Transition from two-stage to direct melt-crystallization in isotactic random butene-1/propene copolymers

Tailoring the rigid amorphous fraction of isotactic polybutene-1 by ethylene chain defects

“…This observation suggests that the exothermic peak around 0 C is due to the transition of Form II into Form I crystals, though direct formation of Form I' crystals from the melt cannot be excluded. Note that direct formation of Form I crystals from the melt, termed Form I' crystals [46,47], bypassing the intermediate formation of Form II crystals, has been suggested a possible route of crystallization of random butene-1 copolymers containing large amount of co-units [19,48].…”

Morphology of Form I′ crystals of polybutene-1 formed on melt-crystallization

“…There was not detected a transformation of the formed structure into a higher-stability crystal polymorph, as would be expected on formation of Form II mesophase. The former characterization of the random copolymer employed in this work revealed furthermore inclusion of the propylene co-units into the crystal phase, and a crystallinity of close to 50% [15,22].…”

“…1 shows height-contrast AFM images of the semicrystalline morphology of the random butene-1/propylene copolymer with 18.3 mol% propylene, representing sample areas of 2 Â 2 (top image) and 1 Â 1 mm 2 (bottom image), respectively. As outlined above, and as has been analyzed in detail by X-ray techniques and thermal analyses [15,16], slow cooling of this copolymer leads to formation of Form I 0 crystals, containing propylene co-units at an identical concentration as the amorphous structure. Despite the rather large amount of co-units in the macromolecule, due to the acceptance of propylene co-units on crystallization, the crystal fraction of close to 50% is only slightly lower than in the butene-1 homopolymer.…”

“…In the present study we used a random butene-1/propylene copolymer with 18.3 mol% propylene, synthesized using a ZieglereNatta catalyst, as described elsewhere [15]. The numberaverage molar mass and polydispersity of the particular sample were 46 kg mol À1 and 3.8, respectively.…”

“…The numberaverage molar mass and polydispersity of the particular sample were 46 kg mol À1 and 3.8, respectively. Prior investigation of the crystallization behavior of butene-1/propylene copolymers of different propylene concentration by temperature-resolved X-ray analysis showed that slow cooling of the melt of the random copolymer with 18.3 mol% propylene at a rate of 1 K min À1 to ambient temperature leads to direct formation of Form I 0 crystals, as there was detected formation of only negligible amount of Form II mesophase [15]. The result was consistent with an analysis of the crystallization and melting behavior of butene-1/propylene copolymers using calorimetry [22].…”