Steering polymer growth by molding nanochannels: 1,5-hexadiene polymerization in high silica mordenite
Graphical abstract
Incorporation of 1,5-hexadiene molecules in high-silica mordenite at room temperature produces quasi one-dimensional polymers tailored by the molding action of the zeolite framework. The size/shape constraints of the zeolite channels play a key role in directing molecular organization and bond transformation processes towards polymers that fit like a hand in the glove to the host inner spaces.
Introduction
The preparation and exploitation of low-dimensional materials is a fundamental issue in nanoscience and nanotechnology. Microporous materials such as zeolites are of great interest in this context, because of their unique pore topologies [[1], [2], [3]]. The “open space” of zeolites can be filled by suitable encapsulated guest molecules and cations that can diffuse through the pores and form organized low-dimensional aggregates tailored by the zeolite channels [[4], [5], [6], [7]]. Moreover, the fine tuning of their pore architecture and of their hydrophilic/hydrophobic character can improve their performance for technological or industrial applications [[8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]]. Different kinds of reactions can be promoted and accomplished in zeolite pores. For example, the formation of mixtures of long-chain polymers and small oligomers of pyrrole and thiophene have been reported to occur inside transition-metal substituted zeolites, such as Cu- or Ni-mordenites [19,20]. Also, the presence of Brønsted acid sites [[21], [22], [23], [24], [25]] may strongly affect the formation of a polymer inside the zeolite cavities: in particular, acidic zeolites themselves can induce a polymerization reaction [26].
The preparation - via a chemical reaction - of a continuous organic conductive nanowire embedded in zeolite micropores would therefore be of fundamental relevance in advanced materials fabrication. In fact, preparing isolated, self-standing, densely packed conducting polymers is extremely challenging when conventional protocols are adopted, since the aggregation and bending of chains prevent the production of real 1D systems [26]. Conversely, by imposing pressure (a few GPa) on zeolite systems, it is possible to induce a rearrangement of the chemical bonds among guest species by simple mechanical tuning of the intermolecular/interatomic distances [27]. Following this procedure, linear chains of polyethylene [28], polyacetylene [29] and polycarbonyl [30] can be synthesized inside zeolite channels and, very recently, phenylacetylene has been oligomerized at high pressure inside the zeolite Mordenite [31].
The aim of our study, which is a part of a wider project aimed at the preparation of conductive polymers embedded in a protective matrix, is to exploit the template effectiveness of zeolite in inducing a polymerization along preferential directions that would not occur in bulk. This paper is the first step towards the preparation of a hybrid material made from a linear polymer identified as suitable for pyrolysis to obtain a conductive polymer protected inside a hydrophobic matrix. The resulting innovative material would have the potential to be exploited in several technological applications including, for example, gas sensing. In this field, in fact, the ability to fully exploit the properties of such a hybrid (i.e. its hydrophobicity, huge surface area and confinement of the host species) would yield the combined advantages of low cross-sensitivity to humidity and high sensitivity. In addition, an effective host-guest interaction is expected to increase the stability of the guest material. Clearly, these are all desirable characteristics for a gas sensor but, despite several years of investigation using different approaches, their development is yet to be fulfilled.
As a zeolite scaffold, we chose a high silica mordenite (HS-MOR) (Fig. 1a), while as the molecule to polymerize we selected 1,5-hexadiene (hexa) (Fig. 1b). HS-MOR was selected for the following reasons: i) the framework must have a unidimensional channel system to promote the synthesis of isolated 1D polymer chains; ii) the dimensions of the pores must allow the penetration of hexa; iii) a residual porosity should be maintained after polymerization to allow the gas transit for exploitation in gas sensing. The unidimensional system of parallel channels in MOR (see the section “Materials” for a detailed description of the structure) perfectly fits with these requirements since hexa can enter (and consequently may be polymerized) in the 12 MR channels and the gas to be sensed can circulate in the smaller channels (8 MR) and be in contact with the conductive wire through side pockets. Hexa was chosen since its polymerization can result in an almost linear chain and the basic idea is to make the chain conductive after a selective pyrolysis reaction (not treated here).
It is worth noting that, in the absence of confinement, this molecule undergoes a series of complex reactions (e.g. Cope rearrangement [32], dimerization [33], polymerization [34]) characterized by intricate paths, leading to a mixture of products. A regular polymer, using 1,5-hexadiene as a monomer, can be obtained only via a homogeneous Ziegler-Natta catalyst, leading to poly (methylene-1,3-cyclopentane) (PMCP) [34].
