A Novel Method To Prepare ABC Star Copolymers With Hetero-arms And Characterization Of Copolymers

The designation and synthesis of polymers is one of the most important tasks for modern polymer science. Recently, a various of non-linear polymers such as star copolymer, star copolymers with block arms or with hetero-arms, graft copolymers, dendrimeric or hyperbranched copolymer were prepared by means of development of synthetic technology. It aroused widely interests for both theoretical and applied workers due to their special architecture. ABC star copolymer is one type of typical and represented copolymers among non-linear copolymers. It possessed very important significance to prepare the ABC star copolymers using the existing synthetic technology.Polystyrene (PS), polyethylene oxide (PEO) and polyisoprene (PI) are three kinds of polymers with sharp different polarity, it is difficult to prepared their corresponding star triblock copolymers by using the existing synthetic methods. However, this star triblock copolymer is successfully prepared by introducing the succinimidyl carbonate with high reactivity onto the ends of living chain of polymers and using lysine as core molecule. The essential work completed by us shows as follows:1. The α-methoxy-ω-hydroxyl polyethylene oxide (mPEO-OH), α-butyl-ω-hydroxyl polystyrene (PS-OH) and a-butyl-oo-hydroxyl polyisoprene (PI-OH) with narrow molecular weight distribution are prepared respectively by anionic polymerization. Using lysine with two amine and one carboxyl groups as core molecule, the hydroxyls of mPEO and PS are translated to succnimidyl carbonates and coupled with e- and α-amino groups of lysine, the mPEO-PS-Lys-COOH with two arms is obtained. After transformation of the hydroxyl of PI to amine and coupling with carboxyl of the mPEO-PS-Lys-COOH, the final product mPEO-PS-PI is prepared. In the process of preparation, the intermediates and objectproduct are characterized by GPC, NMR, IR and UV in details. It is proved that this route suggested by us to prepare the ABC star triblock copolymer is successful.2. In the above-mentioned route for preparation of mPEO-PS-PI, the mPEO is reacted with lysine first because of the lysine is difficult to dissolve in organic solvents except the water. However, for the most of polymers, especially the polymers prepared by living polymerization, the water-soluble polymers are seldom found, so the first-hydrophilic arm method is restricted. Therefore the first-hydrophobic arm method is suggested. It was found that when the lysine was esterified, the ethyl lysinate can dissolve in organic solvents, so it was used as core molecule and coupled with PS, PI and mPEO in sequence. The hydroxyl end of PS is translated to succinimidyl carbonate first, and then coupled with e-amino group of ethyl lysinate, to obtain the PS-Lys-COOC2H5; the hydroxyl end of PI is also transformed to succinimidyl carbonate and coupled with α-amino of lysine after hydrolysis of PS-Lys-COOC2H5, then the hydroxyl end of mPEO was changed into amine group and reacted with carboxyl group of purified PSPI-Lys-COOH, the final ABC star triblock copolymer is obtained.3. In the mixed solvents (selective solvent/good co-solvent), the micellization of final product is investigated. The global micelle with different sizes could be found with variation of used selective solvents by DLS and TEM. In the system of N, N-dimethylformamide and chloroform with low chloroform content, the micelle composed of PI as core, PS and PEO as shell is formed, the particle size is in the range of 200-300 nm; as the contents of chloroform in the system is increased, size of micelle is also increased but the distribution is widened until the micelle disappeared. In the system using n-heptane as selective solvent to constitute a system with chloroform, the micelle composed of PS and PEO as core, and PI as shell is formed, the size of the particle is in the range of 20-30 nm. When the contents of chloroform is reached to a definite value, the aggregation of micelle is started and the system is turbid, it means the micelle is instable in this time, and when the contents of chloroform is increased further, the micelle disappeared slowly. In the system of chloroform with acetonitrile as selective solvent, the micelle composed of PS and PI as core and PEO as shell is formed, the particle size is about 120 nm. The stable micelle can only be observed in the low concentration of sample because the acetonitrile is not good solvent for PEO.