Effect of poly(vinyl acetate/vinyl alcohol) copolymer with a thiol end group as a steric stabilizer on dispersion polymerization of styrene

In dispersion polymerization of styrene in ethanol, effects of a reactive steric stabilizer, poly(vinyl acetate/vinyl alcohol) copolymer with a thiol end group (P(VAc/VA)-SH), were investigated. In the absence of the thiol end group, the dispersion coagulated at the middle stage of the polymerization, while in the presence of the thiol end group, the polymerization proceeded successfully to result in close to monodisperse particles. The reactive thiol group acts as a site of formation of the block copolymer, that is, polystyrene-b-P(VAc/VA), which is utilized as an effective dispersant. From the measurement on molecular weights during the course of polymerization, two polymerization loci were realized. Addition of butyl methacrylate to styrene affected markedly not only rate of polymerization but also particle size. © 1996 John Wiley & Sons, Inc.     

Comparison of properties of acrylic–polyurethane hybrid emulsions prepared by batch and semibatch processes with monomer emulsion feed

Aqueous acrylic–polyurethane hybrid emulsions were prepared by batch and semibatch polymerization of acrylic monomer mixtures (butyl acrylate, methyl methacrylate and acrylic acid) in the presence of polyurethane dispersion. The acrylic component was introduced in the monomer emulsion feed. The weight ratio between acrylic and polyurethane components was varied to obtain different emulsion properties, microphase structure and mechanical film properties. Scanning electron microscopy, average particle size and molecular weight measurements were performed to characterize the latex systems. Mechanical properties were examined by measuring Koenig hardnesses of dried films. The average particle size increased with the acrylic/polyurethane ratio. Particles of larger than average size and, to some extent, higher than average molecular weights by batch process were formed. Koenig hardnesses decreased with increasing acrylic/polyurethane ratio. Properties of emulsions synthesized by semibatch processes were compared with the results reported for a different polyurethane dispersion. Copyright © 2003 Society of Chemical Industry     

Acrylic ABA triblock copolymer bearing pendant reactive bicycloalkenyl functionality via ATRP and tuning its properties using thiol-ene chemistry

This investigation reports the preparation of tailor-made ABA triblock copolymers (BCP) of 2-ethylhexyl acrylate (PEHA) and dicyclopentenyloxyethyl methacrylate (PDCPMA) bearing pendant reactive cycloalkenyl functionality via atom transfer radical polymerization (ATRP) and thiol-ene modification of the pendant reactive bicycloalkenyl functionality. The chemical structure and molar composition of the polymers were determined by ¹H NMR spectroscopy and molecular weights of the polymers were determined by gel permeation chromatography. AFM as well as DSC analysis showed nanophase-separated morphology in the block copolymers. The pendant reactive bicycloalkenyl group of PDCPMA in the BCPs was successfully modified by thiol-ene reaction and the mechanical properties of the modified BCPs were studied. The thiol modified BCP showed much greater adhesion strength compared to pristine BCP as determined by lap shear test using a UTM. Hardness of the BCP film and UV-cured thiolated BCP film was studied and compared by using a nanoindenter.     

Synthesis and characterization of gold‐based mesoscopic additives for polymers

A method for the controlled synthesis of alkanethiol‐derivatized gold clusters to be used as fillers for polymeric nanocomposites has been developed. Gold clusters embedded in poly(N‐vinyl pyrrolidone) (PVP) were obtained by reduction of AuCl₄^? with ethylene glycol in the presence of PVP as a stabilizer. The gold/PVP system was separated from the reactive mixture by flocculation with acetone, and this material was treated with a dodecanethiol/ethanol solution to produce thiol‐derivatized gold clusters. Then, the clusters were dispersed in polystyrene/chloroform solutions and highly transparent purple‐colored nanocomposite films were obtained by solution casting. This preparative scheme allows one to obtain high‐purity nanocomposites, with complete control over the filler percentage and size. Copyright © 2004 Society of Chemical Industry     

