AB monomer

The preceding discussions of the kinetics and molecular weight distributions in the step-growth polymerization of AB monomers are clearly exemplified by the esterification reactions of such monomers as glycolic acid or co-hydroxydecanoic acid. Therefore one method for polyester synthesis is the following ... 

The discussion of polyamides parallels that of polyesters in many ways. To begin with, polyamides may be formed from an AB monomer, in this case amino acids ... 

One distinction that should be pointed out involves the comparison of Eqs. (5.1) and (5.40). In the former we considered explicitly the AB monomer, while the latter is based on the polymerization of AA and BB monomers. In both instances is obtained by dividing the total number of monomer molecules initially present by the total number of chains after the reaction has occurred to extent p. Following the same procedure for different reaction... 

Polymerization of an AB monomer is illustrated by the polyester formed from glycolic acid. The repeat unit in this polymer has the structure... 

AA and BB monomers and also AB monomers invariably react to form predominantly linear structures in all but the rather special case where the ring structure in reaction (5.CC) has a value of 1 = 5 or 6. This explains why so many of the monomers in step-growth polymerizations are tetra-, hexa-, and decamethylene compounds. 

Poly(arylene ether sulfone)s can be synthesized by two different polysulfonyla-tion reaction routes condensation of AA and BB monomers or self-condensation of AB monomer.26,27 Scheme 6.5 shows two approaches. 

Similar to the synthesis of polysulfones, poly(arylene ether ketone)s can also be prepared by using either AA and BB monomers or an AB monomer. 

Assuming that all B groups have the same reactivity, the chemical reaction giving rise to a branched molecule is identical to the reaction resulting in a linear polymer. Statistically this will eventually result in a hyperbranched polymer. However, dependent on the chemical structure of the monomer, steric effects might favor the growth of linear polymers. Computer simulations of of ABX-monomer condensation and AB -monomers co-condensed with B-functional... 

The use of AB monomers for the preparation of both hyperbranched and dendritic macromolecules leads to the presence of an extremely large number of chain end functional groups for both systems. In analogy with dendrimers, the... 

Liu M, Vladimirov N, Frechet JMJ (1999) A new approach to hyperbranched polymers by ring-opening polymerization of an AB Monomer 4-(2-hydroxyethyl)-e-caprolactone. Macromolecules 32 6881-6884... 

How do dendrimers and hyperbranched polymers compare from an industrial viewpoint Dendrimers offer the potential for producing polymers whose molecular size and structure are more regular and less polydisperse. 1 lyperbranched polymers are easier and cheaper to synthsize—a one-pot synthesis compared to the multipot synthesis for dendrimers. However, not too many AB/ monomers are readily available, and this may modify the overall economics. Hyperbranched polymers will probably find use in larger-scale or commodity applications where lower cost is a necessity and dendrimers in specialty applications where higher cost is justified. 

Fig. 2 Synthetic routes to procure polyesters using lipase catalysis (a) ROP of cyclic esters, (b) polycondensation of AA-BB monomers, and (c) polycondensation of AB monomers...

Extension of DKR to polymer chemistry would readily result in chiral polyesters, polycarbonates, or polyamides from an optically inactive monomer mixture. Scheme 10 describes three variants of chemoenzymatic catalysis applied in polymer chemistry that recently appeared in the literature. Route A uses AA and BB monomers to prepare chiral polymers from racemic/diasteromeric diols. Route B converts an enantiomer mixture of AB monomers to homochiral polymers. Route C is the enzymatic ring-opening polymerization of co-methylated lactones to homochiral polyesters. Details will be given in Sect. 3.4.2. 

Dynamic Kinetic Resolution Polymerization of AA-BB Monomers and AB Monomers... 

A straightforward extension of DKR to polymer chemistry is the use of diols and diesters (AA-BB monomers) or ester-alcohols (AB monomers) as substrates (Scheme 10, routes A and B). Such reactions have been referred to as DKR polymerizations and lead to the formation of oligomers and/or polymers because of the bifunctional nature of the reagents. 

In contrast, Kanca et al. observed that aliphatic AB monomers (Scheme 11) comprising a secondary hydroxyl group and an ester moiety did show high enantioselectivities in a Novozym-435-catalyzed transesterification reaction [104]. The E was high for all monomers studied E > 200). An additional advantage... 

Scheme 11 Novozym-435-catalyzed transesterification reaction of aliphatic AB monomers containing a secondary hydroxyl group [104]...

Hyperbranched polymers are formed by polymerization of AB,-monomers as first theoretically discussed by Flory. A wide variety of hyperbranched polymer structures such as aromatic polyethers and polyesters, aliphatic polyesters. polyphenylenes, and aromatic polyamides have been described in the literature. The structure of hyperbranched polymers allows some defects, i.e. the degree of branching (DB) is less than one. The synthesis of hyperbranched polymers can often be simplified compared to the one of dendrimers since it is not necessary to use protection/deprotection steps. The most common synthetic route follows a one-pot procedure " where AB,-monomers are condensated in the presence of a catalyst. Another method using a core molecule and an AB,-monomer has been described. ... 

The Friedel-Crafts type of technology can also be used for the preparation of monomers that contain one benzocyclobutene and a second functional group which can react with the benzocyclobutene. These types of molecules are commonly called AB monomers. An example of this class of monomer is shown in Fig. 8. 

There are many examples of AB monomers in the polymer literature [104]. In particular there are examples of the Diels-Alder reaction being used in successful AB type approaches to polymer syntheses. There are however several practical problems associated with this type of approach. If the diene or dienophile is highly reactive, the synthesis and purification of the monomer can be very difficult. Furthermore, these reactive monomers can be difficult to store without some partial advancement of the molecular weight. If on the other hand the diene or dienophile is not very reactive under moderate conditions, then low molecular weight polymers are obtained. If more stringent conditions for polymerization are employed, the retro Diels-Alder reaction and other side reactions can become more important and therefore lead to the formation of a low molecular weight polymer. 

Fig. 4. Proposed generic structure for the polymer derived from the Diels-Alder polymerization of a maleimidobenzocyclobutene AB monomer 80...

---