Iodine-initiated,solid-state copolymerization of tetraoxane with 1,3-dioxolane in the presence of methylal. VI. Studies on copolymer composition

In order to elucidate the mechanism of copolymerization of tetraoxane-1,3-dioxolane, the consumption rate of 1,3-dioxolane was measured by using gas chromatography, and the copolymer composition was determined by high-resolution NMR spectroscopy and differential scanning calorimetry. It was found that 1,3-dioxolane is rapidly consumed in the early stage of copolymerization if 1,3-dioxolane is added at once. The copolymer thus obtained is characterized by a heterogeneous distribution of 1,3-dioxolane in the copolymer chain. However, if 1,3-dioxolane is added continuously during the progress of the copolymerization, the distribution and content of 1,3-dioxolane in the copolymer chain was found to be very homogeneous.     

Iodine-initiated,solid-state copolymerization of tetraoxane with 1,3-dioxolane in the presence of methylal. IV. Fractional dissolution of copolymer

A fractional dissolution on the oxymethylene copolymer obtained by the iodine-initiated, solid-state copolymerization of the tetraoxane–1,3-dioxolane-methylal system has been carried out using a mixed solvent which consists of tetrachloroethane, phenol, and cyclohexanol. On the fractional dissolution, the oxymethylene copolymer was divided mainly into two parts: one was the copolymer containing a larger amount of ethylene oxide unit in its main chain and having lower molecular weight; the other was copolymer containing a smaller amount of ethylene oxide unit and having a higher molecular weight. It was reasonably concluded that in this copolymerization system, the reaction proceeds from the surface to the center of the tetraoxane crystal to give a divided copolymer due to the heterogeneous properties such as copolymer composition and molecular weight.     

Iodine-initiated,solid-state copolymerization of tetraoxane with 1,3-dioxolane in the presence of methylal. VIII. Mechanical properties of copolymer

Copolymers obtained by the solid-state copolymerization of tetraoxane with 1,3-dioxolane were pelletized using a vent-type extruder and the mechanical properties were measured. The mechanical properties were found to be largely influenced by the distributions of molecular weight and ethylene oxide, which were controlled by the addition method of the 1,3-dioxolane–methylal solution into polymeric system. The mechanical properties of the copolymers were also found to be intermediate between those of Duracon M90 and Delrin 500.     

Iodine-initiated,solid-state copolymerization of tetraoxane with 1,3-dioxolane in the presence of methylal. VII. Treatment of copolymer after polymerization

The various procedures for removing the residual reactants and impurities from the polymer particle obtained by the solid-state copolymerization of tetraoxane with 1,3-dioxolane have been examined. The removal of the residual reactants by washing with solvents, such as acetone or water, were very difficult, because the residual reactants are mainly located in the central part of the polymerized particle. By evacuation of the polymeric system just after polymerization, however, the residual reactants were found to be easily eliminated from the polymer particle. It was also found that the polymer degradation caused by the acid impurities formed during polymerization can be prevented satisfactorily by neutralization using gaseous ammonia. On the basis of these findings, the simple process for polyoxymethylene production has been achieved; i.e., it was found that the polymer particle including the residual reactants and impurities can be directly pelletized using a vent-type extruder, immediately after the copolymerization procedure and the ammonia gas treatment, to obtain the polyoxymethylene pellet with an excellent thermal stability and a well controlled molecular weight.     

Iodine-initiated,solid-state copolymerization of tetraoxane with 1,3-dioxolane in the presence of methylal. III. Study on larger-scale copolymerization

The iodine-initiated, solid-state copolymerization of tetraoxane with 1,3-dioxolane in the presence of methylal has been studied using 15 l kneader-type reactor. Effects of the addition method of the 1,3-dioxolane–methylal solution on the copolymerization has been mainly discussed. The copolymerization rate, intrinsic viscosity, and thermal stability of the copolymer were found to be largely dependent on the addition method of the 1,3-dioxolane-methylal solution, i.e., if the solution is added all at once, properties of the copolymer are different at the early stage then at the later stage of the copolymerization, while on successive addition of the solution, the copolymer properties become almost constant irrespective of the polymerization time. Therefore, it was suggested that 1,3-dioxolane and methylal can easily diffuse through the copolymer layer formed on the surface of the tetraoxane particle and reacts with an active center as copolymerization proceeds.     