Dispersion polymerization of L-lactide in supercritical carbon dioxide

Triblock (A-B-A) oligomers of ε-caprolactone (ε-CL) (A) and poly(ethylene glycol) with an average molecular weight of 400 (PEG400) (B) were synthesized with three different molecular weight in the range of 2–6 kDa by changing the ratio of PEG400/ε-CL. These oligomers were then used in dispersion polymerization of L-lactide in supercritical carbon dioxide (scCO₂) as stabilizers. 5% stabilizer in the polymerization recipe allowed synthesis of poly(L-lactide) (PLLA) in scCO₂ in the powder form with a weight average molecular weight of around 60 kDa with polymerization yields around 80%. Interestingly, there was almost no effect of stabilizer molecular weight on polymerization. L-lactide polymerization in scCO₂ without any stabilizer was also possible but both the PLLA molecular weight and polymerization yield were lower, and the product was as aggregates instead of powders. A stabilizer concentration of 5% in the polymerization recipe was found adequate. Further increases in the stabilizer load resulted lower molecular weights and lower yields.     

Radiolytic synthesis of Pd-M (M=Ag and Ni) and Pt-M (M=Ru and Ni) alloy colloids

Pd-M (M=Ag and Ni) and Pt-M (Ru and Ni) alloy colloids were successfully prepared in aqueous solution by γ-irradiation using poly(vinylpyrrolidone), PVP, as stabilizer. The PVP-stabilized Pd-M and Pt-M nanoparticles were characterized by UV-Vis spectroscopy, Transmission Electron Microscopy (TEM) and Electrophoretic Light Scattering (ELS) analysis. The influence of molecular size of the PVP on the size and size distribution of the alloy nanoparticles was followed. Pd-Ag nanoparticles were formed by employing PVP with different molecular weights. The size of Pd-Ag alloy nanoparticles was determined by TEM photograph and ELS spectra, respectively. From the TEM photographs, the average diameter of Pd-Ag nanoparticles does not show strong dependence on the molecular weight of the PVP. On the other hand, the average diameter of Pd-Ag alloy colloids prepared by PVP with Mw=40,000 was consistently larger than that of Pd-Ag alloy colloids prepared by PVP with Mw=10,000. A plausible scheme is given to explaining this. The size and size distribution of Pt-M (Ru and Ni) alloy colloids are presented.     

Poly(DL-lactide)/poly(ethylene glycol) copolymer particles. I. Preparation and characterization

In this study, poly(DL -lactide)/poly(ethylene glycol) (PDLLA/PEG) copolymers were synthesized. First, PDLLA homopolymers with three different molecular weights (Mw_n: 7,300, 12,100 and 21,900) were synthesized by the ring opening polymerization of the dimer (i.e., DL-lactide) by using stannous chloride as catalyst. Average molecular weights of PDLLAs were determined by gel permeation chromatography (GPC). They were characterized by Fourier transform infrared and differential scanning calorimetry (DSC). These PDLLA homopolymers were then transesterified with PEG with a molecular weight range of 3,300–4,000. By changing the ratio of PEG to PDLLA, block copolymers with different chain structures were synthesized. DSC and GPC studies were performed to characterize these PDLLA/PEG copolymers. PDLLA and PDLLA/PEG particles in the size range of 2–10 μm were prepared by a modified solvent evaporation technique by using methylene chloride as solvent and methyl cellulose as emulsifier within the aqueous dispersion medium. Particle size was controlled by changing the solvent/polymer ratio, PDLLA molecular weight, and PEG content. Degradation of polymeric particles was investigated in a phosphate buffer at pH 7.4 and at 37°C. Particles prepared with low-molecular-weight PDLLAs degraded much faster. Introduction of PEG within the polymeric matrix caused a pronounced increase in the degradation rate. Bulk degradation was the dominant mechanism. © 1996 John Wiley & Sons, Inc.     

