Number-average Molecular Weight Of Poly Research Articles

Synthesis of poly(4-methoxyphenol) by enzyme-catalyzed polymerization and evaluation of its antioxidant activity

The efficient polymerization of 4-methoxyphenol in an aqueous micelle system has been realized with horseradish peroxidase as an enzymatic catalyst and sodium dodecyl sulfate as a surfactant. The obtained polymer is a kind of light yellow powder, which is completely soluble in acetone, DMF, DMSO and THF. Particle size distribution and 1H NMR analysis indicate that the polymerization is performed mainly in the palisade layer of micelles. The number-average molecular weight of poly(4-methoxyphenol) measured by gel permeation chromatography (GPC) is about 1000. IR analysis shows that both phenylene and oxyphenylene units are contained in the polymer structure. Results of antioxidant activity tests indicate that poly(4-methoxyphenol) possesses excellent antioxidant properties and may be used as a highly efficient antioxidant agent.

Organostibine mediated controlled/living random copolymerization of styrene and methyl methacrylate

The first example of organostibine mediated controlled/living random copolymerization of styrene (St) and methyl methacrylate (MMA) was achieved by heating a solution of St/MMA/organostibine mediator at 100 °C or St/MMA/organostibine mediator/AIBN with various monomer feed ratios at 60 °C. The addition of AIBN significantly decreased the reaction temperature and enhanced the rate of copolymerization. The structure of poly(St-co-MMA) was verified by 1H NMR. The reactivity ratios at 60 °C were determined by the extended Kelen-Tudős method to be γSt = 0.40 and γMMA = 0.44. The ln([M]0/[M]) increased linearly with increasing reaction time. The number-average molecular weights of poly(St-co-MMA) increased linearly with conversion. Poly(St-co-MMA) with expected number-average molecular weight and low polydispersity index was formed. The living characteristic was further confirmed by chain-extension of poly(St-co-MMA) to form poly(St-co-MMA)-b-PMMA.

Zero-valent Iron/RAFT Agent-Mediated Polymerization of Methyl Methacrylate at Ambient Temperature

In this work, zero-valent iron powder (Fe(0)) was used to catalyze the polymerization of methyl methacrylate (MMA) in the presence of a reversible addition−fragmentation chain transfer (RAFT) agent, 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN) without any ligand at ambient temperature. The polymerization behavior complied with the features of typical “living”/controlled radical polymerizations. The number-average molecular weights of poly(methyl methacrylate) increased linearly with monomer conversion, while maintaining narrow molecular weight distributions (Mw/Mn < 1.50). Even at low concentration of Fe(0), such as at [MMA]0:[CPDN]0:[Fe(0)]0 = 200:1:0.2, the polymerization was also controllable; however, it presented a depressed polymerization rate and a prolonged induction period (about 12 h). The polymerization rate also decreased with increasing of CPDN concentration. From experimental results, it was deduced that the initiating species were derived from the cooperative reaction of Fe(0) and CPDN, in which CPDN acted as a pseudohalide alkyl initiator. The control process was supposed to proceed via a synactic mechanism. One mechanism was the synergic mediation by Fe(0) and CPDN, in which Fe(III) formed in situ acted as an deactivator, however, this deactivation was supposed to be ineffective. The other was the RAFT mechanism with CPDN as the RAFT agent, which may dominate the whole control.

Synthesis and properties of N-substituted maleimides conjugated with 1,4-phenylene or 2,5-thienylene polymers

π-Conjugated polymers are particularly interesting in the field of electro-optic materials because of their desirable properties such as electrical conductivity, nonlinear optics and electroluminescence. Coupling polymerizations of 2,3-dibromo-N-substituted maleimide (DBrRMI) (R=benzyl, phenyl, cyclohexyl, n-hexyl and n-dodecyl) were carried out using palladium or nickel catalysts. The number-average molecular weights of poly(RMI-alt-Ph) obtained by Suzuki–Miyaura cross-coupling polymerizations of DBrRMI with benzene-1,4-boronic acid or 2,5-thiophene diboronic acid were 680–1270 by gel permeation chromatographic analyses. By contrast, Yamamoto coupling polymerizations of DBrRMI with diiodobenzene gave random poly(RMI-co-Ph) results. Poly(RMI-co-Ph)s exhibited a higher thermal stability than monomer and poly(RMI-alt-Ph). Copolymers showed strong photoluminescence from yellow to light blue colors in tetrahydrofuran. Coupling polymerizations of 2,3-dibromo-N-substituted maleimide (DBrRMI) (R=benzyl (DBrBnMI), phenyl (N-phenyl-2,3-dibromomaleimide (DbrPhMI)), cyclohexyl (N-cyclohexyl-2,3-dibromomaleimide), n-hexyl (N-n-hexyl-2,3-dibromomaleimide) and n-dodecyl (N-n-Dodecyl-2,3-dibromomaleimide, DBrDMI)) were carried out using palladium or nickel catalysts. Number-average molecular weights (Mn) of poly(RMI-alt-Ph) or poly(RMI-alt-TP) obtained by Suzuki–Miyaura cross-coupling polymerizations of DBrRMI with benzene-1,4-boronic acid (PhDB) or 2,5-thiophene diboronic acid (TPDB) were 680–1270 by GPC analyses. In contrast, coupling polymerizations of DBrRMI with 1,4-diiodobenzene gave random poly(RMI-co-Ph). Poly(RMI-co-Ph)s exhibited higher thermal stability than monomer and poly(RMI-alt-Ph). Copolymers showed strong photoluminescence from yellow to light blue color in THF.

Single-Electron Transfer Living Radical Polymerization (SET−LRP) of Methyl Methacrylate (MMA) with a Typical RAFT Agent as an Initiator

A typical reversible addition−fragmentation chain transfer (RAFT) agent, 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN), was used as a single electron transfer-living radical polymerization (SET−LRP) initiator for methyl methacrylate (MMA) polymerization at 25 °C. At 1:1 molar ratio of [CPDN]0/[Cu(0)]0, the apparent rate constants of propagation (kpapp) were 0.037, 0.049, and 0.072 h−1 for [MMA]0/[CPDN]0 of 225/0.2, 225/0.5, and 225/1, respectively. The number-average molecular weight of poly(methyl methacrylate) (PMMA) increased linearly with monomer conversion, and narrow molecular weight distributions (Mw/Mn < 1.50) were found at most cases. At high molar ratio of [CPDN]0 to [Cu(0)]0, such as 1:0.1 in this work, the polymerization was also controllable, whereas it a presented markedly depressed polymerization rate and an obvious induction period. 1H NMR spectroscope and matrix assisted laser desorption/ionization time-of-flight mass spectrometry confirmed that PMMA chain was end-capped by CPDN species wit...

On the number-average molecular weight of poly(1,4- trans isoprene) determined by conventional GPC

We became aware, in the course of our on-going research, that the number-average molecular weight of poly(1,4- trans isoprene) determined by conventional gel permeation chromatography (GPC) in tetrahydrofuran (THF) using polystyrene standards differs from its true value by a factor 2. As far as we know, the Mark-Houwink coefficients of this polymer in a widespread GPC eluent such as THF have never been determined. We provide in this contribution a simple relationship between the number-average molecular weight of poly(1,4- trans isoprene) determined by GPC in THF using polystyrene standards and its true value.

Radical polymerization of benzylN-(2,6-dimethylphenyl)itaconamate

The polymerization of benzyl N-( 2,6-dimethylphenyl)itaconamate (BDMPI) with benzoyl peroxide (BPO) in N,N-dimethylformamide (DMF) was studied kinetically by ESR. The polymerization rate (R P ) at 70°C was given by R P = k[BPO] 0.78 [BDMPI] 11 . The overall activation energy of polymerization was determined to be 83.7 kJ/mol. The number-average molecular weight of poly( BDMPI) was in the range of 1500-2000 by gel permeation chromatography. From the ESR study, the polymerization system was found to involve ESR-observable propagating radicals of BDMPI under practical polymerization conditions. Using the polymer radical concentration by ESR, the rate constants of propagation (k P ) and termination (k t ) were determined in the temperature range of 50-70°C. The k P value seemed dependent on the chain-length of propagating radical. The analysis of polymers by the MALDI-TOF mass spectrometry suggested that most of the resulting polymers contain the dimethylamino terminal group. The copolymerization of BDMPI (M 1 ) and styrene (M 2 ) at 50°C in DMF gave the following copolymerization parameters; r 1 = 0.49, r 2 = 0.26, Q 1 = 1.2, and e 1 = +0.63. The thermal behavior of poly(BDMPI) was examined by dynamic thermogravimetry and differential scanning calorimetry.

Radical polymerization of benzyl N‐(2,6‐dimethylphenyl)itaconamate

The polymerization of benzyl N-(2,6-dimethylphenyl)itaconamate (BDMPI) with benzoyl peroxide (BPO) in N,N-dimethylformamide (DMF) was studied kinetically by ESR. The polymerization rate (Rp) at 70°C was given by Rp = k[BPO]0.78[BDMPI]1.1. The overall activation energy of polymerization was determined to be 83.7 kJ/mol. The number-average molecular weight of poly(BDMPI) was in the range of 1500–2000 by gel permeation chromatography. From the ESR study, the polymerization system was found to involve ESR-observable propagating radicals of BDMPI under practical polymerization conditions. Using the polymer radical concentration by ESR, the rate constants of propagation (kp) and termination (kt) were determined in the temperature range of 50–70°C. The kp value seemed dependent on the chain-length of propagating radical. The analysis of polymers by the MALDI-TOF mass spectrometry suggested that most of the resulting polymers contain the dimethylamino terminal group. The copolymerization of BDMPI (M1) and styrene (M2) at 50°C in DMF gave the following copolymerization parameters; r1 = 0.49, r2 = 0.26, Q1 = 1.2, and e1 = +0.63. The thermal behavior of poly(BDMPI) was examined by dynamic thermogravimetry and differential scanning calorimetry. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1891–1900, 1997

