Poly triblock copolymers synthesis

Poly(lactide)-Poly(ethylene oxide)-Poly(lactide) Triblock Copolymers Synthesis and Thermal Properties... 

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... 

Poly(lactic acid) (PLA) has also been added to poly(SA) via melt polycondensation to produce the triblock copolymers poly(lactic acid-Wock-sebacic acid-Wock-lactic acid) (P(LA-block-SA-block-LA)) by Slivniak and Domb (2002). The PLA (d-, l-, and dl-) was incorporated by acetylation and addition to the PSA synthesis. They showed the formation of stable stereocomplexed particles with increased melting points and reduced solubility, and studied the degradation and drug release characteristics of the same (Slivniak and Domb, 2002). The stereocomplexes self-assemble as a consequence of the chirality in the PLA portions of the chains (Slivniak and Domb, 2002). 

An example for the synthesis of poly(2,6-dimethyl-l,4-phenylene oxide) - aromatic poly(ether-sulfone) - poly(2,6-dimethyl-1,4-pheny-lene oxide) ABA triblock copolymer is presented in Scheme 6. Quantitative etherification of the two polymer chain ends has been accomplished under mild reaction conditions detailed elsewhere(11). Figure 4 presents the 200 MHz Ir-NMR spectra of the co-(2,6-dimethyl-phenol) poly(2,6-dimethyl-l,4-phenylene oxide), of the 01, w-di(chloroally) aromatic polyether sulfone and of the obtained ABA triblock copolymers as convincing evidence for the quantitative reaction of the parent pol3rmers chain ends. Additional evidence for the very clean synthetic procedure comes from the gel permeation chromatograms of the two starting oligomers and of the obtained ABA triblock copolymer presented in Figure 5. 

Liu L, Jiang M. Synthesis of novel triblock copolymers containing hydrogen-bond interaction groups via chemical modification of hydrogenated poly(styrene-h/ock-butadiene-h/ock-styrene). Macromolecules 1995 28 8702-8704. 

The synthesis of triblock copolymers B-A-B can be achieved by means of a bifunctional initiator a bifunctional a,u-dicarbanionic poly-A precursor is formed, and is used in a second step as the initiator for the polymerization of monomer B, with the same conditions to be observed as above. A number of efficient bifunctional initiators are commonly used, in polar solvent media. Recent work, carried out in several laboratories -- t aimed at the preparation of efficient bifunc-tional Initiators soluble in non polar solvents. Such systems... 

Au NPs have been synthesized in polymeric micelles composed of amphiphilic block copolymers. Poly(styrene)-block-poly(2-vinylpyridine) in toluene has been used as nanocompartments loaded with a defined amount of HAuCl4 and reduced with anhydrous hydrazine. The metal ions can be reduced in such a way that exactly one Au NP is formed in each micelle, where each particle is of equal size between 1 and 15 nm [113]. In another example, the addition of HAuCfi to the triblock copolymer (PS-b-P2VP-b-PEO) (polystyrene-block-poly-2-vinyl pyridine-block-polyethylene oxide) permits the synthesis of Au N Ps using two different routes, such as the reduction of AuC14 by electron irradiation during observation or by addition of an excess of aqueous NaBH4 solution [114]. 

Z. Fodor and R. Faust, Polyisobutylene-based thermoplastic elastomers. IV. Synthesis of poly (styrene-block-isobutylene-block-styr-ene) triblock copolymers using n-butyl chloride as solvent, J. Macromol. Sci.-Chem., 33(3) 305-324, March 1996. 

Y. Kwon, R. Faust, C.X. Chen, and E.L. Thomas, Synthesis and characterization of poly(isobutylene-b-pivalolactone) diblock and poly (pi va lolac tone-b-isobu tylene-b-pivalolactone) triblock copolymers, Macromolecules, 35(9) 3348-3357, April 2002. 

S.J. Taylor, R.F. Storey, J.G. Kopchick, and K.A. Mauritz, Poly[(styr-ene-co-p-methyIstyrene)-b-isobutylene-% textitb-(styrene-co-p-meth-ylstyrene)] triblock copolymers. 1. synthesis and characterization, Polymer, 45(14) 4719-4730, June 2004. 

