Incremental modification of styrene‐butadiene rubber with tert‐nonyl mercaptan

Abstract

A model equation derived for the viscosity-average degree of polymerization (P.) for the incremental addition of modifiers, P, = K ( (exp{arzl] indicates a minimum should occur in a curve of P. versus conversion at which the increments are added, zl. Incremental addition of commercial tertdodecyl mercaptan in the laboratory to SBR recipes a t 5°C. showed effects contrary to those predicted by the model equation, but incremental addition experiments with tert-nonyl mercaptans resulted in a minimum in viscosity versua 21 curves, changed the molecular weight distribution, and required 34 wt.-% less mercaptan than did the tert dodecyl mercaptan control (all the tertdodecyl mercaptan added initially). Incremental additioh of tertnonylmercaptan in pilot plant 20-gal. autoclave reactors gave essentially the same results found in the laboratory bottle experiments. The stress4rain and mixing properties of the incrementally modified polymer and the tertdodecyl mercaptanmodified control were essentially the same within experimental error. Conditions required for successful application of the incremental modifier technique are given.

Kinetics of the styrene emulsion polymerization usingn-dodecyl mercaptan as chain-transfer agent

“…On the other hand, when t-nonyl mercaptan, which diffuses rapidly, was used, a marked advantage of using semicontinuous addition was observed. 18 Echevarria et al 19 developed a closedloop control strategy based on on-line gas chromatographic measurements of both monomer and CTA to obtain emulsion polymers of well-defined MWD. The control strategy was experimentally assessed, producing widely different MWDs in the styrene emulsion polymerization using carbon tetrachloride as CTA.…”

Modification of emulsion polymerization by multiple addition of modifier

“…[exp ( a r~) -~I / [~x Y ( ' +~) I (1) where M o is the initial monomer, SO is the initial modifier concentration, r is the regulating index, a is the Mark-Houwink exponent, and X is the fractional conversion. A P , -r plot gives a concave curve, and eq.…”

“…Equations (1) and (2) can be used to show that modifiers with high regulating indexes are needed for efficient modification of polymerizations terminated at low conversions. If a manyfold incremental modifier experiment is viewed as a sum of a consecutive series of short conversion intervals, than in manyfold addition modifiers with much higher regulating indexes are needed for efficient modification in comparison to the single addition control taken to the same final conversion.…”

Optimization of the chain transfer agent incremental addition in SBR emulsion polymerization

“…Uraneck and Burleigh. 8 studied the incremental addition of TDM and tert-nonyl mercaptan. For TDM it was found that MV and inherent viscosity were higher than the obtained when total CTA was initially added.…”