Oxazolines block copolymers

Scheme 6.3 Amphiphilic poly(2-oxazoline) block copolymers bearing triphenylphosphine and bipyridine moieties respectively as polymeric macroligands for micellar catalysis.

Hoogenboom R, Fijten MWM, Paulus RM et al. (2006) Accelerated pressure synthesis and characterization of 2-oxazoline block copolymers. Polymer 47 75-84... 

A block copolymer of PS and an oxazoline was obtained from an OTs-terminated PS, which was obtained by ethylene oxide termination of PSLi in THE at —78°C followed by addition of tosylchloride. The OTs-terminated polymer served as a cationic macroinitiator for EOz (Mn per block 10-20 kg/ mol, Mw/Mn = 1.3—1.5), which means that control of the EOz polymerisation is limited [145]. Another oxazoline block copolymer was obtained via the polymerisation of EO by a potassium difunctional initiator under /THE/ KPDP/RT//MSC1/ conditions. The a, co-acetal-methylsulfone-terminated PEO was used as a macroinitiator for the cationic polymerisation of 2MOz in nitromethane to yield acetal-terminated PEO-P2MOz, which was hydrolysed to removed the acetyl side chains to yield PEO-PEI (M = 3.2kg/mol MJMn = 1.04 for the PEO 5 < Mn/(kg/mol) < 10.5 1.35 < MJM < 1.56 for the PEO-PEI) [146]. 

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

The polymerization of 2-methyl-2-oxazoline is a clean reaction, which is not disturbed by chain transfer and termination. In this polymerization, the propagating species having the structure of an oxazolinium salt is not fragile, which is conveniently utilized for syntheses of block copolymers and end-reactive polymers [28],... 

Controlled synthesis of ABA type poly(2-ethyl-2-oxazoline)-b-PDMS block copolymers was obtained by the melt reaction of a,c -benzyl halide terminated PDMS oligomers and the oxazoline monomer 291 as shown in Reaction Scheme XX. 

Synthesis of Poly(2-ethyl-2-oxazoline)-b-PDMS (ABA) Block Copolymers 2911... 

Some other degradable (i.e., nonvinyl-type) polymers have been reported as components for amphiphilic block copolymers. For example, Hsiue reported the synthesis of a block copolymer of poly(2-ethyl oxazoline) and PLA by ROP. They reported the use of ABA-type triblock copolymers as pH-responsive polymer... 

Interestingly, the Fe2+ ion in the core can be easily removed by base, the complex dissociates and the individual polymer dimers can be analyzed. Block copolymers of 2-ethyl-2-oxazoline with other substituted oxazolines have also been made [121]. Ru2+(4,4 dichloromethyl-2,2 bipyridine)3 has also been used as the multifunctional initiator for the ATRP of styrene at 110°C [122], It is interesting to note that the Cu+ ions necessary for the polymerization reaction are solubilized via complexation with other bipyridine species. 

Much research has already been devoted in the past couple of years to (i) the immobilization of ATRP active metal catalysts on various supports to allow for catalyst separation and reycycling and (ii) ATRP experiments in pure water as the solvent of choice [62]. A strategy to combine these two demands with an amphiphilic block polymer has recently been presented. Two types of polymeric macroligands where the ligand was covalently linked to the amphiphilic poly(2-oxazo-line)s were prepared. In the case of ruthenium, the triphenylphosphine-functiona-lized poly(2-oxazoline)s described in section 6.2.3.2 were used, whereas in the case of copper as metal, 2,2 -bipyridine functionalized block copolymers were prepared via living cationic polymerization [63] of 2-methyl-2-oxazoline and a bipyridine-functionalized monomer as shown in Scheme 6.8. 

Fijten MWM, Kranenburg JM, Thijs HML, Paulus RM, Van Lankvelt BM, D Hullu J, Spring-intveld M, Thielen DJG, Tweedie CA, Hoogenboom R, VanVliet KJ, Schubert US (2007) Synthesis and structure-property relationships of random and block copolymers a direct comparison for copoly(2-oxazoline)s. Macromolecules 40 5879-5886... 

The sequential addition method also allows the synthesis of many different block copolymers in which the two monomers have different functional groups, such as epoxide with lactone, lactide or cyclic anhydride, cyclic ether with 2-methyl-2-oxazoline, imine or episul-Hde, lactone with lactide or cyclic carbonate, cycloalkene with acetylene, and ferrocenophane with cyclosiloxane [Aida et al., 1985 Barakat et al., 2001 Dreyfuss and Dreyfuss, 1989 Farren et al., 1989 Inoue and Aida, 1989 Keul et al., 1988 Kobayashi et al., 1990a,b,c Massey et al., 1998 Yasuda et al., 1984]. 

