Effect of Chain Transfer to Polymer in Conventional and Living Emulsion Polymerization Process

Hidetaka Tobita

doi:10.3390/pr6020014

Abstract

Emulsion polymerization process provides a unique polymerization locus that has a confined tiny space with a higher polymer concentration, compared with the corresponding bulk polymerization, especially for the ab initio emulsion polymerization. Assuming the ideal polymerization kinetics and a constant polymer/monomer ratio, the effect of such a unique reaction environment is explored for both conventional and living free-radical polymerization (FRP), which involves chain transfer to the polymer, forming polymers with long-chain branches. Monte Carlo simulation is applied to investigate detailed branched polymer architecture, including the mean-square radius of gyration of each polymer molecule, <s2>0. The conventional FRP shows a very broad molecular weight distribution (MWD), with the high molecular weight region conforming to the power law distribution. The MWD is much broader than the random branched polymers, having the same primary chain length distribution. The expected <s2>0 for a given MW is much smaller than the random branched polymers. On the other hand, the living FRP shows a much narrower MWD compared with the corresponding random branched polymers. Interestingly, the expected <s2>0 for a given MW is essentially the same as that for the random branched polymers. Emulsion polymerization process affects branched polymer architecture quite differently for the conventional and living FRP.

Highlights

Chain transfer to polymer during free-radical polymerization (FRP) leads to form branched polymer molecules
Note that the number-average chain length, rn is given by the following equation for the conventional FRP: rn = 1/τ
Is very broad, and high molecular weight polymers conform to the power law, W(r) = r−α with the power exponent α given by α = 1/Pb, where Pb is the probability that the chain end of the primary polymer molecule is connected to a backbone chain

Summary

Introduction

Chain transfer to polymer during free-radical polymerization (FRP) leads to form branched polymer molecules. The distributions of molecular weights, branch points, and the mean-square radii of gyration that represent the three-dimensional (3D) size in space are highlighted. Chain transfer to polymer leads to form short- and long-chain branches. As long as the reaction rate of short-chain branching is much smaller than the propagation reaction, which is usually the case for FRPs, the effect of backbiting on the formed MWD, as well as the radius of gyration, would not be significant. It has been reported that the frequency of short-chain branching is greater than that of long-chain branching, especially for acrylic monomers [2,3], the backbiting reaction is neglected in the present theoretical investigation in which the effects of polymerization process on the MWD and the 3D size distribution are highlighted

Methods

Results

Conclusion