Mesoporous alumina sphere was synthesized under the catalyst of hydrochloride or ammonia in organic solvents. In a typical synthesis, 1.1 g [poly(ethylene oxide)-6-poly(propylene oxide)-6-poly(ethylene oxide) triblock copolymer (Aldrich, average molecular weight 5800, EO20PO70EO20)] was dissovled in 11.0 g (0.268 mol) acetonitrile and 1.10 g (61.1 mmol) water containing 0.1 mmol HC1 or 5 mmol NH3, the solution of 3.0 g (12.2 mmol) aluminum tri-sec-butoxide dissovled in 10 g (0.24 mol) acetonitrile was slowly dropped into with stirring. After stirring for 6 h, the product was filtered and washed with acetonitrile and dried at room temperature in air. The obtained products were calcined in air at 550 °C for 4 h to remove the templates. 

The synthesis of poly(MMA-fr-IB-fr-MMA) triblock copolymers has also been reported using the site-transformation method, where a,site-transformation technique provides a useful alternative for the synthesis of block copolymers consisting of two monomers that are polymerized only by two different mechanisms. In this method, the propagating active center is transformed to a different kind of active center and a second monomer is subsequently polymerized by a mechanism different from the preceding one. The key process in this method is the precocious control of a or co-end functionality, capable of initiating the second monomer. Recently a novel site-transformation reaction, the quantitative metalation of DPE-capped PIB carrying methoxy or olefin functional groups, has been reported [90]. This method has been successfully employed in the synthesis of poly(IB-fr-fBMA) diblock and poly (MMA-fc-IB-fo-MMA) triblock copolymers [91]. 

Due to the lack of vinyl monomers giving rise to crystalline segment by cationic polymerization, amorphous/crystalline block copolymers have not been prepared by living cationic sequential block copolymerization. Although site-transformation has been utilized extensively for the synthesis of block copolymers, only a few PIB/crystalline block copolymers such as poly(L-lactide-fc-IB-fc-L-lactide) [92], poly(IB-fr- -caprolactone( -CL)) [93] diblock and poly( -CL-fr-IB-fr- -CL) [94] triblock copolymers with relatively short PIB block segment (Mn< 10,000 g/mol) were reported. This is most likely due to difficulties in quantitative end-functionalization of high molecular weight PIB. 

We recently investigated a different route for the synthesis of poly(IB-h-f-CL) diblock and poly( -CL-fo-IB-fo- -CL) triblock copolymers by site-transformation of living cationic polymerization of IB to cationic ring-opening polymerization of -CL via the activated monomer mechanism [95]. 

Janus micelles are non-centrosymmetric, surface-compartmentalized nanoparticles, in which a cross-linked core is surrounded by two different corona hemispheres. Their intrinsic amphiphilicity leads to the collapse of one hemisphere in a selective solvent, followed by self-assembly into higher ordered superstructures. Recently, the synthesis of such structures was achieved by crosslinking of the center block of ABC triblock copolymers in the bulk state, using a morphology where the B block forms spheres between lamellae of the A and C blocks [95, 96]. In solution, Janus micelles with polystyrene (PS) and poly(methyl methacrylate) (PMMA) half-coronas around a crosslinked polybutadiene (PB) core aggregate to larger entities with a sharp size distribution, which can be considered as supermicelles (Fig. 20). They coexist with single Janus micelles (unimers) both in THF solution and on silicon and water surfaces [95, 97]. 

In their patents, Sheppared et al. [18,19] proposed the synthesis of a series of di- or triblock copolymers from polyazomacroinitiators including various types of sequences polystyrene, polybutadiene, polyamide, poly(butyl sebacate), polyether, poly(butyl azelate) or polycarbonate. They observed that these... 

Figure 7.55. Reaction scheme for the room-temperature synthesis of a CBABC pentablock copolymer, and GPC traces of a,z-dibromo-terminated polystyrene (A, dotted line), poly(fBA-fe-styrene-fe-fBA) (BAB triblock copolymer macroinitiator, dashed line), and poly(MMA-fe-fBA-fe-styrene-fe-f BA-fe-MMA) (CBABC, solid line). The GPC data shows evidence of a successful polymerization route - low polydis-persity index (PDI), and good control over the number-average molecular weight (Mn). Reproduced with permission from Ramakrishnan, A. Dhamodharan, R. Macromolecules 2003, 36, 1039. Copyright 2003 American Chemical Society.

One great breakthrough in mesoporous material synthesis was the discovery of SBA-15.[113] The typical synthesis of SBA-15 is carried out by using poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock-copolymer as... 

Guan JJ et al (2004) Biodegradable poly(ether ester urethane)urea elastomers based on poly(ether ester) triblock copolymers and putrescine synthesis, characterization and cytocompatibility. Biomaterials 25(l) 85-96... 

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