Table 2 Intraparticle rate constants and equilibrium constants
Styrene
Butyl MA
2-Ethylhexyl MA
1023 K/
dm3 mol21 103 kL/s21
1023 K/
dm3 mol21 103 kL/s21
1023 K/
dm3 mol21
PNP ester
103 kL/s21
TMA-quaternized
Acetate
Hexanoate
Octanoate
1.3
5.7
4.7
2.0
2.1
12.7
9.3
5.9
5.3
2.3
11.8
46
7.4
4.7
4.9
2.3
21
70
TBA-quaternized
Acetate
Hexanoate
Octanoate
11.9
5.8
5.7
3.1
15.1
69
9.5
5.8
5.3
4.1
25
74
9.0
5.8
5.1
5.0
31
88
the binding constant. The much larger increases in the binding
constants from polystyrene–TMA to polystyrene–TBA than
with the corresponding methacrylate latexes is due to the TBA
increasing the aliphatic character of aromatic latexes more than
of aliphatic latexes.
O2N
O2N
O2C(CH2)4Me + 2 OH –
O–
+
–O2C(CH2)4Me + H2O
Parallel synthesis has enabled rapid evaluation of 32 latex
catalysts and selection of the most informative ones for analysis
of intraparticle rate constants and binding constants. This
diversity approach can be used to identify active polymer
catalysts for many other important chemical reactions.
This research was supported by the U.S. Army Research
Office.
Scheme 1
to 16.5 for the 2-ethylhexyl methacrylate–TBA latex (18), and
all alkyl methacrylate–TMA latexes were more active than the
polystyrene–TMA latex. There was a sizable increase of
activity on increase of the alkyl chain length from hexyl (9) to
octyl (10) but only smaller increases between other pairs of C2n-
alkyl methacrylate latexes (1, 9–12). The branched 2-ethylhexyl
methacrylate latex (5) was more active than the linear octyl
methacrylate latex (10) having the same number of carbon
atoms. Fourteen more TMA-quaternized latexes (not shown)
containing mixtures of two methacrylate monomers and VBC
gave rate constants between those of the latexes in Table 1
containing the same individual monomers. Finally Table 1
indicates that particles containing TBA sites (16–18) are more
active than those containing TMA sites (1,5,15).
Notes and References
† E-mail: wtford@osuunx.ucc.okstate.edu
1 W. K. Fife, Trends Polym. Sci., 1995, 3, 214; J. H. Fendler and E. H.
Fendler, Catalysis in Micellar and Macromolecular Systems, Academic,
New York, 1975.
2 W. T. Ford and M. Tomoi, Adv. Polym. Sci., 1984, 55, 49; M. Tomoi and
W. T. Ford, in Synthesis and Separations Using Functional Polymers,
ed. D. C. Sherrington and P. Hodge, Wiley, Chichester, 1988, pp.
181–207.
3 C. A. Bunton and G. Savelli, Adv. Phys. Org. Chem., 1986, 22, 213.
4 J. J. Lee and W. T. Ford, J. Am. Chem. Soc., 1994, 116, 3753; W. T. Ford
and H. Yu, Langmuir, 1993, 9, 1999.
5 R. A. Moss, K. W. Alwis and G. O. Bizzigotti, J. Am. Chem. Soc., 1983,
105, 681; R. A. Moss, A. T. Kotchevar, B. D. Park and P. Scrimin,
Langmuir, 1996, 12, 2200.
6 Y.-C. Yang, J. A. Baker and J. R. Ward, Chem. Rev., 1992, 92, 1729.
7 J. Walker and F. Hoskins, US Army Natick RDEC, personal
communication.
Activities of the styrene, butyl methacrylate and 2-ethylhexyl
methacrylate-based latexes were measured at 5–6 different
particle concentrations. Pseudo-first order intraparticle rate
constants (kL) for the hydrolysis of PNP-acetate, hexanoate, and
octanoate and equilibrium binding constants (K) of the PNP
ester to quaternary ammonium ion sites in the latex were
calculated from double reciprocal plots of duplicate measure-
ments of each rate constant using eqn. (1), where kw is the rate
8 X.-D. Xiang, X. Sun, G. Briceno, Y. Lou, K.-A. Wang, H. Chang, W. G.
Wallace-Freedman, S.-W. Chen and P. G. Schultz, Science, 1995, 268,
1738; G. Briceno, H. Chang, X. Sun, P. G. Schultz and X.-D. Xiang,
Science, 1995, 270, 273; X.-D. Sun, C. Gao, J. Wang and X.-D. Xiang,
Appl. Phys. Lett., 1997, 70, 3353.
9 F. M. Menger, A. V. Eliseev and V. A. Migulin, J. Org. Chem., 1995,
60, 6666; K. D. Shimizu, B. M. Cole, C. A. Krueger, K. W. Kuntz,
M. L. Snapper and A. Hoveyda, Angew. Chem., Int. Ed. Engl., 1997, 36,
1704.
1/(kobs–kw)=1/(kL–kw)K[N+] + 1/(kL–kw)
(1)
constant in the absence of latex.10 (A ‘binding constant’ of the
nonionic PNP ester to the ion exchange sites is a misnomer.
‘Partition coefficient’ would be better, but the binding constant
formalism10 is easy to apply.) The results are reported in Table
2.
The major differences in the activities are due to the binding
constants: the longer the aliphatic chain of the PNP ester, and
the more lipophilic the quaternary ammonium ion, the greater
10 F. M. Menger and C. E. Portnoy, J. Am. Chem. Soc., 1967, 89, 4698.
Received in Columbia, MO, USA, 9th January 1998; 8/00383A
1152
Chem. Commun., 1998