Iodine-initiated,solid-state copolymerization of tetraoxane with 1,3-dioxolane in the presence of methylal. II. Properties of copolymer obtained by beaker-scale copolymerization

In order to elucidate the copolymerization mechanism, the properties of the copolymer obtained by the iodine-initiated copolymerization of the tetraoxane–1,3-dioxolane–methylal system have been studied using gas chromatography, microscopy, scanning electron microscopy, differential scanning calorimetry, and gel permeation chromatography. From the behavior of the thermal stability and gas chromatography of the reaction mixture, it was found that reactivity of 1,3-dioxolane with active center is larger than that of tetraoxane, i.e., more than 90% 1,3-dioxolane is consumed at an early stage of the polymerization. The results obtained by microscopy, DSC, and GPC of the copolymer suggested that the copolymerization proceeds from the surface to the center of the tetraoxane crystal as if it were a core model. It was also suggested that the heterogeniety in copolymer properties can be explained not only by heterogeneous dispersion of 1,3-dioxolane in tetraoxane crystal, but also by the difference of reactivity of 1,3-dioxolane with the active center.     

Iodine-initiated,solid-state copolymerization of tetraoxane with 1,3-dioxolane in the presence of methylal. I. Fundamental study on beaker-scale copolymerization

The iodine-initiated, solid-state copolymerization of tetraoxane with 1,3-dioxolane in the presence of methylal has been studied on a beaker scale. It was found that tetraoxane can be easily copolymerized with 1,3-dioxolane by a small amount of iodine as initiator and gives oxymethylene copolymer with excellent thermal stability in a high yield. The copolymerization was largely influenced by the concentrations of iodine, 1,3-dioxolane, and methylal, i.e., the polymerization rate increased with increase not only in iodine but also in 1,3-dioxolane, and the thermal stability and the molecular weight of the copolymer were mainly affected by 1,3-dioxolane and methylal concentration, respectively.     

Calculation of molecular weight distribution in non-linear free radical copolymerization

An effective method for calculating molecular weight distribution in non-linear free radical copolymerization is proposed in this work. This method is based on the direct integration of a system of non-linear differential equations describing the conservation of ‘dead’ polymer and ‘live’ radicals in a reactor. A fairly general kinetic mechanism was employed to describe the complex kinetics of non-linear copolymerization. Assumptions made were justified by comparing calculated distributions with results obtained without making any assumption. This method may be applied to industrial free radical polymerization systems, thus leading to a more rational design of polymerization reactors.     

Crystallization of polyformals: 2. Influence of molecular weight and temperature on the morphology and growth rate in poly(1,3-dioxolane)

The morphology and growth rates of crystallized molecular weight fractions of poly(1,3-dioxolane) covering the range M_n = 8 800 to 120 000 have been studied by polarized light microscopy. Two different supermolecular structures, dependent on molecular weight and crystallization temperature have been found. Spherulites are formed after rapid crystallization and a more disordered morphology is formed at the lowest undercoolings but there is a temperature region where both forms are observed. The disordered form appears first and a consecutive spherulitic growth takes place. The crystallization kinetics were analysed over the temperature range 10°C to 36°C. At crystallization temperatures lower than 15°–18°C, the growth rate is linear and only spherulites are found. In the temperature range from 18°C to 36°C a well defined break is observed in the growth rate but the spherulitic growth rate is always higher than that of the irregular form. The growth rate temperature coefficient was studied and the usual plots are not linear in the whole range of crystallization temperatures. For the high crystallization temperature region, the slope is about twice as great as the low crystallization temperature slope. This is the region where regular spherulites are formed. The comparison between dilatometric and growth rate data has shown that the overall rate and growth rate temperature coefficients are the same.     

