log r n = log ris - U 2 TTi - V 2.

Size: px

Start display at page:

Download "log r n = log ris - U 2 TTi - V 2."

Allen Dean
5 years ago
Views:

1 P a t t e r n s o f R e a c t i v i t y ( U, V ) P a r a m e t e r s f o r t h e P r e d i c t i o n o f M o n o m e r R e a c t i v i t y R a t i o s a n d T r a n s f e r C o n s t a n t s i n R a d i c a l P o l y m e r i z a t i o n Aubrey D. Jenkins, Jitka Jenkins School of Chemistry, Physics and Environmental Science, University of Sussex, Brighton, Sussex, BN1 9QJ, UK A. Introduction B. Example II-322 C. Transfer Constants II-322 D. Tables of Parameters II-323 Table 1. Monomers II-323 Table 2. Transfer Agents II-326 E. References II-327 A. INTRODUCTION The relation between monomer reactivity ratios and the Alfrey-Price Q-e parameters is explained in the introduction to the tables of monomer reactivity ratios and Q-e values, compiled by Robert Z. Greenley and published in the present volume (1,2). Although very widely used, the Q-e scheme is well known to have serious limitations (3), which have prompted several attempts to improve upon it. One such endeavour was the "Patterns of Reactivity" scheme, first described as long ago as 1959 (4-7), when the Q-e scheme was only about ten years old; despite the indisputably more satisfactory basis of this procedure, it did not achieve popularity but recent revisions have greatly improved both its accessibility and its accuracy (3,8,9). In the Q-e scheme, four parameters (Qi, Q 2, e\, e 2, two for each monomer) are necessary for the prediction of a monomer reactivity ratio (e.g. r\ 2 = &11/&12, where subscript 1 refers to the radical and subscript 2 to the monomer) but the same four parameters also facilitate the prediction of the partner monomer reactivity ratio (?2\ k 22 /k 2 \) because identical Q and e parameters are used to characterise both a given monomer and its derived radical. This device is certainly economical on input data but it introduces an approximation of very doubtful validity. In the "Patterns" scheme (to use the abbreviated title), different parameters are designated for the monomer and its conjugate radical. Hence, while four input parameters are again necessary for the calculation of a single monomer reactivity ratio, eight are required to calculate both r\ 2 and r 2 \. The reward for the greater input of data is a substantial increase in the precision of the result; furthermore, all four parameters for each monomer/radical conjugate pair are experimentally determined from polymerization data, specifically monomer reactivity ratios from Greenley's tabulation, so no arbitrary assignment is involved, as it is with the Q-e scheme. The fundamental equation for the calculation of a reactivity ratio, r\ 2, is given below. log r n = log ris - U 2 TTi - V 2. (Al) Here, the symbol S denotes the monomer styrene, and log ris is the counterpart of Q\ in the Q-e scheme. The counterpart of ei is the polarity parameter TTI; this is usually almost exactly equal to the Hammett a parameter for the substituent(s) present on the oc-carbon atom of the radical derived from monomer 1 but it is best calculated (8) from monomer reactivity ratio data according to Eq. (A2). TT 1 = log[(r 1A )/0.377(n s )] (A2) Here, the symbol A denotes the monomer acrylonitrile. It is truly an astonishing fact that the Hammett a parameter, derived originally from studies of the dissociation of substituted benzoic acids, is equal in value to a simple quantity derived from a knowledge of the monomer reactivity ratios for the reactions of a monomer 1 with (separately) acrylonitrile and styrene. The values of U 2 and V 2, the respective counterparts of the Q-e scheme's e 2 and Q 2, are determined by reference to data for the (separate) copolymerizations of monomer 2 with the members of a Basic Monomer Set. These are five monomers for which reliable data exist in the literature: styrene (S); methyl methacrylate (MM); methyl acrylate

