Effect Of Polymerization Methods Research Articles

Effect of polymerization methods on surface roughness and hardness of commercially available self-curing acrylic resins: a comparative study

Purpose This paper aims to compare the surface roughness and hardness of three commercially available self-curing acrylic resins for dental use, under different polymerization conditions. Design/methodology/approach A comparative in vitro study was conducted using a convenience sample of 12 × 5 × 2 mm blocks with n = 40 for each material (Nic Tone, Arias Plus and Orthocryl®), with subgroups according to the polymerization method: conventional (C) and polymerization under ambient conditions (A). The surface roughness of the materials was measured using a profilometer; hardness was measured with a portable hardness tester. Additionally, surface morphology as well as particles size and morphology were evaluated with scanning electron microscopy. Findings There were significant differences in roughness and hardness values between the three self-curing acrylic resins (p < 0.05), as well as within each self-curing acrylic resin according to the polymerization method used (p < 0.05). The samples polymerized with the conventional method presented lower surface roughness and hardness values. Originality/value This study provides scientific evidence of values not provided by manufacturers in relation to the surface roughness and hardness of these materials, and all of them met the ideal minimum values of surface roughness, regardless of the polymerization technique used.

Poly[3,6-bis(2-thienyl)diketopyrrolopyrrole-selenophene]: Effect of polymerization method on optical, electrochemical, and photovoltaic properties

Diketopyrrolopyrrole-based polymers have attracted considerable interest due to their tunable electronic properties in organic electronic applications. In this work, poly[3,6-bis(2-thienyl)diketopyrrolopyrrole-selenophene] (PDPP-2 T-Se) was synthesized by two different polymerization techniques (Stille coupling and direct C-H arylation) and the effect of polymerization method on chemical and physical properties was studied. The impact of selenium atom on optical, electrical and photovoltaic properties and its comparative studies with previously reported sulfur counterpart poly[3,6-bis(2-thienyl)diketopyrrolopyrrole-thiophene] (PDPP-3 T) were also performed. Chemical and physical characterizations of these polymers were carried out using 1HNMR, FT-IR, gel permeation chromatography, UV-Vis-NIR absorption, photoluminescence, thermal gravimetric analysis, and cyclic voltammetry. Optical absorption spectra indicate that polymer has a broad absorption band from near-infrared region to visible range (950–400 nm). Photovoltaic devices were fabricated using solution-processable deposition of PDPP-2 T-Se as a donor material blended with PC71BM as an acceptor material with device structure ITO/MoOx/active layer/Al and shows a power conversion efficiency of 2.55% under ambient conditions. To get better insight into the structure-properties relationship, computational calculations were carried out on polymers PDPP-2 T-Se and PDPP-3 T.

Investigation of organic thermoelectric materials using potential‐step chronocoulometry: Effect of polymerization methods on thermoelectric properties of poly(3‐hexylthiophene)

AbstractTo establish the correlation between the thermoelectric properties of conducting polymers and their doping levels, we have utilized the potential‐step chronocoulometry for the quantitative estimation of the doping levels. In this paper, three types of poly(3‐hexylthiophene)s synthesized by different polymerization methods were investigated. The electrical conductivities and the Seebeck coefficients of poly(3‐hexylthiophene)s with various doping levels were measured and plotted against the doping level. It was found that the electrical conductivity linearly increased with increasing the doping level in the range of 1–10%, and then saturated. On the other hand, the relationship between the Seebeck coefficient and the doping level showed a good linearity in all the polymers.

Effect of polymerization methods in the cytotoxicity of two resins used in removable prosthodontics – an in vitro study