Section snippets
Materials
High-silica mordenite (HS-MOR, SiO2/Al2O3 ratio ~ 200; Na2O < 0.1 wt%) was purchased from the Tosoh Corporation (Japan) in its protonated form (code HSZ-690HOA). The crystal structure of mordenite [35] (framework type MOR [36]) is built up from an assembly of single 6-membered rings (6 MR) forming sheets linked by single 4-membered rings (4 MR) or else from a combination of 5–1 secondary building units. As shown in Fig. 1a, MOR exhibits a 1D channel system resulting from two types of channels
IR spectroscopy
The loading of 1,5-hexadiene in HS-MOR was monitored by in situ IR spectroscopy and the final sample was later used for thermogravimetry and the XRPD analyses. Fig. 3 shows the IR spectra of 1,5-hexadiene adsorbed on HS-MOR pre-outgassed at r.t. (curve a) and the subsequent evolution as a function of contact time (curves b,c). The spectrum of the molecule in the gas phase (curve a’) is reported for comparison. The assignment of the signals of the molecule in this form, as well as the beginning
Conclusions
In this work, we prepared a hybrid material in which 1,5-hexadiene was polymerized to form an almost linear chain and protected inside a high silica mordenite acting as mold and scaffold. The combination of IR, TGA and diffraction data indicated that: i) the zeolite pores were filled with 1,5-hexadiene; ii) all hexa monomers that entered in the zeolite channels reacted; iii) chains of covalently bonded C atoms run along the main channels of HS-MOR. Combining this evidence with insights from
Funding sources
This work was carried out in the framework of the PRIN project ZAPPING (PRIN2015 Prot.2015HK93L7) funded by the Italian MIUR. FAR2018 Uninsubria is acknowledged for funding.
CRediT authorship contribution statement
Marco Fabbiani: Investigation, Conceptualization, Data curation, Writing - original draft. Giorgia Confalonieri: Investigation, Data curation, Writing - original draft. Sara Morandi: Methodology, Formal analysis. Rossella Arletti: Project administration, Supervision, Funding acquisition. Simona Quartieri: Project administration, Writing - review & editing. Mario Santoro: Visualization, Conceptualization. Francesco Di Renzo: Conceptualization, Visualization. Julien Haines: Conceptualization,
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This paper is dedicated to our friend and colleague Gianmario Martra prematurely passed away during the paper revision process. M. Fabbiani is gratefully indebted to C. Nannuzzi for the support in the in situ experiments and data elaborations. Authors thank the staff of ID15b and ID22, ESRF, for the help in X-ray diffraction data collection. Ms. C. Merrett is acknowledged for the English language revision.
References (79)
- et al.
Microporous Mesoporous Mater.
(2020) - et al.
Microporous Mesoporous Mater.
(1999) - et al.
Microporous Mesoporous Mater.
(2008) - et al.
Appl. Clay Sci.
(2019) - et al.
Chem. Eng. J.
(2019) - et al.
Dyes Pigments
(2018) - et al.
Microporous Mesoporous Mater.
(2020) - et al.
Chem. Phys. Lett.
(2017) - et al.
J. Solid State Chem.
(2012) - et al.
Microporous Mesoporous Mater.
(2012)
J. Colloid Interface Sci.
Microporous Mesoporous Mater.
Microporous Mesoporous Mater.
Microporous Mesoporous Mater.
Microporous Mesoporous Mater.
ChemPhysChem
Angew. Chem. Int. Ed.
J. Chem. Phys.
Int. J. Quant. Chem.
Angew. Chem. Int. Ed.
Int. J. Mol. Sci.
Phys. Chem. Chem. Phys.
Angew. Chem. Int. Ed.
Chem. - A Eur. J.
J. Phys. Chem. C
Angew Chem. Int. Ed. Engl.
J. Chem. Soc. Faraday. Trans.
J. Phys. Chem. B
Phys. Chem. Chem. Phys.
Phys. Chem. Chem. Phys.
Chem. – A Eur. J.
ChemCatChem
J. Phys. Chem.
Phys. Chem. Miner.
Nat. Commun.
Chem. Mater.
Chem. Mater.
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