Block Copolymer Addition

Block copolymers with block compositions equal (or similar) to the components of a polymer blend can be utihzed to compatibilize the blend. The block copolymer will concentrate at the interface and allow for improved adhesion between the phases as noted in Fig. 3.10. The phase behavior of ternary blends based on two homopolymers and a block copolymer containing both components has been reviewed by Hudson and Jamieson [213]. The compatibilization aspects of block copolymers has been reviewed in a book by Datta and Lohse [1]. Specific examples will be discussed in this section. Further discussion of block copolymer blends (including higher levels of addition) is presented in Section 4.9 and in [214]. 

One of the primary examples of compatibilization involves the styrene/ethylene-butylene/sty-rene (SEES) ABA block copolymer addition to polystyrene and polyolefins (PP, PE). 

PS/polyolefin blends exhibit poor mechanical properties that can be significantly improved with the addition of low levels of the SEES block copolymer. The addition of SEES to LDPE or HDPE/PS blends leads to a large decrease in the domain size of the dispersed phase [215,216]. Schwarz et al. [217] showed large increases in the notched Izod impact strength and elongation at break for addition of SEES to HDPE/PS and HDPE/PS/PPO blends. The PS/PPO blend is a miscible system, thus can be considered a modification of the PS phase in the HDPE/PS blends. The SEES block copolymer has been noted to compatibilize PP/PS blends and was proposed for compatibilization of waste materials [218]. 

A hydrogenated polybutadiene-PA6 diblock polymer prepared by anionic polymerization of e-caprolactam onto an isocyanate terminated hydrogenated polybutadiene was studied in LDPE/PA6 blends [223] The block copolymer allowed for a very fine dispersion of PA6 in a 80/20 LDPE/PA6 blend with up to an order of magnitude reduction in particle size. Improvement in mechanical properties at both 80/20 and 20/80 LDPE/PA6 blend composition was also observed with the block copolymer addition. 

A block iaAA Polymer 1 or miscible with polymer 1 B block VVV y it iscible with polymer 2 

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One can have the same type of situation in a blend of two mutually immiscible polymers (e.g., polymethylbutene [PMB], polyethylbutene [PEB]). When mixed, such homopolymers form coarse blends that are nonequilibrium structures (i.e., only kinetically stable, although the time scale for phase separation is extremely large). If we add the corresponding (PEB-PMB) diblock copolymer (i.e., a polymer that has a chain of PEB attached to a chain of PMB) to the mixture, we can produce a rich variety of microstructures of colloidal dimensions. Theoretical predictions show that cylindrical, lamellar, and bicontinuous microstructures can be achieved by manipulating the molecular architecture of block copolymer additives. 

Fig. 2 A first generation of drug-loading micelles, a Schematic illustration of the formation of polymeric micelle of Dox-conjugated PEG-PAsp block copolymer. Additional Dox can be physically entrapped in the micelle, b Chemical structures of PEG-PAsp block copolymer and Dox...

Octadecyl group attachment to surface Silicon containing block copolymer additive Plasma fluoropolymer deposition Plasma siloxane polymer deposition Radiation-grafted hydrogels... 

Lee JH, Ju YM, Lee WK, et al. Platelet adhesion onto segmented polyurethane surfaces modified by PEO- and sulfonated PEO-containing block copolymer additives. J Biomed Mater Res May 1998 40(2) 314-23. 

Heischer et al. [172] measured the interfacial tension reductirai credited to the complexation between carboxy-terminated PBD and amine-terminated PDMS, which were added to an immiscible blend of PBD and PDMS. The changes in interfacial tensimi resembled the behavior observed for block copolymer addition to homopolymer blends there is initially a linear decrease in interfacial tension with the concentration of functional homopolymer up to a critical concentration, at which the interfacial tension becomes invariant to further increases in the concentration of functional material. However, the formation of interpolymer complexes depends on the equilibrium between associated and dissociated functional groups and, thus, the ultimate plateau value for interfacial tension reduction is dependent on the functional group stoichiometry. A reaction model for end-complexation was developed in order to reproduce the interfacial tension reduction data with Fourier transform infrared spectroscopy applied to determine the appropriate rate constants. The model provided a reasonable qualitative description of the interfacial tension results, but was not able to quantitatively predict the critical compositions observed experimentally. 

Bousmina, M Bataille, P Sapieha, S and Schreiber, H.P. (1995) Comparing the effect of corona treatment and block copolymer addition on rheological properties of polystyrene/polyethylene blends./. Rheol, 39, 499-517. 

In this section, we wiU discuss non-reactive systems, while reactive compatibihzation will be covered in later sections. Non-reactive ternary polymer systems include random copolymers, graft copolymers and polymers offering either miscibility or good interfacial adhesion between the blend components. One of the primary examples of ternary polymer addition involves the compatibihzation of polystyrene with polyolefins employing styrene-hydrogenated diene-styrene ABA block copolymers. Block copolymer addition is a specific subset of ternary polymer addition that will be discussed in Section 3.7. 

Endo, H., Schwahn, D., and Colfen, (. (2004) On the role of block copolymer additives for calcium carbonate crystallization small angle neutron scattering investigation by applying contrast variation. Journal of Chemical Physics, 120, 9410-9423. 

In this chapter we have discussed two as yet unresolved issues, finite molecular weight effect and the phase behavior and phase transitions in highly asymmetric block copolymers. We believe that these issues are fundamental enough to require a fresh look, particularly from a theoretical point of view. We do not think that the currently held mean-field theory can explain every conceivable phase behavior and phase transitions experimentally observed in block copolymers. Additionally, most if not all of the physical theories in the literature are based on certain assumptions which were made, more often than not, for the reason of mathematical simplicity. We have suggested that a new theory for phase behavior and phase transitions in block copolymers be developed by relaxing the assumptions made in the formulation of the currently held mean-field theories. 

Compatibilized blends with addition of nanoparticles can become an alternative for conventional compatibilized blends containing block copolymers. Addition of oragnoclays to polymer blend affects multiple features thermodynamic phase behavior of the blend, the kinetics of phase separation and also the morphology formed in the two-phase region. Hemmati et al. proved that incorporation of organoclay evidently enhances the miscibility of PE and ethylene-vinyl acetate [EVA] phases in the amorphous regions of nanocomposites. In addition, the studies revealed that nanofiller influences the diffusion of polymer chains, which contributes to... 

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