Macromonomer Synthesis

Though typically a stepwise procedure was used in which the azide-terminatred polymer was isolated and puri ed before reaction with the alkyne species, an in-situ end group transformation process was also condncted in both the cases in which the azide-terminated polymers were reacted in situ with alkyne-functionahzed methacrylates. This one-pot synthesis is possible due to the orthogonal reactivity inherent in chck chemistry. 

Problem 12,1 Suggest an ef cient route, via ATRP and CuAAC reaction, for the synthesis of a (meth)acry-late terminated polystyrene macromonomer, such as tu-acryloyloxy-polystyrene (DP - 50). 

Problem 12.3 Suggest a method to synthesize, via ATRP and CuAAC reactions, o -(carboxylic acid)-w-hydroxy-polystyrene (PSt), in which the PSt block has a degree of polymerization (DP) of about 30. 

ATRP of styrene is carried out in a Schlenk ask loaded with CuBr to which styrene (much in excess of [St] [CuBr] = 30 1 ratio), phenyl ether (solvent), and N,N,N, N, N -pentrme1iiy diethylene triamine (PMDETA) are added and stirred for 15 min to allow catalyst formation. To the reaction mixture, cooled in an ice bath, the difunctional initiator (P3-I) is added and heated at 90°C in an oil bath till the monomer conversion (measured by H-NMR analysis) corresponding to the target DP of 30 is reached. [The ATRP reactions are stopped at a relatively low (less than 50%) monomer conversion to circumvent loss of bromide end functionality because of termination processes (cf. Problem 12.2).] To quench the polymerization, the reaction mixture is cooled and diluted with CHCI3. 

The reaction mixture is then passed through a basic alumina column to remove the catalyst, allowed to concentrate in a vacuum, and the polymer (P3-II) is recovered by precipitation in methanol and drying in vacuum at 60°C. For conversion to azide end-functionality, NaN3 (10 equiv) is added to DMF solution (0.01 M) of the above ATRP polymer containing bromide end group and the reaction mixture is stirred for 20 h at room temperature. The heterotelechelic polystyrene (P3-III) thus formed is recovered by precipitation in methanol and is dried in vacuum at 60°C. 

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The enzymatic polymerization of 12-hydroxydodecanoic acid in the presence of 11-methacryloylaminoundecanoic acid conveniently produced the methacrylamide-type polyester macromonomer. Lipases CA and CC were active for the macromonomer synthesis. Enzymatic selective monosubstitution of a hydroxy-functional dendrimer was demonstrated. Lipase CA-catalyzed polymerization of 8-CL in the presence of the first generation dendrimer gave the poly(8-CL)-monosubstituted dendrimer. 

These early examples of macromonomer synthesis illustrate some of the chief principles that have subsequently led to a great variety of methods. Ionic polymerization is often preferred because of the long lifetime of the active sites. Transfer reactions in free-radical processes are also used quite often, yielding both acceptable molecular weights and an adequate proportion of terminal functions. 

Macromonomer Synthesis Using Anionic Polymerization Methods... 

Polyethylene oxide)macromonomers were also prepared by reaction of methacryloyl chloride with living monofunctional poly(ethylene oxide) I6) the polymerization of which can be efficiently initiated by diphenylmethyl potassium25 or by potassium alkoxides 26 >. In the latter case care must be taken to avoid any excess of alcohol which would play the role of a transfer agent and impede the macromonomer synthesis. The obtained macromonomers... 

Diene carbanions exhibit a reactivity similar to that of styryl carbanions. Carban-ionic sites of lower reactivity can be functionalized under certain conditions32). Living polymers with alkoxide end groups exhibit the same reactivity as alcoholates with respect to proton-donating substances and activated organic halides. Protonation yields terminal hydroxy groups which are often used in the two-step macromonomer synthesis. 

Since efficient initiators are available and the ring-opening polymerization of oxolane yields living species, the basic principles of macromonomer synthesis that have been developed above should also apply to the following case ... 

Inifer type reactions have been applied to a large number of cationic synthesis, yielding functional polymers 70 72), block copolymers 73), graft copolymers, and even star-shaped polymers73). As far as macromonomer synthesis is concerned three different methods have been used which are described below ... 

It should be recalled that various other two-step macromonomer synthesis have been developed using the inifer technique as an adequate functionalization method for preparing the precursor. Thus, starting from to-chloro-polyisobutene, the de-hydrohalogenation can be followed by hydroboration and selective oxidation to yield almost quantitatively the -hydroxy precursor 78) ... 

We shall discuss in this section alternatives for synthesizing quantitatively co-functional polymers and which allow at least some kind of control of the molecular weight of the species formed. These polymers can thus serve as precursors for macromonomer synthesis. 

It can be asserted that the synthesis of well-defined functional polymers by means of functional free-radical initiators is far from being satisfactory. To our knowledge, this pathway was never used in this simple form as a step in the macromonomer synthesis. 

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