Synthesis and Characterisation of Hydrogels Based on Poly (N-Vinylcaprolactam) with Diethylene Glycol Diacrylate

Abstract

Poly (N-vinylcaprolactam) is a polymer that is biocompatible, water-soluble, thermally sensitive, non-toxic, and nonionic. In this study, the preparation of hydrogels based on Poly (N-vinylcaprolactam) with diethylene glycol diacrylate is presented. The N-Vinylcaprolactam-based hydrogels are synthesised by using a photopolymerisation technique using diethylene glycol diacrylate as a crosslinking agent, and Diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide as a photoinitiator. The structure of the polymers is investigated via Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy. The polymers are further characterised using differential scanning calorimetry and swelling analysis. This study is conducted to determine the characteristics of P (N-vinylcaprolactam) with diethylene glycol diacrylate, including the addition of Vinylacetate or N-Vinylpyrrolidone, and to examine the effects on the phase transition. Although various methods of free-radical polymerisation have synthesised the homopolymer, this is the first study to report the synthesis of Poly (N-vinylcaprolactam) with diethylene glycol diacrylate by using free-radical photopolymerisation, using Diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide to initiate the reaction. FTIR analysis shows that the NVCL-based copolymers are successfully polymerised through UV photopolymerisation. DSC analysis indicates that increasing the concentration of crosslinker results in a decrease in the glass transition temperature. Swelling analysis displays that the lower the concentration of crosslinker present in the hydrogel, the quicker the hydrogels reach their maximum swelling ratio.

Keywords: N-vinylcaprolactam; copolymers; hydrogel; photopolymerisation; swelling behaviour.

Figure 1

Schematic representation illustrating the process of photopolymerisation, showing the conversion of NVCL into PNVCL in the presence of TPO photoinitiator.

Figure 2

PNVCL xerogels produced using different ratios of DEGDA/VAc/NVP with 0.1 wt% TPO: (A) S1, (B) S2, (C) S3, (D) S4, (E) S5, (F) S6, (G) S7, (H) S8, and (I) S9.

Figure 3

FTIR spectra of (top–bottom) VAc monomer, NVP monomer, DEGDA monomer, PNVCL100, and NVCL neat.

Figure 4

FTIR spectra of (top–bottom) S9, S8, S7, S6, S5, S4, S3, S2, and S1.

Figure 5

A representative thermograph of samples C1, S2, and S3.

Figure 6

The appearance of the hydrogel swelling for sample S1 over 262 h at times (A) 0 h, (B) 2 h, (C 29 h, (D) 48 h, (E) 75 h, (F) 100 h, (G) 139 h, and (H) 262 h. (A–E) represent the hydrogels at room temperature, and (F–H) represent the hydrogels at 50 °C.

Figure 7

The swelling ratios of chemically crosslinked samples of PNVCL, PNVCL/DEGDA, PNVCL-DEGDA/VAc, and PNVCL-DEGDA/NVP conducted at temperatures below the LCST (20 °C) and above the LCST (50 °C). (●) S2, (■) S4, and (▲) S6.

Figure 8

The process of determining gel fraction percentage of S2.

Figure 9

Comparison of the Gel fraction among S1, S2, S3, S4, S5, S6, S7, S8, and S9.

Figure 10

The contact angle of sample S2 after 0 and 115 s.

Figure 11

The contact angles of samples S1, S2, S3, S4, S5, S6, S7, S8, and S9 from 0 to 115 s.

Figure 12

Tensile property comparison between samples S1, S2, S3, S4, S5, S6, S7, S8, and S9. (A) Tensile modulus, (B) Ultimate tensile strength, (C) Elongation at break.