Macromonomers having different molecular weights of polyethylene glycol and end group functionalities in dispersion polymerization of styrene

Bifunctional polyurethane-based macromonomers (BPUM) were synthesized from various molecular weights of polyethylene glycol (PEG) and hexamethylene diisocyanate (HDI) with different end group functionalities. The synthesized BPUMs were applied to the dispersion polymerization of styrene in ethanol. Structures of various macromonomers and PS particles were investigated using ¹H NMR. Molecular weights of PEG 1000, 2000, 4000, and 8000 were able to provide stable particles of polystyrene (PS), whereas PEG 400 was not big enough to form stable particles. Although the final conversion was almost constant, average size of the PS microspheres increased with PEG molecular weights. The inverse relationship between the size of particles and molecular weight of PS was observed. In particular, the particle size based on the monomers derived with acrylamide was larger than acrylate derivative monomers. As the molecular weight of PEG increased, the thermal stability was enhanced and leveled off. The grafting ratio of the PS calculated from ¹H NMR spectra exponentially decreased from 1.05 to 0.18 mol% with the increased molecular weight of PEG. Thus, present study suggests that the bifunctional macromonomers act not only as reactive stabilizers, but also as grafting agents in dispersion polymerization.     

Molecular weight distribution in disulfide polymers

The published data on molecular weight distribution in polysulfide are rather contradictory and cannot be correlated with the concept of the existence of thiol–disulfide interchange in these polymers. In the present work the viscosity and molecular weights of liquid thiokols have been investigated (the number-average molecular weight by iodometric titration and by ebulliometry and the weight-average molecular weight by the light-scattering method). When measuring the light scattering in Thiokol Solutions a considerable depolarization of the scattered light was observed. This fact must be taken into account in the molecular weight determination. It has been established that in polydisulfides with thiol endgroups thiol–disulfide interchange reactions take place not only during the synthesis, but also in the polymer itself (in bulk). These reactions lead to the formation of polymers with an equilibrium molecular weight distribution. A relation of log η = f(M _w)^½ has been found that can be used in determining the weight-average molecular weight of liquid Thiokols.     

Dispersion polymerization of acrylamide with 2-acrylamide-2-methyl-1-propane sulfonate in aqueous solution of sodium sulfate

The copolymer of acrylamide (AM) and 2-acrylamide-2-methyl-propane sulfonate (AMPS) was synthesized through free radical dispersion polymerization in an aqueous solution of ammonium sulfate and poly(2-acrylamide-2-methyl-1-propane sulfonate) as a steric stabilizer. The average particle size of the copolymer ranged from 1.0 μm to 4.0 μm, and the molecular weight was 2.0 × 10⁶ ~ 7.0 × 10⁶ g mol⁻¹. The swelling property of the dispersion copolymer was studied by characterizing the apparent viscosity and particle size distribution. When the dispersion was diluted with salt aqueous solution in which the ammonium sulfate concentration kept equal with that of the original dispersion, particle size and particle size distribution of the diluted dispersion changed little, compared with that of the original dispersion. While diluted with deionized water, particle size and particle size distribution could expand several times. The effects of the AMPS/AM molar ratios, the molecular weight of stabilizer, and the initiation temperature were investigated. It was found that with the increase of the AMPS/AM ratios, the molecular weight of copolymers increased, and then decreased. The particle size and conversion of monomers increased. The stability of the copolymer dispersion increased with increasing the molecular weight of stabilizer for a fixed stabilizer concentration. With the increase of the initiation temperature, the molecular weight of copolymer increased at first and then decreased gradually, but the particle size and conversion increased. The optimum conditions for the stable AMPS/AM dispersion were as follows: the AMPS/AM molecular ratio was 15/85, the molecular weight of the PAMPS stabilizer 3.0 × 10⁵ ~ 4.0 × 10⁵, and the initiation temperature 50 °С, respectively.     

高密度聚乙烯阻燃性能的研究

研究了含卤阻燃剂、无机阻燃剂、稳定剂、氯化聚乙烯和不同分子量的基础树脂对高密度聚乙烯的阻燃性和力学性能的影响。     

Dispersion polymerization of styrene in aqueous alcohol solution: Effects of reaction parameters on the polymer particle formation

Dispersion polymerization of styrene in an aqueous alcohol solution using poly(2-ethyl-2-oxazoline) as a polymeric stabilizer was performed to prepare micron-size monodisperse polystyrene particles. As the water content of the solvent increased, the polymerization rate and the molecular weight of the polymer particles increased and the particle size decreased. Effects of concentrations of stabilizer and initiator upon the polymerization and the size of the resulting polystyrene particles have been examined in the solvent containing different water contents.     

