NOVEL FUNCTIONAL ETHYLENE/PROPYLENE ELASTOMERS: SYNTHESIS AND CHARACTERIZATION
Open Access
- Author:
- Kandil, Usama
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- July 15, 2005
- Committee Members:
- T C (Mike) Chung, Committee Chair/Co-Chair
Ian Roland Harrison, Committee Member
Q Wang, Committee Member
Chunshan Song, Committee Member - Keywords:
- Functional Polyolefins
Metallocene Catalysts
Chain Transfer
Reactive Approach
Reactive Rubber Particles - Abstract:
- Abstract This thesis discusses novel chemical approaches to prepare functional ethylene/propylene elastomers. The chemistry involves the preparation of poly(ethylene-co-propylene) reactive intermediate in which the reactive groups are randomly distributed in EP-backbone or located only at the chain-end, depending on the employed metallocene catalyst, type of comonomer/chain transfer agent, and reaction conditions. Several reactive comonomers can act as chain transfer agents, including p-methylstyrene (p-MS), p-hydroxystyrene (p-OHSt), allyl alcohol, allyl amine, and butenyl amine. They are systematically investigated to find the suitable reaction conditions. In turn, the resulting EP copolymers containing such reactive moieties, located in the side chain or at the chain end, are versatile for a wide range of applications. The combination of this reactive approach and metallocene technology enables us to prepare many novel reactive ethylene/propylene (EPR) copolymers with terminal functional groups. In chapter I and II, some historical aspects related to Zieglar-Natta catalysts and subsequent polyolefin developments are discussed, and then followed with a brief summary of the current approaches of polyolefin modifications. I will provide some background information, especially the prior research approaches and experimental results in functionalization of polyolefins. So far, the most effective functionalization chemistry involves the combination of metallocene catalysis and reactive comonomers (or reactive chain transfer agents), which was developed in our group. The chemistry has also been extended to prepare block and graft copolymers having a polyethylene (PE) or polypropylene (PP) main chain. This thesis focuses on ethylene/propylene copolymerization that not only produces useful materials for a wide range of applications but also provides a good understanding in the involved chemistry and reaction mechanism. In chapter III, a chemical route to prepare new ethylene/propylene copolymers (EP) containing a terminal reactive group, such as -CH3 and -OH is discussed. The chemistry involves metallocene-mediated ethylene/propylene copolymerization in the presence of a consecutive chain transfer agent¡Xa mixture of hydrogen and styrene derivatives carrying a CH3 (p-MS) or a silane-protected OH (St-OSi). The major challenge is to find suitable reaction conditions that can simultaneously carry out effective ethylene/propylene copolymerization and incorporation of the styrenic molecule (St-f) at the polymer chain end. In other words, the reaction conditions can alter the St-f incorporation mode from copolymerization to chain transfer. A systematic study was conducted to examine several metallocene catalyst systems and reaction conditions. Both [(C5Me4)SiMe2N(t-Bu)]TiCl2 and rac-Et(Ind)2ZrCl2, under certain H2 pressures, were found to be suitable catalyst systems to perform the combined task. The presence of ethylene along with propylene in the polymerization system provides one more advantage in understanding the chemistry involved and consequently, the detailed behaviors of the applied catalysts. Therefore, the copolymer composition can be derived from an ethylene/propylene mole ratio which is very important information that affords a good understanding of the polymerization mechanism. A broad range of St-f terminated EP copolymers (EP-t-p-MS and EP-t-St-OH), with various compositions and molecular weights, have been prepared with polymer molecular weight inversely proportional to the molar ratio of [St-f]/[monomer]. It is also interesting to search for other olefinic species that can behave like styrenic molecules in selective copolymerization or chain transfer reactions by controlling the reaction conditions. Therefore, in chapter IV, we describe the copolymerization of ethylene and propylene in the presence of protected allylalcohol, allylamine and butenylamine. These monomers were reported to be difficult in the preparation of functional PE and PP polymers, with low catalyst activities and low polymer molecular weights. Our strategy is to first protect the functional monomers with bulky protecting groups from poisoning the catalyst. Then, the protected functional monomer is introduced in the copolymerization reaction. It is very possible that the incorporated functional