2 (MA); methacrylonitrile (MAN); and acrylonitrile (A). Ideally, monomer reactivity ratios should be known for the copolymerization of the monomer of interest (labelled 2 in this case) with each of these five reference monomers. If the reference monomer is monomer 1 in this context, a plot is made of [log r 12 log ris] against TT\; the slope of the resulting straight line is Ui and the intercept on the ordinate axis is V2, in conformity with Eq. (Al). If data for reactions with all five members of the Basic Monomer Set are not available, use can be made of such data as exists, always provided that styrene and acrylonitrile are among the monomers included. This condition ensures that the data are spread over a wide range of radical polarity, represented by TT\, because styrene has a very low value (zero), while acrylonitrile has one of the highest values known (0.701). In Table 1, each monomer is designated either as Basic or assigned to a category according to the number of members of the Basic Monomer Set for which data have been employed in the determination of its U2 and V 2 ; for category 5, all five Basic monomers were involved, and so on down to category 2, where data for only styrene and acrylonitrile are available. Clearly, the higher the category number, the more reliable the w 2 and V 2 values. The procedure described thus far is known as the Patterns U, V Scheme (3). For Group 2 monomers, there is no need to make a plot because the use of just two data points permits algebraic solutions to be found. In fact, it can be shown (3) that the following relations hold. (A3) Substitution in Eq. (Al) leads to the following relationships (A4, A5), giving the two monomer reactivity ratios for the copolymerization of any two monomers, 1 and 2. (A4) (A5) Application of Eqs. (A3-A5) corresponds to the Patterns A, S Scheme (4), so-called, because data for reaction with only acrylonitrile and styrene are involved. According to the Patterns A,S Scheme, it is possible to calculate the two monomer reactivity ratios for copolymerization of monomers 1 and 2, if each of them has separately been copolymerized with acrylonitrile and styrene. (The two monomer reactivity ratios for copolymerization of acrylonitrile and styrene are also required. These are taken to be: r AS = 0.04, r SA = 0.38 (3).) The TT, w, and v values listed in the table below have been derived as explained above, with the Patterns U,V Scheme being used for the monomers in categories 3-5 and the Patterns A,S Scheme for those in category 2. The r\$ values are mean values from the figures supplied in Greenley's table, making due allowance for the consistency of the data. B. EXAMPLE Suppose one wants to evaluate the monomer reactivity ratios for the copolymerization of 2-chlorobutadiene (CB) and 2-vinylpyridine (VP). To use the Patterns U,V Scheme for this purpose, it is first necessary to consult Greenley's table of monomer reactivity ratios for data characterizing the copolymerizations of each of these monomers with as many members of the Basic Monomer Set as possible. In fact, in both cases, values exist for reactions with styrene, methyl methacrylate, methyl acrylate and acrylonitrile, but not methacrylonitrile. The TT values for the four useful basic monomers are, respectively, 0.000, 0.339, and The relevant monomer reactivity ratios are listed in the table below. MONOMER REACTIVITY RATIOS FOR 2-CHLOROBUTADIENE AND 2-VINYLPYRIDINE AND MEMBERS OF THE BASIC MONOMER SET Monomer reactivity ratio 2-Chlorobutadiene 2-Vinylpyridine r xs r XA r s,x r A,x r MM,x r MA,x X = 2-chlorobutadiene or 2-vinylpyridine. Plots of [log r 12 log ris] against TT\, where 2 = CB or VP, are linear with slopes and intercepts that provide the following u and v values (9). For CB, u = , v = 1.44, and for VP, u = and v = All the data are now available for substitution in Eq. (Al), first for CB = monomer 1 and VP = monomer 2, and secondly with the monomers' roles reversed, to obtain values of r\i and rj\. The results are r n = 4.26 and r 2 \ =0.04. The Patterns A,S Scheme can be applied by simply substituting the appropriate monomer reactivity ratio data in Eqs. (A4) and (A5), giving ri2 = 4.71 and r2i=0.05. The corresponding experimental results are ri2 = 5.19 and 7*21 =0.06, while the Q = e scheme predicts that ri2 = 1.07 and r2i =0.07. C TRANSFERCONSTANTS Transfer constants can be predicted by exactly parallel reasoning (3). It is necessary only to realise that whereas the rate constant for the propagation step of a radical with its own parent monomer appears in the numerator of a monomer reactivity ratio (Vi 2 = &11A12X where both rate

$constants refer to propagation reactions, it figures in the denominator of a transfer constant because (C 2) 1 = kn/kn, where k\2 represents a transfer reaction between the radical derived from a$