They started from dihydroxy poly(butadiene), converted it to the ditosylate and allowed this compound to react with 2-oxazoline. The block copolymer obtained was hydrolyzed in aqueous medium to yield the above copolymer which is soluble in chloroform. According to NMR investigations the LPEI unit content in the copolymer was 63 mol-% and the LPEI blocks had an average molecular mass of 4700. 

Ma S-H, Ford C. (1999) Block copolymers of oxazolines and oxazines as pigment dispersants and their use in ink jets, EP0915138. 

Living difunctional poly-THF was therefore used to initiate the cationic polymerization of N-f-butylaziridine [170] or oxazoline [283] to give the corresponding A-B-A block copolymers with polyether block B. 

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. 

Lee, S.C. Kim, C. Kwon, I.C. Chung, H. Jeong, S.Y. Polymeric micelles of poly(2-ethyl-2-oxazoline)-block-poly(-caprolactone) copolymer as a carrier for pachtaxel. 

We have investigated the molecular weight distribution of a block copolymer obtained when poly(ethylene glycol) dltosylate (MW 3500) is used to initiate the cationic polinnerlzatlon of 2-lsobutyl oxazoline (living polymer). 

Fig. 4 Molecular structure of diblock copolymers and side-chain modified lipopolymers whose pressure-area isotherms are presented in Figs. 6 and 7, respectively. Diblock copolymers are poly(2-n-nonyl)-poly(2-methyl or 2-ethyl-2-oxazoline) (NxEy and NxMj,), where x and y denote the block sizes of the hydrophobic nonyl and hydrophilic oxazoline blocks. Side-chain modified lipopolymers, which contain short oligo-EG sidechains in each monomer of the lipopolymer to create a bottle-brush-like structure, are di-octadecanoyl-glycerol 2-(3 -methoxymonoethylene glycol)propyl-2-oxazoline (DiCigMEGOxn) and di-octadecanoyl-glycerol 2-(3 -methoxytiiethyleneglycol)propyl-2-oxazoline (DiCisTEGOxn) (adapted from [7,8])...

Colloidal palladium can also be stabilized with poly(7V-vinyl-2-pyrrolidone).78 Other polymeric stabilizers have also been used with palladium, platinum, and other metals. These include poly(2-ethyl-2-oxazoline), poly(methacrylic acid),79 block copolymers containing COOH groups,80 poly(Wisopropyl acrylamide),81 and poly(styrene-b-4-vinylpyridine).82 Colloidal iron has been stabilized not only by poly(Wvinyl-2-pyrrolidone) but... 

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). 

Oxazolines have been used in block and graft copolymerization. Addition of 2-methyl-OXL to living polyTHF yielded block copolymer l9). Mostly on the basis of solubility data the formation of block copolymers of 2-methyl-2-oxazoline and styrene oxide (initiation with I2) were claimed 20). 

In the preceding section we have disscussed the influence of monomer nucleophilicity on copolymerization behaviour. Only monomers of similar nucleophilicities can be randomly copolymerized. Attempted simultaneous copolymerization of e.g. amines with ethers, and sulfides or oxazolines with ethers gives homopolymers of the more nucleophilic monomer. However, stepwise addition of a more basic comonomer to a living polymer derived from the less nucleophilic heterocycle yields block copolymers (cf. Sect. 15.3.1.2). 

Oxazoline is a relatively strong nucleophile and therefore it can be polymerized in the presence of such nucleophilic counterions as iodide or bromide anions. Thus, the synthesis of block copolymers of styrene (St) and 2-methyl-2-oxazoline (MOXL) was attempted by a method similar to that described in the previous section 10S). 

The synthesis of block copolymers by sequential polymerization requires a living polymer prepared from the less nucleophilic monomer (first block) and the addition of a more nucleophilic monomer to the active species located on this first block. The general order of nucleophilicities of heterocyclic monomers is as follows Siloxanes orthoesters < acetals < ethers < sulfides < oxazolines < amines. Depending on substitution and ring strain some changes may occur in these positions. 

Preliminary results indicate the possibility of preparing ABA block copolymers containing polyacetal (as a middle block) and polyamine blocks 121). When N-t-butylaziridine or 2-phenyl-2-oxazoline are added to a solution of living polyDXP, further polymerization ensues and the products have considerably higher molecular weights than the original polyDXP. NMR analysis confirmed the block character of the product. 

Litt claimed formation of block copolymers of 2-lauroyl-2-oxazoline and 2-methyl-2-oxazine by sequential polymerization 122). Methyl tosylate was the initiator and the polymerization was terminated by water. The proposed structure of the copolymer is ... 

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