Poly(ethylene glycol)-block-poly(N-vinylformamide) Copolymers Synthesized by the RAFT Methodology
Poly(ethylene glycol)-block-poly(N-vinylformamide) Copolymers Synthesized by the RAFT Methodology
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DOI：
10.1021/ma025670z
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发表时间：
2003-03
期刊：
影响因子：
5.5
通讯作者：
Lianjun Shi;Andy M. Chapman;E. Beckman
中科院分区：
文献类型：
--
作者：
Lianjun Shi;Andy M. Chapman;E. Beckman
Block copolymers where one block is poly (ethylene glycol)(PEG) are of interest in diverse applications ranging from commodity surfactants to biocompatible scaffolds for tissue engineering. PEG has many interesting physicochemical properties such as hydrophilicity1 and solubility in both water and common organic solvents. Its biological properties include a lack of toxicity, antigenicity, and immunogenicity. 2-4 As such, investigation of new PEG-based block copolymers is continuing in both academia and industry. Poly (N-vinylformamide)(PNVF) is a novel watersoluble polymer that, 5 because of previous monomer purification problems, has not received wide attention until recently. PNVF is not only a water-soluble polymer but also as an important precursor for preparing poly-(vinylamine). To date, PNVF and its derivatives have been used in water treatment, 6 papermaking, and radiation cure coating. 7, 8 Little published work exists regarding block copolymers containing NVF. Traditionally, block copolymers are made by anionic, 9 cationic, 10 and group-transfer polymerization methods; 11 however, these polymerization methods can be successfully carried out only under controlled conditions (such as low temperature, inert atmosphere, or carefully purified monomers) and only for a limited number of monomers. NVF is not directly suitable for anionic and group transfer polymerization, while only oligomer is obtained via cationic polymerization. 12 Over the previous decade several types of living (controlled) free radical polymerization have been developed, enhancing our ability to easily generate block copolymers through sequential monomer addition. The most three common types of living radical polymerization systems are (1) stable free radical polymerization (SFRP) using nitroxides such as 2, 2, 6, 6-tetramethyyl-1-piperdinyloxynitroxide, 13 (2) atom transfer radical polymerization (ATRP) using a transition metal complex, or (3) reversible addition-fragmentation chain transfer polymerization (RAFT) using dithioesters as chain transfer agents (RAFT agent). 14, 15 The latter has proven to be a versatile method for controlled radical polymerization of a variety of monomers including vinyl acetate. The mechanism involves the chain transfer of active species such as the radicals from decomposition of the initiator and propagating polymer radicals to the RAFT agent, forming an unreactive adduct radical, followed by fast fragmentation to a polymeric RAFT agent and a new radical. The radical then continues polymerization. The equilibrium is established by subsequent chain transfer-fragmentation steps between the propagating radicals and polymeric RAFT agents and continues until all monomer is consumed, resulting in controlled growth of chains. The RAFT method is a very convenient tool for preparation of block copolymers. The sequential polymerization of two monomers has given a number of copolymers such as poly (styrene-b-methyl methacrylate) 16 and poly (sodium 4-styrenesulfonate)-b-poly (sodium 4-vinylbenzoate). 17 In the present paper, we describe the synthesis and characterization of a new PEG macro-RAFT agent containing a xanthate end group and its application in the synthesis of PEG-block-PNVF copolymer. We focused on the use of the RAFT method after our attempts to employ ATRP methodology with NVF were unsuccessful.
