Meso and racemo Additions in Propagation for Radical Polymerization of Dialkyl Fumarates I. Stereoregularity of Poly(dialkyl fumarate)s

Abstract

ABSTRACT:The polymerization temperature dependence of the stereochemical configuration of some poly(dialkyl fumarate)s as poly(substituted methylene) was investigated by the use of 13 C NMR spectroscopy in order to clarify the propagation process in radical polymerization of dialkyl fumarates. The probability of mesa addition (Pm) for polymerization of di-tert-butyl fumarate increased from 0.68 to 0.80, when the polymerization temperature decreased from 120°C to 0°C. On the other hand, it was revealed that Pm for dimethyl fumarate and diisopropyl fumarate decreased by the decreasing polymerization temperature, and that it was almost independent of the temperature for methyl tert-butyl fumarate. From the differences in activation enthalpies and entropies for mesa and racemo additions, the effect of the ester alkyl groups on the propagation manner was discussed.KEY WORDS Dialkyl Fumarate / Radical Polymerization/ Poly(substituted methylene)/ 13 C Nuclear Magnetic Resonance/ Stereoregularity / Activation Enthalpy / Activation Entropy / It has been reported that dialkyl fumarates (DRF) with bulky ester alkyl groups homopolymerize readily to give high molecular weight polymers in a radical mechanism despite of the 1,2-disubstituted ethylene structure, and that the resulting poly(DRF)s consist of a semiflexible poly(substituted methylene) structure. 1 -5 The polymerization reactivity (polymerization rate and molecular weight of the polymer) and the flexibility of poly(DRF)s depend intensively upon the structure (bulkiness) of the ester substituents, indicating that the polymerization of DRF shows unique characteristics different from ordinary vinyl polymerizations. It has been also revealed that stereochemical structure of poly(DRF)s is dependent of the structure of the ester alkyl groups. 6 • 7 The tacticity of poly(DRF)s is dominated by both opening mode of carbon-to-carbon double bond and direction of monomer addition to the propagating polymer radical.As each carbon atom in the mam chain of poly(DRF) as poly(substituted methylene) is pseudo-asymmetric, the stereochemistry based on the methylene unit should be considered as is shown in Figure 1. When Bernoullian probability is applied to the stereochemistry of poly(DRF)s, two parameters, Pm (P,) and P ',,, (P~) are required, which represent the probability of meso (racemo) addition and opening, respectively. However, because the opening of double bond is restricted to trans mode for polymerization of DRF, i.e., P',,, = 1 and P~ = 0, the stereoregularity of poly(DRF) can be determined with solely Pm· 6 • 7 In the previous paper,7 we investigated the Pm values for polymerization of di-tert-butyl fumarate (DtBF), methyl tert-butyl fumarate (MtBF) and dimethyl fumarate (DMF) by the use of 13 C NMR spectroscopy, and confirmed that meso addition was preferable in the propagation ofDRF having a tert-butyl group as is shown in Figure 2. Furthermore, pre-1191

Meso and racemo Additions in Propagation for Radical Polymerization of Dialkyl Fumarates II. Determination of the Absolute Rate Constants

“…1 7 Polymerization was carried out in a sealed glass tube, similarly to the method described in the preceding paper. 16 The measurement of ESR spectra was carried out by the use of a Bruker ESP-300 spectrometer with a variable temperature control. The operating conditions of ESR spectra were as follows; microwave frequency, 9.49 GHz; modulation frequency, lO0kHz; modulation amplitude, 0.1 G; time constant, 655.36 ms.…”

“…In the preceding paper, 16 the differences in free energies of activation for meso and racemo additions (AG!-AG,*) at 60°C were determined, from which Pm values at 60°C were calculated to be 0.73, 0.57 and 0.47 for DtBF, MtBF and DMF, respectively (Table II).…”

Thermal and mechanical properties of random copolymers of diisopropyl fumarate with 1‐adamantyl and bornyl acrylates with high glass transition temperatures

“…35 The probabilities of the fractions of formation of M 1 and M 2 sequences with a repeating length of n (N 1n and N 2n ) are given by eqs 10 and 11, respectively. N 1n 5p 11 n21 p 12 (10) N 2n 5p 22 n21 p 21 (11) where p 11 is defined with the homo and cross propagation rates, R 11 and R 12 , by eq 12.…”

“…The termination rate constants decreased in the order of the isopropyl, cyclohexyl, and tert ‐butyl esters for the DRFs . The rate and fashion of propagation reaction were also influenced by the ester alkyl groups . The comprehensive studies on the radical copolymerization of DRFs were reported .…”

“…[5][6][7][8] The rate and fashion of propagation reaction were also influenced by the ester alkyl groups. [9][10][11][12] The comprehensive studies on the radical copolymerization of DRFs were reported. 13,14 The DRFs readily copolymerized with electron-donating monosubstituted ethylene, such as styrene and vinyl ethers, to yield high-molecular-weight alternating copolymers.…”