Analysis of Network Structure of UV-Cured Acrylates by¹H NMR Relaxation,¹³C NMR Spectroscopy, and Dynamic Mechanical Experiments

Abstract

The network structure of UV-cured acrylates was analyzed by dynamic mechanical experiments, 1 H T2 NMR relaxation, and 13 C NMR spectroscopy. Photocured mixtures of difunctional (poly(ethylene glycol) diacrylate) and monofunctional (2-ethylhexyl acrylate) were studied. The mean crosslink density and fraction of dangling chains were varied in these networks by changing the content of monofunctional acrylate. Examining networks by 13 C NMR spectroscopy, we observed that the conversion is high, and the contribution or the effect of side reactions that generate extra cross-links is negligible. The spatial distribution of cross-links is very heterogeneous in the cured samples; i.e., polyacrylate ziplike network junctions are interconnected by polyether chains. An increase in the content of monofunctional monomer causes a significant decrease in the cross-link density because the monofunctional monomer acts as a chain extender. NMR T 2 relaxation method shows good correlation with mechanical tests with respect to molar mass between cross-links, Mc. Obtained values of Mc are significantly smaller compared to molar mass of diacrylate. As anticipated, it is apparent that classical rubber elasticity theories are not applicable for characterization of this type of networks containing ziplike network junctions.

Real‐Time NMR. How Fast Can We Do It?

“…[8,9] It is well established that NMR transverse magnetization relaxation (T 2 relaxation) is very sensitive to even small differences in the cross-link density, because this relaxation time for rubbery materials is largely governed by constraints on large spatial-scale chain mobility imposed by chemicalandphysicalcross-links.Sincechain motion is strongly coupled to elastomer structure, chemical information can be obtained. A comparison of the cross-link density, as measured by T 2 relaxation experiments, with that obtained by traditional methods for the same samples proves that the NMR method provides quantitative data on the cross-link density.…”

“…A comparison of the cross-link density, as measured by T 2 relaxation experiments, with that obtained by traditional methods for the same samples proves that the NMR method provides quantitative data on the cross-link density. [8] In addition to the mean cross-link density, the analysis of T 2 relaxation can provide information on network defects and heterogeneous distribution of network junctions. [9] The sensitivity of the T 2 experiments to the molecular scale heterogeneity of networks is due to the local origin of the relaxation process, which is predominantly governed by the near-neighbor environment and intrachain effects for T 2 relaxation at temperatures well above the T g .…”

Synthesis and Photopolymerization of 2-(Acryloyloxy)ethyl Pyrrolidine-1-Carboxylate

“…The kinetics of IBOA and AEPC with 0.5 wt% 907 as photoinitiator and a light intensity of 30 mW/cm 2 are shown in Fig. 4 [16][17][18][19][20][21][22][23][24]. It showed that final double-bond conversion, the highest curing rate and the time reaching the highest curing rate were almost the same.…”

“…The mechanical properties of the photopolymers were measured by dynamic mechanical analysis (DMA) [23,25]. Figure 6 shows the typical profiles recorded by DMA for UV-cured samples by monitoring the variation of the storage modulus (E ) and the tensile loss factor (tan δ) with increasing temperature.…”

Synthesis and photopolymerization of 2‐(acryloyloxy)ethyl piperidine‐1‐carboxylate and 2‐(acryloyloxy)ethyl morpholone‐4‐carboxylate

“…[43][44][45][46] Figure 7 shows typical profiles recorded by DMA for UV-cured samples through the monitoring of the variation of the storage modulus and the tensile loss factor with an increase in the temperature. The glass-transition temperatures and storage moduli of the photocured samples of AEPC II/CN964 and AEMC/CN964 were lower than those of IBOA/CN964 (37.5 and 45.6 versus 57 C).…”