The synthesis and characterization of novel self-complementary multiple hydrogen-bonded (SCMHB) polymers containing pendant 2-ureido-4[1H]-pyrimidone (UPy) units are described. SCMHB pendant polymers, poly(butyl acrylate-co-SCMHB methacrylate), were prepared via free radical copolymerization of butyl acrylate (BA) and a novel SCMHB methacrylate (SCMHB MA) monomer, which was synthesized via a quantitative coupling reaction between 2-isocyanatoethyl methacrylate (ICEMA) and methyl isocytosine (MIS) in DMSO. The glass transition temperatures of poly(BA-co-SCMHB MA) increased in a linear fashion as the SCMHB MA content increased. Thermogravimetric analysis of the copolymers exhibited an onset of weight loss at 217 °C. Solution viscosity analysis indicated that SCMHB pendant polymers strongly aggregated in nonpolar solvents, such as toluene and CHCl3, and dissociated in polar solvents, such as THF. Based on melt rheological characterization, the melt viscosity of soluble SCMHB pendant polymers was an order of magnitude higher than that of PBA due to strong aggregation in the melt state. SCMHB pendant polymers exhibited thermoreversible characteristics, and complete dissociation in the melt state was observed at 80 °C, which was consistent with our earlier studies involving SCMHB-terminated poly(styrene) (PS), poly(isoprene) (PI), and PS-b-PI block copolymers. In addition, SCMHB units completely dissociated at 80 °C in toluene on the basis of 1H NMR measurements. The 90° peel strength values for SCMHB-containing polymers increased as the SCMHB units increased due to the strong interaction of SCMHB units with the glass surface. Thin-layer chromatography indicated that the interaction of SCMHB pendant polymers with silica was more favorable compared to PBA homopolymer.

The synthesis and characterization of terminal multiple hydrogen-bonded (MHB) polymers, such as poly(styrene) (PS), poly(isoprene) (PI), and microphase separated PS-b-PI block copolymers, possessing controlled molecular weights and narrow molecular distributions are described. Hydroxyl-terminated polymeric precursors were prepared using living anionic polymerization and subsequent quantitative termination with ethylene oxide. MHB polymers were synthesized in a controlled fashion via end-group modification of these well-defined macromolecular alcohols with excess isophorone diisocyanate and subsequent derivatization of the isocyanate-terminated polymeric intermediate with methyl isocytosine. The glass transition temperatures of the terminal MHB polymers were reproducibly higher than both nonfunctionalized and hydroxyl-terminated polymers at nearly equivalent number average molecular weights. Thin-layer chromatography analysis indicated that the interaction of terminal MHB polymers with silica was stronger as compared to both nonfunctionalized and hydroxyl-terminated polymers. Rheological characterization indicated that the melt viscosity at constant shear rate for various MHB polymers was more than 100 times higher than those for nonfunctionalized and hydroxyl-terminated polymers. Interestingly, the melt viscosity of MHB polymers was higher than those of nonfunctionalized polymers with twice the number average molecular weight. In addition, DSC and rheological characterization also suggested that terminal MHB polymers formed aggregates and not simple dimers in the melt state, and the aggregates were observed to completely dissociate at 80 degrees C.

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...

Hydrogen bonding uracil functionalized polystyrenes and poly(alkyl acrylate)s were synthesized via stable free radical polymerization. Quantitative chain end functionalization was achieved using novel uracil containing TEMPO-and DEPN-based alkoxyamine unimolecular initiators. Polymerizations were conducted at 130°C and yielded functionalized homopolymers with narrow molecular weight distributions (M w/Mn ∼ 1.20) and predictable molecular weights. Polymerizations of both n-butyl acrylate and styrene using the DEPN-and TEMPO-based alkoxyamines resulted in molecular weight control over a wide range of conversions. Terminal functionalization of poly(alkyl acrylate)s with hydrogen bonding groups increased the melt viscosity at temperatures below 80°C, which was defined as the dissociation temperature, and as expected, the viscosity approached that of the nonfunctional analogues above this temperature. The hydrogen bonding effect was also evident in thermal (DSC) analysis and 1 H NMR spectroscopic investigations, and low molar mass polystyrenes exhibited glass transition temperatures that were consistent with a higher apparent molar mass. 1 H NMR spectroscopy confirmed the presence of a single hydrogen bonding group at the chain terminus, which was consistent with a well-defined initiation process for two families of novel alkoxyamines.

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