Influence of Diester Content in Macromonomers on Performance of MPEG-Based PCEs

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Title: Influence of Diester Content in Macromonomers on Performance of MPEG-Based PCEs

Author(s): Johannes Paas, Maike W. Müller, and Johann Plank

Publication: Special Publication

Volume: 302

Issue:

Appears on pages(s): 199-210

Keywords: cement; crosslinking; diester; dispersing performance; macromonomer; polycarboxylate ether; superplasticizer

Date: 6/1/2015

Abstract:
Macromonomers for MPEG type of PCEs are produced through esterification of methacrylic acid (MAA) with methoxypoly(ethylene glycol) (MPEG) yielding the MPEG-MAA ester. However, PEG impurities present in MPEG may lead to MAA diester (PEG-di-MAA) formation. Such diester can cause crosslinking of the PCE polymer which might reduce its dispersing power. To investigate this effect, MPEG-MAA macromonomers containing 0 – 20 wt. % of PEG-di-MAA diester were used in PCE synthesis. It was found that when the PEG-di-MAA content in the macromonomer exceeds 2 wt. %, then dispersing effectiveness starts to decrease and the solution viscosity of the PCE increases. Surprisingly, incorporation of the diester into the PCE polymer does not occur randomly. Instead, two distinct species of crosslinked PCE molecules (Mw ~ 300.000 and ~ 3 mio g/mol) are formed within the first minutes of copolymerization. Apparently, the crosslinked PCE species counteract the dispersing effect of the main product.