Macromolecules
ARTICLE
Typical Copolymerization Procedure. Monomer I (1.5 g, 4.31
mmol) along with required amount of B3 core (II or IIb or III) and 2 mol
% of pyridinium camphorsulfonate (PCS) was taken in a test tube
shaped polymerization vessel. The mixture was degassed for 10 min and
maintained at a temperature of 110 °C under continuous N2 purge, to
ensure homogeneous mixing of catalyst and monomers. The polymer-
ization was then carried out at 150 °C under N2 for 1 h with constant
stirring. Subsequently, using a Kugelr€ohr apparatus, the polymerization
was continued for an additional period of 45 min at 150 °C under reduced
pressure (2 Torr), with continuous mixing of the melt by rotation. The
resultant polymer was dissolved in 2 mL of THF, the acid-catalyst was
neutralized with solid NaHCO3 and then the solution was filtered. The
filtrate was concentrated under reduced pressure to a 1 mL of viscous
solution and precipitated in 10 mL methanol. The polymer was purified
once more by dissolution in 1 mL of THF and reprecipitation into 10 mL
of methanol.
Prog. Polym. Sci. 2004, 29, 183. (e) Peleshankoa, S.; Tsukruk, V. V. Prog.
Polym. Sci. 2008, 33, 523.
(2) (a) Sunder, A.; Hanselmann, R.; Frey, H.; M€ulhaupt, R. Macro-
molecules 1999, 32, 4240. (b) M€ock, A.; Burgath, A.; Hanselmann, R.;
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Macromolecules 2000, 33, 3212.
(3) Bernal, D. P.; Bedrossian, L.; Collins, K.; Fossum, E. Macro-
molecules 2003, 36, 333.
(4) (a) Yan, D.; Zhou, Z. Macromolecules 1999, 32, 819. (b) Zhou,
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(5) Bharathi, P.; Moore, J. S. J. Am. Chem. Soc. 1997, 119, 3391.
(6) (a) Yokozawa, T.; Yokoyama, A. Chem. Rev. 2009, 109, 5595.
(b) Ohta, Y.; Fujii, S.; Yokoyama, A.; Furuyama, T.; Uchiyama, M.;
Yokozawa, T. Angew. Chem., Int. Ed. 2009, 48, 5942. (c) Ohta, Y.;
Kamijyo, Y.; Fujii, S.; Yokoyama, A.; Yokozawa, T. Macromolecules 2011,
44, 5112.
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39, 1615.
(8) Jayakannan, M.; Ramakrishnan, S. Chem. Commun. 2000,
19, 1967.
Polymer 3a (Poly-3a) (Scheme 1) was prepared similarly using
monomer IV and the required amount of core III.
Typical AzideÀYne Click Reaction (Poly-3b). A mixture of the
Poly-3a (200 mg, 0.034 mmol; with respect to propergyl group) and
coumarin azide (22 mg, 0.102 mmol) were taken in 5 mL of THF. To the
reaction mixture, 30 μL aqueous sodium ascorbate (2 mg, 0.01 mmol)
(9) Behera, G. C.; Ramakrishnan., S. J. Polym. Sci., Chem. Ed. 2004,
42, 102.
(10) Gittins, P. J.; Alston, J.; Ge, Y.; Twyman, L. J. Macromolecules
2004, 37, 7428. Gittins, P. J.; Twyman, L. J. J. Am. Chem. Soc. 2005,
127, 1646.
and CuSO4 5H2O (1.27 mg, 0.005 mmol) was added under N2 atmo-
3
sphere. N2 purging was continued for another 10 min to remove dissolved
oxygen from the reaction mixture. The content was heated to 50 °C for 3
days. After completion, the polymer solution was concentrated under
reduced pressure to a viscous solution and precipitated in DMSO; the
polymer was further purified twice by dissolution in THF and pre-
cipitated into DMSO to yield the polymer 3b.
(11) Roy, R. K.; Ramakrishnan, S. J. Polym. Sci., Chem. Ed. 2011,
49, 1735.
(12) Behera, G. C.; Ramakrishnan., S. Macromolecules 2004, 37, 9814.
