An experimental investigation of the kinetics of the thermally initiated free radical polymerization of p-methyl styrene in bulk at temperatures of 120°, 140° and 160° in the conversion range, 0–96% is reported. Conversions were measured gravimetrically and by gas chromatography and molecular weight distributions and weight-average molecular weights by size exclusion chromatography (SEC) and low angle laser light scattering photometry (LALLSP). A kinetic model which accounts for diffusion-controlled termination and predicts conversion/time and molecular weight and long chain branching development for nonisothermal polymerizations has been developed. This model should find use in the design, simulation and optimization of poly(p-methyl styrene) reactors. 相似文献
The cobalt‐mediated radical polymerization of acrylonitrile in DMSO using cobalt (II) acetylacetonate [Co(acac)2] as mediator is studied. Both the evolution of molecular weight and conversion over time under various conditions are monitored. Molecular weights increase sharply at the beginning of the reaction and subsequently grow linearly with conversion. No branching of the polymer is observed by 13C NMR. By a careful design of the reaction parameters, number‐average molecular weights >1.2 · 105 g · mol?1 with a PDI around 2.4 together with conversions of up to 90% within 24 h are achieved. The copolymerization parameters of acrylonitrile with methyl methacrylate in DMSO at 30 °C are determined using the Kelen‐Tüdõs approach giving rAN = 0.33, rMMA = 0.71.
A novel mathematical model is developed that predicts the detailed macromolecular structure of an acrylonitrile-butadiene rubber (NBR) produced in an industrial emulsion polymerization. The model consists of: (i) a basic module that calculates the monomer conversion and the copolymer composition; (ii) a particle size distribution module; and (iii) a macromolecular structure module that calculates the bivariate chain length distributions of the linear fraction and of each branched topology (characterized by the number of branching points per molecule). From the bivariate distributions, the univariate distributions of molecular weights, copolymer composition, and degrees of branching are obtained. The model was validated from global measurements of conversion, average molecular weights, average composition, and average degrees of branching. 相似文献
Summary
The anionic polymerization and copolymerization of butyl and benzyl malolactonates initiated with potassium acetate/dibenzo-18-crown-6
or [222] complex have been studied at 40°C in bulk and in dichloromethane and tetrahydrofuran solutions. Kinetics and polymer
molecular weights were followed by SEC. In bulk and for conversion below 30%, molecular weights are close to those calculated
for a living process then the conversion increase leads to a significant discrepancy between theoretical and measured molecular
weights. In solution, side reactions take place significantly and no evident relationship between molecular weight and initiator
concentration can be established, even at low conversion. Same situation was observed in the case of block copolymers synthesis.
At last, evidence for transfer reactions has been shown by using model reactions.
Received: 11 September 1997/Revised version: 22 January 1998/Accepted: 23 January 1998 相似文献
The aqueous polymerization of methyl methacrylate in the absence and in the presence of some anions of nickel salts was carried out at temperatures of 40°C, 50°C, and 60°C using sodium bisulfite as initiator. The nitrate anion (NO) was found to have the highest catalytic effect and resulted in polymers having the least average molecular weights, while the sulfate anion (SO) was found to have the least catalytic effect and resulted in polymers having the highest average molecular weights. The apparent activation energy for the polymerization process was found to be 4.3, 3.6, 3.8, and 4.8 × 104 J/mol in the absence and in the presence of Ni(NO3)2, NiCl2, and NiSO4 containing the same amount of nickel (0.00587 g). 13C-NMR spectra for the polymers obtained in the absence and in the presence of different nickel anions were found to result in nearly the same tacticity. 相似文献
One-phase microemulsion regions at 25 and 60 °C and the polymerization at 60 °C in o/w microemulsion formed by 1,3-butadiene,
water, and a mixture of the surfactants, dodecyltrimethylammonium bromide, and didodecyldimethylamonium bromide (3/1 w/w),
are reported. The polybutadienes obtained here have similar characteristics to those of their homologous obtained by emulsion
polymerization, with the only difference that the average particle size of the former (25–30 nm) was smaller by an order of
magnitude. The obtained polymer had high average molecular weights, but the gel content at high conversion is lower than the
value for a conventional emulsion polymerization. The DSC measurements showed that the polymer has a single glass transition
temperature at −72.5 ± 1.5 °C. 相似文献
Block copolymerization of 2‐(N,N‐dimethylamino)ethyl methacrylate (DMAEMA) with 2‐hydroxyethyl methacrylate (HEMA) via atom transfer radical polymerization (ATRP) was studied in methanol using a macroinitiator method and a “one‐pot” sequential addition method. The polymerization sequence of the two monomers strongly affected the block copolymer formation. When DMAEMA was used as the first monomer, both methods produced block copolymer samples containing significant amounts of DMAEMA homopolymer chains, because of the elimination of active halogen chain‐ends during the preparation of polyDMAEMA. Well‐controlled block copolymers with various block lengths were obtained via the macroinitiator method when polyHEMA was used as macroinitiator to initiate the polymerization of DMAEMA. The sequential addition method, in which HEMA was polymerized first with 90% conversion and DMAEMA was subsequently added, also yielded controlled block copolymers when the polymerization was carried out at room temperature with the DMAEMA conversion below 60%. Increasing the temperature to 60 °C promoted the copolymerization rate but the reaction suffered from gel formation. The addition of water to the system accelerated the polymerization rate, but led to the loss of the system livingness.
Gel permeation chromatograms of poly(HEMA‐b‐DMAEMA). The samples were prepared in methanol at room temperature with different block molecular weights using the macroinitiator method. 相似文献
A polymerizable hindered amine light stabilizer (HALS) 1,2,2,6,6-pentamethyl-piperidin-4-yl acrylate (PMPA) was synthesized, and it was copolymerized with styrene to prepare poly(St-co-PMPA) by reversible addition fragmentation chain transfer (RAFT) polymerization. The reaction conditions, such as chain transfer agent (CTA)/initiator ratio, monomer/CTA ratio, and St/PMPA ratio, were found to affect the polymerization reaction. Poly(St-co-PMPA) with high molecular weight and narrow distribution could be obtained under suitable conditions. The molecular weight is about 3.0 × 103 to 5.0 × 103 and the molecular weight distribution is about 1.07 to 1.25. The result showed that PMPA was effectively added to the polymer chain and the polymerizations were found to proceed in controlled fashions under a lower conversion. Moreover, the tensile strength and notched impact strength of ABS/poly(St-co-PMPA) are significantly improved, respectively, after 800-h UV irradiation, which was both higher than that of pure ABS. The results showed that poly(St-co-PMPA) was an effective high molecular weight HALS. 相似文献
Abstract Vinyl acetate (VAc) was bulk-polymerized at 30, 40 and 50°C using a low temperature initiator, 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN), and effects of polymerization temperature and initiator concentration were investigated in terms of polymerization behavior and molecular structures of poly(vinyl acetate) (PVAc) and corresponding poly(vinyl alcohol) (PVA) obtained by saponifying it with sodium hydroxide. Low polymerization temperature and low conversion by adopting ADMVN proved to be successful in obtaining PVA of high molecular weight. PVAc having number-average degree of polymerization (Pn) of 6,800–10,100 was obtained, whose degree of branching for acetyl group of 0.6–0.7 at 30°C, 0.8–1.1 at 40°C, and 1.0–1.9 at 50°C at conversion of below 40%. Saponifying so prepared PVAc yielded PVA having Pn of 3,100–6,200, and syndiotactic diad (S-diad) content of 51–53%. The whiteness, S-diad content, and crystal melting temperature were higher with PVA prepared from PVAc polymerized at lower temperatures. 相似文献
The effect of reaction conditions on the composition of native potato starch–polyacrylonitrile graft copolymers initiated by manganic pyrophosphate onto starch slurries at 30°C has been examined. In general, when the Mn3+ ion concentration was increased from 0.15 × 10?3M to 3.0 × 10?3M (other conditions kept constant), an increase in conversion of monomer to polymer and % add-on was observed, whereas frequency of grafts (anhydroglucose units, AGU, per grafted chain) decreased. Also, the average molecular weights of grafts showed a decrease from 2.2 × 105 to 1.5 × 105. Increasing the concentration ratio of starch to monomer during polymerization by a factor of 3 produced an increase in the conversion of monomer to polymer, whereas an increase in frequency of grafts (AGU/chain) was obtained. Values of % add-on and average molecular weights of the grafts showed, however, a decreasing tendency. It was observed that grafting onto starch took place readily even at acid additions as low as 10 × 10?3M H2SO4 (pH ?1.8). Selective solvent extraction of homopolymer and extremely low conversions of monomer to polymer (0.1%–1.5%) in duplicate runs without addition of starch indicated that grafting efficiencies were high in all cases. An attempt has been made to interpret the results in terms of variations in factors such as initial ratio of (Mn3+)/(AGU), termination rate of acrylonitrile chain radicals by oxidation by Mn3+ ions, oxidation rate of radicals formed on anhydroglucose units by Mn3+ ions, and physical factors such as diffusion rate of Mn3+ ions through the polyacrylonitrile-grafted starch granules for terminating the radicals. 相似文献