Copper-Mediated Atom Transfer Radical Polymerisation (ATRP) of Acrylates in Protic Solution.

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1 Copper-Mediated Atom Transfer Radical Polymerisation (ATRP) of Acrylates in Protic Solution. Laura. Pilon *, Steven P. Armes *, Paul Findlay, Steven Rannard. * School of Chemistry, Physics and Environmental Science, University of Sussex, Falmer, Brighton, East Sussex. B1 9QJ. Molecular Science Unit, Unilever Research, Port Sunlight, Quarry Road East, Bebington, Wirral. CH63 3JW.

2 ATRP activation R X + Cu(I)X R Wang, J-S.; Matyjaszewski, K. J. Am. Chem. Soc. 1995, 117, 5614 deactivation R' propagation + Cu(II)X 2 termination Kato, M.; Kamigaito, M.; Sawamoto, M.; Higashimura, T. Macromolecules 1995, 28, 1721 Usually copper, but other metals can be used. R R R H + R Usually in organic solvent at elevated temperatures. Low M w /M n (~ ) possible. Synthesis of block copolymers possible by macro-initiator route or by sequential monomer addition (in some cases).

3 ATRP of Methacrylates in Protic Solvents Water: - non-toxic, cheap - rapid polymerisation of hydrophilic monomers - often poor living character. Alcohols: - relatively cheap (and IPA has low toxicity) - faster polymerisation than non-polar solvents, but slower than water - efficient block copolymer formation in many cases. Ashford, E.J.; aldi, V.; Dell, R.; Billingham,.C.; Armes, S.P. Chem. Commun. 1999, 1285 Zeng, F.; Shen, Y.; Zhu, S.; Pelton, R. J. Polym. Sci.: A: Polym. Chem. 2, 38, 3281 Robinson, K.L.; Khan, M.A.; de Paz Báñez. M.V.; Wang, X.S.; Armes, S.P. Macromolecules 21, 34, 3155

4 ATRP of Acrylates - Literature Examples. Mainly MA and t BuA, bulk conditions, copper with multidentate amine ligands or bipyridine. High conversions (> 9%) and low polydispersities (M w /M n = ). ATRP of HEA (only literature example of a hydrophilic acrylate) shows reasonable control in bulk (M w /M n = 1.2), but is less controlled in water (M w /M n = 1.34). ATRP of glycidyl acrylate (reactive functional acrylate) in bulk goes to high conversion (>95 %) with relatively low polydispersity (M w /M n = 1.25). Matyjaszewski, K. J.M.S.-Pure Appl. Chem. 1997, A34, 1785: Xia, J.; Matyjaszewski, K. Macromolecules 1997, 3, 7697: Xia, J.; Gaynor, S.G.; Matyjaszewski, K. Macromolecules 1998, 31, 5958: Coca, S. Jasieczek, C.B.; Beers, K.L.; Matyjaszewski, K. J. Polym. Sci.: A: Polym. Chem. 1998, 36, 1417: Matyjaszewski, K.; Coca, S.; Jasieczek, C.B. Macromol. Chem. Phys. 1997, 198, 411.

5 ATRP of Methyl Acrylate - Variation of Ligand Ligand Time Conversion M n(gpc) M n(mr) M n(theory) M w /M n PMDETA ~ 72 h 89 % HMTETA 29 h 98 % Bipy 192 h 96 % MPMA 144 h 95 % PPMA ~ 48 h 8 % Me 6 -TRE ~ 24 h 9 % Me 6 -TRP ~ 24 h 87 % HMTETA gives highest conversion in shortest time with relatively low M w /M n. [MA]:[CuCl]:[L]:[MBP] = 5:1:2 (bipy, MPMA) or 1 (other L):1 [MA] = 5 w/v%, 75 o C, solvent = ethanol. MPMA PPMA

6 ATRP of Methyl Acrylate - Comparison of Initiators. ln([m]/[m]) MBP EBIB MBP EBIB Time/ h Br Br Mn Mn/MBP 1.9 Mn/EBIB 1.8 Mw/Mn /MBP 1.7 Mw/Mn /EBIB Conversion/ % Mw/Mn [MA]:[CuX]:[HMTETA]:[I] = 5:1:1:1, CuCl/MBP, CuBr/EBIB. Faster polymerisation (and lower M w /M n ) with bromide chain ends, but increased termination at high conversions.

