Kelen-Tudos method reactivity ratios

A new organotin monomer tributyltin -chloroacrylate (TCA) was synthesized in our laboratory. Detailed studies on homopolymerization and copolymerization were undertaken. Copolymerization was carried out with styrene (ST), methyl methacrylate (MMA) and acrylonitrile (AN). Both homopolymer and copolymers were characterized by IR, IF and C-13 NMR and tin analysis. Reactivity ratios were determined using Kelen-Tudos method. Reactivity ratios were r =0.500 and r = 0.170 for TCA-ST, r = 1.089 and r = 0.261 for TCA-MMA and r =1.880 and r = 0.243 for TCA-AN respectively. Micro-structures of homopolymer and copolymers were studied using C-13 NMR spectroscopy. Data obtained were compared with those of tributyltin methacrylate (TBTMA) and its corresponding copolymers. The results indicate that TCA is more reactive than TBTMA. 

The next step in the protocol answers the question about what is the best method to estimate the reactivity ratios. Historically, because of its simplicity, linearization techniques such as the Fineman-Ross, Kelen-Tudos, and extended Kelen-Tudos methods have been used. Easily performed on a simple calculator, these techniques suffer from inaccuracies due to the linearization of the inherently nonlinear Mayo-Lewis model. Such techniques violate basic assumptions of linear regression and have been repeatedly shown to be invalid [117, 119, 126]. Nonlinear least squares (NLLS) techniques and other more advanced nonlinear techniques such as the error-in-variables-model (EVM) method have been readily available for several decades [119, 120, 126, 127]. 

Random copolymers of 4-vinylphenol with n-alkyl methacrylates were prepared by free radical copolymerisation of4-t-butyldimethylsilyloxystyrene and the corresponding alkyl methacrylates in benzene at 60C using AIBN as initiator. Reactivity ratios were determined by the Kelen-Tudos method. Selective removal of the t-butyldimethylsilyl protective group was effected by tetrabutylammonium fluoride in THE at ambient temperature. The copolymers were characterised by IR spectroscopy. 20 refs. 

Table I lists monomer feed compositions, copolymer compositions and conversions obtained in the copolymerization experiments. The copolymerization diagram of the system (Fig. 4) shows a tendency towards alternation with an azeotropic point at 70 mole % MA. Reactivity ratios for the aFS-MA copolymerization system, determined by the Kelen-Tudos method were r =0.26 and The KT-plot is shown in Figure 5. Average monomer feed compositions were used for this determination whenever the conversion was above 10 wt. percent. Almost identical values of the reactivity ratios were obtained when calculated by the Tidwell-Mortimer method. The reactivity ratio product for this copolymerization system ( MA aFS" 2) indicates a tendency for alternation.

The composition of the copolymer was determined by either NMR analysis at 90 MHz according to the equations derived by Mochel (21) or by infrared. (22) The agreement of these methods was 2% when applied to copolymer taken to 100% conversion. The reactivity ratios were calculated according to the Mayo-Lewis Plot (13,15), the Fineman-Ross Method (14), or by the Kelen-Tudos equation.(16,17,18) The statistical variations recently noted by 0 Driscoll (23), were also considered. 

The reactivity ratios were determined by performing a thermal polymerization at 135°C of several styrene-butylmethacrylate mixtures in which the mole fraction of styrene varied from 0.1 to 0.9 (3). Except for the mixture with a styrene mole fraction of 0.1, all mixtures showed thermal polymerization. When these mixtures had reached a conversion of 5 to 10%, the polymerization was stopped by cooling the mixture rapidly. The polymer monomer mixture was precipitated in methanol and dried in a vacuum oven. The different copolymers were analyzed by elemental analysis. The determination of the carbon and oxygen content in the copolymer gave the amount of styrene in the copolymer. The results are shown in Figure 8.4. By using the method of Kelen-Tudos (4-6), the reactivity ratios were determined at ri = 0.40 0.03 and r2 = 0.86 0.03 (styrene is monomer A). 

Kelen T, Tudos, F. Analysis of the hnear methods for determining copolymerization reactivity ratios. I. A new... 

PRINT Calculation of reactivity ratios by the method of Kelen and Tudos ... 

The experimental values of V- and M-centred triads from [ H] triads were compared with the theoretical values from Harwood s [171] statistical model using copolymerisation reactivity ratios. The reactivity ratios for free-radical solution copolymerisation of V with M were calculated using the Kelen-Tudos (KT) [172] and the nonlinear error in variables (EVM) [173] methods using the RREVM [174] program. Homonuclear H-2D-COSY and 2D-NOESY NMR of the copolymer sample were recorded for determining the interactions between different protons in the copolymer chain. 

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