Copolymers, triblock properties

Property Physical units Copolymers Multiblock copolymers Triblock copolymers... 

Mural and co-workers [57] also optimised the mechanical properties of an rPP and recycled high impact polystyrene (rHIPS) blend at a composition of 70/30 wt%. Consequently, this composition was mixed with a styrene-ethylene-butylene-styrene (SEES) block copolymer triblock copolymer and Cloisite 20A OMMT. Using X-ray diffraction, the samples containing 3 wt% of nanoclay were found to lack the characteristic nanoclay peak, which indicated the mixed intercalated and exfoliated clay layers where the intercalated layers were further pushed toward the interphase [76]. The incorporation of a compatibiliser and nanoclay also improved the thermal stability of the PP/HIPS blend. SEES and nanoclay performed as an interfacial compatibiliser, which led to the reduction in particle size of rHIPS and the promotion of interfacial adhesion. 

PEO/PPO/PEO triblock copolymers exhibit properties similar to typical surfactants, i.e. they reduce surface and interfacial tension of aqueous solutions and form micellar aggregates above a critical micellar concentration [74, 78]. For some compounds of this type, like P104 (EOigPOsgEOis), P123 (E02oP07oE02o)> 3nd F127 (EO106PO70EO106), a similarly located cubic phase like the one of the aminoxide systems has been found in tbe binary aqueous system [74, 79]. 

Styrenic block copolymers (SBCs) are also widely used in HMA and PSA appHcations. Most hot melt appHed pressure sensitive adhesives are based on triblock copolymers consisting of SIS or SBS combinations (S = styrene, I = isoprene B = butadiene). Pressure sensitive adhesives typically employ low styrene, high molecular weight SIS polymers while hot melt adhesives usually use higher styrene, lower molecular weight SBCs. Resins compatible with the mid-block of an SBC improves tack properties those compatible with the end blocks control melt viscosity and temperature performance. 

Butadiene copolymers are mainly prepared to yield mbbers (see Styrene-butadiene rubber). Many commercially significant latex paints are based on styrene—butadiene copolymers (see Coatings Paint). In latex paint the weight ratio S B is usually 60 40 with high conversion. Most of the block copolymers prepared by anionic catalysts, eg, butyUithium, are also elastomers. However, some of these block copolymers are thermoplastic mbbers, which behave like cross-linked mbbers at room temperature but show regular thermoplastic flow at elevated temperatures (45,46). Diblock (styrene—butadiene (SB)) and triblock (styrene—butadiene—styrene (SBS)) copolymers are commercially available. Typically, they are blended with PS to achieve a desirable property, eg, improved clarity/flexibiHty (see Polymerblends) (46). These block copolymers represent a class of new and interesting polymeric materials (47,48). Of particular interest are their morphologies (49—52), solution properties (53,54), and mechanical behavior (55,56). 

J.H. Grezlak, The Preparation and Physical Properties of Polyester-Poly(Methyl Methacrylates) Triblock Copolymers , TR for Jan 1— March 1, 1975, Contract N00014-67-A-0151-0011. Princeton Univ, Princeton (1975)... 

Similar types of lamellar morphologies were observed for triblock copolymers of diphenylsiloxane and dimethylsiloxane having 40 wt% polydiphenylsiloxane, using electron microscopy, 47-148>. The lamellae thickness was approximately equal to the chain length of the rigid polydiphenylsiloxane blocks. These copolymers showed elastomeric properties comparable to those of conventional silica-reinforced, chemically crosslinked silicone rubbers. Tensile tests yielded an initial modulus of 0.5-1 MPa, tensile strength of 6-7 MPa and ultimate elongation between 400 and 800 %. 

Antony, P., Puskas, J.E., and Kontopoulou, M. The Rheological and Mechanical Properties of Blends Based on Polystyrene-Polyisobutylene-Polystyrene Triblock Copolymer and Polystyrene. Proceedings of MODEST, International Symposium on Polymer Modification, Degradation and Stabilization, Budapest, Hungary, 2002. 

Hong, B. K. and Jo, W. H. (2000) Effects of molecular weight of SEBS triblock copolymer on the morphology, impact strength, and rheological property of syndiotactic polystyrene/ ethylene-propylene rubber blends. Polymer, 41, 2069-2079. 

Drug Release from PHEMA-l-PIB Networks. Amphiphilic networks due to their distinct microphase separated hydrophobic-hydrophilic domain structure posses potential for biomedical applications. Similar microphase separated materials such as poly(HEMA- -styrene-6-HEMA), poly(HEMA-6-dimethylsiloxane- -HEMA), and poly(HEMA-6-butadiene- -HEMA) triblock copolymers have demonstrated better antithromogenic properties to any of the respective homopolymers (5-S). Amphiphilic networks are speculated to demonstrate better biocompatibility than either PIB or PHEMA because of their hydrophilic-hydrophobic microdomain structure. These unique structures may also be useful as swellable drug delivery matrices for both hydrophilic and lipophilic drugs due to their amphiphilic nature. Preliminary experiments with theophylline as a model for a water soluble drug were conducted to determine the release characteristics of the system. Experiments with lipophilic drugs are the subject of ongoing research. 

Triblock copolymers, as shown in Fig. 5.8 d), comprise a central homopolymer block of one type, the ends of which are attached to homopolymer chains of another type. As with other block copolymers, the components of triblocks may be compatible or incompatible, which will strongly influence their properties. Of particular interest are triblocks with incompatible sequences, the middle block of which is rubbery, and the end blocks of which are glassy and form the minor phase. When such polymers phase-segregate, it is possible for the end blocks of a single molecule to be incorporated into separate domains. Thus, a number of rubbery mid-block chains connect the glassy phases to one another. These materials display rubber-like properties, with the glassy domains acting as physical crosslinks. Examples of such materials are polystyrene/isoprene/polystyrene and polystyrene/polybutadiene/polystyrene triblock copolymers. 

Statistical and block copolymers based on ethylene oxide (EO) and propylene oxide (PO) are important precursors of polyurethanes. Their detailed chemical structure, that is, the chemical composition, block length, and molar mass of the individual blocks may be decisive for the properties of the final product. For triblock copolymers HO (EO) (PO)m(EO) OH, the detailed analysis relates to the determination of the total molar mass and the degrees of polymerization of the inner PPO block (m) and the outer PEO blocks (n). 

ABA triblock copolymers of the styrene-diene type are well known, and owe their unique properties to their heterophase morphology. This arises from the incompatibility between the polystyrene A blocks and the polydiene B blocks, leading to the formation of a dispersion of very small polystyrene domains within the polydiene matrix. This type of elastic network, held together by the polystyrene "junctions", results in thermoplastic elastomer properties. 

In this study, the effects of the variations in block sequence and composition (and thus relative block length) on the material properties of two series of triblock copolymers has been investigated. One of the blocks, the hydrogenated polybutadiene (HB), is semicrystalline, and the other block, the hydrogenated polyisoprene (HI) is rubbery at room temperature. Thus in one series, the HBIB block copolymers, the end blocks are semi-... 

Figure 15A. Temperature dependence of E at 110 Hz. Effect of variation in composition on properties of triblock copolymers on H1B1 as compared to those of HB. All films are press-quenched.

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