Polymerisation of Sodium 4-Styrenesulfonate via Atom Transfer Radical Polymerisation Peter D. Iddon, Kay L. Robinson and Steven P. Armes ACS Philadelphia Meeting August 2004 Email: P.Iddon@shef.ac.uk
Introduction Atom Transfer Radical Polymerisation [ATRP] is a versatile living radical polymerisation technique independently developed by Matyjaszewski s group 1 and Sawamoto and co-workers 2 in 1995. ATRP is tolerant of functional groups and requires less stringent reaction conditions than many alternative living polymerisation techniques. k act R X M n Y / L 2 R X M n1 Y / L 2 k deact k monomer k t termination 1. Wang, J.S.; Matyjaszewski, K. J. Am. Chem. Soc. 1995, 117, 5614. 2. Kato, M.; Kamigaito, M.; Sawamoto, M.; Higashimura, T. Macromolecules 1995, 28, 1721.
ATRP in Protic Media Recent work in our laboratory suggests that aqueous ATRP is very rapid but has less than ideal living character. 1 For many hydrophilic methacrylates, better living character is obtained in methanol, which leads to slower, more controlled polymerisation. 2 Unfortunately, for many ionic monomers such as sodium 4- styrenesulfonate [NaStS], water is essential for solution polymerisation. Thus, there is considerable scope for optimising ATRP syntheses of ionic monomers in mixed aqueous solution. 3 1. Wang, X.S.; Jackson, R.A.; Armes, S.P. Macromolecules 2000, 33, 255. 2. Weaver, J.V.M.; et al. Macromolecules 2004, 37, 2395. 3. Li, Y.; et al. Macromolecules 2003, 36, 8268.
Poly(NaStS): Applications NaStS is a commercially important anionic monomer. Poly(NaStS) and its copolymers are used in a wide range of applications: Proton exchange membranes for fuel cells. Multilayer polyelectrolyte membranes for controlled release of pharmaceutical compounds. Stabilisers for emulsion polymerisation and inorganic dispersions. Ion exchange resins. Dopants/steric stabilisers for conducting polymers. Medical treatments for potassium or lithium poisoning. Additives for use in the oil industry. S 3 - Na NaStS Commercial synthesis of low polydispersity poly(nasts) is commonly achieved through sulfonation of polystyrene.
Routes to Poly(NaStS) Near-monodisperse poly(nasts)-based copolymers were first synthesised by selective sulfonation of poly(2-vinyl pyridine-block-styrene) prepared by anionic polymerisation. 1 The first direct polymerisation of NaStS was by nitroxidemediated polymerisation [NMP] at 125 ºC. 2 The use of NMP to prepare diblock copolymers of NaStS and sodium 4-vinylbenzoate [NaVBA] was first reported by our group. 3 Reversible addition-fragmentation chain transfer [RAFT] polymerisation has also been used to prepare NaStS homopolymer. 4 1. Varoqui, R.; et al. Macromolecules 1979, 12, 831. 2. Keoshkerian, B.; et al. Macromolecules 1995, 28, 6381. 3. Gabaston, L. I.; et al. Polymer 1999, 40, 4505. 4. Chiefari, J.; et al. Macromolecules 1998, 31, 5559.
ATRP of NaStS Aqueous ATRP of NaStS was first reported by Matyjaszewski s group. 1 Pure water gave poor control; a 1:1 water/pyridine mixture was required to give a polydispersity of 1.26 at a conversion of 70 %. Choi and Kim described the homopolymerisation of NaStS, and reported polydispersities of around 1.2 in water or water/methanol mixtures. 2 More recently, Masci et al. polymerised a related monomer, potassium 3-sulfopropyl methacrylate, in a 1:1 water/dmf mixture and obtained polydispersities as low as 1.2. 3 1. Tsarevsy, N.V.; et al. Abstr. Pap. Am. Chem. Soc. 2002, 224, 466. 2. Choi, C.K.; Kim, Y.B. Polym. Bull. 2003, 49, 433. 3. Masci, G.; et al. Macromolecules 2004, 37, 4464.