Screen printing of silver nanoparticle suspension for metal interconnects

Silver nanoparticle suspensions were synthesized by chemical reduction method using a formaldehyde reductant. Polyvinyl pyrrolidone (PVP) of two different molecular weights (M.W.=8,000 and 29,000) was used as a stabilizer for the suspensions. PVP of a smaller molecular weight could produce silver suspensions of nanoparticle size around 20 nm. Water-based conductive silver inks with different silver concentrations were prepared and tested for suitability for screen printing. We have successfully printed silver metal lines on glass substrates using a 400 mesh screen-mask with 60wt.% silver ink prepared in this study. Curing at a low temperature of 200 °C for an hour was found sufficient to reach the lowest resistivity value with the synthesized ink. For a line with a width and thickness of 0.5 mm and 2.12 μm, respectively, it exhibited a resistivity of 3.3×10⁻⁵ Ω·cm, which could serve as conducting lines for various electronic applications.     

Graft copolymers from thiolated starch and vinyl monomers

Thiol starches of degree of substitution (D.S.) 0.005–0.162 were prepared by displacing starch tosyloxy groups with xanthate and treating the resulting xanthate esters with either sodium hydroxide or sodium borohydride. Acrylonitrile, styrene, acrylamide, acrylic acid, and dimethylaminoethyl methacrylate were grafted onto the thiol starches with hydrogen peroxide as initiator. The peroxide caused both grafting of monomer and coupling of thiol groups to disulfide. Treating graft copolymers with sodium borohydride regenerated thiol groups from disulfide groups so that the grafting sequence could be repeated. By regenerating the thiol groups and repeating the grafting steps, high add-on and high-frequency starch graft copolymers were prepared. During four grafting sequences, acrylonitrile reacted with D.S. 0.162 thiol starch to give graft copolymers that contained increasing amounts of polyacrylonitrile (46.0–66.5%). Grafting frequency increased from 183 to 71 anhydroglucose units (AGU)/graft, while molecular weights of the grafted chains ranged between 20,000 and 25,200. The final product was hydrolyzed with potassium hydroxide solution to a copolymer, which absorbed up to 400 ml water per gram. Styrene was grafted onto thiol starch to give products containing 34.4–69.5% polystyrene with 986–3520 AGU/graft and having molecular weights of grafted chains between 276,000 and 364,000. Graft copolymers containing 48.9% polyacrylamide, 21.2% poly(acrylic acid), and 77.7% poly(2-methacryloyloxyethyldimethylammonium acetate) were obtained under similar conditions.     

Dual Effect of Low‐Dosage Poly(Ethylene Oxides) on Methane Hydrate Formation

Time‐dependent isochoric formation of methane hydrate was investigated in the presence of low‐dose poly(ethylene oxides) (PEOs). The effect of different molecular weights of PEO on methane hydrate nucleation time and storage capacity was studied and compared. Kinetic measurements revealed a dual effect of PEO, including inhibition and stabilization effects, on methane hydrate formation. The nature and type of the effect arises from the difference in molecular weights and concentration ranges of PEOs. These parameters directly affect the nucleation time and storage capacity of methane hydrate. Generally, in comparison with pure water, PEO improved the storage capacity of methane hydrate. PEO (1000 kD) at a concentration of 0.5 wt % exhibits a significant kinetic inhibitory performance. However, it was an efficient low‐dosage hydrate stabilizer at a concentration of 0.25 wt %, along with producing gas‐rich methane hydrate suitable for gas fuel storage and transportation.     

