Oxazolines polymerization

Hoogenboom R, Fijten MWM, Schubert US (2004) Parallel kinetic investigation of 2-oxazoline polymerizations with different initiators as basis for designed copolymer synthesis. J Polym Sci Part A Polym Chem 42 1830-1840... 

The existence of centres with non-ionic character has already been suspected in studies of polymerizations which are supposed to proceed on carbocat-ions the theory of pseudo-cationic polymerization was proposed [137] (see Chap. 3, Sect. 3.1). The transformation of an ion pair to a covalent compound will evidently be easier for acid centres with heteroatoms, i.e. in heterocycle or vinyl ether polymerizations. Propagation on covalent bonds has actually been observed, first in the studies of oxazoline polymerization [138] and later even with THF [139, 140] and with other monomers (see, for example, refs. 131, 141 and 142). 

Bis(chlorodimethylsilyl)benzene-AgPF6 system was shown to act as a bifunctional initiator of substituted oxirane polymerization [42], Tri-methylsilyl iodide and triflate were used also as initiators of the cationic polymerization of oxazolines [43]. In this system, however, in contrast to typical initiation mechanism of oxazoline polymerization, O-silylation leads to initiation, because of the unfavorable charge distribution in N-siiyiated species ... 

More recent efforts investigating the kinetics and mechanism of cationic polymerization of oxazolines are aimed at the preparation of various types of functional polymers as described in a recent review [181] (cf., Section IV.D). One of the examples is the development of efficient di- and tetrafunctional initiators of oxazolines polymerization, allylic or benzylic dihalides and allylic tetrahalides [182], e.g. ... 

All limitations described above do not apply for the systems, which seem to be of considerable practical interest, namely oxazolines. Polymerization of these monomers proceeds practically irreversibly on long-living active species and, as discussed in Section III.F., chain transfer to polymer does not interfere with propagation. On the other hand, due to the possibility of obtaining oxazolines (or 6-membered analogs) with different substituents R ... 

Thus, termination of oxazoline polymerization with potassium hydroxide gave hydroxy-terminated polymers, which in the presence of tin octoate were capable of initiating the anionic polymerization of -caprolac-tone [287] giving the corresponding block copolymer, acting as effective compatibiliser. 

Termination of oxazoline polymerization with 3-aminopropyltri-ethoxysilane produced polyoxazolines containing —Si(OR)3 end groups. These materials were grafted on the surface of silica gel [293] ... 

Oxazoline polymerization has a living type character and therefore a great variety of block and graft polymers can also be produced. 

The versatile oxazoline ring has been utilized in reactions with novolacs. Oxazolines polymerize readily to give thermoplastics of various molecular weights [see Eq. (10)]. Reaction of a bisoxazoline with a novolac gives a cross-linked system that has properties dependent on the relative amounts of bisoxazoline to novolac... 

Another cooperative effort arose between Samuel McManus of the University of Alabama in Huntsville and our group. This cooperation produced results in pure heterocyclic organic chemistry, oxazoline polymerizations,96 and siloxane polymers.97 Oxysilane ferrocene-containing polymers were explored.98,99 Several bis(dimethylamino)silanes were made and reacted with 1,1 -bis(hydroxymethyl)ferrocene to give the early ferrocene oxysilane polymers 69 and 70 (Scheme 1.12).98... 

ABA and AB block copolymers were synthesized by the initiation of 2-oxazoline polymerization by a polymer containing tosylate (140-143) or alkyl halide end groups (144-147). 

The type of propagating species is mainly determined by the nucleophilicity of the monomer and basicity of the leaving group of the initiator, whereby covalent propagating species are present when the basicity of the counterion is higher than the nucleophilicity of the monomer and cationic propagating species are present if the basicity of the counterion is lower than the monomer nucleophilicity. The most nucleophilic monomer, 2-methyl-2-oxazoline, polymerizes via cationic propagating species with all counterions except... 

No.16,15th Aug. 2001, p.2821-31 NOVEL FUNCTIONAL INITIATORS FOR OXAZOLINE POLYMERIZATION... 

The fundamental chemistry of oxazoline polymerization has been extensively accomplished over the past four decades. The main trend of oxazoline polymerization, therefore, is currently and will be in the future toward application studies by utilization of the unique properties of the PROZO polymers. 

The reaction of the polymerization of 2-oxazoline is very clean, which is not disturbed by chain-transfer and termination. In the following scheme which exemplifies the 2-oxazoline polymerization, the propagating species having a structure of 2-oxazolin-ium salt is not fragile, which is conveniently utilized from the syntheses of block copolymers and end-reactive polymers. 

P—CH2CH2OH MePhS02Cl, pyridine P—CH2CH20S02PhMe 1. 2-Oxazolines (polymerization) 2. PhCH2NH2, giving P—NHCH2Ph 137, 138... 

The CROP of 2-oxazolines was first reported in 1966 by four independent research groups [62-65]. The major advantage of the 2-oxazoline polymerization, compared to cationic cyclic ether polymerizations, is the large difference in nudeophihcity of the cydic imine of the 2-oxazoline monomer and the amide of the ring-opened... 

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