Recently, many searches have been done in the field of macromonmomer according to the importance of their synthesis and application in the industry. Macromoners, macromolecular monomers or macromers are defined as polymer or oligmer carrying a functional group or more than one at their chain end, these functional groups can be polymerized by many methods. Therefore, macromonomer comprise two sections. The first one is the polymer chain which carries the physical properties, and the second is the functional group at the end of the polymer chain which is responsible about the chemical reactivity of the macromonomer to the polymerization reactions, so the chemical reactivity of the macromonomer can be varied by variation the function group, and different kind of macromonomer can be obtained by changing the polymer chain. The molecular weight of macromonomer described in many paper , it was between 500 to 20000 g / mol-1.
An unsaturation or heterocycle (such as oxirane ring) function group is most common in mono-functional macromonomer that it is used on the preparation of graft copolymers with well defined structure . An active double bond function at the both end of the macromonomer chain is one of the most common in bi-functional macromonomer. Moreover, if two functions attached to one end of the macromonomer chain, it is called multi-macromonomer. It is indicated that Bi-function and multi-fuction macromonomer are used in the formation of polymer networks or gels.
MONO -FUNCTIONAL MACROMONOMER
History of macromonomers :
The first macromonomer was prepared by Greber and co-works in 1962. polydimethylsiloxane macromonomers (they were called polymer ,at that time , macromonomer phrase used 1978) with p-vinylphenyl group chain end obtained by reacted ω -chlorodimethylsiloxane oligomers with p-chlorostyrene's Grignard derivative . Then, these types of macromonomers were copolymerized with different monomers to use them to synthesis graft copolymers.
An unsaturated macromonomers with low molecular weight were prepared by Greber by anionic deactivation. The average molecular weight of the macromonomer which was prepared by reacted a living ω-carbanionic polystyrene with p-vinylphenyldimethyl-chlorosilane was obtained by vapor pressure osmometry and the double bond analysis.
Gillman and Senogles had another try to synthesize maceomonomers, but on different basis to prepare graft copolymers. They used 2-hydroxyethanethiol (HO--CH2--CH2--SH) as an efficient transfer agent in the free radical polymerization of methyl methacrylate. According to this, the polymer molecules were attached to 2-hydroxyethanethiol end group from the transfer reaction by lowering their molecular weight. After that, the ω-hydroxy polymer was reacted with metharyloyl chloride to obtain a nacromonomers with methacrylic ester function group. Then, they copolymerized the poly methyl methacrylate macromonomers with many vinylic monomers to obtain graft copolymers.
After many years of the previous works, no much attention had been paid to macromonomers before Milkovich described the concept of macromonomers in 1974. Recently, a large number of papers and articles in universities and industries have been published in macromonomers field duo to the wide range of their applications.
Preparation of macromonomers:
There many methods to prepare macromonomers such as ionic polymerization, and transfer reaction in free radical polymerization.
Anionic polymerization methods of synthetic macromonomers :
Well defined macromonomers with a goood control of the molecular weight, and low polydispersities can be obtained by anionic polymerization. In this type of polymerization, macromonomers can be prepared either by anionic initiation processes, end capping of living polymeric anions, or other process.
Anionic initiation procedures:
The first try to anionic initiation was by Waak. An unsaturated lithiumorganic compound, called vinyllitium was used as a reagent. Tetravinylzinc and butyllithium were reacted to provide vinyllithium.
Vinyllithium was used to polymerize styrene, and other monomer, but the low rate of the molecular weight, and the rate of initiation were disadvantage of this work. In addition, the product was carried an allylic double bond at the end of the chain which causes a low reactivity of the radical in radical polymerization. On other work Waak used other unsaturated lithium initiators to polymerize styrene , but the same drawbacks of the previous work obtained.
On other work, oxirane polymerized by ring opening polymerization using alkoxides as an initiator, and polyoxyethylene macromonomer wes prepared using an unsaturated alcoholate . It is proved that, Potassium p-isopropenyl benzylate is an efficient initiator to polymerize the oxirane. Thus , living end of α-methylstyry of polyethyleneoxides can be deactivated by alkyl halide or proton.
The light scattering, NMR, GPC, and UV spectrometry showed that, the reaction has been done and structure of the macromonomer was as expected.