Macromers, controlled initiation

Macromers by Controlled Initiation. New and unique graft copolymers can be prepared by copolymerizing macromers (macromolec-ular monomers) with conventional monomers. The synthesis of poly(butyl acrylate- -isobutylene), i.e., the first graft synthesis that involves carbocationic controlled initiation, has recently been accomplished by the following route (9) ... 

MACROMER (10) is a trademark by CPC International of a new family of monomers. Because they are synthesized via anionic chemistry, their molecular weight is controlled by the ratio of monomer to initiator and they also have very narrow molecular weight distributions. The typical polymeric portions of MACROMEHf that have been investigated are polystyrene, polydiene, and blocks of the two (5, lCi). Some of the typical MACROMER functional groups that were examined are shown in Figure 8. These are shown to indicate the wide variety of functional groups that are useful for various polymerization mechanisms (4). 

The preparation of prepolymers [111] or macromers with functional end groups, so called telechelic polymers, is another approach to structurally unconventional architecture. The functional end groups are introduced either by functional initiation or end-capping of living polymers, or by a combination of the two. In this way, monomers that are not able to copolymerize can be incorporated in a copolymer. Telechelic prepolymers can be linked together using chain extenders such as diisocyanates [112]. In this process, it is essential that the structure and end groups of the prepolymers can be quantitatively and qualitatively controlled [113]. 

By reactions (82)-(84), 8 wt. % Br was introduced into the oligomers, an average of 1.95 Br atoms per chain. This work was extended by Kennedy and Smith [91] who selected the co-initiator from a group of transfer agents, which thus had a double function. This new technique they called the inifer method (from co-initiator-trans/er agent). When the rate of transfer to monomer is much less than to the inifer, the formation of the reactive macromer end groups can be better controlled. Macromer formation can be represented by the scheme... 

An elegant alternative to living polymerization for the preparation of block polymers is to use functionalized Grignard initiators. The polymerization of methyl methacrylate to isotactic (in toluene at — 78"C) or syndiotactic polymers (in THF at — llO C) can be initiated by o-, m-, and p-vinylbenzylmagnesium chloride. The polymers had a low polydispersity and contained one vinylbenzyl group at the chain end, by H-NMR. The poly(methylmethacrylate) macromers thus obtained were polymerized or copolymerized with styrene to give graft and block polymers of controlled architecture [50,51]. 

The second step involved the ROMP of the functionalised PEO macromer using the well-defined Schrock (hexa-fluorinated) or Grubbs initiating complexes. Each initiator had a metal core (molybdenum or ruthenium) with bulky ligands that controlled the approach and co-ordination of the reactive carbene bond to the double bond of the norbomene group... 

Cordova and co-workers [106] prepared macromonomers using Candida antarctica lipase B as catalyst. Ring opening polymerisation of e-CL was initiated by alcohols which included 9-decenol, cinnamyl alcohol, 2-(4-hydroxyphenyl) ethanol and 2-(3-hydroxyphenyl) ethanol. In another approach acids and esters which included n-decanoic acid, octadecanoic acid, oleic acid, linoleic acid, 2-(3-hydroxyphenyl)acetic acid, 2-(4-hydroxyphenyl)acetic acid and 3-(4-hydroxyphenyl)propanoic acid were added to the prepolymerised e-CL. Consequently, acid terminated PCL was formed. In the first approach 9-decenol-initiated PCL was formed (24 hours, 99% conversion of e-CL) with an average MW of 1,980 Da. In the second approach linoleic acid terminated PCL was formed with an average MW of 2,400 Da (51 hours, 99% conversion). In an effort to simultaneously control both the hydroxyl and carboxyl end groups of macromers, esters, e.g., 9-decenyl oleate, 2-... 

The introduction of monofunctional POSS macromers into an organic polymer by polymerization at the single reactive site leads to POSS-modified polymers. POSS macromers were incorporated in linear polymers, such as methacrylates, styrenics, norbomenes, ethylenes, propylenes, and urethanes in order to improve mechanical or thermal properties. If a multifunctional POSS with cross-linkable functions is used cross-linked materials are indeed formed. Star polymers are achieved if a multifunctional POSS unit contains initiator groups and a controlled polymerizatiOTi occurs, such as atom transfer radical polymerization. 

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