monomer at the propagating chain-end may stop the polymerization due to steric or electronic reasons. However, subsequent chain-transfer to hydrogen or MAO could take place and regenerate the catalyst for a new polymerization cycle. Therefore, the resulting polymer should contain a terminal functional group. The protection methods have been chosen in such a way that they would not only lead to the steric shielding, but also to afford electronic neutralization of the functional groups. A systematic study of metallocene-mediated ethylene/propylene /protected polar monomer polymerization in the absence and presence of H2, with varying catalysts, polar monomer concentrations, and hydrogen pressures, has been conducted. With a combination of a metallocene catalyst and controlled hydrogen pressure, it is possible to direct the incorporation of simple polar monomers, from copolymerization to chain transfer mode, to form NH2 and OH terminated EP copolymers with a broad range of polymer molecular weight and E/P mole ratios. In chapter V, a new chemical route to prepare graft copolymers containing both an elastic main chain and elastic side chains is discussed, especially EP-g-PI graft copolymers having ethylene/propylene copolymer (EP) main chain and several polyisoprene (PI) side chains. Such a polymer may provide the much needed solution to address the weak rubber-rubber interface adhesion problem, currently facing the tire industry. The chemistry is centered on a reactive EP copolymer intermediate containing few reactive side groups that are very effective for subsequent grafting reactions. The reactive EP-copolymers are used as the main chains for preparing graft copolymers, which involve both ¡¥living¡¦ anionic graft-from and graft-onto polymerization with isoprene monomers. The incorporated reactive sites randomly distributed along the EP chain provide the grafting points to join the PI side chains. In the EP copolymer containing p-MS reactive groups, the benzylic protons in p-MS units were transformed to benzylic anions before introducing isoprene for an anionic graft-from reaction to prepare EP-g-PI graft copolymer. Another way to prepare such a graft copolymer was the coupling reaction between the chloro group in EP-p-CMS and living polyisoprene anions via graft-onto reaction. A third studied system was the graft-from and graft-onto anionic copolymerization between EP-co-DVB and isoprene. An effective fractionation method was developed to separate any traces of isoprene homopolymer that might be generated during such grafting copolymerizations and all the fractionation products were subjected to composition analysis using FT-IR and 1HNMR spectroscopy. The purity of the spectra and the increase in molecular weight provide another indication of the success of such grafting and fractionation techniques. Various grafting techniques, including graft-onto and graft-from processes, have been studied. As will be discussed, the suitable grafting chemistry is dependent on the reactive sites. In chapter VI, a novel method to synthesis reactive rubber particles is described. Considered as a frontier engineering material, reactive rubber particles will find the way in almost all applications. The process involves two steps: metallocene-mediated E/P/DVB terpolymerization followed by emulsion or suspension thermal crosslinking. The particles contain reactive styrenic moieties on the surface which are very versatile in many applications. The first step of preparing these reactive rubber particles involves the synthesis of linear ethylene/propylene/divinylbenzene (EP-DVB) terpolymer via metallocene-mediated polymerization using selected catalysts. Then, in the second step, this soluble EP-DVB terpolymer is emulsified using soap-in-situ method to sub-micro size particles, followed by crosslinking via a thermal coupling reaction of pendent styrene moieties in the bulk of particle. A suspension process in which EP-DVB terpolymer is suspended in water containing PVOH then thermally crosslinked to form 1 to 10 ƒÝm size particles was also developed. Some remaining styrene moieties on the surface were then used for further functionalization reactions, including maleation and epoxidation or graft reactions (via graft-onto, graft-from, and graft-through mechanisms) which provide excellent adhesion with brittle polymers. Several polymers have been studied, including Nylon, PP, PS, and SAN polymers. The combination of SEM and TEM results indicates the effectiveness of the grafting reaction and consequently the interfacial adhesion between the dispersed rubber particles and the continuous polymer domain. Finally, in Chapter VII, the conclusions of this work, with the emphasis on some important topics that need further investigation for future work are summarized.