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42256-AC7
Anionic Polymerization Chemistry of Epoxides and Lithium Compounds

Roderic P. Quirk, University of Akron

ACS PRF # 42256-AC7 Anionic Polymerization Chemistry of Epoxides and Lithium Compounds

The efficiency of reactions of polymeric organolithium compounds with epoxides suggested that polyepoxides should be useful linking agents. The reaction of poly(styryl)lithium (PSLi) with 1,3-butadiene diepoxide produced the corresponding in-chain, dihydroxyl-functionalized polystyrene in quantitative yield by attack of PSLi on the least-substituted methylene carbons of 1,3-butadiene diepoxide as determined by 13C NMR and 135 DEPT NMR. The purified in-chain, diol-functionalized polystyrene exhibited a narrow molecular weight distribution (Mw/Mn = 1.02). The structure of the product was analyzed by MALDI-TOF MS; the monomodal distribution exhibited monoisotopic peaks corresponding to the expected structure, C4H9-(C8H8)n-CH2CH(OH)CH(OH)CH2-(C8H8)17-n-C4H9•Na+. It is noteworthy that to our knowledge there are no previous reports of quantitative syntheses of in-chain, dihydroxyl-functionalized polymers. Reaction of the dihydroxy compound with potassium naphthalenide generated the corresponding potassium alkoxide, used to initiate polymerization of ethylene oxide. The resulting polystyrene-star-poly(ethylene oxide) heteroarm, star polymer (all arms equal length by stoichiometry) exhibited a narrow molecular weight distribution by SEC analysis (Mn = 5100 g/mol; Mw/Mn = 1.05). The star polymer composition was confirmed by 1H NMR analysis. MALDI-TOF MS analysis confirmed the formation of star polymer. This work provides a new, method for the synthesis of heteroarm, star polymers. This PRF grant supported the completed MS thesis of Asfiya Contractor, published in Macromol. Chem. Phys. 2006, 207, 2280-2288.

Since the reaction of PSLi with 1,3-butadiene diepoxide proved that epoxides are efficient functionalizing/linking agents, a trifunctional triepoxide was investigated to prepare higher order, functionalized stars. Excess PSLi was reacted with the commercially available triepoxide, N,N-diglycidyl-4-glycidyloxyaniline. The purified star polymer exhibited a narrow molecular weight distribution (Mn = 4,400 g/mol; Mw/Mn = 1.03). The MALDI-TOF MS of the product showed two distributions: one corresponding to the expected trifunctional, star product and another lower molecular weight distribution corresponding to the dimer product, but with 44 fewer m/z units. It was concluded that an intramolecular displacement of an epoxide group by an alkoxide anion occurred competitively with a third PSLi addition at the dimer stage. The effects of temperature, added Lewis base, excess PSLi, lithium chloride, potassium alkoxide and chain-end structure (PS-oligo-PBD)Li were investigated to optimize formation of three-armed star product. The highest yield (94 %) of three-armed star was obtained with 3.6 equivalents of PSLi in benzene using 10 equivalents of tetrahydrofuran at 30 oC. 1H NMR analysis provided evidence for the presence of the methylene carbon between nitrogen and oxygen in the expected five membered 1,3-oxazolidine ring at ä 5.7-6.1 ppm. 13C NMR and 135 DEPT NMR analyses confirmed the formation of the three-armed star polymer. It is noteworthy that this product contains in-chain hydroxyl groups that can be used to initiate polymerization of heterocyclic monomers such as ethylene oxide to prepare hetero-armed star polymers.

In view of the difficulties in eliminating the side reaction to form coupled product in the preparation of three-armed polystyrene stars with N,N-diglycidyl-4-glycidyloxyaniline as linking agent, it was desired to try a different commercially available triepoxide as linking agent, i.e. Tactix 742, 2,4'4”-trihydroxytriphenylmethane triglycidyl ether. After reaction of Tactix 742 with five equivalents of PSLi (Mn = 1400g/mol), the SEC chromatogram of the purified product exhibited a monomodal curve (Mn = 4,700 g/mol; Mw/Mn = 1.14). From these results, the average number of arms per star was calculated to be 3.4. The MALDI-TOF MS of the product showed that the major distribution corresponded to the expected three-armed star product, [C4H9-(C8H8)n-CH2CH(OH)CH2O(C6H4)]3-CH•Na+. Another smaller distribution corresponded to coupled polymer from a difunctional impurity in Tactix 742 (incomplete reaction of the triphenol with epichlorohydrin). Another distribution corresponding to 5-armed, star-branched polymers was found by MALDI-TOF MS; a pentafunctional epoxide was probably formed during the Friedel-Crafts step for synthesis of the triepoxide. The calculated g' value for a three-armed star is 0.83; the value for this product was 0.80 [ēstar/ēlinear]. Although a mixture of linked and star products was formed, it was concluded that Tactix 742 is an efficient (no unreacted epoxide groups) and useful linking agent for the formation of in-chain functionalized, star polymers.

This PRF grant also supported the investigation of a new method for the preparation of well-defined, in-chain functionalized polymers. A pure in-chain, silyl hydride-functionalized polystyrene was prepared by reaction of excess PSLi with methyldichlorosilane followed by reaction of unreacted PSLi with ethylene oxide. The purified, in-chain Si-H functionalized polymer was characterized by SEC, 1H and 13C NMR and MALDI-TOF MS (one characteristic distribution in good agreement with expected structure). The Si-H functionalized polymer was reacted with allyl cyanide in the presence of Karstedt's hydrosilation catalyst to form the corresponding in-chain, cyanide-functionalized polymer characterized by FTIR, NMR and MALDI-TOF MS. Development of this new functionalization method and the triepoxide linking chemistry was carried out as part of the Ph.D. thesis of Manuela Ocampo (Ph.D. December, 2007).

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