A review of chain transfer catalysis and catalytic homopolymerization of acrylates and styrene

الملخص EN

-Low molecular weight polymers are used in industry for the production of high-solids automotive finishes, adhesives, coatir polymer blends, and other similar applications.

These polymers are usually obtained by adding thiols or mercaptans as moleci weight regulators during polymerization of the respective monomers.

Because of the low reactivity of thiols or mercaptanes rat high concentrations are required which in tum impart undesirable properties, such as toxicity, color, and odor, to the finisl product.

This limitation on the use of thiols or mercaptans justifies a need for finding alternatives for use as regulators in the f radical initiated polymerization.

Although a very rapidly growing interest is evident from literature, no review on this subject ha; far appeared nor have the trends emerging from the growing research been identified.

The present paper is an effort to consolidate the existing literature on chain transfer catalysis.

The paper is divided into two pa (a) a review of all chain transfer catalysts reported so far in the literature is given, and (b) the work involving application of a n catalyst for bulk homo polymerization of acrylates and styrene is reported.

The basis of the undergoing research on Catalytic Chain Transfer Catalysts lies in successful use of metal-chelates such cobalttetra(aryl)porphyrine (TAP(Co")* (the dot indicating the radical nature of cobalt(II)), and cobaIt(II)dimethylglyoxima [Co(dmg-2H)2(BF2)2], at ppm levels, as very effective Catalytic Chain Transfer Agents (CCTA) for regulating the molecular wei of the polymeric acrylates.

The [Co(dmg-2H)2(BF2),J complex has been patented as a CCTA by DuPont.

The experimental section involves: (a) the synthesis and characterization of new metal chelates used as CCTAs, (b) bulk homopolymerization of acrylates and styrene in the presence of the CCTA, and (c) polymerization as a function of concentration of the CCTA.

Our studies using [Co(afdo-2H)2(BF2),] (afdo= a-furildioxime) as a CCTA for AIBN-initiated (AIBN = azobis(isobutyronitr: bulk homopolymerization of MMA revealed that its catalytic activity is similar to the DuPont catalyst [Co(dmg-2H)2(BF2 observed for homopolymerization of MMA and styrene.

An approximately 10-fold decrease in the molecular weight of PMMA v observed with concentration of [Co(afdo-2H)2(BF2)2] at PPM levels.

The molecular weight of the PMMA as well as of polystyrt depends upon factors such as the time of addition of the CCTA relative to the initiator, concentration of the CCTA, and the react temperature.

Similar retardation of molecular weight was observed in AIBN-initiated bulk co-polymerization of MMA and styre A large volume of plastics is based upon polystyrene and/or polyacrylates.

Low molecular weight polyacrylates, polystyrene, styrene/acrylates macro-monomers are useful materials for several industrial applications.

The use of metal chelate as CCTA v afford the synthesis of new polymeric materials avoiding the problems of toxicity, odor and color, associated with the use of thi or mercaptans as polymer chain growth interceptors.

The co-polymerization of styrene with polyacrylates in the presence o CCTA will offer an entirely new class of polymeric materials.

In addition to its commercial importance, catalysis of chain transfer remains a growing area of research because beside industrial application, it provides a unique opportunity for obtaining fundamental knowledge on elementary reactions of b( organometallic and free radical polymerization chemistry.