Simple and green strategy for the synthesis of miktoarm star copolymers by multi-mode polymerizations

Many reactions are carried out with the help of solar energy by itself in ecosystem. Therefore, chemists are inspired from this energy and apply these photochemical strategies on different chemical synthesis. Photoinitiated polymerization is an important research area for polymer chemistry due to the necessity of low energy and temperature. To obtain polymers at lower temperatures than the traditional polymerization with rapid rates leads to the suppression of side reactions, so that polymerization reaction can be controlled easily. Photopolymerization is most importantly applied to heat sensitive monomers and biochemical systems. Ring opening polymerization (ROP) is a technique used for the polymerization of cyclic compounds such as unsaturated cyclic ethers, cyclic esters (lactones), cyclic amides (lactams) and cyclic amines (imines). Poly(butylene oxide), poly(ethylene oxide), poly(ethylene imine) and poly(caprolactam) are some examples of polymers frequently used in industry synthesized by ROP. ROP possesses some similarities with addition polymerization including addition of monomers to the polymer chains by one by and reaction takes places only between active chains and monomers. In spite of the fact that the similarities, there are also some differences between ROP and addition polymerization. For instance, there must be double-bounded compounds in addition polymerization yet in ROP there is no obligation for this kind of monomers. Besides, in addition polymerization, high molecular weighted polymers are obtained at the beginning of polymerization process while in some of the ROPs they are obtained at the last stages of polymerization. Free radical polymerization is an important field of polymer chemistry whose mechanism was discovered by Flory in 1937. He suggested that the free radical polymerization contains three steps namely initiation, propagation and termination. A great number of physical or chemical factors can initiate the polymerization. At propagation step, chain grows via radicals. Finally, the polymerization terminates either disproportination or coupling. In this thesis, a simple and green strategy for the synthesis of miktoarm star copolymers by the combination of ROP and free radical polymerization is described. Using a multifunctional initiator, bearing primary hydroxyl and tertiary amine functionalities, vinyl and lactone monomers were sequentially polymerized under mild conditions. In the first step, phosphazene base (P2-t-Bu) catalyzed ROP of ε-caprolactone is employed. Secondly, thus obtained poly(ε-caprolactone) with amine end groups was used as co-initiator for the polymerization of methyl methacrylate by utilizing conventional Type II photoinitiators such as camphoroquione, benzophenone and thioxanthone. The structures, molecular weight characteristics and thermal properties of the polymers are analyzed by NMR, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) measurements, respectively.