Isoprene matrix, block copolymers

Shenoy, A.V. and Saini, D.R. (1986) Quantitative estimation of matrix filler interactions in ferrite-filled styrene-isoprene-slyrene block copolymer systems, Polym. Composites, 7,96-100. 

Short fiber reinforcement of TPEs has recently opened up a new era in the field of polymer technology. Vajrasthira et al. [22] studied the fiber-matrix interactions in short aramid fiber-reinforced thermoplastic polyurethane (TPU) composites. Campbell and Goettler [23] reported the reinforcement of TPE matrix by Santoweb fibers, whereas Akhtar et al. [24] reported the reinforcement of a TPE matrix by short silk fiber. The reinforcement of thermoplastic co-polyester and TPU by short aramid fiber was reported by Watson and Prances [25]. Roy and coworkers [26-28] studied the rheological, hysteresis, mechanical, and dynamic mechanical behavior of short carbon fiber-filled styrene-isoprene-styrene (SIS) block copolymers and TPEs derived from NR and high-density polyethylene (HOPE) blends. 

The effect of blending LDPE with EVA or a styrene-isoprene block copolymer was investigated (178). The properties (thermal expansion coefficient. Young s modulus, thermal conductivity) of the foamed blends usually lie between the limits of the foamed constituents, although the relationship between property and blend content is not always linear. The reasons must he in the microstructure most polymer pairs are immiscible, but some such as PS/polyphenylene oxide (PPO) are miscible. Eor the immiscible blends, the majority phase tends to be continuous, but the form of the minor phase can vary. Blends of EVA and metallocene catalysed ethylene-octene copolymer have different morphologies depending on the EVA content (5). With 25% EVA, the EVA phase appears as fine spherical inclusions in the LDPE matrix. The results of these experiments on polymer films will apply to foams made from the same polymers. 

Fig. 3.52 Left (a) Schematic of intermittent contact mode AFM and phase imaging right (b) intermittent contact AFM phase image of a 30 nm thin block copolymer films on silicon [(poly(isoprene)-b-poly(ferrocenyl dimethylsilane), 29 kg/mol/15 kg/mol], which displays a in-plane worm-like surface pattern of poly(ferrocenyl dimethylsilane) in a matrix of poly (isoprene). From the 2D FFT analysis (inset) an average repeat period of 33 nm was estimated. Reprinted with permission from [116]. Copyright 2000. American Chemical Society...

The most extensively studied block copolymers prepared by anionic polymerization are the styrene-butadiene or styrene-isoprene rubbers. Shell Chemical Company s Kraton thermoplastic elastomers are ABA block copolymers of this type. Their elastomeric properties are excellent, yet they differ from other rubbers in that vulcanization is not required. These elastomers consist of a rubbery polybutadiene matrix with the styrene segments serving as anchors in thermoplastic microdomains. 

Richards and Thomason observed several peaks in the scattering curves from styrene-isoprene block copolymers, which indicate that the copolymer separates into two domains. By comparing the observed scattering curves with model calculations, the domains were characterized as a face-centred cubic array of polystyrene spheres in a polyisoprene matrix. The spheres had a radius of 130 A, were 383 A apart and there was a 29 A thick interfacial layer around them. 

Styrene-1,3-butadiene-styrene (SBS) or styrene-isoprene-styrene (SIS) triblock copolymers are manufactured by a three-stage sequential polymerization. One possible way of the synthesis is to start with the polymerization of styrene. Since all polystyrene chains have an active anionic chain end, adding butadiene to this reaction mixture resumes polymerization, leading to the formation of a polybutadiene block. The third block is formed after the addition of styrene again. The polymer thus produced contains glassy (or crystalline) polystyrene domains dispersed in a matrix of rubbery polybutadiene.120,481,486... 

AB copolymers of isoprene and methyl methacrylate have been synthetized by Rossi A hexagonal structure formed by cylinders of polyisoprene in a matrix of poly(methyl methaaylate) has been demonstrated by low-ai e X-ray diffraction and electron miaoscopy for copolymers containing about 30% of polyisoprene ABA copolymers poly(methyl methacrylate)-polyisoprene-poly(methyl methacrylate) havii polyisoprene with a high vinyl content as central block have been nthetized by Cole et al. Dynamic mechanical properties of films of these ABA copolymers have been studied as a function of the copolymer composition, the temperature and the nature of the solvent (carbon tetrachloride, toluene, ethyl acetate, methylethyl ketone, dioxane) used for film preparation ... 

Since the dimensions to be probed are of the order of few nanometers, the most useful microscopic method would be that of the transmission electron microscopy (TEM). Using this technique Fayt et al. [1986] observed location of P(S-b-HB) compatibilizer in a PE/PS blends. The authors inserted a short sequence of isoprene between the styrenic and hydrogenated butadiene blocks. After staining the isoprene double bonds with OsO, the authors were able to observe presence of the copolymer at the interface between the matrix and dispersed phase. Thickness of the interphase could then be measured. The experiments also demonstrated presence of the added compatibilizer as dispersed micelles inside the PE phase. This technique is applicable, however, only when selective staining affects only the compatibilizer. 

To this group of blends belong mixtures of PP with st)oene-elastomer copolymers, styrene-diene blocks styrene-butadiene-st)a ene (SBS), sty-rene-ethylene/butylene- t30 ene (SEBS), st)rrene-isoprene-styrene (SIS), with acrylonitrile-butadiene-styrene terpol)nners (ABS), acrylonitrile-styrene-acrylate (ASA), or with EPR/EPDM grafted with styrene and acrylonitrile (AES or AXS). The first blends of this type date from the early 1960s. In these systems, PP is either the main component to be modified, or an additive to enhance performance of the styrenic matrix. 

A thin solution-cast film of a diblock copolymer consisting of a polystyrene block (M 50,000) and a deuterium-substituted polyisoprene block (A/ 100,000) was stimulated at room temperature with a O.r/i-amplitude, 23-Hz dynamic tensile strain. In this composition range, diblock copolymers of styrene and isoprene produce a hexagonally packed regular array of rod-like polystyrene microdomains embedded in a continuous matrix of the polyisoprene block. The diameter of each polystyrene microdomain is well below 0.1 pm. 

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