Introduction: Polymethylmethacrylate resins are essential materials in the Oral Rehabilitation field. However, their use is being called into question once they can cause adverse reactions in the adjacent tissues [1]. Previous work has shown that ProBase® Cold releases a higher amount of monomers MMA and HEMA when compared to the heat-polymerized ProBase® Hot [2]. Having that in consideration, it is important to know if polymerization methods have influence in cytotoxicity of these materials. In this in vitro study, our aim is to evaluate the cytotoxicity level of ProBase® Hot and ProBase® Cold in fibroblastic cell line through cell viability assay and our hypothesis is that ProBase® Cold is more cytotoxic than ProBase® Hot. Materials and methods: Specimens of each resin were prepared according to manufacturer’s instructions for clinical use. Then, 4 disks (5mm in diameter x 2mm in height) were immersed in 7mL of culture medium and incubated for 4 different times (30 minutes, 24 hours, 7 days and 14 days). Serial dilutions of the previously incubated resin extracts were placed in contact with 4×103 of 3T3 mouse fibroblasts that have been plated in a 96 well plate the day before. After 24 hours of exposition, cell viability was evaluated through the Crystal Violet assay. Absorvance was measured at 595nm in a microplate reader (Biorad 680). The results were evaluated by Student’s t-test (SPSS, Chicago, IL) and the level of significance was chosen as p-value <0.05. Results: Undiluted extracts of both resins produce significant differences in mouse fibroblasts viability when they were incubated for 14 days (Figure 1). Even though, with all dilutions and incubation times of the extracts tested, cell viability was never below 70%, which is the threshold stated in ISO 10993-5:2009 to be considered cytotoxic [3]. Figure 1. Cell viability of 3T3 fibroblasts when exposed to ProBase® resins. The values are present as mean ± SD in relation to non-exposed cells (defined as 100% cell viability). *p < 0.05 when compared to non-exposed cells. Discussion and conclusions: Our results show that ProBase® Hot and ProBase® Cold are not cytotoxic in our cell model. In this case, our hypothesis was not verified. The polymerization method of both resins does not influence their cytotoxicity.

Effect of polymerization method and fabrication method on occlusal vertical dimension and occlusal contacts of complete-arch prosthesis.

PURPOSEThis study evaluated the dimensional stability of a complete-arch prosthesis processed by conventional method in water bath or microwave energy and polymerized by two different curing cycles.MATERIALS AND METHODSForty maxillary complete-arch prostheses were randomly divided into four groups (n = 10): MW1 - acrylic resin cured by one microwave cycle; MW2 - acrylic resin cured by two microwave cycles: WB1 - conventional acrylic resin polymerized using one curing cycle in a water bath; WB2 - conventional acrylic resin polymerized using two curing cycles in a water bath. For evaluation of dimensional stability, occlusal vertical dimension (OVD) and area of contact points were measured in two different measurement times: before and after the polymerization method. A digital caliper was used for OVD measurement. Occlusal contact registration strips were used between maxillary and mandibular dentures to measure the contact points. The images were measured using the software IpWin32, and the differences before and after the polymerization methods were calculated. The data were statistically analyzed using the one-way ANOVA and Tukey test (α = .05).RESULTShe results demonstrated significant statistical differences for OVD between different measurement times for all groups. MW1 presented the highest OVD values, while WB2 had the lowest OVD values (P<.05). No statistical differences were found for area of contact points among the groups (P=.7150).CONCLUSIONThe conventional acrylic resin polymerized using two curing cycles in a water bath led to less difference in OVD of complete-arch prosthesis.

The Effect of Polymerization Methods and Fiber Types on the Mechanical Behavior of Fiber-Reinforced Resin-Based Composites.

Glass fibers were introduced to increase the fracture resistance ofresin-based composites restorations; however, the poor polymerization between fibers andresin-based compositewere sometimes noted and can cause debonding and failure. The purpose of this study was to investigate the effects of different polymerization methods as well as fiber types on the mechanical behavior of fiber-reinforcedresin-based composites. Seventy-five specimens were fabricated and divided into one control group and four experimental groups (n = 15), according to the type of glass fiber (strip or mesh) and polymerization methods (one- or two-step). A 0.2-mm-thick fiber layer was fabricated with different polymerization methods, on top of which a 1.8 mmresin-based compositelayer was added to make a bar-shape specimen, followed by a final polymerization. Specimens were tested for flexural strength and flexural modulus. The failure modes of specimens were observed by scanning electron microscopy. The fiber types showed significant effect on the flexural strength of test specimens (F = 469.48, p < 0.05), but the polymerization methods had no significant effect (F = 0.05, p = 0.82). The interaction between these two variables was not significant (F = 1.73, p = 0.19). In addition, both fiber type (F = 9.71, p < 0.05) and polymerization method (F = 12.17, p < 0.05) affected the flexural modulus of test specimens; however, the interaction between these two variables was not significant (F = 0.40, p = 0.53). The strip fibers showed better mechanical behavior than mesh fibers and were suggested for resin-based composites restorations reinforcement; however, different polymerization methods did not have a significant effect on the strength and failure mode of fiber-reinforcedresin-based composites.

Effects of polymerization method on flexural and shear bond strengths of a fiber-reinforced composite resin.