酶促木质素与酚聚合反应分子量及分布实验

在反相微乳液系统中 ,进行了过氧化物酶催化木质素与酚共聚反应实验 ,考察了酶浓度、WO(水 /表面活性剂 ,质量比 )、表面活性剂浓度、单体 (酚、木质素 )浓度及醇烃比对聚合物分子量的影响。结果表明 ,聚合物重均分子量可用表面活性剂浓度、酶浓度、单体浓度及油相中醇烃比来调控。用单纯形优化法关联了实验数据 ,得到了聚合物重均分子量的关联式 :M =6 2 7× 10 4 (Y1× 10 7) -0 .3 4Y0 .982 Y0 .83 Y2 .4 64 Y1.0 55。聚合物分子量分布出现双峰 ,是两种反应机理竞争的结果。     

Contribution of the solid phase polymerization to the molecular weight distribution in acrylonitrile precipitation copolymerization

Molecular weight distribution of copolyacrylonitrile, which was obtained from precipitation copolymerization without and with using dispersants in mixed solution, is studied. The contribution ratio of liquid phase polymerization and solid phase polymerization under different polymerization conditions could be worked out through the formula, which has been deduced in literature. From the calculated results, common points of each reaction system are, i) contribution ratio (r) of solid phase to liquid phase decreases with the increase of water content; thus the solid phase polymerization is gradually strengthened, which is apt to form chain of high molecular weight, ii) the higher temperature leads to higher compatibility between water and DMSO; thus the solid phase polymerization contribution would decrease, while the value of r is considerably larger. The limit molecular weight distribution of the system without dispersants in 100% water is approaching to 2; thus the corresponding r becomes larger, the molecular weight distribution ratio (Q) decreases in the system with dispersants.     

Studies of molecular weight distribution,particle morphology,and rheological behavior of ultra-high molecular weight suspension PVC

In this paper, the particle characteristics and rheological behavior of ultra-high molecular weight PVC (UHMWPVC) produced in both Japan and mainland China were studied. The molecular weight and its distribution of UHMWPVC were measured by GPC. By means of a series of techniques such as SEM, the measurement of surface pore size, plasticizer absorption, and photographic analysis, the morphology and general characteristics of UHMWPVC particles were investigated. A model of particle structure was proposed. It was found that compared to general PVC, UHMWPVC resins are more porous, having better plasticizer absorption properties. Similarly, compared to UHMWPVC made in mainland China, UHMWPVC made in Japan possesses particle characteristics preferred in PVC processing. In the studies of rheological behavior, the programmed temperature Brabender torque rheometer was used to study and compare the melting process of UHMWPVC resins and their plasticized systems under the same shear stress. The capillary rheometer and Brabender extrusion-rheometer were applied to investigate the rheological and extrusion properties of the plasticized systems mentioned above. The results showed that in melting and extrusion process, the particle characteristics of UHMWPVC result in the easy breakage of particles and the formation of “molecular flow,” On the other hand, the high molecular weight is unfavorable to processing. Generally speaking, much more research work is needed to improve the flow properties of UHMWPVC.     

Thermal degradation of poly(vinyl chloride) in presence of additives part III. Studies in molecular weight distribution

The changes in molecular weight and molecular weight distribution of PVC degraded in presence of maleic anhydride, benzoquinone and anthraquinone were studied by gel permeation chromatography. Chain scission and crosslinking reactions were indicated on the basis of M?_n and M?_w of degraded samples. Crosslinking was predominant when degradation was carried out in presence of anthraquinone.     

Molecular weight and distribution of copolymer of lignin‐phenol in copolymerization catalyzed by peroxidase

The molecular weight and distribution of lignin‐cresol polymer in peroxidase‐catalyzed copolymerization of lignin with cresol in the reversed micellar system can be controlled by adjusting the surfactant concentration and other factors. The maximal mean molecular weight of copolymer obtained is 1890 kDa. The surfactant sustains chain growth. The cresol and/or polycresol is incorporated into the copolymer, and the thermal property of the copolymer is improved. A correlation for copolymer mean molecular weight is developed. The synthesized copolymer drops out of solution and can be easily recovered. The materials appear to act as thermosets and may have applications as replacements of conventional phenolic resins. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2408–2418, 2001     

Bulk copolymerization of 1,3,5-trioxane and 1,3-dioxolane in presence of phosphotungstic acid catalyst and tetrahydrofuran as retarder: crystallinity and thermal properties

In this study, cationic ring opening in situ copolymerization of 1,3,5-trioxane (TOX) and 1,3-dioxolane (DOX) occurred during bulk polymerization in the presence of phosphotungstic acid as a catalyst. In another part of the study, copolymerization occurred in the presence of retarder tetrahydrofuran (THF), and its effect on the crystallization and thermal stability of the samples was also investigated. The findings from ¹HNMR spectrometry indicated that the synthesized samples of random acetal copolymer are comprised of an independent oxyethylene unit in an oxymethylene main-chain sequence. The findings from DSC indicated that crystallinity decreases with increasing comonomer content. Furthermore, the sample with retarder revealed greater crystallinity than the samples without retarder. From TGA results, it was revealed that the sample with retarder caused a larger quantity of comonomer to enter the chain and increased the thermal stability compared to the samples without retarder.     

