Poly block copolymers crystal growth

The effect of poly(methyl methacrylate), PMMA, on the crystallization kinetics of poly(ethylene oxide) has been investigated using the Avrami equation to analyze the results (80). The crystallization-rate constant, k, decreased as the concentration of PMMA increased. This and other results indicated that, in the blends, crystallization proceeds by a predetermined nucleation and this is followed with a two-dimensional growth. There has been evidence of melt compatibility for these two polymers (81-84) see Section V. Crystallization behavior of blends of poly(ethylene oxide) with poly(propylene oxide) (85) and with poly(vinyl acetate) (83) have been studied, as well as star and block copolymers of ethylene oxide and styrene (86). 

The influence of block length on the spherulite growth rate can be found in a set of urethane linked poly(ethylene oxide) block copolymers.(75) The copolymers consisted of uniform block length of either 34,45 or 90 repeating units with total molecular weights that varied from several thousand to 3-6 x 10. The 34 repeating unit blocks (M = 1500) always crystallized in extended form. In contrast the 90 repeating unit blocks (M = 3900) crystallized in a folded structure at all... 

A well studied example is given by the poly(oxyethylene-Z locfc-styrene). In case of atactic sequences of polystyrene, only the poly(oxyethylene), POE, can crystallize. A typical morphology of the POE is shown in Fig. 5.55. Single crystals of the copolymer can be grown from a common solvent which keeps both components mobile up to the time of crystallization of the POE-component. Figure 7.53 illustrates a growth spiral out of poly(oxyethylene-fclocfe-styrene), grown at 293 K from a solution of ethylbenzene (AB diblock, 28 wt-% oxyethylene block with a molar mass of about 10,000 Da). The crystal is comparable to the lamellar crystals of Fig. 5.55, i.e., the poly(oxyethylene) crystals are chain-folded with about 2.5 nm amorphous polystyrene layers at the interfaces. 

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