ur Homopolymer Synthesis ur preliminary experiments indicated poor results with Cu(I)Br catalyst in combination with these two initiators: N Br In view of this, our preferred ATRP initiator is sodium 4- bromomethylbenzoate [NaBMB], with Cu(I)Cl catalyst. or 8 Br Br n Cu(I)X, bipy water/methanol mixtures 20 ºC 18-24 h n X Na - NaBMB S 3 - Na NaStS Na - S - 3 Na Poly(NaStS)
Water: Methanol [v/v %] 1 : 0 3 : 1 3 : 1 3 : 1 3 : 1 1 : 1 1 : 1 1 : 1 1 : 1 1 : 1 Homopolymer Syntheses Iddon, P.D.; Robinson, K.L.; Armes, S.P. Polymer 2004, 45, 759. Reaction Time [hours] 21 18 19 26 19 18 18 20 18 19 Conv. [%] 94 94 98 98 98 78 81 80 92 90 Target M n a 8,900 3,700 6,700 9,300 18,400 3,100 5,500 7,600 13,100 16,900 Aqueous GPC Data b Exp. M n 13,700 5,200 9,300 12,500 23,800 4,000 6,900 11,000 16,800 24,000 M w /M n 2.03 c 1.38 1.48 1.63 1.66 1.30 1.26 1.30 1.55 1.47 Relative molar ratios of NaBMB:Cu(I)Cl:bpy were 1:1:2; all reactions were carried out at 20 ºC. a. Target M n was calculated as follows: [Initiator M n (Target D p Monomer M n )] Conversion. b. Calibrated using near-monodisperse poly(nasts) standards. c. This weight GPC peak and had polydispersity. a lower molecular weight shoulder. 1:1 water/methanol gives the best control over molecular
Homopolymerisation Kinetics Conversion Versus Time Plots Semi-Logarithmic Plots 100 3.5 Conversion by 1H NMR [%] 90 80 70 60 50 40 30 20 10 All reactions at 20 ºC 100 % water 3:1 water/methanol 1:1 water/methanol Ln([M]0/[M]) by 1 H NMR 3.0 2.5 2.0 1.5 1.0 0.5 0 0 1 2 3 4 5 6 7 8 Time [hours] 0.0 0 1 2 3 4 5 6 7 8 Time [hours] All plots show pronounced curvature; least deviation from linearity is for the 1:1 water/methanol synthesis.
Evolution of M n and M w /M n 16 6 14 Mn by GPC (10 3 ) 12 10 8 6 4 5 4 3 2 Mw / Mn by GPC & 100 % water & 3:1 water/methanol & 1:1 water/methanol 2 0 1 0 10 20 30 40 50 60 70 80 90 100 Conversion [%] M n is almost independent of conversion in 100 % water, but becomes more linear as the methanol concentration is increased.
Homopolymer Aqueous GPC Data GPC Data for NaStS Homopolymers Higher M n Lower M n Chain-Extended Homopolymers 1:1 water/methanol Chain-extended homopolymer Precursor homopolymer RI Response 100 % water 3:1 water/methanol 1:1 water/methanol RI Response 3:1 water/methanol Chain-extended homopolymer 100 % water Chain-extended homopolymer Precursor homopolymer Precursor homopolymer 9 10 11 12 13 14 15 16 17 Elution Time [minutes] 8 9 10 11 12 13 14 15 16 17 Elution Time [minutes] Unimodal GPC traces observed in all cases. Most efficient chain extension occurs in 1:1 water/methanol.
