Poly isotactic/atactic blends

Essentially the same features are found in isotactic-atactic blends of poly(3-hydroxy butyrate).(58,59) The rate maximum that is observed in the pure isotactic polymer is maintained in the blends. The growth rate and maxima are systematically reduced with dilution. The maximum temperatures do not vary by more than just a few degrees. 

Fig. 4.1 Plot of melting temperature against percentage atactic poly(styrene) for isotactic-atactic poly(styrene) blends. Molecular weights of atactic poly(styrene) are indicated in the figure. (From Yeh and Lambert (21))...

Poly(cyclohexyl acrylate) was shown to be miscible with PS with ucst behavior [720]. Random copolymers of cyclohexyl acrylate with n-butyl acrylate showed miscibility with PS above 50% cyclohexyl acrylate[721]. Poly(cyclohexyl methacrylate)/isotactic PS blends showed miscibility based on calorimetry and NMR studies [722]. The NMR results showed homogeneous behavior at a scale of 2.5-3.5 nm. Poly(4-trimethylsilyl styrene) miscibility with polyisoprene was observed with a lest behavior (critical temperature = 172 ° C at degree of polymerization of 370) [723]. The interaction parameter, showed the following relationship = 0.027—9.5/T. Isotactic and syndiotactic polystyrene both exhibit crystallinity, whereas atactic polystyrene is amorphous. Atactic PS/isotactic PS blends exhibited crystallization kinetics, which decreased linearly with atactic PS addition indicating miscibility [724]. The TgS of aPS and iPS are identical, thus Tg methods could not be employed to assess miscibility. Atactic PS/syndiotactic PS blends were also noted to be miscible with rejection of atactic PS in the interfibrillar region between the lamellar stacks of sPS [725]. 

An interesting set of binary mixtures are those between polymers of different stereo structures. Among others the crystallization kinetics of isotactic poly(styrene)-atactic poly(styrene), (25,54,55) syndiotactic poly(styrene)-atactic poly(styrene), (56) isotactic poly(propylene)-atactic poly(propylene) (55,57) and blends of isotactic and atactic poly(3-hydroxy butyrate),(58,59) and poly(D-lactic acid) with poly(L-lactic acid) (60) have been studied. In analyzing the kinetics of such blends the distinction still needs to be made as to whether the components are miscible in all proportions, partially miscible, or immiscible at all concentrations. Surprising as it may seem, this is an important consideration for these kinds of mixtures. 

A typical example of the spherulite growth rates of these blends is given in Fig. 11.28 for the isotactic-atactic poly(styrene) pair as a function of temperature for different compositions.(54) The molecular weights in this mixture are 5.5 x 10 and 4.8 x 10 for the isotactic and atactic polymers, respectively. The usual rate maximum for the pure polymer is found at about 180 °C and is maintained for all the blends, even the most dilute one. There is a systematic, continuous decrease in growth rate as the atactic component is added. Similar results are found with... 

Fig. 11.28 Spherulite growth rates of isotactic poly(styrene) in blend with atactic poly(styrene) at indicated composition. (From Yeh and Lambert (54))...

Fig. 11.30 Spherulite growth rate, G, of isotactic poly(propylene) in blend with atactic poly(propylene) as a function of crystallization temperature. Compositions of blends indicate in figure. (Data from Keith and Padden (55))...

Fig. 11.43 Plot of initial growth rate G for a 60/40 isotactic-atactic poly(styrene) blend as a function of molecular weight of the atactic component, at indicated crystallization temperatures. (From Okada et al. (94))...

Unlike most crystalline polymers, PVDF exhibits thermodynamic compatibiUty with other polymers (133). Blends of PVDF and poly(methyl methacrylate) (PMMA) are compatible over a wide range of blend composition (134,135). SoHd-state nmr studies showed that isotactic PMMA is more miscible with PVDF than atactic and syndiotactic PMMA (136). MiscibiUty of PVDF and poly(alkyl acrylates) depends on a specific interaction between PVDF and oxygen within the acrylate and the effect of this interaction is diminished as the hydrocarbon content of the ester is increased (137). Strong dipolar interactions are important to achieve miscibility with poly(vinyhdene fluoride) (138). PVDF blends are the object of many papers and patents specific blends of PVDF and acryflc copolymers have seen large commercial use. 

