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

Sprong, Ewan (2003-12)

Thesis (PhD)--Stellenbosch University, 2003.

Thesis

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

AFRIKAANSE OPSOMMING: Alkali-oplosbare reologie-modifiseerders word kommersieël gesintetiseer d.m.v. konvensionele vrye-radikaal polimerisasieprosesse. Hierdie prosesse lewer gewoonlik 'n eindproduk met sekere tekortkominge, a.g.v. swak beheer oor molekulêre massa, molekulêre massa-verspreiding, en polimeerkettingstruktuur (Eng. chain architecture). Hierdie tekortkominge kan oorbrug word deur gebruik te maak van 'n beheerde/lewende vrye-radikaal polimerisasieproses, soos byvoorbeeld die RAFT-proses (Eng. RAFT: reversible addition-fragmentation chain transfer polymerisation). Hierdie alternatiewe metode is in die studie gebruik om model alkali-oplosbare reologiemodifiseerders te sintetiseer. Die struktuur-eienskapverhoudings van die model alkali-oplosbare reologie modifiseerders wat d.m.v. die RAFT-proses gesintetiseer is, is bestudeer. Model alkali-oplosbare reologiemodifiseerders van verskillende molekulêre massas en kettingstrukture (blok, ko- en ter-polimere) is suksesvol gesintetiseer d.m.v. RAFT-polimerisasie van metielakrilaat, metakrielsuur en hidrofobiese makromonomere. Die verskillende alkali-oplosbare reologiemodifiseerders is in organiese oplosmiddel sowel as in mini-emulsie gesintetiseer. Elkeen van die sisteme het sekere voordele en nadele getoon. In die reaksies wat in organiese oplosmiddels gedoen is, is slegs 60 % van die monomere ingebou in die polimeerkettings en die tydsduur van hierdie reaksie was heelwat langer as by die wat uitgevoer is in mini-emulsie. Meer as 60 % van die monomere is omgeskakel na polimeer tydens die reaksies wat in mini-emulsie uitgevoer is, die reaksietempo was vinniger en dit was nie nodig om die organiese oplosmiddel te verwyder nie. Ongelukkig was dit nie moontlik om al die verskillende tipes assosiatiewe-reologiemodifiseerders (Eng: associative rheology modifiers) in miniemulsie te sintetiseer nie. Die lateks wat met konvensionele reologiemodifiseerders (ko-polimere) verdik is, het kontrasterende eienskappe (reologie-profiel en dinamiese eienskappe) getoon teenoor die van die lateks-oplossings wat met assosiatiewe-reologiemodifiseerders (ter-polimere) verdik is. Die AB-tipe blok ko-polimere gee reologieresultate vir die lateks-oplossings wat lê tussen die wat bepaal is vir konvensionele reologieodifiseerders en assosiatiewe reologiemodifiseerders. Variasie in die aantal etileenoksiedeenhede in die hidrofobiese makromonomere van die assosiatiewe reologiemodifiseerders het 'n betekenisvolle invloed op die reologie-eienskappe van die lateks, sowel as die alkali-oplossings gehad. Namate die aantal etileenoksiedeenhede van 20 tot 100 vermeerder is, het 'n betekenisvolle verhoging in die "zero-shear " viskositeit van die lateks oplossings wat met die assosiatiewe reologiemodifiseerders verdik is voorgekom. Teenstrydige resultate is verkry vir die polimeeroplossings met geen lateks teenwoordig nie: die assosiatiewe reologiemodifiseerders met die hoogste aantal etieleenoksiedeenhede (EO = 100) het die laagste viskositeitsresultate opgelewer en die reologiemodifiseerders met slegs 50 etieleenoksiedeenhede het die hoogste viskositeitsresultate gelewer.

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