3 constants refer to propagation reactions, it figures in the denominator of a transfer constant because (C 2) 1 = kn/kn, where k\2 represents a transfer reaction between the radical derived from a monomer (species 1) and a transfer agent (species 2); the equations for calculating transfer constants are thus easily obtained from the equations above by replacing log r n by -log (C2)1. The only formal difference between the two cases is that, for transfer, there is no symmetrical counterpart of the equations representing reaction of a radical of type 2 with a transfer agent of type 1. Thus, the equivalent of Eq. (Al), for transfer is Eq. (A6), and this enables the Patterns U,V Scheme to be applied to chain transfer. (A6) For use of the Patterns A,S Scheme in transfer, a parallel derivation to that used in copolymerization leads to the following equation, where (C2) s an d (C 2) A are, respectively, the (known) transfer constants for reaction of the same transfer agent (species 2) with radicals derived from styrene and acrylonitrile (species 1). (A7) Since IT A and r A s=0.04, this equation can be reduced to Eq. (A8) for general use. (A8) The transfer constants used here are taken from two tabulations, one due to Eastmond (10) and one in the Polymer Handbook (11). D. TABLES OF PARAMETERS As explained above, each monomer or transfer agent is assigned to a category, designated by Basic or the number 2, 3, 4, or 5, according to the number of members of the Basic Monomer Set with which this reagent has been reacted to obtain data for the evaluation of w, v and (in the case of monomers) TT. Although it must be true that the higher the category, the more reliable the derived parameters, the difference between Categories 2 and 5 is not so great as might appear at first sight. In all cases, two of the basic monomers involved are styrene, S, (the least polar) and acrylonitrile, A, (the most polar), so the role played by other basic monomers is merely to add intermediate points to what should be a straight line joining the data points for S and A; if the data for these two latter monomers are accurate, intermediate points add little or no value beyond confirmation of the slope and intercept. They do contribute valuable weighting when there are some discrepancies in the data, but parameters have not been recorded here in cases where the discrepancies are large. Where either r\$ or r ia was reported as zero, the value 0.05 has been assigned arbitrarily in order to make it possible to calculate an approximate value for the TT parameter but the values of the u and v parameters are not influenced by this device; entries of this type are printed in italics in Table 1. Sometimes both r\s and n A are reported to be zero; when this happens, TT cannot usefully be estimated but u and v can still be determined, if positive values of r$\ and r A i are available. Nomenclature In the tables below, compounds are listed in alphabetical sequence in accordance with the following rules: The primary listing is based on the root name of the compound and the secondary sequence on the name(s) of the substituent(s) or the esterifying moiety. For example, the compounds, p-methyl styrene, N-vinyl carbazole, and ethyl acrylate, will be found listed under Styrene, p-methyl, Carbazole, N-vinyl, and Acrylate, ethyl, respectively. In deciding on the appropriate order of names, all prefixes (alphanumeric, Greek or whatever) and spaces are ignored, and reliance is placed solely on the alphabetical priority of the strictly chemical part of the name. In styrene, p-methyl, for example, the prefix p- plays no part in determining the place of this name in the list; this is governed by the m in methyl. TABLE 1. MONOMERS Monomer Category r ls r 1A r A1 r S i log(ri S ) n u v Acenaphthalene Acetylene, phenyl Aconitate, trimethyl Acrolein Acrolein, methyl Acrylamide Acrylamide, iv-methylol Acrylamide, N-octadecyl Acrylate, benzyl Acrylate, butyl Acrylate, 2-chloroethyl Acrylate, oc-chloro-, methyl O.fe References page II - 327

