Polyoxazolines

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 

Schema 6.15 Synthesis of poly(2-oxazoline) block copolymers by the sequential monomer addition method. 

16) [105]. Multifunctional initiators based on, for example, cyclotriphosphazine [106], silesquioxane [107], porphyrin [108] and bipyridine metal complex [109, 110] cores were also successfully used for the living cationic ring-opening (co)polymerization of 2-oxazolines, resulting in star-shaped (co)polymers. The use of polymeric initiators also allowed the construction of well-defined complex macro molecular architectures, such as triblock copolymers with a non-poly(2-oxazo-line) middle block that is used to initiate the 2-oxazoHne polymerization after functionalization with tosylate end-groups [111-113]. In addition, poly(2-oxazoline) graft copolymers can be prepared by the inihation of the CROP from, for example, poly(chloromethylstyrene) [114, 115] or tosylated cellulose [116]. 

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The dried polyoxazoline-modified silica gel was immersed into distilled water. The adsorption property of the resulting gel was estimated by the water content. The water uptake was calculated from an expression of (W -W)jW, where Wis the weight of dried gel and W is the weight of water-absorbed gel. The modified gel showed a higher water-adsorption property than that of untreated silica gel, which absorbed 10.8 multiples of water. The water uptake of modified gel was up to 13.7 multiples of the weight of dried gel. Thus, silica gel has been made more hydrophilic by a polyoxazoline segment. 

The obtained gels were purified by Soxhlet extraction with chloroform to remove the unreacted polyoxazoline. Table 6 summarizes the results of the preparation of polymer hybrids together with their water adsorptions. In comparison with the silica gel without polyoxazoline segments, the modified silica with 50% polyoxazoline was found to show higher water adsorption. 

Second, in the case of polyoxazoline hybrid, the characteristic property of high compatibility of organic polymer with polar organic commodity polymers such as poly(vinyl chloride) or polyamide can be used as a type of compatibilizer. That is, it makes possible to incorporate the third organic polymer in the polyoxazoline-silica gel hybrid. 

Very recently the synthesis of BA and ABA type polyoxazoline(B)-polydimethyl-siloxane(A) block copolymers have been demonstrated 290,291). These types of materi-... 

Preparation of Linear Poly(ethyleneimine) by Hydrolysis of Polyoxazoline... 

Waschinski CJ, Herdes V, Schueler L et al. (2005) Influence of satellite groups on telechelic antimicrobial functions of polyoxazolines. Macromol Biosci 5 149-156... 

A special technique was employed by Naka et al. for the preparation of A2B stars, A being PEO and B polyoxazoline (POX) [26] according to Scheme 8. Ru(III) complexes with bipyridyl terminated polymers were utilized in this method. Characterization data were not provided for these miktoarm star copolymers. 

The first demonstration of this GDS method employed polyoxazoline methodology to produce Comb-burst poly(ethyleneimine) — poly(2-ethyl-2-oxazo-line copolymers and poly(ethyleneimine) homopolymers. 

Chujo Y, Sada K, Saegusa T (1990) Reversible gelation of polyoxazoline by means of Diels-Alder reaction. Macromolecules 23 2636-2641... 

Linear (difunctional) and star-shaped (tetrafunctional) polyoxazolines with M up to 8000 and MJM < 1.3 were prepared using these initiators [182]. 

Due to the high nucleophilicity of oxazoline monomers, their polymerization may be initiated by C—Cl bond even in the absence of silver salt. Thus, chloromethylated polystyrene [290] or polychloroprene [291] were used to prepare corresponding graft copolymers. More recently, polyoxazoline was grafted on poly(vinyl ether)s containing certain proportion of chloroethyl groups [292],... 

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] ... 

The properties and applications of linear PEI are described in the polyoxazoline chapter. 

The core-first method, which uses an active multifimctional core to initiate growth of polymer chains, was apphcable to make hybrid POSS-core star-shaped polyoxazohnes that showed an increase in Tg, compared to that of polyoxazohne initiated by methyl p-toluenesulfonate (MeOTs) with poly(2-methyl-2-oxazohne) (POZO) [76]. Other hybrid star-shaped polyoxazohnes initiated by cube-OTs or cube-benzyl revealed the same phenomenon. This was attributed to the reduction of segmental mobifity of POZO in starshaped polyoxazolines, which was caused by the incorporation of hard, compact POSS moiety to the core of star polymer with the core-first technique. The conclusions were drawn that the thermal stabilities of star-shaped polymers increased as the POSS wt % was increased, and this was used as a measure of the effect of the inorganic POSS unit on polymer thermal properties. 

In a following study, it was confirmed that the gelation transition was not limited to PEG lipopolymers because comparable viscoelastic properties were observed on monolayers of polyoxazoline lipopolymers as well [12], This called into question... 

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