Synthesis And Characterization Of Amphiphilic Comb-shaped Graft Copolymer With Fluorosiloxane Side Chains

The amphiphilic copolymers with polyacrylic acid (PAA) chains have broad potential applications in the field of stable dispersion of organic pigments. If this kind of amphiphilic copolymers contains polysiloxane chains, it is expected to be the multi-functional organic pigment dispersants. However, the molecular weight and molecular weight distribution of amphiphilic copolymers is the key for its applications. How to use the controlled /"living"polymerization methods to synthesize amphiphilic copolymers with controlled molecular composition and structure has been a focus topic.Because of the carboxyl group, acrylic acid (AA) cannot be directly polymerized by the methods of living anionic polymerization, group transfer polymerization (GTP), and atom transfer radical polymerization (ATRP) to obtain PAA or copolymers with other monomers. However, the block copolymers containing PAA with controlled structures could be obtained via controlled /"living"polymerization of tert-butyl acrylate (tBA) and followed by hydrolysis of polymers. The reversible addition- fragmentation chain transfer (RAFT) radical polymerization need mild polymerization conditions and has potential industrial applications. Therefore, the RAFT radical polymerizations of tBA and styrene (St), as well as tBA and macromonomer containing fluorosiloxane, were carried out in this paper. And the main results were shown as follows:(1) p-Vinyl phenyl-terminated fluorosiloxane macromonomer (FS-MM) was prepared with controlled structure.In this paper, a two-step procedure was took to prepare p-vinyl phenyl-terminated fluorosiloxane macromonomer:①(p-Vinylphenyl)dimethylchlorosilane was synthesized by the reaction between the Grignard reagent of p-chlorostyrene and dichlorodimethylsilane.②The anionic ring-opening polymerization of 1,3,5- tris[(3,3,3-trifluoropropyl)methyl]cyclotrisiloxane (F3) was carried out in tetrahydrofuran (THF) by using n-butyllithium (n-BuLi) as the initiator, and then (p-vinylphenyl)dimethylchlorosilane was introduced into the reactor by means of a syringe. The obtained macromonomer has controlled molecular weight and molecular weight distribution (DPI = 1.07). The molecular structure of FS-MM was also verified by 1H NMR measurement.(2) Controlled polymerization of tBA with high conversion was achieved via RAFT radical polymerization in ethyl acetate. In this paper, the RAFT radical polymerizations of tBA were carried out in ethyl acetate at 70℃using AIBN as the initiator and 1-phenylethyl phenyldithioacetate (PEPDTA) as the RAFT reagent. The GPC results showed that there was a linear relationship between the number average molecular weight of poly(tert-butyl acrylate) (P(tBA)) and the conversion rate. The polydispersity index (PDI) of P(tBA) were less than 1.11 with the yields more than 93%, which indicating the controlled /"living"polymerization mediated by PEPDTA.(3) Block copolymers of tBA and St was synthesized in ethyl acetate via RAFT radical copolymerization.Block copolymerizations of tBA and St were carried out in ethyl acetate at 70℃using AIBN as the initiator and PEPDTA as the RAFT reagent. The results showed that poor controlled structures of block copolymers were obtained when tBA was polymerized firstly and St polymerized thereafter. There are side reactions such as radical-radical termination or homopolymerization of St during the block copolymerization. However, narrow molecular weight distributions (PDI<1.2) block copolymers of polystyrene (PS) and P(tBA) could be successfully synthesized via a sequential monomer addition of St and tBA using AIBN as the initiator and PEPDTA as the RAFT reagent. That is, the sequence of monomer addition was important to obtain good result. The reason may be the low reactivity between the active propagating radicals and the dormant polymeric thiocarbonylthio compounds.(4) RAFT radical copolymerization of tBA and FS-MM in the ethyl acetate was achieved in this paper.The RAFT radical copolymerizations of tBA and FS-MM were carried out in ethyl acetate at 70℃using AIBN as the initiator and PEPDTA as the RAFT reagent. The results showed that high conversions of macromonomer were not obtained during the RAFT radical homopolymerizations. However, all macromonomer was closed to completely polymerized during the process of copolymerization with tBA, and copolymers of FS-MM and tBA (P(tBA)-co-P(St-g-PMTFPS) )was obtained. The structures of copolymers were also conformed by 1H-NMR and GPC measurements.