This study investigated the effects of indirect composite polymerization on the postcuring mechanical properties of a fiber-reinforced composite. An indirect composite seated on glass fibers preimpregnated with polymerized monomer was polymerized by 1) photoirradiation using a halogen-fluorescent polymerizing unit for 5 min, 2) method 1 plus secondary heating at 100°C for 15 min, 3) photoirradiation using a metal halide light unit for 60 s, or 4) preliminary polymerization using a halogen light unit for 20 s followed by method 3. After polymerization, the flexural and shear bond strengths of the fiber-reinforced composite were examined, as was the flexural strength of non-fiber-reinforced composite specimens polymerized using the same methods. Among non-fiber-reinforced composite specimens, flexural strength was lower for method 1 than for the other three methods; however, among fiberreinforced composite specimens, the four methods did not significantly differ in flexural strength or shear bond strength. Composite-fiber interface separation without breakage of the fiber after flexural strength testing was not observed in specimens polymerized by methods 2 or 4. In conclusion, use of a conventional unit for high-intensity light irradiation after preliminary irradiation, or light irradiation followed by secondary heating, is recommended for polymerization of composite material seated on polymerized glass fiber.

有机硅改性聚丙烯酸酯纳米乳液的聚合稳定性研究

以甲基丙烯酸甲酯(MMA)和丙烯酸丁酯(BA)为主单体，利用不同乳液聚合工艺合成了有机硅改性聚丙烯酸酯纳米乳液，通过测定聚合过程的凝聚率及单体转化率，考察了聚合工艺、反应温度、乳化剂用量、乙烯基三乙氧基硅烷(A-151)用量、甲基丙烯酸羟基乙基酯(HEMA)用量、甲基丙烯酸(MAA)用量、pH值等因素对反应稳定性的影响。结果表明：采用半连续滴加工艺，温度在80℃~85℃，引发剂、复合乳化剂、有机硅A-151、HEMA、MAA的质量百分含量分别为0.5%、3%、4%、2%、2%时反应过程稳定性较好，凝聚物的质量百分含量低于0.5%，乳液粒径为80 nm左右，固含量40%。提高乳化剂用量有利于改善聚合反应的稳定性；升高温度、增加A-151用量不利于聚合反应过程的稳定；而搅拌速率、pH值和引发剂用量均存在使乳液聚合过程稳定的最佳值。 Organosiloxane modified acrylate nanolatex was synthesized by different emulsion polymerization processes with methylmethacrylate (MMA) and butylacrylate (BA) as main monomers. The effects of polymerization methods, reaction temperatures, amounts of initiator, emulsifier, vinyl-triethoxysilane (A151), 2-hydroxyethl methacrylate (HEMA), methyl acrylic acid (MAA) contents and pH on polymerization stability were investigated by measuring coagulation rate and monomer conversion. The results showed that with semi-continuous emulsion polymerization, organosiloxane modified acrylate nanolatex with particle size of about 80 nm and with low coagulation rate of 0.5% as well as solid content of 40 wt% was obtained under the condition of the better reaction stability when temperature at 80˚C - 85˚C, the mass fraction of initiator, emulsifier, A151, HEMA, MAA at 0.5%, 3%, 4%, 2%, 2% respectively. The increase of emulsifier contents can improve the stability of the polymerization process; but the temperature increase and the more dosage of A-151 are not conducive to the reaction stability. The optimal values for the stirring speed, pH and dosage of initiator exist for the stable state in emulsion polymerization.

Effects of Polymerization Methods and Functional Monomers on Curcumin Imprinted Polymer Properties

Curcumin molecularly imprinted polymers (cur-MIP) were synthesized by three different polymerization methods including bulk, suspension, and precipitation polymerization resulting in irregular-shaped granules, microspherical, and nanospherical beads, respectively. Synthesized polymers are characterized by scanning electron microscopy and attenuated total reflectance FT-IR analysis. The binding capabilities of the imprinted polymers are assessed by equilibrium binding analysis. Two curcumin analogues were employed to study the binding selectivity. Results showed that the highest specific sorption capacity could be achieved by precipitation polymerization where the methacrylic acid-based and acrylamide-based cur-MIP provided specific sorption capacity of 89.3 and 37.4 nmol/g, respectively. For the selectivity testing, cur-MIP prepared by precipitation polymerization using methacrylic acid exhibited the highest selectivity towards curcumin. These results indicate that the precipitation polymerization using methacrylic acid as a functional monomer is suitable for synthesis of cur-MIP which can serve as a promising tool for curcumin extraction.

