Polymers oxazoline terminal groups

Oxazolines may be used to react with terminal groups on condensation polymers to improve stability, particularly against hydrolysis. This appears to be of particular interest with poly (ethylene terephthalate). 

Also of interest is the use of bis-2-oxazolines, which have molecular weights in excess of 1000 and oxazoline groups at each end of the molecule. These can then react with various terminal groups of condensation polymers to bring about... 

Poly(2-alkyl oxazoline)s having methacrylate or acrylate end groups were prepared by two methods [182]. a) Living polyoxazoline chains, prepared using methyl p-toluene sulphonate as initiator, were end-capped by reaction with metal salts or tetraalkylammonium salts of acrylic or methacrylic acid or a trialky-lammonium salt or trimethylsilyl ester of methacrylic acid (functional termination). b) The living polymers were terminated with water in the presence of Na2C03 to provide hydroxyl-terminated chains. Subsequent acylation with acry-loyl or methacryloyl chloride in the presence of triethylamine led to the formation of the macromonomers. The procedures are outlined in the following Scheme 51. 

Amphiphilic ABA-type triblock copolymers containing PDMS, two poly(2-methyl-oxazoline) -PMOXA- side blocks and methacrylate terminal groups have a eomplex selfassembling behavior, which allows for the synthesis of covalently cross-linked hydrogels, with applications as contact lenses [106]. Cross-linked vesicles of such polymers are nano-and microcapsules which act as stable nanoreactors with controlled permeability [107-109]. 

Currently, anionic polymerization is regarded as one of the best methods available to prepare end-functionalized polymers. Vinyl polymers with haloalkyl groups at one chain end were prepared by anionic polymerization, followed by termination of the living anion with an excess of 1,2-dichloroethane or 1,4-dibromobutane [102]. These polymers served as macroinitiators for the polymerization of 2-methyl-2-oxazoline (MeOZO) and aromatic vinyl monomers (Scheme 11.27). 

Similarly, in cationic polymerization of oxazoline initiated by methyl-iodide, the inert polymer terminated by the CH2I group is in equilibrium with its reactive ionized form. 

CM is also very useful if the objective is to modify branched polymers or to introduce some convenient functional groups. This was the case of two original studies conducted by the Meier s research team. The first study [26] described the reaction of a poly(2-oxazoline) containing terminal double bonds in the side chains with various functional acrylates in the presence of a HG-II. The second (more recent) study [27] involved the synthesis of a polymalonate bearing C9 aliphatic side chains with terminal double bonds used for grafting-onto reactions by ruthenium-catalysed CM. 

The SG effect is not restricted to poly(2-oxazoline)s since it was shown by Gellman and coworkers that the N- and C-terminals of nylon-3 random copolymers strongly influenced the bioactivity of these polymers with regard to selectivity and hemolysis.Additional investigations were performed by Griesser and coworkers, who studied the impact of end groups on the hemolysis and antimicrobial activity of antimicrobial polymethacrylates. 

If both blend components are nomeactive, it is necessary to add two reactive polymers which provide - after reaction at the interface - an effective compatibilizer. Thus, the interfacial adhesion in PP/PE blends was enhanced by the addition of PP-g-MA and poly(ethen-co-vinylalcohol) [152] or in PP/PS blends using PP carrying oxazoline groups and carboxyl-terminated PS [153]. 

As described in this chapter, the living CROP of THF and 2-oxazolines are versatile methods for the preparation of well-defined polymers, whereby both the initiation and termination steps provide the possibility of introducing a variety of functional groups. Poly(tetrahydrofuran) has a low Tg, and is often used as soft block in for example, thermoplastic elastomers. As such, it is expected that the living CROP of poly(tetrahydrofuran) will remain an important method in the preparation of soft polymeric materials, whereby the easy introduction of functional groups can be used to prepare novel functional materials. 

---