Abstract
Hydrogen-bonds structure in poly(2-hydroxyethyl methacrylate) (PHEMA) were investigated by means of temperature-dependent infrared (IR) spectroscopy. Spectral variations involved with the OH…OH and C=O…HO types of hydrogen-bonds were found around the glass transition temperature of 80°C. Hydrogen-bonds among the hydroxyl groups gradually dissociate with increasing temperature. In contrast, discontinuous variation in the carbonyl bands was observed around the glass transition temperature. An association of the C=O…HO type of hydrogen-bond with increasing temperature above the glass transition temperature was revealed. These were concluded from the present study that hydrogen-bonds among the hydroxyl groups in each side chain terminal suppress the main chain mobility in the polymer matrix below the glass transition temperature, while the dissociation of the OH…OH type of hydrogen-bonds induces the association of the C=O…HO type of hydrogen-bond. As a result, the mobility of the main chain is induced by the change in hydrogen-bonds structure at the glass transition temperature.
Highlights
Poly(2-hydroxyethyl methacrylate) (PHEMA) contains one carbonyl (C=O) and one hydroxyl (OH) groups on each side chain (Montheard et al, 1992)
Our recent study revealed that 47.3% of the OH group on the PHEMA side chain terminal are engaged in the OH· · · O=C type of hydrogen-bond, while the remaining 53.7% contributes to the OH· · · OH type of hydrogen-bond at ambient temperature (Morita et al, 2009)
Assignments of the two bands given in our previous study (Morita et al, 2009) are summarized in DISCUSSION An evidence of gradual dissociation of the OH· · · OH type of hydrogen-bonds with increasing temperature was found in the O-H stretching region
Summary
Poly(2-hydroxyethyl methacrylate) (PHEMA) contains one carbonyl (C=O) and one hydroxyl (OH) groups on each side chain (Montheard et al, 1992). The OH group acts as both proton donor and proton acceptor, while the C=O group as only proton acceptor (Jeffrey, 1997; Marechal, 2007) Both OH· · · OH and C=O· · · HO types of hydrogen-bonds are acceptable in PHEMA. Dimer structure (OH· · · OH) and aggregates structure (· · · OH· · · OH· · · OH· · · ) have been found in many systems including liquid alcohols (Kristiansson, 1999; Ohno et al, 2008) and solid polymers (Morita et al, 2008, 2009) Such the hydrogen-bonds structure in polymers plays important roles for their macromolecular functions in artificial polymers (Brunsveld et al, 2001) as well as biopolymers (Watanabe et al, 2006, 2007). Our recent study revealed that 47.3% of the OH group on the PHEMA side chain terminal are engaged in the OH· · · O=C type of hydrogen-bond, while the remaining 53.7% contributes to the OH· · · OH type of hydrogen-bond at ambient temperature (Morita et al, 2009)
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