Copolymer Syntheses Iddon, P.D.; Robinson, K.L.; Armes, S.P. Polymer 2004, 45, 759. NaStS-based diblock copolymers using PE macro-initiators. n = 22, 45, 113 n PE Macro-initiator Br Target Composition Conversion Target Aqueous GPC Data [%] M n a PE 22 -b-nasts 40 PE 22 -Br: Diblock: 84 7,700 PE 45 -b-nasts 40 PE 45 -Br : Diblock: 86 8,800 PE 113 -b-nasts 30 PE 113 -Br : Diblock: 46 5,200 Exp. M n M w /M n 1,000 b < 1.1 b 11,100 c 1.21 c 2,000 b < 1.1 b 19,100 c 1.31 c 5,000 b < 1.1 b 12,000 c 1.24 c Conditions: 3:1 (v/v %) water/methanol at 20 ºC for 24 h. a. Target M n calculated as follows: [Initiator M n (Target D p Monomer M n )] Conversion. b. Calibrated using near-monodisperse PE standards. c. Calibrated monomer using near-monodisperse conversion. poly(nasts) standards. Polydispersities are improved, although at the expense of
Copolymer Syntheses Iddon, P.D.; Robinson, K.L.; Armes, S.P. Polymer 2004, 45, 759. Target Composition Conversion Target Aqueous GPC Data b [%] M a n Exp. M n M w /M n NaStS -b-navba 45 30 NaStS 45 Homo: 92 8,800 16,700 1.71 Diblock: 90 13,200 23,600 1.66 Conditions: 3:1 (v/v %) water/methanol at 20 ºC for 24 h. a. Target M n calculated as follows: [Initiator X M n (Target D p Monomer M n )] Conversion. b. Calibrated using near-monodisperse n m poly(nasts) standards. 70 S - 3 Na Na Na NaStS-b-NaVBA Diblock Copolymer ph responsive diblock copolymer. 1. Matsuoka, H.; et al. Macromolecules 2003, 36, 5321. Surface Tension versus ph 1 Surface Tension [mn/m] 65 60 2 4 6 8 10 ph
ph Responsive Behaviour X A g f g 46 d e c d b c a - Na b i c, d, e, g & h 13 C NMR spectra (D 2 /H 2 ) for: h h i S 3 - Na f A NaStS 46 homopolymer. B NaStS 80 -NaVBA 54 diblock copolymer at ph 10. C NaStS 80 -NaVBA 54 diblock copolymer at ph 2. X a k m n C 2 - Na S3 - Na i - Na 180 170 160 150 140 130 120 δ / ppm B C i i b k
Conclusions Homopolymerisation of NaStS by aqueous ATRP is poorly controlled. Addition of methanol slows the rate of reaction, improves control and lowers the final polydispersity. Self-blocking experiments in methanol/water mixtures indicate a reasonable degree of control, with little homopolymer contamination. PE macro-initiators can be used to prepare well-defined diblock copolymers with relatively low polydispersities. Diblock copolymers can be prepared, but the presence of water precludes the use of more hydrophobic monomers with this protocol.
Comparison with Literature Under the conditions examined, the ATRP of NaStS becomes more controlled with increasing methanol concentration. However, the living character of this polymerisation is less than ideal and poorer than that reported for other monomers. 1,2 ur results are not as good as those reported by Choi & Kim. 3 However, we were unable to compare kinetics, chain-extension efficiencies, or diblock copolymer formation, as these were not included by the Korean group. 1. Save, M.; et al. Macromolecules 2002, 35, 1152. 2. Lobb E.J.; et al. J. Am. Chem. Soc. 2001, 123, 7913. 3. Choi, C.K.; Kim, Y.B. Polym. Bull. 2003, 49, 433.
ph-tunable DEA core Applications PE-[QDMA/DMA]-DEA ph 2 NaH ph > 7.5 20 ºC 27 nm PE-NaStS - - - - - - 20 ºC - - - - - - - - 35-50 nm cationic QDMA inner-shell PE stabilising corona ur PE 113 -NaStS 34 diblock copolymer was successfully used as an ionic cross-linker to form shell cross-linked micelles from a cationic ABC triblock copolymer. 1 The shell cross-linked micelles had good tolerance to added salt. This ionic cross-linking strategy produces no small molecule byproducts, and uses a non-toxic, non-volatile polymeric reagent. A diblock copolymer architecture was demonstrated to be essential, as NaStS homopolymer was not an effective cross-linker. 1. Weaver, J.V.M.; et al. Angewandte Chem., Int. Ed. 2004, 43, 1389.
Acknowledgements Professor Steven Armes (PhD supervisor). EPSRC (PhD studentship). Avecia (CASE award). Dr. Stuart Richards (Avecia). Dr. S. Liu, Dr. K. Robinson, Dr. F. Malet, and Dr. J. Weaver (PE-Br initiators). Dr. J. Weaver (DLS measurements). Dr. Tony Avent ( 13 C NMR data). The rest of the Armes Research Group. Email: P.Iddon@shef.ac.uk