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A New Solid-State Nmr Method Reveals the Influence of Chain Structure and Thermal History on the Crystal- Amorphous Interface in Polyethylenes

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A New Solid-State Nmr Method Reveals the Influence of Chain Structure and Thermal History on the Crystal- Amorphous Interface in Polyethylenes A NEW SOLID-STATE NMR METHOD REVEALS THE INFLUENCE OF CHAIN STRUCTURE AND THERMAL HISTORY ON THE CRYSTAL- AMORPHOUS INTERFACE IN POLYETHYLENES By ARIFUZZAMAN TAPASH Bachelor of Science in Applied Chemistry & Chem. Tech. University of Dhaka Dhaka 2005 Masters of Science in Applied Chemistry & Chem. Eng. University of Dhaka Dhaka 2006 Submitted to the Faculty of the Graduate College of the Oklahoma State University in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY May, 2016 A NEW SOLID-STATE NMR METHOD REVEALS THE INFLUENCE OF CHAIN STRUCTURE AND THERMAL HISTORY ON THE CRYSTAL-AMORPHOUS INTERFACE IN POLYETHYLENES Dissertation Approved: Dr. Jeffery L. White Dissertation Adviser Dr. Frank D. Blum Dr. Toby Nelson Dr. Jimmie Weaver Dr. Rob Whiteley ii Name: ARIFUZZAMAN TAPASH Date of Degree: MAY, 2016 Title of Study: A NEW SOLID-STATE NMR METHOD REVEALS THE INFLUENCE OF CHAIN STRUCTURE AND THERMAL HISTORY ON THE CRYSTAL-AMORPHOUS INTERFACE IN POLYETHYLENES. Major Field: CHEMISTRY Abstract: Clear understanding of polymer morphology is important as it is directly related to the final properties. A simple solid-state NMR method is presented in this contribution to quantitatively determine the distribution of solid polyethylene chain segments in different morphological regions. The rigid chain in the crystalline phase with all-trans chain conformations, the non-crystalline (amorphous) mixed trans-gauche chains undergoing essentially isotropic reorientation, all-trans chains with higher mobility (mobile all-trans), and non-crystalline chains with limited mobility (constrained amorphous) fractions were reliably quantified using a new double-acquisition solid-state 13C NMR experiment. A wide range of well-characterized PE samples was studied, which reveals that the amount of interface region increases with the chain length of linear metallocene-PE. Topologically different polyethylenes that contain short-chain branches (SCB), long-chain branches (LCB), and LCB’s with SCB’s exhibit unique morphological behavior relative to the linear PE’s of similar Mw. The method also reveals the variations in morphology due to different thermal histories. Thermally quenched polyethylene was found to have higher interface content than that of the annealed or untreated PEs. Phase composition results obtained by this simple experiment are quantitative, reliable and reproducible as all of the data was collected in a single experiment. The results suggest a route to large-scale design and control of interfacial morphology in polyethylenes and related properties. In a separate project, a 1H NMR experiment based on slow/fast magic-angle spinning (MAS) and a spin-counting strategy are presented to quantitatively determine the amount of soft and hard phase of styrene-butadiene gradient copolymers in component specific resolution. The experiments provide bulk rigidity and the amount of polybutadiene (or polystyrene) partitioned into both soft and hard phases. It was found that the partitioning of each comonomer depends on the synthesis conditions and we propose that the hard-soft interface is responsible for the differential partitioning. Both experimental methods presented here can also be used to study different polymer systems. iii TABLE OF CONTENTS 1 MOTIVATION ............................................................................................................1 2 INTRODUCTION AND THEORETICAL BACKGROUND..................................................5 2.1 Historical Background of Polyethylene ..........................................................................5 2.2 Main Types of Polyethylenes .........................................................................................7 2.2.1 Low-density polyethylene (LDPE)........................................................................7 2.2.2 Linear low-density polyethylene (LLDPE) ............................................................8 2.2.3 High-density polyethylene (HDPE) ....................................................................10 2.3 Catalysts Used in Polyethylene Manufacture ...............................................................10 2.3.1 Ziegler – Natta catalysts17b, 30 ............................................................................10 2.3.2 Metallocene catalysts6a, 19, 30a ...........................................................................11 2.3.3 Phillips catalysts31 .............................................................................................11 2.4 Polyethylene Morphology ...........................................................................................12 2.4.1 Crystalline lamellae ..........................................................................................12 2.4.2 Phase composition and chain types ..................................................................16 2.5 Polyethylene Molecular Dynamics49 ............................................................................17 2.5.1 Translation and rotation in the crystalline phase49 ...........................................18 2.5.2 Crankshaft motion in the amorphous phase .....................................................19 2.5.3 Cooperative motion in the interface54 ..............................................................19 2.6 Physical and Mechanical Properties of PE6a .................................................................20 2.7 Historical and Theoretical Background of NMR Spectroscopy55 ...................................21 2.8 The Development of NMR55b .......................................................................................22 2.9 Basics of NMR55, 63 .......................................................................................................23 2.9.1 The vector model55a, 63a.....................................................................................26 2.9.2 Boltzmann distribution and the spin temperature64 .........................................28 2.9.3 The effect of radiofrequency pulse55a, 63a, 65 ......................................................29 2.9.4 Free induction decay (FID)55, 63a ........................................................................31 iv 2.9.5 Chemical shift55b, 65 ...........................................................................................32 2.9.6 Pulse sequence63a .............................................................................................33 2.10 Essential Techniques for Solid-State NMR4a, 55 .............................................................34 2.10.1 Dipole-dipole interaction4a, 55a .......................................................................34 2.10.2 Chemical shift anisotropy (CSA)4a, 55a .............................................................35 2.10.3 Magic-angle spinning (MAS)4a, 4b, 55a ..............................................................35 2.10.4 High power proton dipolar decoupling55a, 66 ..................................................36 2.11 Special Features of NMR .............................................................................................37 2.11.1 Spin relaxation55a, 67 ......................................................................................37 2.11.2 Nuclear Overhauser Effect (NOE)68 ...............................................................39 2.11.3 Cross-polarization (CP)69 ...............................................................................41 2.12 Application of NMR Spectroscopy in Polymer Science4a, 70 ...........................................42 3 DEVELOPMENT OF THE SOLID-STATE NMR EXPERIMENTAL METHOD TO DETERMINE THE CRYSTAL-AMORPHOUS INTERFACE IN POLYETHYLENES ................................45 3.1 Introduction ................................................................................................................45 3.2 Method Development .................................................................................................47 3.2.1 Properties of PE chains .....................................................................................47 3.2.2 Feature of 13C NMR spectrum and response to conformational difference .......48 13 3.2.3 Chain dynamics and C spin-lattice relaxation time, T1C ...................................50 3.3 Method Development Scheme ....................................................................................53 3.3.1 T1 filter to acquire ‘mobile-only’ spectrum .......................................................56 3.3.2 The ‘rigid-only’ data..........................................................................................58 3.3.3 EASY: a double-acquisition background suppression pulse sequence ...............60 3.3.4 Modified-EASY pulse-sequence ........................................................................62 3.3.5 Improved results with the modified-EASY pulse sequence ................................65 3.4 Spectral Deconvolution and Data Calculation ..............................................................65 3.5 Conclusions .................................................................................................................69 4 THE INFLUENCE OF CHAIN LENGTH AND CHAIN ARCHITECTURE ON THE CRYSTALLINE/AMORPHOUS INTERFACE IN SOLID POLYETHYLENE ...........................................70 4.1 Introduction ................................................................................................................70 4.2 Experimental Section...................................................................................................75
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