Benzoyl Peroxide Concentration Research Articles

Catalytic and inhibiting effects of ferrocene on the bulk radical–coordination polymerization of methyl methacrylate from the standpoint of formal kinetics

The kinetic curves and rates of bulk radical–coordination polymerization of methyl methacrylate initiated by the benzoyl peroxide–ferrocene system at 293–373 K, initial benzoyl peroxide concentrations of 10–4–10–1 mol/L, and a constant initial ferrocene concentration of 10–3 mol/L have been calculated using a mathematical model in which the process is considered from the standpoint of formal kinetics. The calculations have demonstrated that, at low methyl methacrylate conversions, ferrocene catalyzes the process at any benzoyl peroxide concentration; at medium and high methyl methacrylate conversions, deficient amounts of ferrocene with respect to benzoyl catalyze the process as well, while excess ferrocene inhibits the process. The observed effect is explained by the specific ferrocene–benzoyl peroxide interaction, which, depending on the ferrocene: benzoyl peroxide ratio, either increases or decreases the concentration of radicals in the reaction mass.

Preparation of pH‐responsive crosslinked materials from natural rubber and poly(4‐vinylpyridine)

AbstractStimuli‐responsive elastomers are smart materials for sensing applications. Natural rubber (NR) is a renewable elastomer with excellent elasticity and fatigue resistance. In this work, a straightforward method for the preparation of pH‐responsive crosslinked materials from NR and poly(4‐vinylpyridine) (P4VP) via free radical crosslinking reaction using benzoyl peroxide (BPO) as an initiator is described. The effects of P4VP and BPO concentrations, reaction time and reaction temperature on immobilization percentage were investigated. It was found that the immobilization percentage reached 90% when using a P4VP concentration of 150 phr and a BPO concentration of 10 phr for 24 h at 90 °C. The pH responsiveness of the crosslinked materials was studied via water swelling, water contact angle and dye release measurements. Unlike unmodified rubber, the P4VP‐crosslinked NR was found to be pH‐responsive in acidic solution. Indigo carmine adsorption studies showed the Langmuir isotherm suggesting monolayer coverage of dye on the rubber surface. The dye could also be released upon increasing the pH of solution above 4. Based on these results, the introduction of pH responsiveness to NR will lead to novel responsive rubber‐based materials that can be used in biomedical and sensing applications. © 2016 Society of Chemical Industry

Obtaining of polymethacrylate additives and studying of operational properties of an alloyed industrial oil

The study explored the influence of temperatures and the impact of concentrations of the initiator and the monomer on the kinetics of lauryl methacrylate homopolymerization in benzene. The reaction sequence with respect to the initiator (1.38±0.07), the monomer (1.69±0.02) and also the activation energy (Е а =96.4±0.506 kJ/mol) was determined according to the experimental points of the first fixed area in the polymerization process (S ≤ 10 %). The numerical values of the reaction order for this system were high due to the high structuring of the LMA and a high viscosity of the system. The optimal conditions for obtaining polymethacrylate additives were determined on the basis of kinetic studies and the following parameters: the temperature of 80 ± 1°C, the concentration of benzoyl peroxide of 0.5 wt.% based on the total monomers’ weight, the ratio of lauryl methacrylate : benzene = 1:1, and the reaction time of 3 to 4 hours. The qualitative composition of the additives was confirmed with the infrared spectrometry. According to a thermogravimetric analysis, it has been found that synthesized (co)polymers are thermally stable up to the temperatures of 255–265°C. The influence of polymethacrylate additives in the oil I-20A on the rheological, depressor and antiwear properties was also studied. The viscosity curves for the obtained systems were described. The viscosity index of the obtained alloyed oil was determined according to the kinematic viscosity values at the temperatures of 50°C and 100°C. The depressor and antiwear properties of the lubricant were investigated at the optimal concentration of the additive in the amount of 2 wt.% in the oil. The operational properties of the industrial oil with an additive in the amount of 1.4 wt.% were also summarized in the study. The antiwear properties of the alloyed oil I–20A were tested in friction on a four ball machine. It has been found that the PMA20 additive with concentration of 2 wt.% in the oil can be used to obtain an alloyed industrial lubricant as a commodity with desirable operational properties (VI = 140 at T Fr = –19°C). The obtained lubricant can be used for friction reduction and wear protection of equipment elements of power plants.

In‐process thermochemical analysis of in situ poly(ethylene glycol methacrylate‐co‐glycidyl methacrylate) monolithic adsorbent synthesis

ABSTRACTThermomolecular mechanisms associated with the synthesis of polymethacrylate monoliths are critical in controlling the physicochemical and binding characteristics of the adsorbent. Notwithstanding, there has been limited reported work on probing the underlining synthesis mechanism essential in establishing the relationship between in‐process polymerization characteristics and the physicochemical properties of the monolith for tailored applications. In this article, we present a real‐time thermochemical analysis of polymethacrylate monolith synthesis by free‐radical polymerization to probe the effects on the physicochemical characteristics of the adsorbent. The experimental results show that an increase in the crosslinker monomer concentration from 30 to 70% resulted in a peak temperature increase from 96.3 to 114.3 °C. Also, an increase in the initiator (benzoyl peroxide) concentration from 1 to 3% w/v resulted in a temperature increase from 90.7 to 106.3 °C. A temperature buildup increases the kinetic rate of intermolecular collision associated with microglobular formation and interglobular interactions. This reduces the structural homogeneity and macroporosity of the polymer matrix. A two‐phase reactive crystallization model was used to characterize the rate of monomeric reaction after initiation and microglobular formation from the liquid monomeric phase to formulate the theoretical framework essential for evaluating the kinetics of the polymer formation process. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43507.

