Cyclization Of Monomers Research Articles

The effect of CX (alkyl groups) on the migration insertion polymerization (MIP) of PFpCX [PFp = (PPh2(CH2)3Cp)Fe(CO)2

Migration insertion polymerization (MIP) of organometallic monomers, PFpCX [PFp = (PPh2(CH2)3Cp)Fe(CO)2, CX = (CH2)X-1CH3, X = 12 or 18] was performed under various conditions. The oligomerization occurred in accompany with the monomer cyclization generating PFpCX small rings at the early stage, which was followed by a complete cyclization of the oligomers generating P(PFpCX)n macrocycles. PFpCX small rings could be completely removed via precipitating the crude products in a poor solvent for the macrocycles. The solution and bulk MIP of PFpCX (X = 12 or 18) had a similar cyclization rate but both were significantly accelerated at a higher MIP temperature (100 °C). It is explained by the temperature-dependent tendency for the cyclization. The dependence of degree of polymerization (DP) on the MIP conditions was discussed and the self-assembly of resultant P(PFpC12)n was examined.

Oriental Energy once again selects Grace's UNIPOL PP process technology

Migration insertion polymerization (MIP) of organometallic monomers, PFpCX [PFp = (PPh2(CH2)3Cp)Fe(CO)2, CX = (CH2)X-1CH3, X = 12 or 18] was performed under various conditions. The oligomerization occurred in accompany with the monomer cyclization generating PFpCX small rings at the early stage, which was followed by a complete cyclization of the oligomers generating P(PFpCX)n macrocycles. PFpCX small rings could be completely removed via precipitating the crude products in a poor solvent for the macrocycles. The solution and bulk MIP of PFpCX (X = 12 or 18) had a similar cyclization rate but both were significantly accelerated at a higher MIP temperature (100 °C). It is explained by the temperature-dependent tendency for the cyclization. The dependence of degree of polymerization (DP) on the MIP conditions was discussed and the self-assembly of resultant P(PFpC12)n was examined.

Competition between Ring-Closing Migratory Insertion Polymerization and Monomer Cyclization

Migratory insertion polymerization (MIP) of PFpR [PFp = (PPh2(CH2)3Cp)Fe(CO)2, R = (CH2)4CH═CH2 or (CH2)5CH3] (1) involved competitive MIP ring-closing polymerization and monomer cyclization (MC), producing P(PFpR) macrocycles (2) and PFpR rings (3), respectively. MC, generating 3, occurred at the early stage of MIP, while the growing polymer chains exclusively underwent ring-closing cyclization without producing any linear analogues. The effect of solvent, temperature, and the concentration of 1 on the competition between the ring-closing MIP and MC was investigated. 3 was synthesized as the only product in THF with a low concentration of 1 (1 wt %), while the ring-closing MIP predominated under the condition at 60 °C with a high concentration of 1 in THF (>70 wt %), resulting in 2 with Mn up to 17 500 g/mol. This effective synthesis of ring molecules is attributed to the piano-stool coordination geometry and the low rotation barrier of Cp–Fe bond and will facilitate further exploration of ring molecules as functional materials and supramolecular building blocks.

On-Surface Synthesis of BN-Substituted Heteroaromatic Networks.

We report on the bottom-up fabrication of BN-substituted heteroaromatic networks achieved by surface-assisted polymerization and subsequent cyclodehydrogenation of specifically designed BN-substituted precursor monomers based on a borazine core structural element. To get insight into the cyclodehydrogenation pathway and the influence of molecular flexibility on network quality, two closely related precursor monomers with different degrees of internal cyclodehydrogenation have been employed. Scanning tunneling microscopy shows that, for both monomers, surface-assisted cyclodehydrogenation allows for complete monomer cyclization and the formation of covalently interlinked BN-substituted polyaromatic hydrocarbon networks on the Ag(111) surface. In agreement with experimental observations, density functional theory calculations reveal a significantly lower energy barrier for the cyclodehydrogenation of the conformationally more rigid precursor monomer, which is also reflected in a higher degree of long-range order of the obtained heteroaromatic network. Our proof-of-concept study will allow for the fabrication of atomically precise substitution patterns within BNC heterostructures.

