This review summarizes the different categories of topochemical polymerizations for the synthesis of fully-organic polymers and their design strategies.

We report 11 simple halobenzyl alcohols, each comprising of only 16 atoms, as organogelators for aliphatic hydrocarbon solvents. Their self-assembly is similar in both gel and crystal states and involve OH⋯O, CH⋯O, CH⋯π, O⋯X, CH⋯X and X⋯X interactions.

Unsaturated polymers are important materials having a lot of applications. Among polymers, polyamides possess a prime position due to their thermal and chemical stability. Herein, we report a simple, greener, catalyst-free, and solid-state synthesis of two unsaturated polyamides via a topochemical azidealkyne cycloaddition reaction. Two designed fumaramide monomers M1 and M2, functionalized with complementary azide and alkyne reactive motifs at the termini, reacted upon heating their crystalline powders and resulted in the formation of triazolyl-linked unsaturated polyfumaramides P1 and P2, respectively. We have characterized the reaction using various time-dependent techniques such as NMR, FTIR, PXRD, and DSC measurements. Interestingly, the monomer M1 resulted in 1,5-disubstituted triazole-linked unsaturated polyfumaramide (P1), whereas the monomer M2 polymerized into a polyfumaramide having both 1,4-disubstituted and 1,5-disubstituted triazole linkages (P2). Also, the trans-olefinic bond of both the fumaramide monomers was unaffected in the polymerization process and hence yielded unsaturated polymers having trans-olefin units in the repeating unit. Demonstrating the scope of postsynthetic modification, we have shown that unsaturation can be exploited for cross-linking via a light-induced [2 + 2] cycloaddition reaction. This first report on the solid-state synthesis of unsaturated polyfumaramides will be of great interest.

We report self-healing in crystals during topochemical polymerization. Pursuing our interest in chiral crystalline polymers, we synthesized a squaramide-based monomer for topochemical azide-alkyne cycloaddition polymerization. The squaramide unit biased the molecular packing in the crystal and aligned the molecules in head-to-tail fashion as designed, positioning the azide and alkyne units of adjacent molecules at proximity in an arrangement suitable for their topochemical click reaction. This monomer undergoes single-crystal-to-single-crystal (SCSC) polymerization, spontaneously at room temperature, via regiospecific 1,3-dipolar cycloaddition, yielding the corresponding triazole-linked polymer, in a few days. When heated at 60 oC, the polymerization completes in 24 h, in a SCSC manner. Interestingly, upon continuous heating from rt to 110 oC, the monomer crystals develop multiple cracks and they self-heal immediately. Increase in heating rate leads to the formation of longer and wider cracks, which also heal instantaneously. The self-healed crystals retained their integrity and for the first time, crystal structure of a self-healed crystal could be analyzed by single-crystal X-ray diffraction. The quality of the self-healed crystal and its diffraction data are as good as the fully reacted crystals, at rt or 60 oC, without developing cracks. Rational analyses for cracking and self-healing are presented.