Dispersion polymerization of acrylamide with 2‐acrylamido‐2‐methyl‐1‐propane sulfonate in aqueous solution

The copolymer of acrylamide (AM) and 2‐acrylamido‐2‐methyl‐1‐propane sulfonate (AMPS) was synthesized through the free radical dispersion polymerization in an aqueous solution of ammonium sulfate and in the presence of poly(2‐acrylamido‐2‐methyl‐1‐propane sulfonate) as stabilizer. The average particle size of the copolymer ranged from 1 to 4 μm, and the molecular weight was from 2.0 × 10⁶ to 7.0 × 10⁶ g mol^?1. By analyzing apparent viscosity and particle size, the swelling property of the dispersion copolymer was studied. When the dispersion was diluted with salt water in which the ammonium sulfate concentration kept equal with that of the original dispersion, particle size and particle size distribution of the diluted dispersion changed a little, compared with that of the original dispersion. While diluted with deionized water, particle size and particle size distribution could expand several times. The effects of varying concentrations of the stabilizer, the monomer, the salt and the initiator on particle size, and molecular weight of the copolymer were investigated, respectively. The reaction conditions for preparing stable dispersion were concentrations of 20–28% of the salt, 6–14% of monomers, and 1.8–2.7% of the stabilizer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:2379–2385, 2006     

Bulk grafting of decyl methacrylate onto poly(vinyl chloride) in the presence of a lead carboxylate stabilizer

In order to improve the permanence of the plasticizer in a poly(vinylchloride) (PVC) compound we have studied the free radical polymerization and grafting of decyl methacrylate (DMA) onto PVC in the presence of a lead stabilizer. The influence of different parameters has been investigated and homogeneous PVC-g-PDMA copolymers have been obtained. Their molecular weights and the glass transition temperatures were consistent with the grafted nature of the copolymers.     

Nonaqueous emulsion copolymerization of ethyl methacrylate/lauryl methacrylate in propylene glycol. I. Evaluation of stabilizing efficiency for PEO‐PS‐PEO triblock copolymers

Sixteen poly(ethylene oxide)–polystyrene–poly(ethylene oxide) (PEO‐PS‐PEO) triblock copolymers were synthesized by anionic polymerization. They were characterized by gel permeation chromatography and proton NMR. The molecular weight of these 16 PEO‐PS‐PEO triblock copolymers ranged from 5100 to 13,300. The polystyrene (PS) block length was between 13 and 41. The PEO block length was between 41 and 106. The polydispersity index for these PEO‐PS‐PEO triblock copolymers were 1.05 ± 0.02. When using these stabilizers in the emulsion copolymerization of ethyl methacrylate and lauryl methacylate in propylene glycol, only a narrow window of stability was observed. Stable latexes were formed only when the molecular weights of the PEO blocks were within the range of 5300–7700 and the molecular weights of the PS blocks were 2000–4000. The stabilizer ability for these triblock copolymers was correlated with their molecular weight and conformation in propylene glycol. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1951–1962, 2001     

Polyalkylene sulphides

The polymerisation of alkylene sulphides, particularly ethylene sulphide and propylene sulphide, initiated by salts of cadmium and zinc, or ammonia and tertiary amine catalysts, is discussed. Kinetic features of the reactions are considered and practical recipes for high and low molecular weight polymers are given. Side reactions leading to rearranged polymers or to desulphuration are discussed. Polyethylene sulphide is a high melting point, plastics material whilst polypropylene sulphide is a soft rubber or, in the isotactic form, a low melting point plastics material. Homopolymers of propylene sulphide or its unsaturated copolymers give useful oil-resistant rubbers. The molecular weight of polypropylene sulphide is readily controlled by the addition of thiol chaintransfer agents, and low molecular weight polymers of variable functionality with thiol, amine or other reactive end-groups are readily made. These polymers are co-reactive with phenolic, amino or epoxy resins in laminates, adhesives and coatings.     

A study on new polymerization technology of styrene

The classic polymerization technology of polystyrene is a high‐cost and nonfriendly environmental technology. Furthermore, the weight‐average molecular weight of polystyrene is hard to enhance up to 400,000 in the classic polymerization technology. The disadvantages limit the growth rate of polystyrene. The solution for increasing the growth rate of polystyrene lies in new technology. The reactive extrusion process of polystyrene was studied in detail and the whole reactive extrusion process of polystyrene was obtained. By means of controlling the flow rate of styrene and the initiator and the screw rotational speed, samples of polystyrene with different molecular weights were synthesized by the twin‐screw extruder. The properties of synthesized polystyrene with different molecular weights were studied; the mechanic properties of polystyrene will increase with an increase of the weight average molecular weight of polystyrene. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2130–2135, 2002