Water‐soluble copolymers. V. Synthesis of low molecular weight amphoteric polyacrylamide by foamed copolymerization

Amphoteric polyacrylamide of acrylamide, acryloyloxyethyl trimethylammonium chloride, sodium acrylate, and acrylic acid was synthesized by foamed copolymerization. The effects of monomer concentration and composition, initiator concentration and composition, sodium bicarbonate and stabilizer content on the polymer intrinsic viscosity and monomer conversion were examined. The monomer conversion increased with increasing initiator concentration, sodium bicarbonate and stabilizer content. The polymer intrinsic viscosity decreased with increasing initiator concentration. The structure and low molecular weight of the amphoteric polymer were identified by fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC), respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Change of molecular weight distribution of statistical poly(styrene-co-acrylonitriles) with compositio of copolymer

Statistical poly(styrene-co-acrylonitrile) (SAN) copolymes with varying mole fractions of comonomer units have been synthesized in a batch reactor. The intrinsic viscosity and gel permeation chromatography (GPC) patterns of model copolymer samples were the basic experimental results. Chromatographic patterns of SAN copolymer samples were converted into molecular weight distributions and afterwards fitted to the theoretical distribution functions. The correlation between the composition of copolymers and the best fitted model distribution (Schulz's two parameters distribution in this case) was established. The treatment of data shows that parameter α is inversely proportional to the content of acrylonitrile units in the sample and indicates the molecular weight interval. Parameter b shows the invariability of the molecular weight distribution shape.     

阴离子溶聚丁戊橡胶分子量的研究

以正丁基锂为引发剂，分别以二氧六环（DOX）和二乙二醇二甲醚（2G）为极性调节剂研究了异戊二烯和丁二烯阴离子共聚物分子量随反应时间的变化规律。实验发现，聚合物的分子量与活性种的活性有关，高温严重破坏活性种的活性，调节剂用量是杀死活性种活性的另一因素。聚合前期，分子量随时间的增加而增大；温度升高后，高温破坏了活性种的活性，活性链解缔合导致的粘度下降，所以聚合后期分子量降低。2G对活性链的破坏受温度的影响要小于DOX受温度的影响。     

Studies in the molecular weight distribution of epoxide resins. II. Chain branching in epoxide resins

The extent of side chain branching in epoxide resins based on bisphenol A has been determined by nuclear magnetic resonance spectrometry. The results indicate that for the resins studied in this paper, the extent of branching is very small. The number of branch points varies between 0.09 to 0.06 per molecule for epoxide resins whose number-average molecular weight lies between 1500 and 4000.     

Mechanochemical tuning of molecular weight distribution of styrene homopolymers as postpolymerization modification in solvent-free solid-state

Mechanochemical degradation by planetary ball milling (PM) is used for postpolymerization modification of styrene homopolymers (PS). A complete factorial design was chosen to study the effect of radical scavengers, milling time, initial molecular weight, and revolution radius (R_p), on the shape of molecular weight distributions (MWDs) of PS. Size-exclusion chromatography analysis shows the feasibility of fine-tuning MWD of PS at up to 40% conversion. Distributions ranged from unimodal to bimodal in a PM with R_p = 150 mm at different stage of milling, whereas in a PM with R_p of 60.8 mm the adjustment of unimodal distributions is achieved. Initial polydispersity is more important to develop bimodal distributions when compared with initial molecular weight. Fourier transform infrared and X-ray electron spectrometry analysis show some suppression of PS degradation and complete oxidation inhibition of macromolecular radicals with the incorporation of radical scavengers, which we considered as additional aids when adjusting the MWDs.