PMMA-grafted silica aerogel nanoparticles via in situ SR&NI ATRP: Grafting through approach

Abstract

An organic modifier with vinyl moiety, 3-(trimethoxysilyl)propyl methacrylate (MPS), was employed to surface modification of hydrophilic silica aerogel nanoparticles. After that, double bond moieties on the surface were incorporated in grafting through polymerization of methyl methacrylate (MMA) via in situ simultaneous reverse and normal initiation technique for atom transfer radical polymerization (SR&NI ATRP). Grafting through polymerization of MMA results in tailor-made poly(methyl methacrylate) (PMMA) with twofold chains. Successful surface modification of hydrophilic silica aerogel nanoparticles with MPS is demonstrated by Furrier transform infrared spectroscopy and thermogravimetric analysis (TGA). Nitrogen adsorption/desorption isotherm is applied to examine surface area and structural characteristics of the synthesized silica aerogel nanoparticles. Evaluation of size distribution and morphological studies were performed by scanning and transmission electron microscopy. Conversion and molecular weight determinations were carried out using gas and size exclusion chromatography respectively. Addition of MPS-functionalized silica aerogel nanoparticles by 3 wt% results in decrement of conversion from 87 to 66%. By adding 3 wt% MPS-functionalized silica aerogel nanoparticles, molecular weight (Mn) of free MMA chains decreases from 13,563 to 9365; however, polydispersity index (PDI) value increases from 1.19 to 1.56. Although PDI values of attached MMA chains are increased from 1.48 to 2.08, Mn values reveal an increment by adding MPS-functionalized silica aerogel nanoparticles content. Low PDI values of the products can appropriately demonstrate the living nature of polymerization. An increment of thermal stability of the nanocomposites by increasing MPS-functionalized silica aerogel nanoparticles is demonstrated by TGA results. Differential scanning calorimetry also shows a decrement in glass transition temperature by increasing MPS-functionalized silica aerogel nanoparticles loading.