Fast and eco-friendly synthesis of new hydrolysable and biodegradable copolyurethanes derived from L-leucine cyclodipeptide and different molecular weights of PEG in TBAB under microwave irradiation

In this study novel multi block polyurethane (PU) copolymers containing cyclodipeptide were synthesized under microwave irradiation using a quaternary ammonium salt (QAS) as reaction media. For this, L-leucine cyclodipeptide (LC) was prepared and then a new class of poly(ether-urethane-urea)s (PEUUs) was synthesized in tetrabutylammonium bromide (TBAB) via two-step polymerization method. In the first step, 4,4′-methylene-bis-(4-phenylisocyanate) (MDI) was reacted with LC to produce isocyanate-terminated oligo(imide-urea) as hard segment. The reaction of the aforementioned pre-polymer with poly(ethylene glycols) (PEG) with different molecular weights (PEG400, 600, 1000, and 2000) was the second step to furnish a series of new PEUUs. These PEUUs are thermally stable, soluble in amide-type solvents, hydrolysable, and biodegradable. The resulting PEUUs have inherent viscosities in the range of 0.37–0.67 dL/g. The effects of polymerization method and soft segment length on some of the polymers’ properties and their structural characteristics were compared. The protocol presented here has the merits of environmentally benign, simple operation, convenient work-up, short reaction time and good yields without using volatile organic solvents or catalysts. Ammonium type reaction medium was air and water stable, and relatively cheap, which makes it suitable for applications. The results demonstrate that it can be easily separated and reused without losing activity which makes the method cost effective and eco-benign.

Effect of Polymerization Methods on Peripheral Nerve Regeneration

Baghmanli, Ziya MD; Urbanchek, Melanie G. PhD; Wei, Benjamin MD; Shim, Bong Sup PhD; Sugg, Kristoffer B. MD; Martin, David C. PhD; Kuzon, William M. Jr MD, PhD; Cederna, Paul S. MD

Effect of polymerization method on structure and properties of cationic polyacrylamide

AbstractAcrylamide and 2‐(methacryloyloxy)ethyltrimethylammonium chloride (AM/MADQUAT) copolymers were synthesized by solution and inverse microemulsion polymerization using (NH4)2S2O8/NaHSO3 as redox initiator at the same feed mole ratio, and their microstructure, such as sequence distribution and composition distribution, was calculated from monomer reactivity ratios of different polymerization methods. The results show that charge distribution is more uniform for copolymer prepared in inverse microemulsion than that in solution, and copolymer composition distribution is close to unity, and maintains approximately at the feed ratio. Furthermore, the influence of the two structures of cationic polyacrylamides on kaolinite floc size and effective floc density, reduction of Zeta potential and floc compressive yield stress had been investigated at pH 7. The results show that the kaolinite floc size and effective floc density are strongly dependent upon copolymer microstructure, with greater floc size and lower effective floc density being observed for copolymer prepared in inverse microemulsion than for that in solution. Copolymer microstructure has a marked effect on the Zeta potential, whose reduction in the magnitude was much greater in the presence of copolymer prepared in inverse microemulsion than that in solution. Greater compressive yield stress was achieved for the strong flocs produced by copolymer prepared in inverse microemulsion than for the weak flocs produced by that in solution. The difference in flocs compressive yield stress may be attributed to flocs structure. Therefore, in this article, a correlation between the cationic polyacrylamide structure and flocculation property for kaolinite suspension was established. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effect of polymerization methods on the residual monomer level of acrylic resin denture base polymers

AbstractWearing dental acrylic prosthesis causes adverse reactions to oral tissues due to bioactive leachables from resins such as residual methyl methacrylate (MMA). The aim of this study is to apply the high performance liquid chromatography (HPLC) method to quantify and compare the amount of MMA monomers released from denture base resin polymers processed by the conventional compression molding method (Paladent), microwave polymerization (Acron MC), and injection molding technique (PalaXpress). Six specimens of 10 ± 0.2 mm in diameter and 2.0 ± 0.2 mm in thickness of each material were prepared according to manufacturer's instructions. Specimens were stored in nanopure water at room temperature (23 ± 2°C) for 4 hr, 48 hr, 8 days, and 15 days separately. Residual MMA released into water was determined with HPLC for all time intervals. Data for all time intervals were analyzed among each group using the Friedman test and differences were found to be statistically significant for all time intervals for Acron MC, Paladent, and PalaXpress (p &gt; 0.05). Kruskal–Wallis test was used to compare changes of residual MMA within time intervals among denture base resin groups and statistically significant differences were found between all time intervals (p &gt; 0.05). Acron MC exhibited significantly lower residual MMA leach compared both to Paladent and PalaXpress, and Paladent showed more residual MMA leach compared to PalaXpress. Residual MMA leach for Acron MC, PalaXpress, and Paladent showed statistically significant leach in the first 48 hr of immersion in water followed by gradual longer‐lasting moderate increase until the 15 day interval which was not statistically significant (p &lt; 0.05). Copyright © 2007 John Wiley &amp; Sons, Ltd.