After having studied in our laboratory, polymer blends of amorphous polymers poly-c-caprolactone and poly (vinyl chloride) (1,2) (PCL/ PVC), blends with a crystalline component PCL/PVC (3,4), poly(2,6-dimethyl phenylene oxide) (PPO) with isotactic polystyrene (i-PS) (5) and atactic polystyrene (a-PS) with i-PS (6), we have now become involved in the study of a blend in which both polymers crystallize. The system chosen is the poly(1,4-butylene terephthalate)/poly(ethylene terephthalate) (PBT/PET) blend. The crystallization behavior of PBT has been studied extensively in our laboratory (7,8) this polymer has a... 

Tsuji, H. and Ikada, Y. (1995) Blends of isotactic tmd atactic poly(lactide)s. I. Effects of mixing ratio of isomers on crystallization of blends from melt. Journal of Applied Polymer Science, 58, 1793-1802. 

Tsuji, H. and Ikada, Y. (1996) Blends of isotactic and atactic poly(lactide) 2. Molecultir-weight effects of atactic component on crystallization and morphology of equimolar blends from the melt. Polymer, 37, 595-602. 

Other symbols occasionally used in the literature include (br) for branched materials and (iso), (syndio), and (a) for isotactic, syndiotactic, and atactic structures respectively. No symbol appears to exist for mechanical blends, although these materials are obviously important. Where necessary the symbol -m- will denote a mechanical blend, for example, poly(styrene-m-butadiene) for a mechanical blend of polystyrene with polybutadiene. 

Abe H, Doi Y, Kumagai Y (1994a) Synthesis and characterization of poly[(R,S)-3-hydroxybu-tyrate-b-6-hydroxyhexanoate] as a compatibilizer for a biodegradable blend of poly[(R)-3-hydroxybutyrate] and poly(6-hydroxyhexanoate). Macromolecules 27 6012-6017 Abe H, Dd Y, Satkowski MM, Noda I (1994b) Miscibility and morphology of blends of isotactic and atactic poly(3-hydroxybutyrate). Macromolecules 27 50-54 Abe H, Matsubara I, Doi Y (1995) Physical properties and enzymic degradability of polymer blends of bacterial poly[(R)-3-hydroxybutyrate] and poly [(R,S)-3-hydroxybuty rate] stereoisomers. Macromolecules 28 844-853... 

Park SJ, Park JP, Lee SG (2002) Production of poly(3-hydroxybutyrate) from whey by fed-batch culture of recombinant Escherichia coli in a pQot-scale fermenter. Biotechnol Lett 24 185-189 Pearce R, Marchessault RH (1994) Multiple melting in blends of isotactic and atactic poly(P-hydroxybutyrate). Polymer 35 3990-3997... 

Fig. 6. Comparison of cloud point curves for blends of a-methylstyrene/acrylonitrile copolymer with isotactic poly(methyl methacrylate), with poly(ethyl methacrylate), and with atactic poly(methyl methacrylate). (From Goh, Paul, and Barlow )...

Other mixtures of chemically identical polymers such as isotactic and atactic poly(lactides) (25) and blends of bacterial poly( 6-hydroxybutyrate) and its atactic counterpart (26,27,28) also show very small melting point depressions with modest to high molecular weight atactic components. Another example of the basic colligative nature of the melting point depression in such binary blends is given in... 

Funke, Z., Schwinger, C., Adhikari, R. Kressler. (2001). Surface Tension in Polymer Blends of Isotactic Poly(propylene) and Atactic Polystyrene J. Macromol Mater Eng, 286,744-751. 

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