4 TABLE 1. cont'd Monomer Category r ls r la r Al r S i log(ri S ) n u v Acrylate, a-cyano-, methyl Acrylate, ,4-epoxyhexahydrobenzyl Acrylate, P-ethoxy-, ethyl Acrylate, ethyl Acrylate, methyl B Acrylate, octadecyl Acrylate, octyl Acrylate, 2-nitrobutyl Acrylate, a-phenyl-, methyl Acrylate, di-zinc Acrylonitrile B Acryloyl chloride Allyl acetate AUyI chloride Aniline, N,N-divinyl Benzothiazole, vinylmercapto Butadiene Butadiene-1-carboxylic acid Butadiene- 1-carboxylate, ethyl Butadiene-1,4-dicarboxylic acid Butadiene, 1,4-dicarboxylate-, diethyl Butadiene, 2-chloro Butadiene, 2-fluoro Butadiene, trimethylsilyloxy- Carbazole, TV-vinyl Cinnamonitrile Citraconimide, TV-methyl Crotonaldehyde Crotonate, a-acetyl-, methyl Crotonate, a-carboethoxy-, ethyl Crotonate, a-chloro-, ethyl Crotonate, a-cyano-, ethyl Crotonate, ethyl Crotonate, u-methoxy-, methyl Crotonate, OL-methyl-, methyl Crotonicacid Diallyl phthalate Ethylene Ethylene, tetrachloro Ethylene, trichloro Ethylene, diphenyl Fumarate, diethyl Fumarate, diisopropyl Hexatriene, tetrachloro Imidazole, yv-vinyl Isoprene Isopropenyl isocyanate Isopropenyl methyl ketone Itaconicacid Itaconic anhydride Maleate, diethyl Maleic anhydride Maleimide, N-(2-chlorophenyl) Methacrylamide, /V-phenyl Methacrylate, benzyl Methacrylate, 2-bromoethyl Methacrylate, butyl Methacrylate, isobutyl

5 TABLE 1. cont'd Monomer Category r ls r 1A r A1 r S i log(ri S ) n u v Methacrylate, 2-chloroethyl Methacrylate, ferrocenylmethyl Methacrylate, glycidyl Methacrylate, 2-hydroxyethyl Methacrylate, methyl B Methacrylate, ,5-dimethyladamantyl Methacrylate, ,2,6,6-tetramethyl- 4-piperidinyl- Methacrylate, phenyl Methacrylic acid Methacrylonitrile B Methacryloylacetone Methylenebutyrolactone Naphthalene, 1-vinyl Oct-l-ene,6,6-dimethyl ,8-dioxaspiro(2,5)- Oxazoline, 2,2-isopropenyl Oxazoline, 2,2-isopropenyl ,4-dimethyl- Pentadienoate, rra^-4-ethoxy ,4-,ethyl Phthalimide, N-vinyl Propene, 3,3,3-trichloro Pyridazinone, (2-vinyl)-6-methyl- Pyridazinone, (2-vinyl)-6-methyl- 4,5-dihydro- Pyridine, 2-methyl-5-vinyl Pyridine, 2-vinyl Pyridine, 2-vinyl-5-ethyl Pyridine, 4-vinyl Silane, 3-methacryloxypropyl, trimethoxy- Styrene B Styrene,/7-acetoxy Styrene, 3-tri-rc-butylstannyl Styrene, 2,5-dichloro Styrene, p-chloromethyl Styrene, p-1 -(2-hydroxypropyl)- Styrene, a-methoxy Styrene, a-methyl Styrene, p-methyl Succinimide, N-vinyl Tetrazole, 1-vinyl Tetrazole, 5-phenyl (4 '-vinyl)-phenyl- Toluenesulfonamide, N,N-methyl-vinyl- Triallyl citrate Vinyl acetate Vinyl benzoate Vinylbenzoic acid, p Vinyl benzyl methyl carbinol Vinyl bromide Vinyl isobutyl ether Vinyl butyl sulfide Vinyl isobutyl sulfide Vinyl tert-butyl sulfide Vinyl chloride Vinyl chloroacetate Vinyl dichloroacetate References page