(13) The effect of generation on the compactness of dendrimers and,
therefore, on the extent to which GPC would underestimate Mn has
been well-established. See: Hawker, C. J.; Malmstrom, E. E.; Frank,
C. W.; Kampf, J. P. J. Am. Chem. Soc. 1997, 119, 9903.
(14) The Mn and PDI values are of purified samples and hence may
be affected by the loss of some of oligomers during reprecipitation
process. To ensure uniformity, all the three copolymers were purified by
reprecipitation under identical conditions using the same quantities of
solvent and nonsolvent. See Supporting Information for experimental
details.
Typical ThiolÀEne Click Reaction (Poly 3c). A mixture of the
Poly-3b (35 mg, 0.11 mmol) and napthalene thiol (130 mg, 0.33 mmol)
were taken in 5 mL of toluene. To the reaction mixture, the photo-
initiator 2,2-dimethoxy 2-phenyl acetophenone (1.12 mg, 0.004 mmol),
was added. The content was irradiated with UV light for 8 h. The
polymer solution was concentrated under reduced pressure to a viscous
solution and precipitated in methanol; the polymer was further purified
twice by dissolution in chloroform and reprecipitation into petroleum
ether to yield the polymer 3c.
1
(15) (a) ) The H-NMR spectra of both the parent methoxy and
butoxy cores (II and IIb), however, exhibited only a single methoxy
proton peak corresponding to all the three methoxy groups; this could
be due to the rapid switching that occurs in the small core molecules,
while this dynamics be inhibited (or considerably slowed down) when
bulky substituents, such as in the case of the polymer, are present.
(16) Kaur, N.; Singh, N.; Cairns, D.; Callan, J. F. Org. Lett. 2009,
11, 2229.
’ ASSOCIATED CONTENT
S
Supporting Information. Detailed experimental schemes
b
and procedures, kinetic plots comparing the relative reactivities
of the two cores, NMR spectral variation during the polymeri-
zation and the corresponding kinetic plots, and fluorescence
spectra. This material is available free of charge via the Internet at
(17) Chae, J. Arch. Pharm. Res. 2008, 31, 305.
(18) (a) Serin, J. M.; Brousmiche, D. W.; Frꢀechet, J. M. J. Chem.
Commun. 2002, 2605. (b) Serin, J. M.; Brousmiche, D. W.; Frꢀechet,
J. M. J. J. Am. Chem. Soc. 2002, 124, 11848. (c) Weil, T.; Reuther, E.;
M€ullen, K. Angew. Chem., Int. Ed. 2002, 41, 1900. (d) Devadoss, C.;
Bharathi, P.; Moore, J. S. J. Am. Chem. Soc. 1996, 118, 9635. (e) Balzani,
V.; Capagna, S.; Denti, G.; Juris, A.; Serroni, S.; Venturi, M. Acc. Chem.
Res. 1998, 31, 26. (f) Gilat, S. L.; Adronov, A.; Frechet, J. M. J. Angew.
Chem. 1999, 111, 1519. Angew. Chem., Int. Ed. Engl. 1999, 38, 1422.
(g) Nantalaksakul, A.; Reddy, D. R.; Bardeen, C. J.; Thayumanavan, S.
Photosynthesis Research 2006, 87, 133.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: raman@ipc.iisc.ernet.in.
’ ACKNOWLEDGMENT
(19) The presence of vibrational fine-structure in the case when the
coumarin is clicked to the core of the HBP may be due to effective
isolation of the fluorophore that precludes interaction with other
coumarin units; which evidently is not the case of the model chromo-
phore. A similar observation of fine-structure was also made in another
study where the coumarin azide was clicked on to a conjugated polymer.
Saptarshi and Ramakrishnan, unpublished work.
S.R. would like to thank the Department of Atomic Energy for
the ORI-Award for the period 2006À2011.
’ REFERENCES
(1) (a) Voit, B. I.; Lederer, A. Chem. Rev. 2009, 109, 5924. (b) Wilms,
D.; Stiriba, S.-E.; Frey, H. Acc. Chem. Res. 2010, 43, 129. (c) Kricheldorf,
H. R. Macromol. Rapid Commun. 2007, 28, 1839. (d) Gao, C.; Yan, D.
(20) Similar observations of incomplete FRET were reported also
in the case of star polymer carrying several donors on the periphery
8405
dx.doi.org/10.1021/ma201817a |Macromolecules 2011, 44, 8398–8406