Pore Size Tuning and Multifunctional Porous Polymer Matrices Using Mixtures of Polymerizable Porogens

Use of polymerizable porogens (PolyPo), wherein the porogenic segment is linked to the polymerizable moiety either via a readily cleavable covalent bond or it is electrostatically bound as a counterion, was earlier shown by us to be an effective strategy for the preparation of porous polymers with a high density of functional groups lining the internal pore walls. The pore size was shown to vary with the size of the porogenic segment in both cases. Here, we examine the possibility to tune the pore size by mixing multiple pore-forming agents during polymerization. Three types of systems were studied: (i) the PolyPo, St-PEG-350, was mixed with varying amounts of free MPEG350 and polymerized in the presence of 50 wt % of divinyl benzene (DVB); (ii) St-PEG-350 was mixed with free MPEG of different molecular weights, namely, MPEG350, MPEG750, and MPEG-2000, and polymerized in the presence of 50 wt % of DVB; and (iii) a mixture of equal weights of two PolyPos, carrying MPEG segments of different molecular weights, was polymerized in the presence of 50 wt % of DVB. BET nitrogen adsorption and electron microscopy studies reveal an intricate interplay of several factors, namely, the relative amounts of the two porogenic components, their relative sizes, and finally whether the second component is an inert additive or another PolyPo influences the outcome. In summary, these systems provide an alternate strategy to regulate the nature of the porous polymer without having to resort to the synthesis of additional PolyPos. Finally, we explore an exciting possibility of preparing mesoporous monoliths, carrying both amine and carboxylic acid groups, in a single step; here, polymerization of DVB was done in the presence of a covalently linked PolyPo (source of amine) and an ionic PolyPo (source of carboxylic acid). It was noticed that the porogenic segments of the two porogens do not collocate but microphase-separate independently during the polymerization and hence leave behind amines and acid groups in distinct pores within the same matrix; this approach opens up an opportunity to design multifunctional catalytic matrices.