1. Field of the Invention
The invention is directed generally to a method of functionalizing nucleophilic high molecular weight polymers (HMP-XH) by alkylation using a substituted metal-hetero-alkyl (MHTA) base. The novel scheme disclosed herein can also be used to functionalize nucleophilic high molecular weight PEO (HMPEO-XH) in order to generate PEO-based macro-initiators for controlled radical polymerizations and other functional materials.
Previous U.S. patent application Ser. No. 13/946,924, filed Jul. 19, 2013, which is the parent application to this application, was directed generally to a method of functionalizing hydroxyl-containing high molecular weight polymers (HMP-OH), a subset of nucleophilic high molecular weight polymers (HMP-XH), by alkylation using substituted metal amide (MAd) bases, a subset of substituted metal-hetero-alkyl (MHTA) bases. The novel scheme disclosed therein could also be used to synthesize PEO-based macro-initiators for controlled radical polymerizations.
Nanostructured polymer electrolytes can be used in lithium batteries to improve safety and cycle-life by restricting lithium-ion transport to ionically-conductive lamellar domains. Such a structure can be made through the self-assembly of di-or tri-block copolymers containing at least two distinct phases a hard, structural phase and a soft, ionically-conductive phase. The soft phase, which can be PEO or PEO-based, provides a nano-domain for lithium ion transport; the hard phase, usually a high Tg polymer (a high Tg being one that is above the cell operating temperature), provides a nano-domain for mechanical stability in the polyelectrolyte thin film and prevents formation of lithium dendrites that can otherwise grow from anode to cathode, shorting the battery. An example of such a PEO-based polymer electrolyte is PS-b-PEO-b-PS tri-block copolymer, where polystyrene (PS), the hard component, phase separates from PEO, the ionically conductive component, to form a nanostructured block copolymer electrolyte for a lithium battery.
It has been difficult to establish a synthetic route to produce such block copolymers on an industrial scale, especially a route that is reproducible, safe, and economical. Generally, block copolymers based on PEO are grown from PEO-based macro-initiators, which in turn are obtained from telechelic PEO with reactive end groups such as α,ω-dihydroxy PEO, α,ω-di(aminoethyl) PEO, or α,ω-di(mercaptoethyl) PEO. A common approach to generate PEO-based macro-initiators for atom transfer radical polymerization (ATRP) is by a simple esterification of the terminal hydroxyl or nucleophilic groups (OH, SH or NH2) with an acid halide in the presence of a mild base such as triethylamine (Et3N). For example, as shown in (1) below, reaction of α-bromoisobutyryl bromide with HX-PEO-XH in the presence of Et3N results in a macro-initiator with α-bromoisobutyryl groups at the chain-ends. The reaction is highly exothermic, so it can be performed using relatively low temperatures and short times and still produce substantial yields. Once the macro-initiator is in place, a variety of vinyl monomers can be polymerized through atom transfer radical polymerization (ATRP) to generate various triblock copolymers. Unfortunately, some of the newly formed —X—C(═O)— linkers through this method are susceptible to hydrolysis even under mild acid or basic conditions. In addition, a block copolymer electrolyte containing an —X—C(═O)— will readily degrade when in contact with lithium metal, which is a strong reducing agent, making electrolytes produced in this way unsuitable for lithium batteries.

Another method for synthesizing PEO-based macro-initiators is to terminate a living chain PEO using an electrophilic initiator such as α-bromoisobutyryl bromide. This also produces an —X—C(═O)— (X is O in this case) between the polymer components, making it unsuitable for synthesis of electrolytes for lithium batteries.
Linkers based on —X—CH2— (ether, thioether, or amine), as shown with PEO in (2) below, are chemically more robust when compared to an —X—C(═O)— groups, but they are not as easy to synthesize because formation of these robust bonds require a stronger base and more stringent conditions (e.g., longer reaction times, elevated temperatures) than for an —X—C(═O)— bond. In addition, high molecular weight polymers may degrade during such high temperature processing conditions.RCH2—X—PEO—X—CH2R  (2)                X=O, NH, NR′, S, —C6H5—O, —COO etc        R=A simple alkyl chain, electroactive, photoactive, bioactive or other functional groups.        
There are several reactions that are known to produce PEO-based macro-initiators and other functional polymers using X—CH2-linkers, but there are drawbacks to most of these. For example, commonly used hydroxides for alkylation of PEO, potassium hydroxide (KOH) and sodium hydroxide (NaOH), are soluble only in polar solvents such as DMF, DMSO, water, and methanol. After alkylation, removal of such polar solvents and excess hydroxides from functionalized PEO is very difficult even after several stages of purifications.
PEO can also be functionalized using hydrides such as sodium hydride (NaH) and potassium hydride (KH); however, these reagents are pyrophoric and are unsafe for use in large-scale manufacturing. Also, removal of hydroxides, a byproduct of alkylation using hydrides, from PEO is extremely difficult.
Similarly, organo-metallic bases such potassium naphthalenide and diphenylmethyl potassium that are synthesized in-situ from the highly pyrophoric potassium metal can be used for PEO functionalization. These bases are highly reactive and flammable when exposed to air and are not commercially available, making them extremely poor candidates for alkylation on a large scale.
What is needed are methods for functionalizing and isolating nucleophilic high molecular weight polymers (HMP-XH). It would be especially useful if such methods used materials that are effective, safe, inexpensive, readily available, and appropriate for functionalization of HMP-XH on a commercial scale. It would also be useful if such methods resulted in functionalized and isolated nucleophilic high molecular weight polymers (HMP-XH) did not adversely affect the stability of such polymers.
USPTO Backgrounds
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