The emulsion polymerization of 2,3‐dimethylbutadiene‐1,3

Abstract

A study has been carried out on the kinetics of the emulsion polymerization of 2,3‐dimethylbutadiene‐1,3. The kinetic treatment of Smith and Ewart was applied for the direct determination of the absolute propagation rate constant kp. The following expression was obtained: kp = 8.9 × 107 exp {−9000/RT} liter/mole/sec. A previously developed treatment was applied to the determination of the relative and absolute crosslinking rates of 2,3‐dimethylbutadiene‐1,3. The results led to the following expression for the absolute crosslinking rate constant kx: kx = 3.0 × 106 exp {−14400/RT} liter/mole/sec. A comparison of these rate constants was made for the three dienes, viz., butadiene, isoprene, and dimethylbutadiene. The propagation rate constants were found to vary only by a factor of 2–3. However, the crosslinking rates were found to decrease considerably in going from butadiene to isoprene to dimethylbutadiene. This was attributed, mainly, to the decreased side‐vinyl content of the latter two monomers, compared to butadiene, as well as to the steric hindrance imposed by the presence of the methyl group.

Synthesis and cross-linking of polyisoprene latexes

“…Moreover, these data give a value of k p at 60 8C of 2.0 £ 10 2 M 21 s 21 , contrasting with a value of 3.2 £ 10 2 M 21 s 21 inferred from emulsion polymerization wherein it appeared that the system had reached the plateau where n ¼ 1=2; [33], whence kp can be inferred from the polymerization rate. Morton et al [34] inferred values of k p from overall polymerization rates by assuming this limiting value of n ¼ 1=2; but there was no reliable test of this assumption in their treatment. Indeed, their data yield an activation energy of 41 kJ mol 21 , whereas the highest value for an activation energy of propagation deemed fully reliable (i.e., from consistent PLP data obtained by different groups in different laboratories) is 32.5 kJ mol 21 for styrene [30].…”

Surface‐Initiated RAFT Polymerization of 2,3‐Dimethyl‐1,3‐butadiene on Silica Nanoparticles for Matrix‐free Methyl Rubber Nanocomposites

“…Poly(2,3‐dimethyl‐1,3‐butadiene) (PDMB), also known as methyl isoprene or methyl rubber in industry, is an historically significant rubber, which was used in Germany during WWI as a substitution for natural rubber . The early synthesis of the monomer involved a conversion of acetone to pinacol in the presence of aluminum oxide as a catalyst, and then dehydrogenation of pinacol to form the diene . The polymerization of DMB has not been widely studied because the resulting rubber is softer than natural and synthetic rubber .…”

“…The synthesis of PDMB through free‐radical polymerization is commonly used to produce very high molecular weight polymers with broad molecular weight distribution . There are few reports on the controlled radical polymerization of DMB, which could arise from the lack of control due to steric hindrance of this monomer and the unsuitability of the derived rubber for industrial applications such as tires .…”