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Effect of Chain End Functional and Chain Architecture On EFFECT OF CHAIN END FUNCTIONAL AND CHAIN ARCHITECTURE ON SURFACE SEGREGATION A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Master of Science Zimo Zhang June, 2017 EFFECT OF CHAIN END FUNCTIONAL AND CHAIN ARCHITECTURE ON SURFACE SEGREGATION Zimo Zhang Thesis Approved: Accepted: ______________________________ ______________________________ Advisor Dean of the College Dr. Mark D. Foster Dr. Eric J. Amis ______________________________ ______________________________ Faculty Reader Dean of the Graduate School Dr. Li Jia Dr. Chand Midha ______________________________ ______________________________ Department Chair Date Dr. Coleen Pugh i ABSTRACT The objective of the research was to study the effects on surface segregation in binary polymer blends of both chain end functionalization of linear chains, and changes in architecture. An important question for the formation and application of a polymer thin film is the degree to which end group functionalization can influence the segregation of a chain to the air/polymer and polymer/substrate interfaces. For the first part of this study, well-defined polystyrene and hydroxyethylated functionalized polystyrene of exactly the same molecular weight (Mn = 6000 g/mol) were synthesized using anionic polymerization in order to minimize the impact of factors other than end group functionalization in the study of the segregation driven by the functionalization. Thin (90 nm) films of blends of these two chains spun cast on silicon substrates were investigated. Key to the study was use of a new method called Surface Layer Matrix Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (SL-MALDI-TOF-MS) which determines the composition at the surface (< 2 nm depth) of entire polymer chains, rather than the segment or chain end composition measured with other techniques. This technique requires no isotopic labeling. The most striking finding is that the surface region is not only depleted in the high energy chain end functionality, but, in fact, depleted in chains containing the functional group. Thus, for the first time, depletion of the entire chain, driven by only a single functionalized end group, was observed directly. The depletion of the surface in ii functionalized chains varies with composition and is more pronounced for blends of near- symmetric composition. For the study of the effect of architecture on surface segregation, star-branched polymers with two different architectures were synthesized. Well-defined 5.5k 4-arm star was successfully synthesized using a combination of anionic polymerization and silane linking chemistry. The structure of the product was characterized using Size Exclusion Chromatography (SEC) and MALDI TOF MS. The results show controlled molecular weight, a well-defined structure, and very high purity. “H-shaped” polymers have been much less commonly studied than star polymers and are more challenging to synthesize. Well-defined H-shaped polystyrene was synthesized using end linking of living arms to a polymeric linking agent. The α,ω-functionalized polymeric linking agent was made using a combination of anionic polymerization with a difunctional initiator and a silicon chloride functionalization reaction with inverse addition. The final product was characterized using multi-detector SEC with MALDI quantified parameters of the structure. The overall molecular weight matches well those of a series of well-defined branched chains already studied for their blend surface segregation and pure melt surface fluctuations behavior, allowing for insightful comparisons. iii ACKNOWLEDGEMENTS I would like to thank my advisor Dr. Mark D. Foster for his guidance in this research. I would like to thank my co-advisor Dr. Roderic P. Quirk for his helping in anionic polymerization. I would like to thank Dr. Li Jia as a reader and a committee member for this thesis. I would like to thank Dr. Chrys Wesdemiotis for the help in MALDI-TOF characterization. I would like to thank my senior students Dr. Qiming He and Mr. Fan Zhang for their helping in the synthetic work. I would like to Thank Mr. Jake Hill and Mr. Kevin Endres for the help in the research for surface segregation. I would like to thank Mr. Selim Gerislioglu for the MALDI measurements. I would also like to thank Dr. Foster’s research group for the support in my research progress. I would like to thank all my friends especially, Ji-Song for the encouragement during my two-year study in U.S. Finally I would like to thank my father and my mother to give me this great chance to study in The University of Akron. iv TABLE OF CONTENTS CHAPTER Page ABSTRACT ................................................................................................................ ii ACKNOWLEDGEMENTS ........................................................................................ iv TABLE OF CONTENTS ............................................................................................ v LIST OF FIGURES .................................................................................................... ix INTRODUCTION ....................................................................................................... 1 1.1 Anionic Chain End Functionalization ............................................................... 1 1.2 Anionic Synthesis of Star-Branched Polymers .................................................. 4 1.2.1 Arm-First Method ....................................................................................... 4 1.2.2 Core-First Method ...................................................................................... 6 1.3 Surface Segregation ........................................................................................... 7 1.4 Surface Layer Matrix-Assisted Laser Desorption Ionization- Time of Flight Mass Spectrometry (SL-MALDI-TOF MS) ................................................................. 10 1.5 Statement of the Problem ................................................................................. 11 EXPERIMENTAL ..................................................................................................... 13 2.1 Inert atmosphere techniques ............................................................................ 13 v 2.1.1 High vacuum techniques ........................................................................... 13 2.1.2 Dry Box Manipulation .............................................................................. 15 2.2 Purification of Reagents .................................................................................. 16 2.2.1 Solvents..................................................................................................... 16 2.2.2 Monomer ................................................................................................... 18 2.2.3 Terminating Agent and Linking agent ...................................................... 19 2.3 Synthesis of 6k hydroxyethylated functionalized polystyrene ........................ 21 2.4 Synthesis of Difunctional Initiation system ..................................................... 24 2.4.1 Purification of 1,3-bis(1-phenylethenyl)benzene (DDPE) ....................... 24 2.4.2 DDPE\sec-BuLi system ............................................................................ 25 2.5 Synthesis of Branched Chains ......................................................................... 26 2.5.1 Synthesis of 4-Arm-Star polystyrene ........................................................ 26 2.5.2 Synthesis of H-shaped polystyrene ........................................................... 30 2.6 Molecular and Blend Surface Characterization ............................................... 37 2.6.1 Size Exclusion Chromatography .............................................................. 37 2.6.2 1H NMR and 13C NMR spectroscopy ....................................................... 37 2.6.3 MALDI-TOF mass spectrometry ............................................................. 37 2.7 Characterization of Surface Composition ........................................................ 38 2.7.2 SL-MALDI-TOF MS Measurement ......................................................... 39 vi CHAPTER III ............................................................................................................ 40 3.1 Molecular weight and distribution determination............................................ 40 3.2 Chain end functional group characterization ................................................... 41 3.3 MALDI-TOF mass spectrometry .................................................................... 44 3.4 Surface segregation due to the chain end functionalization ............................ 46 3.4.1 Calibration using Bulk MALDI-TOF mass spectrometry measurement .. 46 3.4.2 SL- MALDI-TOF mass spectrometry for polymer blends ....................... 48 3.4.3 Comparison Between Surface and Bulk Measurements ........................... 53 SUMMARY ............................................................................................................... 56 CHAPTER IV ............................................................................................................ 57 4.1 Preparation of Hydrocarbon Soluble Difunctional initiator ............................ 57 4.1.1 Purification of DDPE ................................................................................ 57 4.1.2 Synthesis of the
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