Studies on atom transfer radical polymerization of acrylates and styrenes with controlled polymeric block structures

Abstract

Atom transfer radical polymerization (ATRP) was applied to homo and block copolymerization of vinyl monomers methacrylates, acrylates, and styrene with iron (FeCl2.4H2O) as the transition metal in most cases. As complexing ligand either a commercially available ligand (triphenyl phosphine) (PPh3) or synthetic aliphatic amines were used. As initiators, methyl 2-bromopropionate, ethyl 2-bromoisobutyrate, α,α-dichloroacetophenone, and poly(ethylene oxide) macroinitiator were employed.

Block copolymerization of n-butyl methacrylate-b-tert-butyl acrylate (BMA-b-tBA) was performed by two-step ATRP method. The results showed that, for well-defined copolymers, a low conversion macroinitiator (conversion 35%) is preferable to a high conversion one.

Four tetradentate nitrogen ligands, viz. dichloro{[N,N'-diphenyl-N,N'-di(quinoline-2-methyl)]-1,2-ethylene diamine} (1), {[N,N'-dioctyl-N,N'-di(quinoline-2-methyl)]-1,2-ethylene diamine} (2), {[N,N'-dibenzyl-N,N'-di(quinoline-2-methyl)]-1,2-ethylene diamine} (3), and (1R,2R)-(-)-N,N'-di(quinoline-2-methyl)diiminocyclohexane (4), were synthesised at the University of Helsinki, and used as complexing ligands in iron-mediated polymerization of methyl methacrylate. High to moderate conversions (87%, 43%) were obtained in relatively short times (90 min for 1 and 30 min for 2), which indicates an efficient catalyst system. When the bulkiness of the substituents was significantly increased, as in ligand 3, polymerization rate was decreased and control was lost. Ligand 4 was less efficient than the other ligands, probably because the ethylene bridge was replaced by cyclohexane bridge.

Poly(ethylene oxide) monochloro macroinitiators and poly(ethylene oxide) telechelic macroinitiators (Cl-PEO-Cl) were prepared from monohydroxy functional and dihydroxy functional poly(ethylene oxide) in the presence of 2-chloro propionyl chloride and applied to the polymerization of styrene (S) or methyl methacrylate (MMA). The polymerization of styrene was carried out in bulk at 140 °C and catalysed by copper(I) chloride (CuCl) in the presence of 2,2' -bipyridine (bipy) ligand (CuCl/ bipy), but the polymerization of MMA was carried out in the presence of (FeCl2.4H2O)/ (PPh3) catalytic system. With most of the macroinitiators, the living nature of the polymerizations led to block copolymers with narrow molecular weight distribution (Mw/Mn < 1.3). Adjustment of the content of the PEO blocks (>90% by mass) allowed the preparation of water-soluble/water-dispersible block copolymers. Small amounts of the PEO-PS-based block copolymers were applied to modify the paper surface. Chain length of the hydrophilic block and/or the amount of hydrophobic block was found to play an important role in modification of the paper surface. It was also found that water-dispersible triblock copolymer containing 10 wt-% PS makes the paper surface highly hydrophobic (contact angle >115° ) and retards water absorption on both light weight coated base paper (LWC) and fine base paper (FP). The effect on oil absorption was less significant.