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Polyolefin cubic silsesquioxane nanocomposites
Abstract
This thesis focuses on the synthesis and characterization of polyolefin nanocomposites containing polyhedral oligomeric silsesquioxane (POSS) units. Two copolymerization methods were developed utilizing either ring-opening metathesis polymerization or metallocene-catalyzed reactions to incorporate cubic silsesquioxane into polyolefins. Ring-opening metathesis copolymerizations of cyclooctene and the POSS-norbornylene macromonomer have been performed using Grubbs' catalyst RuCl2(=CHPh)(PCy3)2. Random copolymers have been prepared and characterized with POSS loadings as high as 55 wt%. Diimide reduction of these copolymers affords polyethylene-POSS random copolymers. Polyethylene (PE) and isotactic polypropylene (PP) copolymers incorporating POSS have also been prepared using a metallocene/methylaluminoxane (MAO) cocatalyst system. A wide range of POSS concentrations was obtained in these polyolefin POSS copolymers under mild conditions; up to 56 wt% for PE-POSS copolymers and 73 wt% for PP-POSS copolymers were prepared. Copolymerizations of styrene and the POSS-styryl macromonomer have been performed using CpTiCl 3 in conjunction with MAO. Random copolymers of syndiotactic polystyrene and POSS copolymers have been formed and characterized. Novel nanocomposites of PE-POSS have been characterized using Wide Angle X-ray Scattering (WAXS). From both line broadening of the diffraction maxima and also the oriented diffraction in a drawn sample, we conclude that POSS forms anisotropically shaped crystallites. On the basis of this result, a novel approach to obtain nanocomposites containing inorganic nanolayers is proposed. Cubic silsesquioxane (POSS) nanoparticles are used to achieve the nanolayered “clay-like” structure through controlled self-assembly. The organic polymer, covalently connected to POSS, is intended to regulate the POSS crystallization into a two-dimensional lattice. The concept is demonstrated by random copolymers of polybutadiene and POSS. The data from WAXS and transmission electron microscopy clearly show the formation of lamellar nanostructure of POSS aggregates, which bares the similarity at low POSS loadings to the morphology of exfoliated polymer clay nanocomposites. By taking the advantage of controlled interactions between polymer chains, we open the door to the design of polymeric materials at important nanometer length scales beyond their primary sequence length. Ultimately, this may provide materials with properties bridging the performance gap between polymer and ceramics.
Subject Area
Polymers|Materials science
Recommended Citation
Zheng, Lei, "Polyolefin cubic silsesquioxane nanocomposites" (2002). Doctoral Dissertations Available from Proquest. AAI3068607.
https://scholarworks.umass.edu/dissertations/AAI3068607