Semicontinuous heterophase copolymerization of styrene and acrylonitrile

Abstract

The synthesis of styrene‐acrylonitrile copolymers by semicontinuous heterophase polymerization is reported here. The effect of feed composition at a fixed addition rate of monomer mixture on kinetics, particle size, polymer content, and molar masses, was studied. This process permits the synthesis of nanolatexes containing narrow size‐distribution particles with number‐average diameter (Dn) of about 18 nm, polymer content as high as 23 wt %, and copolymer‐to‐surfactant weight ratios between 23 and 25, depending on monomer feeding rate, which are larger than those reported for microemulsion copolymerization of several comonomers. Copolymers with homogeneous composition similar to the feeding monomers composition were obtained thorough the reaction, which is difficult to achieve by batch polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Swelling Behavior of Poly(N-isopropylacrylamide) Nanogels with Narrow Size Distribution Made by Semi-continuous Inverse Heterophase Polymerization

“…Previously we reported similar results, i.e., smaller particle size and narrower particle size distributions as R a decreased for the SIHP of another water-soluble monomer (acrylamide) (32) and for the semi-continuous heterophase polymerization (SHP) of several water-insoluble monomers (35)(36)(37). The reason is that in this type of processes, the main controlling parameter is the monomer addition rate that controls particle size and particle size distribution.…”

“…From the literature, it is known that the polymers synthesized by BIMP have large molar masses (>10 6 Dalton) (28) whereas those made by SIHP exhibit smaller molar masses (∼ 10 5 Dalton) that increase as R a augments and tend to the BIMP limit (32). Similar results were reported for several alkyl methacrylates synthesized by SHP compared to those obtain by oil/water microemulsion polymerization (33,(35)(36)(37). Detailed explanations given in the just referred papers, indicate that due to the smaller particle size, the probability of a radical produced by chain transfer to monomer is small due to the smaller particle size and to the low monomer concentration in the particle, specially under highly monomer starved conditions (where monomer concentration within the particles is extremely low), which makes chain transfer to monomer improbable.…”

“…Moreover, since the amount of surfactant employed in these two processes was the same, then P/S of the SIHP at both addition rates are larger than the one obtained by BIMP (Table 1). Similar results, i.e., smaller particle size, narrower distributions and larger polymer production per amount of employed surfactant (P/S), than those reported for microemulsion polymerization, have been reported for the SIHP of acrylamide (32) and for the SHP of several water-insoluble alkyl methacrylates (33,(35)(36)(37). TEM was used to determine the size (D z0 ), size distribution (D w /D n ) and the shape of the dry nanogels.…”

“…Since no monomer is initially present in SIHP or SHP, particles are continuously nucleated by reacting with free radicals in the continuous phase upon addition of monomer. When the addition rate is slow enough to achieve highly monomer starved conditions, most of the monomer is engaged in nucleation of particles by reacting with the radicals in the continuous phase, which are stabilized by surfactant molecules from the inverse micelles, as pointed out elsewhere (32,33,(35)(36)(37). As the addition rate is increased, monomer molecules can react in the continuous phase but also they can diffuse into the existing particles, promoting particle growth and the broadening of the particle size distribution.…”

“…Detailed explanations given in the just referred papers, indicate that due to the smaller particle size, the probability of a radical produced by chain transfer to monomer is small due to the smaller particle size and to the low monomer concentration in the particle, specially under highly monomer starved conditions (where monomer concentration within the particles is extremely low), which makes chain transfer to monomer improbable. Hence, the main reason of the lower molar masses and because the low polymerization rate per particle (32,33,(35)(36)(37), is that another free radical can enter into the particle before chain transfer to monomer can occur to terminate the reaction. Here, however, the molar masses of the PNIPA made by SIHP and BIMP are not reported here, since the PNIPA nanogels were crosslinked.…”