers are the best compatibilizers, however within the random structures, the more blocky structures is a more effective interfacial modifier than the statistically random copolymer which is more effective than an alternating-random structure. 

Nonetheless, Monte Carlo results suggest that in order for a copolymer to be an effective compatibilizer in polymer blends, the copolymer must be blocky in nature. This interpretation of the simulation results are in agreement with the experimental results which show that the random copolymers that are better than the diblock copolymer at compatibilizing a blend are those that are blockier than a statistical random copolymer. The copolymers that do not behave as effectively as a compatibilizer are more alternating than a statistically random copolymer. 

Xu et al. (1999a) prepared compatibilized blends of PS and the Zn salt of sulfonated PS by addition of poly(styrene-b-4-vinylpyridine) diblock copolymer. Characterization methods included SEM, DSC, SAXS, and FTIR. The effect of block copolymer level was studied. Evidence was found for Zn-mediated cross-linking between sulfonate groups and pyridine nitrogen. 

Contradictory results have been published on the effect of block copolymers with different numbers of blocks. In some papers, diblock copolymers have been found more efficient compatibilizers than triblock copolymers (51,154,155), whereas in several other studies, the opposite results have been obtained (156-158). Still others state that there is no difference between diblocks and triblocks (159). Some more recent articles show the compatibilizing efficiency of multiblock (tetrablock, pentablock, heptablock) copolsrmers (160-162), which seems to be supported also by some theoretical studies (163,164). 

Cavanaugh and co-workers (166) have studied the compatibilization efficiency of various styrene-butadiene copolymers in polystyrene (PS, Mw = 202,000)/polybutadiene (PB, Mw = 320,000) blends. The most effective compat-ibilizer proved to be a long, asymmetric diblock (M = 182,000 PS content 30%), which could entangle in both homopolymer phases. Short diblock copolymers and most of the random copolymers were inadequate as interfacial agents. Moderate improvement in impact strength was observed for a S-B multiblock. 

Diblock copolymers are known to be the most effective compatibilizers for improving the interfacial interactions between two polymers that are immiscible. This is particularly interesting for iPP, since its lack of functionality and the poor compatibility between iPP and other materials have imposed limitations for iPP applications in many areas, including polymer blends and composites. The synthesis of iPP with terminal functional groups (OH, NH2, etc.) offers a good opportunity to carry out chain extensions through simple coupling reactions with suitable polymers. These may be carried out in solution or in the polymer melt. Reactive extrusion of two chain-end reactive polymers... 

You Chang-jiang and Jia De-min. Effects of styrene-ethylene/propylene diblock copolymer (SEP) on the compatibilization of PP/PS blends. Chinese J. Polym. Sci. 21 no. 4 (2003) 443-446. 

Anastasiadis et al. [45] investigated the compatibilizing effect of an anionically synthesized model FS-b-FYE diblock copolymer on the interfacial tension between PS and PVE model polymers as a function of the concentration of the copolymer additive. They utilized the pendant drop method [155] to measure the interfacial tension between the immiscible polymer fluids. A sharp decrease in interfacial tension was observed with the addition of small amounts of copolymer (Fig. 24),... 

Commingled post-consumer recyclates containing mixtures of polymers that differ in structure and polarity with limited miscibility have low tensile and impact properties. Both nonreactive and reactive compatibilizers are applied. Nonreactive compatibilizers are diblock or multiblock copolymers. Compatibilizers principally consisting of mixtures of POs are of major interest for recyclates. Random E/P eopolymers are effective compatibilizers for LDPE/PP, HDPE/PP or LLDPE/PP blends [94], Other examples are given in Table 12. 

HDPE + nylon 6 was compatibilized by adding polyethylene ionomer, which gave finer domain size due to emulsification and lower interfacial tension [70]. LLDPE + polyvinyl chloride was compatibilized by adding up to 5% of isoprene-4-vinyl pyridine diblock copolymer, acting as an emulsifier to reduce phase diameter and interfacial tension. Polystyrene-acrylic acid diblock copolymer was somewhat less effective [49]. 

The nitroxide-mediated homopolymerization of AA under its nonprotected form was performed in 1,4-dioxane solution at 120 ° C and was initiated by an SG1 -based alkoxyamine. The results showed a good control over the polymerization and the chain-end structure toward moderate molar mass poly-mers. °° ° When high molar masses were targeted, chain transfer to the solvent and to the polymer had a nonnegligible effect on the structural quality. Those living PAA macroalkoxy-amines found applications in the synthesis of amphiphilic diblock copolymers, either in solution or in aqueous emul-sion. ° ° They were also employed as stabilizers/ compatibilizers of carbon nanotubes/polymer composites. ... 

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