Synthesis and Characterization of Alkyl Substituted Vinyl Ester Resins

 

Jyoti Chaudhary¹, Supriya Dadhich¹*, Suman Jinger¹, Radha Chaudhary²

¹Department of Polymer Science, M.L. Sukhadia University, Udaipur (Rajasthan) India

²Department of Chemistry, G.I.T.S., Udaipur (Rajasthan) India

*Corresponding Author E-mail: dadhichsupriya6@gmail.com

Vinyl ester resins of epoxy 2, 6-dimethylol-4-nitrophenol (EDMN) naphthol have been synthesized using methyl acrylate (MA) / ethyl acrylate (EA) and they were structurally characterized by FT-IR and ¹H- NMR spectroscopic methods. The estrification reaction was carried out using triethylamine and hydroquinone.

 

 

 

INTRODUCTION:

Vinyl ester (VE) resins are chemically prepared by the reaction of epoxy resins to ethylenically unsaturated monocarboxylic acids like acrylic acids using styrene as a coreactant. So they have similar properties to epoxies and unsaturated polyester like reasonably priced, cure rapidly, excellent process ability etc. Usually these resins have better toughness, excellent chemical resistance, and low volumetric shrinkage as compared to unsaturated polyester.^1-3

 

These resins have terminal unsaturation (vinyl groups) which report high reactivity and high tensile elongation. Due to the presence of double bond they are very reactive and cure rapidly to form cross linked network structures with a free radical polymerization mechanism. These resins have unreacted hydroxyl groups which are derived from the epoxide moiety. These hydroxyl groups are partly responsible for their excellent adhesive properties with various substrate such as glass, plastics etc. Fiber reinforced composites, based on high temperature polymers are stronger and very light in weight.^4-6

 

MATERIALS AND METHODS:

(A)Materials:

4-nitrophenol, formaldehyde, methyl acrylate, ethyl acrylate, 1-naphthol and epichlorohydrin etc.

 

(B)Synthesis of epoxy resin:

The epoxy resin was prepared in accordance to Chandaliya et al. ^[5] In two necked flask 4-nitrophenol and formaldehyde in 1:2 ratio were charged.

 

The solution was heated in the presence of NaOH solution with constant stirring at 70^oC-80^oC, and then adds 1-naphthol to prepare phenolic resin. The prepared phenolic resin was refluxed with epichlorohydrin for 8-10 hours to form epoxy resin. The reaction scheme is shown in Scheme 1.

 

(C) Synthesis of vinyl ester resin:

In two necked flask the resultant epoxy resin and methyl acrylate/ethyl acrylate were charged. The reaction mixture was refluxed at 90^oC -100^oC in presence of triethylamine and hydroquinone for 6 hours.

 

Then the synthesized resin was dissolved in toluene and filtered with Whatman filter paper to remove salt. After it, toluene was distilled off under reduce pressure and then the obtain product was dried at about 60^oC in the oven. The resultant resin was formed in viscous form. The reaction scheme is shown in Scheme 2.

 

 

Scheme 1: Reaction pathway for the synthesis of epoxy resin

 

R= -CH₃, -C₂H₅

Scheme 2:Reaction pathway for the synthesisof VER resin

 

RESULT AND DISCUSSION:

FT-IR and ¹H-NMR spectroscopy were used to determine the structure of the synthesized resins. FT-IR spectra were recorded on a FT-IR Perkin-Elmer spectrometer with KBr pallet technique. ¹H-NMR spectra were measured on BRUKER AVENCE II 400 MHz NMR spectrophotometer with TMS as an internal reference. Elemental analysis was evaluated on Carlo-Ebra NA – 500 auto-micro analyzer. The C, H, N contents of resultantare summarized in Table 1.

 

Table 1 Preliminary Characterization of Resins

Resin code	Molecular Formula	Elemental Analysis
		%C (Calc. / Found)	%H(Calc. / Found)
EPOXY	C37H33O8N	71.72/70.87	5.33/6.15
VER I	C49H51O14N	67.04/66.74	5.81 /6.25
VER II	C52H57O14N	67.89/67.01	6.20/5.72

The structures of the synthesized epoxy resin and vinyl ester resin were confirmed by using FT-IR. Furthermore, the structure of VER is also confirmed with NMR techniques.

 

The FT-IR spectrum of epoxy resin is shown in fig.1 (a). The 929 cm^-1 absorption band in epoxy resin is due to oxirane ring and the absorption band near 1457 cm^-1, 1509 cm^-1 and 1592  cm^-1  etc. may be due to aromatic C=C bond. Figure 1 (b) and (c) show the FT-IR spectrum of vinyl ester resin. The absence of absorption band due to oxirane ring in vinyl ester resins spectra indicate that epoxy groups are completely used during the reaction. The bands at 1629 cm^-1 and 1632 cm^-1indicate the presence of olefinic band which confirms the formation of vinyl. The band at 1731 cm^-1 and 1737 cm^-1 are due to the –C=O stretching vibration of ester group. The absorption band at 1259 cm^-1 and 1260 cm^-1 is due to the C-O-C stretching for ethers.

 

¹H-NMR spectra of vinyl ester resins (figure-2) showed the chemical shift of vinylic protons of methyl and ethyl acrylate show in the range of 5.8 to 6.5 ppm. Aromatic protons show the signal in the region of 6.9-8.3 ppm. Signals at 3.4- 4.5 ppm were observed due to methylene protons. These spectral results were reliable with the earlier work by many researchers [7, 8, 9 ].

 

 

(a)

 

 

(b)

 

(c)

Fig. 1 FT-IR Spectra of (a) Epoxy resin; (b) Vinyl ester resin of nitro phenol with methyl acrylate (VER I); and (c) Vinyl ester resin of nitro phenol with ethyl acrylate (VER II)

 

(a)

 

(b)

Fig. 2 ¹H-NMR Spectra of (a) VER I; and (b) VER II

 

 

 

CONCLUSION:

Synthesis of vinyl ester resins by the reaction of epoxy resin based on 2, 6- dimethylol-4-bromonaphthol with methyl acrylate and ethyl acrylate using triethylamine and hydroquinone have been investigated. The CHN data of resin is consistent with the predicted structure of the vinyl ester resins. The structures of synthesized epoxy and vinyl ester resins are supported with their spectral analyses.

 

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Received on 26.05.2017         Modified on 28.06.2017

Accepted on 12.07.2017         © AJRC All right reserved