Synthesis of 4-iodotetrahydropyran-containing polymersvia TMSI-promoted Prins cyclization

4-Iodotetrahydropyran (THP)-containing polymers were synthesized via Prins cyclization of monomers with an aldehyde moiety and a homoallylic alcohol moiety. The progress of polymerization was confirmed by NMR and GPC analysis. The deiodination of the THP in the polymer structure was carried out by reductive hydrogenation using AIBN and tributyltin hydride. Thermogravimetric analysis (TGA) was performed for the THP-containing polymers.

Mechanistic studies of ammonia borane dehydrogenation

Ammonia borane (NH3BH3, AB) has received extensive attention as a potential hydrogen storage medium, however hydrogen release mechanisms from AB are not well understood. AB follows different reaction routes if the dehydrogenation occurs in solvent or solid state, but a comparative study for AB dehydrogenation in these two states is not available. In this work, a detailed study of AB dehydrogenation mechanism in diglyme and solid state is presented, and a comprehensive reaction network for both cases is proposed. The experimental and DFT results suggest that two main reaction pathways occur; one involves cyclization of monomers which results in faster dehydrogenation at lower temperature, while the other involves propagation to acyclic intermediates which requires higher temperature to carry out the cyclization step. AB dehydrogenation in solid state was experimentally found to be initiated by B–N bond cleavage and not by direct dehydrogenation, which agrees with high level CCSD(T)/MP2 calculations reported previously. It was found that diglyme plays a significant role in hindering B–N bond cleavage of AB which facilitates the cyclization pathway. In solid state, experiments including labeled AB (ND3BH3) mapped out the source of hydrogen (from hydridic or protonic ends), and a clear difference in the degree of dehydrogenation from the two ends is demonstrated.

Click to Join Peptides/Proteins Together

Copper(I) is able to catalyze Huisgen 1,3-dipolar cycloaddition in a "click" fashion. This copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction presents excellent chemoselectivity and occurs over a wide-range of reaction conditions. It shows tolerance to variation in both pH and solvent polarity, thereby facilitating the ligation of peptides and proteins to produce peptidomimetics and synthetic proteins. In addition, the only product formed is a 1,4-disubstituted-1,2,3-triazole moiety, in many aspects resembling the natural peptide bond, including hydrogen-bonding capability, planarity, distance between the 1 and 4 substituents, and conformational restriction of the peptide backbone; thus the triazole-backbone-modified peptide, in which a triazole replaces the amide bond, may be anticipated to present a secondary structure similar to that of its natural counterpart. This Focus Review describes the scope and applications of copper(I)-catalyzed alkyne–azide cycloaddition in synthetic peptide/protein chemistry.

Viscoelastic Shear Response and Network Structure in Polycyanurates

The shear response of polycyanurate networks with different cross-link densities, varied by changing the ratio of difunctional to monofunctional cyanate ester, is measured from shear stress relaxation and dynamic experiments. Master curves are constructed following the time−temperature superposition principle, and the temperature dependence of the shift factors is examined. The discrete relaxation time spectra are calculated from the viscoelastic responses and are found to be independent of cross-link density over the time/frequency range measured. The cross-link density, determined from the rubbery modulus, and the sol content, measured from sol extraction experiments, are modeled for the fully cured polycyanurate networks using the recursive method; a monomer cyclization reaction is assumed in the modeling based upon the chemical composition of the sol which was determined by mass spectroscopy. The effect of monomer cyclization on the conversion at gelation of dicyanate esters is discussed.

Unusually facile cyclopolymerization of a new allyl ether substituted acrylate and confirmation of repeat unit structure by INADEQUATE NMR

Ethyl α-[(allyloxy)methyl]acrylate and allyl α-(hydroxymethyl)acrylate were synthesized and polymerized. The allyl ether was found to undergo virtually complete cyclopolymerization in solution and in bulk. Ring size was determibed using the two-dimensional INADEQUATE NMR method. 13 C solution NMR spectral characterization gives well-defined chemical shift differences for cis and trans isomers, which can be explained by γ-gauche shielding for carbons in or next to the polymer backbone. Two dimensional INADEQUATE analysis conclusively confirms monomer cyclization exclusively to five membered rings with a ratio of trans to cis ring configurations in the polymer backbone of approximately 2.2