A SANS Study of the Self-Assembly in Solution of Syndiotactic Polypropylene Homopolymers, Syndiotactic Polypropylene-block-poly(ethylene-co-propylene) Diblock Copolymers, and an Alternating Atactic−Isotactic Multisegment Polypropylene

Abstract

We have studied by small-angle neutron scattering (SANS) the crystallization of syndiotactic polypropylene (sPP) homopolymer in dilute hydrocarbon solution in parallel with the self-assembling behavior of crystalline-amorphous block copolymers of (syndiotactic propylene)-block-poly(ethylene-copropylene) [sPP-P(E-coP)] and atactic-isotactic multiblock polypropylene copolymers (aPP-iPP). Homopolymers and diblock copolymers of various molecular weights and volume fractions were investigated in decane over a wide temperature range (between 160 and-20°C) while the temperature evolution of the aPP-iPP aggregates was studied in dodecane starting from 175°C. The homopolymer crystallizes by forming platelets of a thickness of about 60-65 Å, independent of the molecular weight or polymer volume fraction in solution. The diblock copolymers aggregate by forming a complex morphology that shows a multilevel structure. This was investigated with SANS and ultra-SANS (USANS) over 3 orders of magnitude in size scale. At small scale (tens of angstroms) an overall 2-dimensional structure seems to be formed. It evolves at intermediate scale (hundreds of angstroms) into a rodlike structure. The rods associate in bundles that at a micrometric scale form supramolecular structures like networks. Such an association could be promoted by the PE sequences present within the P(E-coP) block. The multiblock copolymer forms very open rodlike aggregates and demonstrates that the general morphology of self-assembling materials with multiple alternating crystalline-amorphous blocks appears to be 1-dimensional. 2.1. Samples. The syndiotactic polypropylene homopolymer, sPP, and the crystalline-amorphous diblock polymers, sPP-P(E-coP), were prepared via a living polymerization in toluene at 0°C using a bis(salicylaldiminato)titanium complex. 8 All air-and moisture-sensitive chemistry was carried out in a Braun Labmaster drybox or using standard Schlenk line techniques. The solvents were dried on solvent columns containing molecular sieves, alumina, and activated copper. Propylene (Matheson, Polymer Grade) was purified by a column containing molecular sieves and alumina.. Ethylene (Matheson, Polymer Grade) was used as received. Methylaluminoxane (MAO-IP, 12.9 wt % Al in toluene, Akzo Nobel) was dried under vacuum at 60°C for 24 h. The alternating aPP/iPP multisegment polypropylene was made with a hafnium tert-butyl catalyst with the structure [(2-(3,5-(t-Bu) 2PhInd)2-HfCl2)]. The polymerization was performed in liquid propylene under pressure at 50°C using MAO with [Al/Hf]) 1000. 9 The polymer 1 H NMR spectra were recorded on a Varian Inova 500 MHz spectrometer and referenced to nondeuterated † Jü lich GmbH.

Living Olefin Polymerization and Block Copolymer Formation with FI Catalysts

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On the Mn–C Short-Range Ordering in a High-Strength High-Ductility Steel: Small Angle Neutron Scattering and Ab Initio Investigation

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