7 ln([m]/[m]) Comparison of CuCl/CuBr with EBIB as Initiator for MA polymerisation. CuCl, ln([m]/[m]) 4 CuBr, ln([m]/[m]) 3 CuCl, conversion 2 CuBr, conversion Time/ h Conversion/ % Mn CuCl, Mn CuBr, Mn CuCl, Mw/Mn CuBr, Mw/Mn Conversion/ % Polymerisation very much slower with CuCl than CuBr, due to halide exchange between the catalyst and polymer chain end and the stronger C-Cl than C-Br bond. [MA]:[CuX]:[HMTETA]:[EBIB] = 5:1:1:1, [MA] = 5 w/v% in EtH at 75 o C Mw/Mn

8 ATRP of Methyl Acrylate - Blocking Efficiency. M n = 4,6 M w /M n = 1.5 M n = 2,4 M w /M n = 1.3 [MA]:[CuCl]:[HMTETA]: [MBP] = 3+3:1:1:1. [MA] = 5 w/v% in EtH at 75 o C Retention Volume (ml) Clear shift in MWD to higher M n. Increase in M w /M n caused by tailing to low molecular weight. Use of EBIB initiator should reduce M w /M n.

9 ATRP of Functional Acrylates H H 2-hydroxyethyl acrylate (HEA) 2-hydroxypropyl acrylate (HPA) 2-diethylaminoethyl acrylate (DEAEA) 2-dimethylaminoethyl acrylate (DMAEA) Monomer X Ligand Initiator Solvent Temp/ o C Conv/% Time M n,th M n,mr M n,gpc M w /M n HEA Cl HMTETA MBP MeH h HPA Cl HMTETA MBP EtH h DEAEA Cl HMTETA MBP IPA h DEAEA Br Me4-Cyclam EBIB EtH h DMAEA Br Me4-Cyclam EBIB EtH s 735 GPC performed with THF as eluent (phea and pdmaea insoluble in THF). Conversion determined by MR. M n by MR only possible where initiator groups visible. IPA used as solvent for DEAEA to minimise transesterification. [M]:[CuX]:[L]:[I] - 5:1:1:1, [M] = 5 w/v%. Poorer control than for MA. Polymerisation of DEAEA very slow, possibly due to coordination of monomer/polymer to catalyst.

10 ATRP of HPA - Kinetics Conversion/ % [HPA] = 5 w/v% in EtH at 75 o C, [HPA]:[CuCl]:[HMTETA]: [MBP] = 5:1:1: Time/ h Curvature of semilog plot 2 1 ln([m]/[m]) Mn Conversion/ % Mw/Mn Lack of control in initial stages of reaction Linear increase in M n with conversion, but below target M n. Poor blocking efficiency.

11 Aqueous Solution Properties of HPA. Cloud Point/ o C H Degree of Polymerisation [phpa] = 1 %, ph 6.5. [phema] =.5 %. H HEMA and HPA are isomeric (both C 6 H 1 3 ). Both show inverse temperature solubility behaviour. Cloud point determined by turbidimetry and depends on molecular weight of polymer.

12 Aqueous Solution Properties of PEG 45 -HPA 4 Block Copolymer. 5 nm Turbidimetry of PEG 45 -HPA 4 Cloud point occurs at ~ 53 o C T/ o C Cloud point of block copolymer occurs at higher temperature than that of homopolymer. PEG apparently not sufficiently hydrophilic at cloud point temperature to support HPA-core micelles. Block copolymer does not form unimers in aqueous solution, even at 5 o C, while HPA homopolymer dissolves molecularly (by dynamic light scattering). Hydrogen bonding complexes are suspected. PEG M n, th = 7, M n, GPC = 6,6, M w /M n = 1.28 M n, MR = 6,9 HPA Br H

13 Aqueous Solution Properties of GMA-HPA H GMA HPA H n Block Copolymers. m Br H Both polymers form aggregates even at 5 o C (by dynamic light scattering). Reasons for this under investigation. Synthesis of copolymers not possible by a one-pot method (bipy not a good ligand for HPA polymerisation and HMTETA not a good ligand for GMA polymerisation). M n, theory DP GMA MR DP HPA MR M n, GPC (DP GMA, DP HPA ) M w /M n Cloud point/ o C d agg / nm Polydispersity GMA 4 -HPA 4 11, ,1 (15, 28) PEG 45 -GMA 3 -HPA 5 13, ,4 (24, 24) Light scattering performed at 45 o C on.5 % solution of polymer, turbidimetry performed on.5 % solution of polymer, GPC performed using THF as eluent on benzoate protected polymer.

14 Conclusions. ATRP of MA and some functional acrylates possible in protic solvents. Resulting polymers have relatively low polydispersities in most cases (M w /M n < 1.4). Temperature dependent solubility of phpa analogous to that of phema. Synthesis of block copolymers possible, the aqueous solution properties of which are under investigation. Acknowledgements. EPSRC and Unilever are thanked for an Industrial CASE studentship. Jon Weaver and Kay Robinson for phema cloud point results. University of Sussex polymer group.