Dataset Information

Examining the Initiation of the Polymerization Mechanism and Network Development in Aromatic Polybenzoxazines.

ABSTRACT: Three bis-benzoxazine monomers based on the aniline derivatives of bisphenol A (BA-a), bisphenol F (BF-a), and 3,3'-thiodiphenol (BT-a) are examined using a variety of spectroscopic, chromatographic, and thermomechanical techniques. The effect on the polymerization of the monomers is compared using two common compounds, 3,3'-thiodiphenol (TDP) and 3,3'-thiodipropionic acid (TDA), at a variety of loadings. It is found that the diacid has a greater effect on reducing the onset of polymerization and increasing cross-link density and T_g for a given benzoxazine. However, the addition of >5 wt % of the diacid had a detrimental effect on the cross-link density, T_g, and thermal stability of the polymer. The kinetics of the polymerization of BA-a were found to be well described using an autocatalytic model for which values of n = 1.64 and m = 2.31 were obtained for the early and later stages of reaction (activation energy = 81 kJ/mol). Following recrystallization the same monomer yielded values n = 1.89, m = 0.89, and E_a = 94 kJ/mol (confirming the influence of higher oligomers on reactivity). The choice of additive (in particular the magnitude of its pK_a) appears to influence the nature of the network formation from a linear toward a more clusterlike growth mechanism.

SUBMITTER: Hamerton I

PROVIDER: S-EPMC3707310 | biostudies-literature | 2013 Jul

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Examining the Initiation of the Polymerization Mechanism and Network Development in Aromatic Polybenzoxazines.

Hamerton Ian I McNamara Lisa T LT Howlin Brendan J BJ Smith Paul A PA Cross Paul P Ward Steven S

Macromolecules 20130626 13

Three bis-benzoxazine monomers based on the aniline derivatives of bisphenol A (BA-a), bisphenol F (BF-a), and 3,3'-thiodiphenol (BT-a) are examined using a variety of spectroscopic, chromatographic, and thermomechanical techniques. The effect on the polymerization of the monomers is compared using two common compounds, 3,3'-thiodiphenol (TDP) and 3,3'-thiodipropionic acid (TDA), at a variety of loadings. It is found that the diacid has a greater effect on reducing the onset of polymerization an ...[more]

PMID: 23853391

Similar Datasets

Project description:NphB is an aromatic prenyltransferase that catalyzes the attachment of a 10-carbon geranyl group to aromatic substrates. Importantly, NphB exhibits a rich substrate selectivity and product regioselectivity. A systematic computational study has been conducted in order to address several question associated with NphB-catalyzed geranylation. The reaction mechanism of the prenylation step has been characterized as a S(N)1 type dissociative mechanism with a weakly stable carbocation intermediate. A novel ?-chamber composed of Tyr121, Tyr216, and 1,6-DHN is found to be important in stabilizing the carbocation. The observed difference in the rates of product formation from 5- and 2-prenylation arises from the differing orientations of the aromatic substrate in the resting state. 4-Prenylation shares the same resting state with 5-prenylation, but the lower free energy barrier for carbocation formation makes the latter reaction more facile. The high free energy barrier associated with 7-prenylation is caused by the unfavorable orientation of 1,6-DHN in active site pocket, along with the difficulty of proton elimination after the prenylation step. A water-mediated proton transfer facilitates the loss of hydrogen at the prenylation site to form the final prenylated product. Interestingly, the same crystallographically observed water molecule has been found to be responsible for proton loss in all three experimentally identified products. After proton transfer, the relaxation of the final product from a sp(3) carbon center to a sp(2) center triggers a "spring-loaded" product release mechanism which pushes the final product out of the binding pocket toward the edge of the active site. The hydrogen bond interactions between the two hydroxyl groups of the aromatic product and the side chains of Ser214 and Tyr288 help to "steer" the movement of the product. In addition, mutagenesis studies identify these same two side chains as being responsible for the observed regioselectivity, particularly 2-prenylation. These observations provide valuable insights into NphB chemistry, offering an opportunity to better engineer the active site and to control the reactivity in order to obtain high yields of the desired product(s). Furthermore, the S(N)1 reaction mechanism observed for NphB differs from the prenylation reaction found in, for example, the farnesyltransferase, which proceeds via an S(N)2-like reaction pathway. The spring-loaded release mechanism highlighted herein also offers novel insights into how enzymes facilitate product release.

Dataset Information

Examining the Initiation of the Polymerization Mechanism and Network Development in Aromatic Polybenzoxazines.

Publications

Examining the Initiation of the Polymerization Mechanism and Network Development in Aromatic Polybenzoxazines.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets