Contactless Raman Spectroscopy-Based Monitoring of Physical States of Silyl-Modified Polymers during Cross-Linking

Abstract

Cross-linking of silyl-modified polymers occurs at the alkoxysilane groups attached to the ends of polymer chains by hydrolysis and polycondensation mechanisms in the presence of moisture. During these reactions, three different physical states can be identified (viscous, skin effect and cross-linked state). Knowledge of the evolution of these states at each reaction time is essential to determine the open time for the adhesive industry and is generally obtained by a manual method. Automation of this monitoring could avoid operator error and could be used for very long cross linking reactions or to screen a large number of catalysts. Thus, a contactless micro process technology was developed to correlate these physical states with an optical technology, Raman spectroscopy, by monitoring the decrease in intensity of the Si-OCH 3 groups during chemical reactions. This online characterization method can also be used to compare the efficiencies of several catalysts for the cross-linking of silylmodified polymers, using a minimum amount of chemical materials.

Simultaneous In Situ Monitoring of Trimethoxysilane Hydrolysis Reactions Using Raman, Infrared, and Nuclear Magnetic Resonance (NMR) Spectroscopy Aided by Chemometrics and Ab Initio Calculations

“…It is challenging to investigate the kinetics of sol-gel reactions that form silsesquioxanes due to the many transient intermediate species. 10 Many different analytical techniques have been employed such as Raman spectroscopy, [11][12][13][14][15] infrared (IR) spectroscopy, [16][17][18][19] nuclear magnetic resonance (NMR), [20][21][22][23] and computational calculations. 18,19,[24][25][26][27] This is an example where the combination of NMR, Raman, and IR provide complimentary information.…”

Hybrid Xerogels: Study of the Sol-Gel Process and Local Structure by Vibrational Spectroscopy

“…For instance, multiple reactions take place simultaneously in the process, making it difficult to extract information from experimental procedures [ 20 ]. To date, many studies have attempted to elucidate the influence of precursors on the hydrolysis, condensation reactions, and crosslinking by applying different characterization and analysis techniques, including gas chromatography (GC) [ 21 ], nuclear magnetic resonance 29 Si NMR [ 22 , 23 ], Raman spectroscopy [ 24 ], and Fourier transform infrared spectroscopy (FTIR) [ 25 , 26 ]. Among these approaches, FTIR not only provides complementary information on the bonds and structures formed during the synthesis process but also, when combined with deconvolution methods, yields valuable data on the microstructure of siliceous materials [ 27 , 28 , 29 ].…”