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. 2023 Mar 8;15(6):1353.
doi: 10.3390/polym15061353.

Phase Behavior of NR/PMMA Semi-IPNs and Development of Porous Structures

Jacob John  1 , Damir Klepac  2   3 , Mia Kurek  4 , Mario Ščetar  4 , Kata Galić  4 , Srećko Valić  2   3   5 , Sabu Thomas  6 , Anitha Pius  1
Affiliations

Phase Behavior of NR/PMMA Semi-IPNs and Development of Porous Structures

Jacob John et al. Polymers (Basel). .

Abstract

In this research, the porous polymer structures (IPN) were made from natural isoprene rubber (NR) and poly(methyl methacrylate) (PMMA). The effects of molecular weight and crosslink density of polyisoprene on the morphology and miscibility with PMMA were determined. Sequential semi-IPNs were prepared. Viscoelastic, thermal and mechanical properties of semi-IPN were studied. The results showed that the key factor influencing the miscibility in semi-IPN was the crosslinking density of the natural rubber. The degree of compatibility was increased by doubling the crosslinking level. The degree of miscibility at two different compositions was compared by simulations of the electron spin resonance spectra. Compatibility of semi-IPNs was found to be more efficient when the PMMA content was less than 40 wt.%. A nanometer-sized morphology was obtained for a NR/PMMA ratio of 50/50. Highly crosslinked elastic semi-IPN followed the storage modulus of PMMA after the glass transition as a result of certain degree of phase mixing and interlocked structure. It was shown that the morphology of the porous polymer network could be easily controlled by the proper choice of concentration and composition of crosslinking agent. A dual phase morphology resulted from the higher concentration and the lower crosslinking level. This was used for developing porous structures from the elastic semi-IPN. The mechanical performance was correlated with morphology, and the thermal stability was comparable with respect to pure NR. Investigated materials might be interesting for use as potential carriers of bioactive molecules aimed for innovative applications such as in food packaging.

Keywords: delivery of bioactive molecules; electron spin resonance/electron paramagnetic resonance ESR/EPR-spin probe; interpenetrating networks (IPN); macroporous polymers; morphology; novel food packaging.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Chemical structures of (a) polyisoprene (NR) and (b) methyl methacrylate (MMA).
Figure 2
Figure 2
SEM images of various semi-IPNs: (a) 2NRM20; (b) 2NRM35; (c) 2NRM55; (d) 4NRM50. Photos taken in magnification from ×1600 to ×2000.
Figure 2
Figure 2
SEM images of various semi-IPNs: (a) 2NRM20; (b) 2NRM35; (c) 2NRM55; (d) 4NRM50. Photos taken in magnification from ×1600 to ×2000.
Figure 3
Figure 3
SEM images of porous semi-IPNs after the PMMA removal: (a) 2NRM55; (b) 2NRLM50; (c) 0.8NRM65.
Figure 4
Figure 4
SAXS profile of the highly crosslinked 4NRM50 semi-IPN.
Figure 5
Figure 5
Storage modulus of semi-IPNs and homopolymers as a function of temperature.
Figure 6
Figure 6
The ESR spectra of 2NRM35 and 4NRM50 semi IPNs at 75 °C.
Figure 7
Figure 7
The effect of PMMA concentration in crosslinked semi-IPNs on (a) tensile strength, (b) elongation at break, and (c) tensile modulus.
Figure 8
Figure 8
TGA curves of (a) crosslinked pure NR (2NR) and semi IPN samples, (b) 2NRM35, (c) 2NRM55, and (d) 4NRM50.
Figure 9
Figure 9
DSC curves of: (a) pure NR (2NR) and semi-IPNs (b) 2NRM35, (c) 2NRM55, (d) 4NRM50, and (e) 2NRLM50.
See this image and copyright information in PMC

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