Synthesis and Characterization of Novel Complementary Multiple-Hydrogen Bonded (CMHB) Macromolecules via a Michael Addition

Abstract

The synthesis and characterization of novel complementary multiple hydrogen-bonded poly-(styrene) (CMHB-PS) oligomers possessing controlled molecular weights and narrow molecular distributions are described. Novel CMHB-PS oligomers comprising terminal heterocyclic base units were synthesized in a controlled fashion via derivatization of well-defined hydroxyl-terminated PS. The heterocyclic-terminated oligomers were synthesized via a Michael addition of the corresponding heterocyclic compounds such as adenine, thymine, and 2,6-purine with acrylated PS. The acrylated PS precursors were prepared in a quantitative fashion via reaction of hydroxyl-terminated PS with acryloyl chloride in the presence of triethylamine. Terminal heterocyclic bases were introduced via a Michael addition in the presence of potassium tert-butoxide (t-BuOK). Novel CMHB-PS aggregates were prepared via subsequent solution blending of PS with complementary heterocyclic base units. 1 H NMR analysis confirmed that a 1:1 mixture of adenine-PS or purine-PS with thymine-PS formed complementary multiple hydrogen bonding and exhibited thermoreversibility. In addition, 1 H NMR analysis confirmed that complementary hydrogen bonds dissociated at 95°C in deuterated toluene. IntroductionMultiple hydrogen bonding in molecular design has recently received significant attention due to the propensity to form new supramolecular structures that exhibit thermoreversible characteristics. In addition, reversible molecular recognition is also attainable due to relatively weak noncovalent bonds compared to covalent bonds. 1-7 Multiple hydrogen bonding scaffolds are classified into two different families: (1) selfcomplementary multiple hydrogen bonds (SCMHB), which are formed between identical hydrogen bonding units and (2) complementary multiple hydrogen bonds (CMHB), which are formed between dissimilar hydrogen bonding units containing complementary donor and acceptor sites. Meijer et al. recently reported the versatility of SCMHB between 2-ureido-4[1H]-pyrimidone (UPy) units, which strongly self-dimerize through four hydrogen bonds arranged in donor-donor-acceptoracceptor sites. [8][9][10][11][12][13][14][15][16][17] The aggregated molecules containing SCMHB units exhibited polymer-like properties including shear thinning in the melt phase, viscoelastic behavior in the solid state, and glass transition temperatures. Supramolecular structures possessing CMHB units have also received significant attention in the literature. [18][19][20][21][22] In particular, heterocyclic base pairing between adenine, guanine, thymine, uracil, and tyrosine in DNA and RNA are well-known as tailored CMHB pairs in biological systems. Recent research efforts in this rapidly evolving area have focused on the design of supramolecular structures consisting of tailored CMHB with extremely high dimerization constants. Initial supramolecular systems based on CMHB were reported by Lehn, [24][25][26][27][28][29] Kato and Fréchet,[30][31][32][33][34][35] These diverse efforts focused on the sele...

Model Transient Networks from Strongly Hydrogen-Bonded Polymers

“…n-Butyl acrylate was chosen as the primary monomer in the random copolymers due to its low T g , but it was expected that copolymerization with the UPy acrylate monomer might increase the overall T g of the polymer, either due to the presence of hydrogen bonds and slowing of the chain dynamics or simply due to the steric effects on the backbone. As shown in Figure 1, a linear increase in T g with increasing incorporation of UPy was observed, consistent with prior reports of UPy-functional random copolymers; 49,55 note, however, that even at high UPy loadings, the polymer T g is still below room temperature and at least 40°C below the lowest temperature for rheological measurements. Figure 2 shows the overall effects on rheological properties of the increase in mole fraction of UPy acrylate in random copolymers at constant molecular weight (irreversible changes in the rheological data began to occur at temperatures greater than 120°C so higher temperature data are not included in the master curves).…”

Supramolecular Biomaterials. A Modular Approach towards Tissue Engineering

“…63 Nucleobases were used as recognition motifs to functionalize low molecular weight prepolymers by the groups of Rowan 64,65 and Long. [66][67][68] Upon modification of the bisamino end-groups of telechelic PTHF with a molecular weight around 2 kg mol À1 with adenine-or cytosine-derivatives, respectively polymers 1 and 2, the material properties changed dramatically from a soft waxy solid to flexible materials with enough mechanical stability to be processed into fibers and films (Fig. 16).…”

“…Long and co-workers have functionalized poly(styrenes) (PS) with adenine, thymine, or uracil. 66,67 They found assemblies of adenine-PS and thymine-PS in solution. Besides that, they also showed the synthesis of uracil-modified poly(n-butyl)acrylate.…”

Phase Behavior of Complementary Multiply Hydrogen Bonded End-Functional Polymer Blends

“…19 The nature of the interaction varies widely and most commonly consists of either metal-ligand, 20,21 ionic, 22,23 or hydrogen bonding. 24,25 Incorporation of these into various macromolecular architectures such as diblock, [26][27][28][29][30][31][32][33][34][35] triblock, [36][37][38] multiblock, [39][40][41] star 42 and graft copolymers, [43][44][45] blends, 35,46 and gels 47,48 has resulted in remarkably simple thermal control over the polymer structure and related properties.…”