Effects of polymerization method on structure and properties of thermoplastic polyurethanes

AbstractThe effects of the dynamic polymerization method and temperature on the molecular aggregation structure and the mechanical and melting properties of thermoplastic polyurethanes (TPUs) were successfully clarified. TPUs were prepared from poly (ethylene adipate) glycol (Mn = 2074), 4,4′‐diphenylmethane diisocyanate and 1,4‐butanediol by the one‐shot (OS) and the prepolymer (PP) methods in bulk at dynamic polymerization temperatures ranging from 140 to 230 °C. Glass‐transition temperatures (Tgs) of the soft segment and melting points (Tms) of the hard segment domains of OS‐TPUs increased and decreased, respectively, with increasing polymerization temperatures, but those of PP‐TPUs were almost independent of the polymerization temperature. Tgs of the soft segment and Tms of the hard segment domains of these TPUs polymerized above 190 °C were almost the same regardless of the polymerization method. Solid‐state nuclear magnetic resonance spectroscopy (NMR) analyses of OS‐ and PP‐TPUs showed that the relative proton content of fast decay components, which corresponds to the hard segment domains, in these TPUs decreased with increasing polymerization temperatures. These results clearly show that the degree of microphase separation becomes weaker with increasing polymerization temperatures. The temperature dependence of dynamic storage modulus and loss tangent of OS‐TPUs coincided with those of PP‐TPUs at polymerization temperature above 190 °C. The apparent shear viscosity for OS‐ and PP‐TPUs polymerized above 190 °C approached a Newtonian behavior at low shear rates regardless of the polymerization method. These results indicate that TPUs polymerized at higher temperatures form almost the same molecular aggregation structures irrespective of the dynamic polymerization method. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 800–814, 2007

A comparative study on effects of two kinds of polymerization methods on grafting of polymer onto silica surface

AbstractIn this article we present the result of a comparative study of two kinds of polymerization methods—solution polymerization (sol. poly.) and dispersion polymerization (dis. poly.) for grafting polymer onto silica. As a model for the grafting polymerization reaction, styrene was chosen as the monomer and azo diisobutyronitrile (AIBN) as the initiator. The study aims at supplying theoretical reference for better selecting polymerization method to graft polymer on the silica particle surface. First, monolayers of 3‐methacryloylpropyl trimethoxysilane were chemically bonded onto the surfaces of micrometer‐sized silica gel particles, and so double bonds were immobilized onto the silica surface. Second, the copolymerizations between the immobilized double bonds and the monomer styrene were carried out, homopolymerizations of styrene followed, and finally polystyrene was grafted to the silica surfaces. Two kinds of polymerization methods, sol. poly. and dis. poly., were adopted respectively, and the effects of polymerization methods on grafting process were examined mainly. At the same time, the effects of different polymerization conditions on the grafting degree were researched. It was found that in the dis. poly. system the grafting degree is obviously higher than that in the sol. poly. system under the same polymerization conditions, and the grafting degree can go up to 47%, i.e. 47g/100g. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5808–5817, 2006

Properties of PHMS-g-p [butylacrylate (BA)-N-hydroxyl-methyl acrylamide (NMA)] graft copolymer emulsions

Emulsion graft copolymerization of poly(hydrogenmethylsiloxane) (PHMS) and butyl acrylate (BA) in the presence of functional comonomer N-hydroxyl-methyl acrylamide (NMA) was conducted by batch emulsion copolymerization to modify the properties of polysiloxane. Morphology of graft copolymer particles was characterized by transmission electron microscopy. The effect of polymerization method, PHMS content, initiator concentration, and NMA content on stability of emulsion, morphology, size of particle, and rheological properties were investigated. It has been found that stability of emulsion is better by semicontinuous emulsion polymerization than that of batch emulsion polymerization and it increased with increasing PHMS-NMA concentration. Increasing PHMS concentration and NMA concentration, the particle size and the viscosities increase. The property of resistance to electrolytes of graft copolymer emulsions and swelling property of film were also discussed. Results showed PHMS-g-P [butylacrylate (BA)-N-hydroxyl-methyl acrylamide (NMA)] graft copolymer emulsion has good resistance to electrolytes and the water absorption of its film increases with increasing BA-NMA content grafted onto PHMS. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2209–2217, 1999