Anionic Synthesis Of Functionalized Polymers

The synthesis of well-defined functionalized polymers is an important area of research due to their wide array of applications. The work presented herein can be divided into three categories: a) functional initiator synthesis; b) chain-end and in-chain functionalization and c) functional monomer synthesis and polymerization. All three methods involve both anionic polymerization and hydrosilation. In this work, all anionic polymerizations were performed at room temperature in hydrocarbon solvent with an alkyllithium initiator. A functional 4-pentenyllithium initiator was prepared in 70% yield and was used for the synthesis of [alpha] and [alpha,omega]-functionalized polystyrene. 4-Pentenyllithium was used to initiate styrene polymerization in benzene in the presence of 5 equivalents of tetrahydrofuran. Narrow polydispersity indices and good agreement between calculated and observed molecular weights were observed for the methanol-terminated product. [alpha]-Triethoxysilyl-functionalized polystyrene was quantitatively prepared by hydrosilation with triethoxysilane and [alpha]-4-pentenylpolystyrene. [alpha]-4-Pentenyl-[omega]-silyl hydridefunctionalized polystyrene and [alpha]-4-pentenyl-[omega]-thiol hydride functionalized polystyrene were quantitatively prepared by terminating [alpha]-4-pentenylpoly(styryl)lithium with chlorodimethylsilane and ethylene sulfide, respectively. The [alpha]-4-pentenyl-[omega]-silyl hydride-functionalized polystyrene showed good agreement between calculated and observed molecular weights and a narrow polydispersity. [alpha]-4-Pentenyl-[omega]-thiolfunctionalized polystyrene showed a dimer peak due to oxidative coupling when quenched with methanol. Triethoxysilyl-functionalized, high-1,4-polybutadiene was prepared by reacting the pendant double bonds of the 1,2-units with triethoxysilane via hydrosilation. High-yielding reactions between the polymeric organolithium chain-ends and silyl chlorides were used to obtain the desired polymeric silyl hydrides for further functionalization. In-chain and chain-end cyano-functionalized polystyrenes were prepared. Chain-end, silyl hydride-functionalized polystyrene was prepared quantitatively. Hydrosilation of chain-end, silyl hydride-functionalized polystyrene with allyl cyanide resulted in [omega]-cyano-functionalized polystyrene, which was prepared in 87% yield. In-chain, silyl hydride-functionalized polystyrene was prepared by terminating excess poly(styryl)lithium with dichloromethylsilane. The remaining poly(styryl)lithium was terminated with ethylene oxide to aid in chromatographic separation to yield the pure in-chain, silyl hydride-functionalized polystyrene in 96% yield. Hydrosilation of in-chain, silyl hydride-functionalized polystyrene with allyl cyanide resulted in cyano in-chain functionalized polystyrene in 58% yield after 2 weeks of reaction time at elevated temperature. [omega]-Silyl dihydride-functionalized polystyrene was prepared in 92% yield by inverse addition of poly(styryl)lithium to dichloromethylsilane then reduction with lithium aluminum hydride. Functionalization with allyl cyanide yielded [omega]-dicyanofunctionalized polystyrene quantitatively. Synthesis of functionalized polymers from silyl hydride-substituted monomers was also investigated. para-Dimethylsilylstyrene was prepared from 4-chlorostyrene in 84% yield. Homopolymerization, copolymerization, and end-capping of poly(styryl)lithium in cyclohexane with this monomer was investigated, and it was found that a linking reaction is occuring. meta-Dimethylsilylstyrene was prepared from 3-bromostyrene in 75% yield. Anionic homopolymerization, and copolymerization of this monomer were investigated, and it was found that a more vigorous linking reaction was taking place compared to the para-substituted analog.

