Polymerization of styrene initiated by a novel initiator sodium formaldehyde sulfoxylate and sodium lauryl sulfate

Abstract

Sodium formaldehyde sulfoxylate (SFS) along with sodium lauryl sulfate (SLS) was used as a novel initiator for aqueous polymerization of styrene (St) at 80°C. The rather stable emulsion lattices and a uniform size distribution of lattice particles were obtained. The polymerization behaviors and the qualities of the product were determined. The course of polymerization is similar to the traditional emulsion polymerization including three reaction periods: formation of the particle, a constant number of particles and a first-order reaction. The rate of polymerization almost does not depend upon the St concentration and depends on a 0.7-power on the concentrations of SFS and SLS. The aqueous solutions consisting of SFS, SLS and St at 80°C exhibited the free radical spectrum of electron paramagnetic resonance. The conductivity measurement showed that SLS does not exhibit the critical micelle concentration in the aqueous solution containing SFS. The polymerization is assumed to be a soap-free emulsion one. The polystyrene obtained showed a small Z-direction thermal expansion coefficient (431 μm m −1 (°C) −1), a very small specific refractive index increment (d n/d c=0.0664 ml g −1), a smaller second virial constant ( A 2=1.41×10 −4 mol-cm 3 g −2), and a high glass transition temperature ( T g=106°C) as well as a high film formation temperature (MFT = 120°C).