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Synthesis and characterization of blends of poly(ethylene-b-(atactic)propylene) with polyethylene
Abstract
Polymer blends involving a semi-crystalline/amorphous diblock copolymer and the corresponding semi-crystalline homopolymers were prepared and investigated to increase the understanding of the effect that crystallizability has on the phenomenon of microphase separation. Monodisperse symmetric diblock copolymers of poly(butadiene-b-2-methyl-pentadiene) and corresponding homopolymers of polybutadiene and poly(methylpentadiene) were synthesized by living anionic polymerization and characterized by GPC and NMR. These polymers were hydrogenated to form the saturated crystalline-amorphous diblock (DEP) and crystalline (PE) and amorphous (APP) homopolymers. Blends were prepared using solution routes and physical mixing (the latter for DSC measurements only). A problem of spherulite formation arose due to the route of solution blending which was employed. Melt pressing and melt-annealing for several days was found to return the sample to the microphase separated state and to enhance the long-range order that was reduced by pressing. Blends were quenched in liquid nitrogen and their thermal properties measured by TG and DSC. The change in the crystallization peak which had been in previous studies seen by DSC for the blends with the APP was no longer present. It is proposed that the mechanism which was previously responsible for the change in crystallization peak (the continuity of the PE phase) was no longer applicable and that the cooling rate (10°C/min) was insufficient to prevent spherulite formation (possibly due to the solution casting technique used). TEM showed the latter to be true and that the morphology was directed by the increased driving force for crystallization, even upon rapid cooling from the melt using liquid nitrogen. Neutron reflectometry (NR) was used to investigate the interfacial behavior and miscibility of a diblock copolymer of deuterated-PE and APP when blended or in contact with polyethylenes and atactic polypropylene homopolymers while in the melt. A study on the effect of the amount of short chain (ethyl) branching on miscibility at the PE/APP interface determined that the combination of molecular weight, polydispersity, and the presence of additives had more of an effect on miscibility than did branch content, as an HDPE sample was found to have a wider interface than did an ethylene-1-butene (EB) copolymers. The form (as a film or in a blend) and location of the labeled diblock were found to have a large effect on the mobility and diffusion behavior. When blended with the amorphous homopolymer, simulations indicated that migration of the diblock to the free surface occurred, possibly due to surface free energy effects. Substantiation of this interpretation is studied using AFM. When placed as a film, the diblock appears to dissolve into either one or both of the homopolymers as micelles or as individual chains.
Subject Area
Polymers|Plastics
Recommended Citation
Bushelman, Andrew A, "Synthesis and characterization of blends of poly(ethylene-b-(atactic)propylene) with polyethylene" (1999). Doctoral Dissertations Available from Proquest. AAI9932300.
https://scholarworks.umass.edu/dissertations/AAI9932300