6 TABLE 1. cont'd Monomer Category ri S r 1A r A1 r Si log(ri S ) n u v Vinyl 2-chloroethyl ether CX Vinyl chloromethyl ketone ' Vinyl cymantrene Vinyl dodecyl ether : Vinylene carbonate : Vinyl ethyl ether Ol Vinyl ethyl oxalate Vinyl ethyl sulfide ' Vinyl ethyl sulfoxide ' Vinylferrocene Vinyl hendecanoate Vinylidene chloride < Vinyl isocyanate Vinyl isothiocyanate ! Vinyl methyl ketone < Vinyl phenyl ether Vinyl phenyl sulfide ! Vinyl stearate LL Vinyltriethoxysilane : Vinyl-tris(trimethoxysiloxy) silane Vinyltrimethylsilane : TABLE 2. TRANSFER AGENT Transfer agent Category Cs CA U V Acetaldehyde Acetamide, N,N-dimethyl Acetic acid Acetone Acetonitrile Allyl chloride Aluminium, hydrodiisobutyl Aluminium, triethyl Aluminium, triisobutyl Aniline Aniline, WV-dimethyl Anthracene Benzene Benzene, bromo Benzene, tert-butyl Benzene, chloro Benzene, ethyl /7-Benzoquinone Borane, tributyl Butanone Butyl alcohol sec-butyl alcohol tert-butyl alcohol Butyl mercaptan Butyric acid, 4-hydroxy-y-lactone Cadmium, dibutyl Carbonic acid, cyclic ethylene ester Carbon tetrabromide, See methane, tetrabromo- Carbon tetrachloride, See methane, tetrachloro- Chloroform Copper(II) chloride Cumene Cyclohexane

7 TABLE 2. cont'd Transfer agent Category Cs CA U V Dimethyl sulfoxide Diphenylamine-T Ethane, 1,2-dichloro Ethane, 1,1,2,2-tetrachloro Ether, dodecyl vinyl Ethyl acetate Formamide, WV-dimethyl oc-d-glucoside, methyl, 6-deoxy-6-mercaptooc-D-Glucoside, methyl-, di-o-benzyla-d-glucoside, methyl-, ,3,4,6-tetra-O-acetyla-D-Glucoside, methyl-, (p-toluene sulfonyl)- a-d-glucoside, methyl-, O-triphenylmethyl- P-D-Glucoside, methyl-, deoxy-6-dipropylamino- Glycerol Heptanol, dodecafluoro Indium, triethyl Iron(III) chloride Isobutyl alcohol Isobutyronitrile Lead, tetraethyl Mercury, diethyl Methane, dichloro Methane, tetrabromo Methane, tetrachloro Methane, nitro Methanol Octadiene, 2,6-dimethyl Oxime, acrolein Oxime, crotonaldehyde Oxime, ethyl isopropenyl ketone Oxime, methacrolein Oxime, methylacrolein Oxime, methyl isopropenyl ketone Oxime, methyl vinyl ketone Pentanol, octafluoro Silane, tetraethyl Stibine, tributyl Tin, tetrabutyl Toluene Triethylamine Tripropylamine Zinc, diethyl E. REFERENCES 1. R. Z. Greenley, "Polymer Handbook", this volume, p R. Z. Greenley, "Polymer Handbook", this volume, p A. D. Jenkins, J. Polymer ScL, 34, 3495 (1996). 4. C. H. Bamford, A. D. Jenkins, R. Johnston, Transactions. Farad. Soc, 55, 418 (1959). 5. C. H. Bamford, A. D. Jenkins, J. Polymer ScL, 53,149 (1961). 6. C. H. Bamford, A. D. Jenkins, Transactions. Farad. Soc, 58, 530 (1962). 7. A. D. Jenkins, Eur. Polymer J., 1, 177 (1965). 8. A. D. Jenkins, Macromol. Chem. Phys. Rapid Commun., 17, 275 (1996). 9. A. D. Jenkins, J. Jenkins, Macromol. Chem. Phys., Macromol. Symp., Ill, 159 (1996). 10. G. C. Eastmond, Comprehensive Chemical Kinetics, (C. H. Bamford, C. F. H. Tipper (Eds.)), 14A, 105 (1976). 11. A. Ueda, S. Nagai, "Polymer Handbook", this volume, p. 97.

Isomerism CH 4 C 2 H 6 C 3 H 8 C 4 H 10 C 5 H 12. Constitutional isomers...

Isomerism CH 4 C 2 H 6 C 3 H 8 C 4 H 10 C 5 H 12. Constitutional isomers... Isomerism 4 2 6 3 8 4 10 5 12 onstitutional isomers... 3 8 Positional isomers... Functional isomers... ow many constitutional isomers are there for the formula 4 8? arbon atoms are often classified as