Polyethylene (PE) and isotactic polypropylene (PP) constitute nearly two-thirds of the world's plastic. Despite their similar hydrocarbon makeup, the polymers are immiscible with one another. Thus, common grades of PE and PP do not adhere or blend, creating challenges for recycling these materials. We synthesized PE/PP multiblock copolymers using an isoselective alkene polymerization initiator. These polymers can weld common grades of commercial PE and PP together, depending on the molecular weights and architecture of the block copolymers. Interfacial compatibilization of phase-separated PE andPP with tetrablock copolymers enables morphological control, transforming brittle materials into mechanically tough blends.

A study of the crystallization from the melt and of the polymorphic behavior of isotactic poly(1-butene) (iPB) prepared with metallocene catalysts is presented. Samples of isotactic polybutene of different stereoregularity, containing different concentrations of stereodefects (rr triads defects) and regiodefects (4,1 units) have been prepared with different C 2 -and C 1 -symmetric metallocene catalysts. The concentration of defects and the molecular mass are controlled through a rational choice of the catalyst structure and conditions of polymerization. Highly isotactic samples with concentration of rr stereodefects lower than 2 mol %, crystallize from the melt in the metastable form II. This is a common polymorphic behavior observed in iPB samples prepared with Ziegler-Natta catalysts and extensively reported in the literature. More stereodefective iPB samples, containing concentration of stereodefects higher than 2 mol %, crystallize form the melt as mixtures of form II and form I, the fraction of crystals of form I increases with increasing concentration of defects and decreasing cooling rate from the melt, and samples with concentration of rr defects of 3-4 mol % crystallize from the melt in the pure form I at low cooling rates. This is the first experimental observation of the crystallization of the stable trigonal form I of iPB from the melt at atmospheric pressure. This result may be of interest because the crystallization of the metastable form II from the melt and the spontaneous transformation at room temperature of form II into the stable form I has been considered for long time an unavoidable problem that stands in the way of the industrial development of the Ziegler-Natta iPB.

We report the cocrystallization of the regio- and stereoregular chiral copolymer poly(limonene carbonate). To the best of our knowledge, this marks the first example of an amorphous, enantiomerically pure polymer that becomes crystalline upon stereocomplexation with its complementary enantiomer. By analyzing X-ray powder diffraction data, we propose a packing model in which sheets of enantiopure chains interdigitate with layers of the opposite enantiomer, forming a "steric zipper".

A study of the morphology and the mechanical properties of the mesomorphic form of isotactic polypropylene (iPP) that crystallizes in samples of different stereoregularity prepared with metallocene catalysts is reported. Highly isotactic samples slowly crystallized from the melt in the α form show the typical lamellar morphology with organization in spherulites. Bundle-like elongated crystalline entities and needle-like crystals of γ form are instead observed for stereoirregular samples slowly crystallized from the melt in the γ form. All samples crystallize by fast quenching the melt at 0 °C in the mesomorphic form, regardless of stereoregularity. Crystals of the mesomorphic form always exhibit a nodular morphology and absence of lamellar spherulitic superstructures, independent of the stereoregularity. This morphology accounts for the similar good deformability of all the quenched samples, whatever the concentration of stereodefects. For all samples and any stereoregularity, the nodular morphology with absence of spherulites is preserved after annealing and transformation of the mesophase into α form. The formation of a nodular α form accounts for outstanding properties of high ductility and mechanical strength of the annealed samples crystallized in the α form. The most stereoirregular sample with rr concentration of 11% shows elastic behavior either when it is slowly crystallized in the γ form or when it is crystallized in the mesomorphic form and also after annealing and transformation of the mesophase into the nodular α form

A study of the crystallization behavior and mechanical properties of random isotactic butene–ethylene copolymers prepared with a metallocene catalyst is presented. The use of the metallocene catalysis ensures a fine control over the molecular structure with low concentration of rr stereodefects (0.8%), negligible amount of regiodefects, and random and uniform distribution of ethylene constitutional defects. This molecular characteristic has allowed evidencing the only effect of the presence of ethylene units on the polymorphic behavior and mechanical properties of isotactic polybutene (iPB). The presence of ethylene accelerates the transition of form II into form I at room temperature and at concentration of nearly 6 mol % favors the direct crystallization from the melt of the stable form I. The presence of ethylene also affects the mechanical behavior of iPB and produces increase of flexibility and ductility with increasing ethylene content. A significant modification of the properties of iPB is observed for ethylene concentration higher than 8 mol %, with development of elastomeric properties, never observed for the iPB homopolymer prepared with Ziegler–Natta catalysts and not observed in the iPB homopolymer with similar content of stereo defects. In these samples, elastomeric properties are due to the low degree of crystallinity that develops upon aging at room temperature by direct crystallization of form I′ from the amorphous phase.