A Study of Poly(hydroxyalkanoate)s by Quantitative 31P NMR Spectroscopy: Molecular Weight and Chain Cleavage

Quantitative 31 P NMR spectroscopy has been found to be a valuable tool for the determination of number-average molecular weight of poly(hydroxyalkanoate) (PHA) homo- and copolymers. Due to the 100% natural abundance of 31 P, the technique is highly sensitive and can be used for high molecular weight polymers with satisfactory results. Furthermore, it is shown that quantitative 31 P NMR can contribute to the understanding of the mechanism of acid hydrolysis of PHA and the microstructure sof acid hydrolysis products

Determination of the end-group concentration and molecular weight of poly(ethylene naphthalene-2,6-dicarboxylate) using infra-red spectroscopy

Infra-red (i.r.) end-group analysis is used to determine the hydroxyl and carboxyl end-group concentrations and therefore the number-average molecular weight of poly(ethylene naphthalene-2,6-dicarboxylate)(PEN) film samples in the solid state. The end-group i.r. spectrum of a sample is obtained by subtracting the i.r. spectrum of a deuterated control sample from the experimental sample i.r. spectrum. We have used integral absorbances obtained from fitted absorption bands in the i.r. spectra of PEN for the calculation of end-group concentrations. Using this method, the limitations of chemical methods of determination of end-group concentrations caused by the poor solubility of PEN are avoided. In addition, corrections can readily be made to allow for difference in crystallinity between the control and the experimental samples. The extinction coefficients for the OH stretching vibration in the hydroxyl and for the carboxyl end-groups have been determined for PEN as well as for poly(ethylene terephthalate). Both the hydroxyl and the carboxyl end-group concentrations, and the number-average molecular weight of the samples, can then be easily determined from the i.r. absorbances.

Catalytic Chain Transfer for Molecular Weight Control in the Emulsion Polymerization of Methyl Methacrylate and Methyl Methacrylate−Styrene

The application of catalytic chain transfer in the emulsion homopolymerization of methyl methacrylate and copolymerization of methyl methacrylate and styrene has been examined. [Bis[μ-[(2,3-butanedione dioximato)(2−)-O:O‘]] tetrafluorodiborato(2−)-N, N‘,N‘‘,N‘‘‘]cobalt (COBF, 1) has been used as a low-spin cobalt(II) catalytic chain transfer agent. The number-average molecular weight of poly(methyl methacrylate) is decreased from over 120 000 in the absence of catalytic chain transfer agent to less than 3000 on addition of 36 ppm of 1 remaining constant throughout the reaction while the polydispersity index was maintained at approximately equal to 2. The mechanism is essentially the same as in solution or bulk with very small amounts of primary radical initiation, undetectable by matrix-assisted laser desorption ionization time of flight mass spectrometry, and vinyl unsaturation at the terminal end of each polymer molecule. Copolymerization of methyl methacrylate with styrene has also been demonstrated. Catalytic chain transfer polymerization has been shown to be an extremely effective method of controlling molecular weight under emulsion conditions. The effects of catalytic chain transfer agent level, feed conditions, and styrene level are presented. The behavior of catalytic chain transfer in emulsion proves to be more complicated than in solution, due to partitioning of the catalytic chain transfer agent in the compartmentalized system. COBF partitions almost equally between the organic and aqueous phases. The feed profile of each reaction ingredient is important, with the best results being obtained when catalyst is fed continually as a solution in the monomer feed. A critical level of catalyst is apparent which is shown to be related to the number of catalyst molecules per particle.

Evaluation of number‐average molecular weight of poly(tetrafluoroethylene) irradiated with γ rays

AbstractThe number‐average molecular weight of poly(tetrafluoroethylene) (PTFE) irradiated from a 60Co source in air at room temperature has been estimated from the experimental results of tensile creep measurements and electron microscopy. The viscoelastic method which makes use of the maximum relaxation time was used for samples with low radiation doses. The mean chain length of highly irradiated samples, which can form fully extended chain crystals upon crystallization from the melt, was obtained from the bandwidth distribution on micrographs of the fracture surfaces. The dependence of the average molecular weight on the radiation dose is derived on the basis of a statistical treatment in which effects of cages in the process of chain scission and of molecules evolved out of the specimen, together with random decomposition of polymer backbone chains, are considered. Good agreement between the experimental and calculated results is attained over a wide range of radiation doses.