Group transfer polymerization (GTP) was announced 20 years ago by DuPont as a method for synthesis of acrylic block polymers. It operates at high enough temperatures to allow reactor cooling by water-cooled reflux condensers, rather than more costly refrigeration units. GTP uses 1-methoxy-1-(trimethylsiloxy)-2-methylprop-1-ene (MTS) as initiator and a carboxylic acid salt as catalyst. The number of growing polymer chains corresponds to the amount of MTS used. Chain growth stops when the monomer is depleted. Addition of a new monomer at this point starts chain growth again to produce a block polymer. DuPont sells pigmented inks containing GTP block polymer dispersing agents.

Group Transfer Polymerization: A Critical Review of Its Mechanism and Comparison with Other Methods for Controlled Polymerization of Acrylic Monomers

The synthesis of polymethacrylates by a repeated silyl Michael addition reaction (GTP)a allows one to control the molecular weight of the polymer by adjusting the monomer/initator ratio. A small amount of cyclic termination occurs but in general low molecular weight dispersity is obtained. Block polymers can be made by sequential addition of monomer. Functionality present on the ketene acetal portion of the initiator will be on one end of each polymer chain. Star polymers result from crosslinking active polymer with a bismethacrylate. Initiation of bismethacrylate with bisinitiator gives a ladder polymer.

The use of group transfer polymerization for the control of polymethacrylate molecular structure

Synthesis of a new block copolymer, Poly(e-caprolactone)-block-Poly(vinyloxytriethylsilane) (PCL-b-PVOTES) was examined by using a bifunctional initiator 4-(2-Hydroxyethoxy)benzaldehyde (4-HEBA) or (5-Hydroxymethyl)furfural (5-HMF) which was responsive to both living ring-opening polymerization (ROP) and aldol-type group-transfer polymerization (Aldol-GTP). The structures of the resulting block copolymers were confirmed by 1H NMR, IR, and size-exclusion chromatography (SEC). Desilylation of this PCL-b-PVOTES copolymer by acidic methanol resulted in an aimed amphiphilic block copolymer, namely Poly(e-caprolactone)-block-Poly(vinyl alcohol) (PCL-b-PVA).

Amphiphilic Poly(ε-caprolactone)-Poly(vinyl alcohol) Block Copolymer : Preparation from a Bifunctional Initiator

The group transfer polymerization of 1-butadienyloxytrimethylsilane (BdTMS) was examined in the presence of various aldehyde and zinc chloride in benzene. The distribution of molecular weight of the resulting polymers, was estimated by a GPC method, depended on aldehydes used: Mw/Mn=1.28, 1.40, 1.51, and 1.86, with p-anisaldehyde, p-tolualdehyde, benzaldehyde, and p-nitrobenzaldehyde, respectively. In 1H NMR monitoring of the initial stage of polymerization, a certain induction period (T) was observed prior to consumption of BdTMS. The initial polymerization rate was almost constant regardless of a variety of aldehydes, indicating that propagation proceeds through a common mechanism. The shorter the induction period was, the narrower was the distribution of molecular weight of the obtained polymer. A plot of TH/TX (X=OCH3, CH3, NO2) vs. Brown-Okamoto’s substituent constants (σ+) showed a linear relationship (ρ=−0.75). Therefore a more electron-donating substituent on the para position of benzaldehyde was advantage to start an initiation reaction (=aldol addition) rapidly, resulting in a narrower distribution of the molecular weight of the polymer.

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Group Transfer Polymerization of 1-Butadienyloxytrimethylsilane: Effects of Aldehydes on the Initiation Reaction

A new acyl-group transfer polymerization of thiiranes using carboxylic acid derivatives and quaternary onium salts was investigated. 3-Phenoxypropylene sulfide (PPS) was polymerized efficiently by S-phenyl thioacetate in the presence of tetrabutylammonium chloride, bromide, or tetrabutylphosphonium chloride to give the corresponding polysulfide with a S-acetyl group at the polymer terminal. The polymerization of 3-butoxypropylene sulfide (BPS) and cyclohexene sulfide (CHS) also proceeded under the similar conditions to afford the corresponding polymers. It was found from the polymer structures and results of post-polymerization that the polymerization proceeded transferring an acyl group in each propagating step. It was demonstrated that the acyl-group transfer polymerization has living nature. Furthermore, di- and tri-block copolymers of a variety of thiiranes were successfully synthesized by the present acyl-group transfer polymerization.

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New Acyl-Group Transfer Polymerization of Thiiranes Using Carboxylic Acid Derivatives and Quaternary Onium Salts

As requirement for the synthesis of new C4-type periodic polymers, group transfer polymerization of 1-butadienyloxytrimethylsilane (BdTMS) was examined. Equimolar Benzaldehyde (BAld)–ZnCl2 catalysts in benzene at 20°C were effective to give a soluble polymer in organic solvents. The structure of the polymer was revealed by NMR and IR analyses as 1,4-trans addition mode of diene. Dispersities (Mw/Mn) of molecular weight distribution evaluated by GPC reduced to about 1.5, clearly differing from about 3 in the case of ZnCl2 alone. SnCl4 or (C2H5)3Al2Cl3 without BAld polymerized BdTMS rapidly, accompanying gelation even at −78°C. Living propagation in BdTMS/BAld/ZnCl2 system was confirmed by the incremental monomer addition method. In NMR-monitoring the equimolar reaction of BdTMS/BAld catalyzed by ZnCl2 in C6D6, it was found that an aldol adduct appeared at the first stage and then a formyl group regenerated in the adduct began to react with the monomer.

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Tetsukazu Itoh

Papers

Group transfer and cationic polymerization of 1-butadienyloxytrimethylsilane