Hydroxyl functionalized, anionic

A combination of anionic and ATRP was employed for the synthesis of (PEO-b-PS) , n = 3, 4 star-block copolymers [148]. 2-Hydroxymethyl-l,3-propanediol was used as the initiator for the synthesis of the 3-arm PEO star. The hydroxyl functions were activated by diphenylmethyl potassium, DPMK in DMSO as the solvent. Only 20% of the stoichiometric quantity of DPMK was used to prevent a very fast polymerization of EO. Employing pentaerythritol as the multifunctional initiator a 4-arm PEO star was obtained. Well-defined products were provided in both cases. The hydroxyl end groups of the star polymers were activated with D PM K and reacted with an excess of 2-bromopropionylbro-mide at room temperature. Using these 2-bromopropionate-ended PEO stars in the presence of CuBr/bpy the ATRP of styrene was conducted in bulk at 100 °C, leading to the synthesis of the star-block copolymers with relatively narrow molecular weight distributions (Scheme 72). 

Double hydrophilic star-block (PEO-fo-PAA)3 copolymers were prepared by a combination of anionic and ATRP of EO and fBuA [150]. Three-arm PEO stars, with terminal - OH groups were prepared by anionic polymerization, using l,l,l-tris(hydroxymethyl)ethane, activated with DPMK as a trifunctional initiator. The hydroxyl functions were subsequently transformed to three bromo-ester groups, which were utilized to initiate the polymerization of f-butyl acrylate by ATRP in the presence of CuBr/PMDETA. Subsequent hydrolysis of the f-butyl groups yielded the desired products (Scheme 74). 

The amphoteric 6-hydroxyquinoline (6HQ) molecule has a weak acidic hydroxyl function (p A = 9.2) and a weak basic imine function (p A = 5.1) in the ground-state [1]. A cationic (quinolinium) form 6HQ(C), an anionic (quinolinate) form 6HQ(A), and a neutral form 6HQ(N) are thus predominantly present in acidic, alkaline, and neutral aqueous solutions, respectively, according to the following acid-base equilibria ... 

Reed 332) has reported that reaction of ethylene oxide with the a,(a-dilithiumpoly-butadiene in predominantly hydrocarbon media (some residual ether from the dilithium initiator preparation was present) produced telechelic polybutadienes with hydroxyl functionalities (determined by infrared spectroscopy) of 2.0 + 0.1 in most cases. A recent report by Morton, et al.146) confirms the efficiency of the ethylene oxide termination reaction for a,ta-dilithiumpolyisoprene functionalities of 1.99, 1.92 and 2.0j were reported (determined by titration using Method B of ASTM method E222-66). It should be noted, however, that term of a, co-dilithium-polymers with ethylene oxide resulted in gel formation which required 1-4 days for completion. In general, epoxides are not polymerized by lithium bases 333,334), presumably because of the unreactivity of the strongly associated lithium alkoxides641 which are formed. With counter ions such as sodium or potassium, reaction of the polymeric anions with ethylene oxide will effect polymerization to form block copolymers (Eq. (80) 334 336>). 

A similar technique was employed for the synthesis of miktoarm stars having PS, PEO, poly(e-caprolactone) (PCL) or PMMA branches [57]. A PS-h-PMMA diblock copolymer possessing a central DPE derivative, bearing a protected hydroxyl function was prepared. After deprotection and transformation of the hydroxyl group to an alkoxide the anionic ring opening polymerization of the third monomer (EO or e-CL) was initiated. Only limited characterization data were given in this communication. 

Cyclopropanols in general, can well serve as homoenolate anion precursors, i.e., the P-anion of ethyl propionate 99), however, to avoid the easy base or acid induced ring opening the hydroxyl function of 42 must be protected when necessary. On simple addition of one equivalent of 3,4-dihydro-2H-pyran to a CH2C12 solution of the a-hydroxy acid 42, the tetrahydropyranyl ether 163 was obtained exclusively,... 

In 1968 Miller and Stirling showed that the 2-tosylethyl ester function (abbreviated TSE) underwent easy base-catalysed elimination in the presence of 1 M sodium hydroxide or sodium carbonate (but not sodium hydrogen carbonate) in aqueous dioxane at room temperature to give p-toluenesulfinate anion, ethylene. and a carboxylate 215 Thus, this ester function complements the methylsul-fonylmethyl function (see section 6.4) derived from methylthiomethyl esters in its base-sensitivity. Electron withdrawing groups (e.g., p-nitro) on the aryl ring increase base lability — a feature that has been exploited for the protection of the 2f hydroxyl function in oligoribonucleotide synthesis.216... 

B-90 and B-91, respectively.390 Another route coupled with cationic ring-opening polymerizations is accomplished for polymer B-92 with the use of a hydroxyl-functionalized initiator with a C—Br terminal, where the OH group initiates the cationic polymerizations of 1,3-dioxepane in the presence of triflic acid.329 Polyethylene oxide)-based block copolymers B-93 are obtained by living anionic polymerization of ethylene oxide and the subsequent transformation of the hydroxyl terminal into a reactive C—Br terminal with 2-bromopropionyl bromide, followed by the copper-catalyzed radical polymerization of styrene.391... 

The seminal work of Schulz and co-workers on anionic polymer initiators which contain protected hydroxyl functionality was reported in 1974." These researchers prepared 2-(6-lithio- -hexyloxy)tetrahydopyran by metal-halogen exchange in diethyl ether, see Figure 1. The lithium chloride co-product was removed by filtration. This initiator was successfully employed in the polymerization of 1,3-butadiene. The resultant functionalized living anion was subsequently functionalized with ethylene oxide or coupled with dimethyldichlorosilane. Mild acid hydrolysis with dichloroacetic acid liberated the telechelic dihydroxy polybutadiene. The polybutadienes produced with this initiator exhibited narrow molecular weight distributions = 1.05-1.08). 

Anionic Synthesis of Hydroxyl-Functionalized Polymers Using Protected, Functionalized Alkyllithium and Isoprenyllithium Initiators... 

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