Structure/property relationship of model alkali-soluble rheology modifiers synthesised via the RAFT process

["Rheology", "Polymerization", "Polymers -- Rheology", "Biological response modifiers", "Viscosity", "Dissertations -- Polymer science", "Theses -- Polymer science"]

Sprong, Ewan ; Sanderson, R. D.

Stellenbosch University

Others  :  https://scholar.sun.ac.za:443/bitstream/10019.1/53604/1/sprong_structure_2003.pdf

瑞士|英语

来源: Stellenbosch University

【 摘 要 】

ENGLISH ABSTRACT:Alkali-soluble rheology modifiers are commercially synthesised via conventional freeradicalpolymerisation processes. This results in the end product having certainlimitations; there is poor control over the molar mass, molar mass distribution and chainarchitecture of the polymer chains. These limitations can be overcome by using acontrolled/living free radical polymerisation process, for example the RAFT process.This alternate method of synthesis was used here to prepare model alkali-solublerheology modifiers. The structure/property relationships of model alkali-soluble rheologymodifiers synthesised via the RAFT process were studied.Model alkali-soluble rheology modifiers of different molar masses and chainarchitectures (block, co- and ter-polymers) were successfully synthesised by the RAFTpolymerisation of methyl methacrylate, methacrylic acid and various hydrophobicmacromonomers.The different types of alkali-soluble rheology modifiers were synthesised in solution andin miniemulsion. Each of the two systems had certain advantages and disadvantages. Theconversion limit of reactions in solution was about 60 % and reaction times were muchslower than those of the miniemulsion reactions. Higher final conversions were recordedfor miniemulsion reactions, reactions were faster and no solvent removal was required.Unfortunately it was not possible to synthesise all the different types of associativerheology modifiers investigated here in a miniemulsion system.The latex solutions thickened with conventional rheology modifiers (co-polymers) showvery contrasting behaviour (rheology profile and dynamic properties) to that of the latexsolutions thickened with the associative rheology modifiers (ter-polymers). The AB blockcopolymers gave the latex solutions rheology results between those obtained withconventional rheology modifiers and those with the associative rheology modifiers.Varying the number of ethylene oxide spacer units in the hydrophobic macromonomersof the associative rheology modifiers had a significant influence on the rheologyproperties of the latex and alkali solutions. As the number of ethylene oxide spacer unitswas increased from 20 to 100 there was a significant increase in the zero-shear viscosityof the latex solutions thickened with the associative rheology modifiers. Contrastingresults were obtained for the polymer solutions (no latex present), where the use of theassociative rheology modifiers containing the highest number (EO = 100) of ethyleneoxide spacer units resulted in solutions with the lowest viscosity, but the rheologymodifiers containing the 50 ethylene oxide spacer units gave the highest steady shearviscosity.