Vibrational Spectroscopic Investigation of 2-Hydroxyethyl Methacrylate (HEMA) and Poly-2-hydroxyethylmethacrylate (P-HEMA)

Objectives: to give a vibrational band assignment for HEMA and p-HEMA and study the vibrational behavior of p-HEMA under pressure.

Methods: IR spectra of HEMA and p-HEMA were recorded on a Bruker IFS IR spectrometer at 2 cm^-1 resolution. High-pressure IR spectra of p-HEMA were then recorded using a diamond-anvil cell up to 45 kbar. The FT-Raman spectra were recorded at ambient pressure and temperature using a Bruker IFS 88 FT-IR spectrometer equipped with an FRA 106 FT-Raman module. The defocused 1064.1 nm line of an air-coolded, Nd:YAG near-IR laser was used to excite the spectra.

Results: the main spectra data and band assignment of IR and FT-Raman for HEMA and p-HEMA are shown in table 1.

Table 1. Infrared and Raman spectra (cm^-1) of HEMA and P-HEMA.

____________________________________________________________        Infrared             FT-Raman                          Assignments

HEMA     PHEMA   HEMA   PHEMA

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3424m    3435s                           OH stretching

3109 w            3109w                  CH antisymmetric stretch,

2957m    2960m    2960s 2953sh    CH₂, CH₃ antisymmetric stretch

2929m    2929sh   2935s 2941s     CH₂, CH₃, symmetric stretch

2887m    2889m    2895m 2893m     CH₂, symmetric stretch

1718vs  1726vs    1714s 1718m     C=O stretching

1636m             1640s           C=C stretching

        1330w           1326w     CH₃ , CH₂, CH₂ deformation

1321s            1316m            CH₂ in-plane deformation

1079m    1076s   1084w   1091w    CO(H) stretching

         749w            736w     CH₂ coupled with skeletal stretching

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The pressure dependences of the IR frequencies are: 1726 cm^-1, 0.11; 1456 cm^-1, 0.11; 1277 cm^-1, 0.17.

Conclusions: the C=O group in P-HEMA is not involved in hydrogen bonding.