scholarly journals Radical polymerization by a supramolecular catalyst: cyclodextrin with a RAFT reagent

2016 ◽  
Vol 12 ◽  
pp. 2495-2502 ◽  
Author(s):  
Kohei Koyanagi ◽  
Yoshinori Takashima ◽  
Takashi Nakamura ◽  
Hiroyasu Yamaguchi ◽  
Akira Harada
Keyword(s):  
Aqueous Solution ◽  
Molecular Weight ◽  
Complex Formation ◽  
Radical Polymerization ◽  
Chain Transfer ◽  
Reaction Yield ◽  
Host Molecule ◽  
Narrow Molecular Weight Distribution ◽  
X Ray ◽  
A Chain

Supramolecular catalysts have received a great deal of attention because they improve the selectivity and efficiency of reactions. Catalysts with host molecules exhibit specific reaction properties and recognize substrates via host–guest interactions. Here, we examined radical polymerization reactions with a chain transfer agent (CTA) that has α-cyclodextrin (α-CD) as a host molecule (α-CD-CTA). Prior to the polymerization of N,N-dimethylacrylamide (DMA), we investigated the complex formation of α-CD with DMA. Single X-ray analysis demonstrated that α-CD includes DMA inside its cavity. When DMA was polymerized in the presence of α-CD-CTA using 2,2'-azobis[2-(2-imidazolin-2-yl)propane dihydrochloride (VA-044) as an initiator in an aqueous solution, poly(DMA) was obtained in good yield and with narrow molecular weight distribution. In contrast, the polymerization of DMA without α-CD-CTA produced more widely distributed polymers. In the presence of 1,6-hexanediol (C6 diol) which works as a competitive molecule by being included in the α-CD cavity, the reaction yield was lower than that without C6 diol.

Synthesis of Polystyrene-B-Poly(Ethylene Oxide)monomethyl Ethermethacrylate Block Copolymers and its Self-Assembly in Aqueous Solution

2011 ◽  
Vol 284-286 ◽  
pp. 769-772
Author(s):  
Qian Qian You ◽  
Pu Yu Zhang
Keyword(s):  
Aqueous Solution ◽  
Molecular Weight ◽  
Block Copolymers ◽  
Self Assembly ◽  
Chain Transfer ◽  
Functional Group ◽  
Transmission Electron ◽  
Reversible Addition ◽  
Ft Ir ◽  
A Chain

The block copolymer of PSt-b-POEOMA with the end of -COOH functional group has been synthesized by reversible addition fragmentation chain-transfer (RAFT) using S,S′-Bis(α,α′-dimethyl-α′′-acetic acid)-trithiocarbonate (BDATC) as a chain transfer agent. The architectures of the copolymers were confirmed by FT-IR and 1HNMR spectra. GPC analysis was used to estimate the molecular weight and the molecular weight distribution of the copolymers. Meanwhile, The nanostructures of the block copolymers PSt-b-POEOMA micelles formed in aqueous solution were observed by transmission electron microscopy (TEM) and dynamic light scattering (DLS).

scholarly journals Further Effects of Chain-Length-Dependent Reactivities on Radical Polymerization Kinetics

2007 ◽  
Vol 60 (10) ◽  
pp. 754 ◽  
Author(s):  
Johan P. A. Heuts ◽  
Gregory T. Russell ◽  
Gregory B. Smith
Keyword(s):  
Molecular Weight ◽  
Radical Polymerization ◽  
Chain Length ◽  
Chain Transfer ◽  
Transfer Constant ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
A Chain ◽  
Chain Transfer Constant ◽  
Independent Chain

In the present paper, we finalize some threads in our investigations into the effects of chain-length-dependent propagation (CLDP) on radical polymerization kinetics, confirming all our previous conclusions. Additionally, and more significantly, we uncover some unexpected and striking effects of chain-length-dependent chain transfer (CLDTr). It is found that the observed overall rate coefficients for propagation and termination (and therefore the rate of polymerization) are not significantly affected by whether or not chain transfer is chain-length dependent. However, this situation is different when considering the molecular weight distributions of the resulting polymers. In the case of chain-length-independent chain transfer, CLDP results in a considerable narrowing of the distribution at the low molecular weight side of the distribution in a chain-transfer controlled system. However, the inclusion of both CLDP and CLDTr yields identical results to classical kinetics – in these latter two cases, the molecular weight distribution is governed by the same chain-length-independent chain transfer constant, whereas in the case of CLDP only, it is governed by a chain-length-dependent chain transfer constant that decreases with decreasing chain length, thus enhancing the probability of propagation for short radicals. Furthermore, it is shown that the inclusion of a very slow first addition step has tremendous effects on the observed kinetics, increasing the primary radical concentration and thereby the overall termination rate coefficient dramatically. However, including possible penultimate unit effects does not significantly affect the overall picture and can be ignored for the time being. Lastly, we explore the prospects of using molecular weight distributions to probe the phenomena of CLDP and CLDTr. Again, some interesting insights follow.

Modelling the Complete Molecular Weight Distribution in Chain Growth Polymerizations

2016 ◽  
Vol 1819 ◽  
Author(s):  
Ramiro Infante-Martínez ◽  
Enrique Saldívar-Guerra ◽  
Odilia Pérez-Camacho ◽  
Maricela García-Zamora ◽  
Víctor Comparán-Padilla
Keyword(s):  
Molecular Weight ◽  
Free Radical ◽  
Radical Polymerization ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Chain Transfer ◽  
Free Radical Polymerization ◽  
Experimental Program ◽  
Chain Growth ◽  
Coordination Polymerization

ABSTRACTThis work shows the development of several models for chain-growth polymerizations that admit the direct calculation of the complete molecular weight distribution of the polymer. The direct and complete calculation implies that no statistical mean values are employed as in the moments method neither numerical approximations like in the minimum-squared based methods. The free radical polymerization of ethylene (LDPE) and the coordination via metallocenes polymerization of ethylene (HDPE) are taken as examples for analysis.In the free radical polymerization case, the conventional scheme for chain-growth polymerization is adopted, with steps for initiation, propagation, chain transfer to small species and the additional step of chain transfer to dead chains [1]. The kinetic parameter are obtained from the open literature. Two kind of reactors were modelled: batch and continuous stirred tank reactor. For this last case, a simulation strategy was considered in which the run started from an initial known population of dead chains. Results show that typical non-linear polymerization profiles for the molecular weight distribution are obtained. For the coordination polymerization of ethylene via metalocenes, the standard coordination model was employed [2]. A two-site catalyst was considered and kinetic parameters reported in the open literature were used. For this study an experimental program in a lab-scale reactor was undertaken in order to obtain modelling data [3]. Results show that the standard model adequately reproduces the experimental data in the kinetic and molecular attributes of the polymer.

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