Novel methods for the synthesis of chain-end and in-chain functionalized polymers, as well as star polymers, were developed using anionic polymerization techniques. A new mechanism for the reaction of polymeric organolithium compounds with thiiranes has been found. The reaction of poly(styryl)lithium and poly(butadienyl)lithium with propylene sulfide and ethylene sulfide was investigated in hydrocarbon solution for the preparation of thiol-functional polymers. It was found by MALDI-TOF mass spectral analysis of the reaction products that the reaction proceeded by attack of the anion on the methylene carbon atom of the thiirane ring followed by ring opening to form the thiol-functionalized polymer. The reaction of poly(styryl)lithium with trimethylene sulfide did not produce the corresponding thiol-functionalized polymer; the resulting methyl-terminated polymer was formed by attack of the anion on the sulfur atom followed by ring opening to form a primary carbanion. A new method for synthesis of alkoxysilyl-functionalized polymers was developed. Using a general functionalization methodology based on the hydrosilation of vinyltrimethoxysilane with [omega]-silyl hydride-functionalized polystyrene, alkoxysilyl-functionalized polystyrene was obtained in high yield (83 %). The main side product was vinylsilane-functionalized polymer. A small amount of dimer (approximately 2 %) was formed from the hydrosilation reaction of silyl hydride-functionalized polymer and vinylsilane-functionalized polymer. Star polymers with an average number of 6.8 arms were obtained by reacting poly(styryl)lithium with 6.6 equivalents of vinyldimethylchlorosilane in benzene at 30 °C. It was found that, in benzene at 30 °C, vinyldimethylchlorosilane is an efficient linking agent for the preparation of well-defined star-branched polymers. In contrast, the reaction of poly(styryl)lithium with 5 equivalents of vinyldimethylchlorosilane in THF at -78 °C produced vinylsilane-functionalized polymer in high yield (> 93 %). Poly(styryl)lithium was reacted with 2.5 equivalents of vinyldimethylethoxysilane; reaction occurred exclusively by the addition of the living anion to the vinyl group. In-chain, dihydroxyl-functionalized polystyrene was prepared by reaction of poly(styryl)lithium and 1,3-butadiene diepoxide. The hydroxyl functionalities were activated with potassium naphthalenide. Addition of ethylene oxide monomer yielded the corresponding heteroarm polystyrene/poly(ethylene oxide) stars. Two commercially available triepoxides, N,N-diglycidyl-4-glycidyloxyaniline and Tactix 742, were used to prepare the corresponding 3-armed stars in high yield.

Most practitioners and students of polymer chemistry are familiar, in general terms at least, with the established methods of polymer synthesis - radical, anionic, cationic and coordination addition polymerization, and stepwise con densation and rearrangement polymerization. These methods are used to synthesize the majority of polymers used in the manufacture of commercially important plastics, fibres, resins and rubbers, and are covered in most introduc tory polymer chemistry textbooks and in most undergraduate and graduate courses on polymer science. Fewer polymer chemists, however, have much familiarity with more recent developments in methods of polymer synthesis, unless they have been specifically involved for some time in the synthesis of speciality polymers. These developments include not only refinements to established methods but also new mechanisms of polymerization, such as group transfer and metathesis polymerization and novel non-polymerization routes to speciality polymers involving, for example, the chemical modification of preformed polymers or the linking together of short terminally functionalized blocks.

Most practitioners and students of polymer chemistry are familiar, in general terms at least, with the established methods of polymer synthesis - radical, anionic, cationic and coordination addition polymerization, and stepwise con densation and rearrangement polymerization. These methods are used to synthesize the majority of polymers used in the manufacture of commercially important plastics, fibres, resins and rubbers, and are covered in most introduc tory polymer chemistry textbooks and in most undergraduate and graduate courses on polymer science. Fewer polymer chemists, however, have much familiarity with more recent developments in methods of polymer synthesis, unless they have been specifically involved for some time in the synthesis of speciality polymers. These developments include not only refinements to established methods but also new mechanisms of polymerization, such as group transfer and metathesis polymerization and novel non-polymerization routes to speciality polymers involving, for example, the chemical modification of preformed polymers or the linking together of short terminally functionalized blocks.

"The synthesis of homopolymers and block copolymers containing metal coordinating ligands is an important area of research due to the potential applications of these polymers in the fields of optics, electronics, and photonics. Specifically, the terpyridine group is very useful, since it can act as a tridentate chelating ligand due to its strategically positioned, three nitrogen atoms. This allows it to form strong complexes with a variety of transition metal ions. The hydroxyl functionality is another important group due to numerous applications of well-defined hydroxyl-functionalized polymers. They can react with other functional groups on other polymers for chain extension, branching, or crosslinking. They can also be used as macroinitiators for the polymerization of other monomers such as lactide and lactone. Alkyllithium-initiated, living anionic polymerization offers excellent control over molecular weight and molecular weight distribution. The absence of termination and chain transfer steps makes these systems ideally suited for the preparation of chain-end functionalized polymers by the reaction of the living chain ends with appropriate monomers or terminating agents. A recently reported general anionic functionalization method was used to create well-defined terpyridine and hydroxyl end-functionalized polymers. In the first step, living polymeric organolithium compounds were reacted with silyl chlorides to form the corresponding silyl hydride-functionalized polymers. Then, these polymers were reacted with substituted alkenes in the presence of a hydrosilation catalyst to form the corresponding functionalized polymers. A new method was also developed, based on similar chemistry, to prepare an in-chain functionalized diblock copolymer where a variety of functional groups can be placed directly at the interface of the two blocks. This method was used to prepare both in-chain hydroxyl- and terpyridine-functionalized polystyrene-b-polyisoprene copolymers. Lewis bases effect dramatic changes in microstructure, initiation rates, propagation rates and monomer reactivity ratios for alkyllithium-initiated polymerizations of vinyl monomers in hydrocarbon solution. The stability of polymeric organolithium compounds and the mechanism of decomposition in the presence of various stoichiometric equivalents of tetrahydrofuran in benzene solutions were studied due the importance of THF as an additive."--Abstract.