Hydroxyl functional monomers

The simplest method to prepare a polyether oligomer by condensation reactions is by the use of hydroxyl functionalized monomers, as described in Figure 3.8. 

The cross metathesis reaction of fatty acid methyl esters with methyl acrylate has been studied (70). A wide variety of unsaturated and acid or hydroxyl functional monomers can be obtained in this way. 

Hydroxyl Functional Monomers. Although it is difficult to prepare hydroxyl functional NVF derivatives using the NVF Michael addition reaction, the nonfunctional NVF/acrylate derivatives readily undergo transamidation reactions to yield a variety of new functional derivatives (Scheme 4). 

Frequently, hydroxyl functional monomers are used as part of the copolymer with the hydroxy group providing the site for crosslinking with, for example, an amino crosslinker, when the coating is stoved. Two hydroxy functional types have been shown. Hydroxyl ethyl has a terminal (primary) hydroxyl group which is more reactive than the secondary hydroxy group on the hydroxy propyl chain. It is thus possible to get more rapid cure response by incorporation of hydroxy ethyl rather than hydroxy propyl functionality in the acrylic copolymer. This, however, may not always be advantageous as frequently rapid cure can lead to poor adhesion. 

As the length and frequency of branches increase, they may ultimately reach from chain to chain. If all the chains are coimected together, a cross-linked or network polymer is formed. Cross-links may be built in during the polymerisation reaction by incorporation of sufficient tri- or higher functional monomers, or may be created chemically or by radiation between previously formed linear or branched molecules (curing or vulcanisation). Eor example, a Hquid epoxy (Table 1) oligomer (low molecular weight polymer) with a 6-8 is cured to a cross-linked soHd by reaction of the hydroxyl and... 

The hydroxylic content of the dextran sugar backbone makes the polymer very hydrophilic and easily modified for coupling to other molecules. Unlike PEG, discussed previously, which has modifiable groups only at the ends of each linear polymer, the hydroxyl functional groups of dextran are present on each monomer in the chain. The monomers contain at least 3 hydroxyls (4 on the terminal units) that may undergo derivatization reactions. This multivalent nature of dextran allows molecules to be attached at numerous sites along the polymer chain. 

Another way to synthesize carboxylic acid functional hyperbranched polyesteramides is to invert the monomer ratio by using an excess of cyclic anhydride with respect to diisopropanolamine. In this case the theoretical A2B building block consisting of 2 carboxylic acid and 1 hydroxyl function can be envisioned (Fig. 14). 

A key point should be to identify the rate-limiting step of the polymerization. Several studies indicate that the formation of the activated open monomer is the rate-limiting step. The kinetics of polymerization obey the usual Michaelis-Menten equation. Nevertheless, all experimental data cannot be accounted for by this theory. Other studies suggest that the nature of the rate-limiting step depends upon the structure of the lactone. Indeed, the reaction of nucleophilic hydroxyl-functionalized compounds with activated opened monomers can become the rate-limiting step, especially if stericaUy hindered nucleophilic species are involved. 

Vinyl azlactone can be also copolymerized with acrylic monomers to give functionalized polymers. The azlactone-functional copolymers, P-, can be reacted with amine-, thiol-, and hydroxyl-functional molecules (Heilmann et ai, 1984) ... 

The concept of PO macroinitiators centers on the introduction of an initiation moiety into an olefinic polymer chain for polymerization. The most effective route for preparing PO macroinitiators is by employing functional polyolefins containing hydroxyl groups or other reactive groups. These functional POs are prepared by copolymerization of olefins with functional monomers and post-polymerization reaction, as mentioned above. In the case where an initiation moiety was at the chain-end of the polyolefins, a block type copolymer is produced. It has been reported that thiol-terminated PP was used as polymeric chain transfer agent in styrene and styrene/acrylonitrile polymerization to form polypropylene-b/odc-polystyrene (PP-b-PS) and polypropylene-btock-poly(styrene-co-acrylonitrile) (PP-b-SAN) block copolymer [19]. On the other hand, polymer hybrids with block and graft structures can be produced if initiation moieties are in the polymer chain. 

A similar technique was employed for the synthesis of miktoarm stars having PS, PEO, poly(e-caprolactone) (PCL) or PMMA branches [57]. A PS-h-PMMA diblock copolymer possessing a central DPE derivative, bearing a protected hydroxyl function was prepared. After deprotection and transformation of the hydroxyl group to an alkoxide the anionic ring opening polymerization of the third monomer (EO or e-CL) was initiated. Only limited characterization data were given in this communication. 

Functionalized monomers are sometimes regarded as polymerizable surfactants. Vinyl or allyl monomers are reacted with ethylene oxide (EO), propylene oxide (PO) or butylene oxide (BO) in a sequential or random addition mode. The terminal hydroxyl group can be optionally reacted with methyl or benzyl chloride to produce Williamson ethers (if the hydroxyl group has to be deactivated) or are further sulfated to deliver electrosteric stabilization. 

A major advantage of RAFT is that it is compatible with a wide range of monomers, including functional monomers containing, for example, acids (e.g. acrylic acid), acid salts (e.g. sodium salt of styrene sulfonic acid), hydroxyl (e.g. hydroxyethyl methacrylate) or tertiary amino (e.g. dimethylaminoethyl methacrylate). It can be used over a broad range of reaction conditions and provides in each case controlled molecular weight polymers with very narrow polydispersion. 

Another decoration pool library L23 was reported by Nestler (49), who presented the appendage of a peptidic chain to the two hydroxylic functions of a steroid scaffold (Fig. 4.15). The library was made up of 10 x 10 x 10 x 10 = 10,000 individuals using a chemical encoding method (39) and L-a-amino acids as monomer sets (R1-R4). The assay of the library as a source of artificial two-armed receptors for enkephalin-related peptides produced positives with micromolar affinity. Much larger libraries could be obtained by simply increasing the monomer sets and the length of the two arms this could lead to a primary library of peptide-binding artificial receptors similar scaffolds have been repeatedly exploited for combinatorial purposes (50-52). 

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