Adhesion property of crosslinked epoxidized (natural rubber)/(acrylonitrile‐butadiene) rubber blend adhesives in the presence of petro resin tackifier

Loop tack, peel strength, shear strength, and morphology of (benzoyl peroxide)‐cured epoxidized natural rubber (ENR 25)/(acrylonitrile‐butadiene) rubber (NBR) blend adhesive were investigated by using petro resin as the tackifying resin. Benzoyl peroxide loading varied from 1 to 5 parts by weight per hundred parts of resin (phr), whereas the petro resin loading was fixed at 40 phr. A SHEEN hand coater was used to coat the adhesive on the polyethylene terephthalate substrate at 30 μm and 120 μm coating thicknesses. (ENR 25)/NBR adhesive was crosslinked at 80°C for 30 min prior to the determination of adhesion strength by a Lloyd adhesion tester operating at 10–60 cm/min. Results show that maximum loop tack and peel strength occur at 2 phr of benzoyl peroxide loading, whereby optimum cohesive and adhesive strength are obtained. However, shear strength increases with increasing benzoyl peroxide concentration, an observation that is associated with the steady increase in the cohesive strength. Scanning electron microscopy micrograph shows that little adhesive remained on the substrate at 0 phr compared with 2 phr of benzoyl peroxide loading, indicating that crosslinking increases the peel strength of the adhesive. In all cases, the adhesion properties increase with coating thickness and testing rate. J.VINYL ADDIT. TECHNOL., 24:93–98, 2018. © 2015 Society of Plastics Engineers

The study of the quantification of the concentration of benzoyl peroxide based on the terahertz spectrum

The quantitative regression analysis of the mixture based on the terahertz spectrum is reported in this paper. The absorption spectrum and the refractive index spectrum of a mixture of benzoyl peroxide and polyethylene were obtained by calculation, and then a mixture of benzoyl peroxide and polyethylene was used experimentally, and then the spectrum obtained was preprocessed using the method of wavelet filter, first derivative model and second derivative model. Partial least squares regression and kernel partial least squares regression were applied to the modelling of the regression analysis of the original absorption spectrum, the first derivative model and second derivative model spectra, and a detailed performance evaluation is presented at the end of the paper.

Synthesis of versatile poly(PMMA‐b‐VI) macromonomer‐based hydrogels via infrared laser ignited frontal polymerization

ABSTRACTIn this work, poly((PMMA‐b‐VI)‐co‐AA) (MMA = methyl methacrylate; VI = 1‐vinylimidazole; AA = acrylic acid) hydrogels and poly((PMMA‐b‐VI)‐co‐AA)/TPU (TPU = thermoplastic polyurethane) IPN (interpenetrating polymer networks) hydrogels have been fabricated via versatile infrared laser ignited frontal polymerization by using poly(PMMA‐b‐VI) macromonomer as the mononer. The frontal velocity and Tmax (the highest temperature that the laser beam detected at a fixed point) can be adjusted by varying monomer weight ratios, the concentration of BPO (BPO = benzoyl peroxide) and the amount of TPU. Moreover, the addition of TPU enhances the reactant viscosity to suppress the “fingering” of frontal polymerization (FP) and decrease Tmax of the reaction, providing a new inert carrier (TPU) to assist FP. Through the characterization of Fourier transform‐infrared spectroscopy (FT‐IR), scanning electron microscope (SEM), and differential scanning calorimetry (DSC), the desired structure can be proved to exist in the IPN hydrogels. Furthermore, poly((PMMA‐b‐VI)‐co‐AA)/TPU IPN hydrogels possesses more excellent mechanical behaviors than hydrogels without IPN structure. Besides, the poly((PMMA‐b‐VI)‐co‐AA) hydrogels present splendid sensitive properties toward substances of different flavor including sourness (CA, citric acid or GA, gluconic acid), umami (SG, sodium glutamate), saltiness (SC, sodium chloride), sweetness (GLU, glucose), enabling their potential as artificial tongue‐like sensing materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1210–1221

Profile of clindamycin phosphate 1.2%/benzoyl peroxide 3.75% aqueous gel for the treatment of acne vulgaris.

Acne vulgaris is a common and chronic skin disease, and is a frequent source of morbidity for affected patients. Treatment of acne vulgaris is often difficult due to the multifactorial nature of this disease. Combination therapy, such as that containing clindamycin and benzoyl peroxide, has become the standard of care. Several fixed formulations of clindamycin 1% and benzoyl peroxide of varying concentrations are available and have been used with considerable success. The major limitation is irritation and dryness from higher concentrations of benzoyl peroxide, and a combination providing optimal efficacy and tolerability has yet to be determined. Recently, a clindamycin and benzoyl peroxide 3.75% fixed combination formulation was developed. Studies have suggested that this formulation may be a safe and effective treatment regimen for patients with acne vulgaris. Here, we provide a brief review of acne pathogenesis, benzoyl peroxide and clindamycin, and profile a new Clindamycin-BP 3.75% fixed combination gel for the treatment of moderate-to-severe acne vulgaris.

Alginate graft polyacrylonitrile beads for the removal of lead from aqueous solutions

Grafting of polyacrylonitrile with sodium alginate was carried out in aqueous medium using benzoyl peroxide (BPO) as initiator. The grafting conditions such as monomer, initiator concentration, reaction time and temperature were optimized. The graft copolymers were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, solid-state 13C-nuclear magnetic resonance and scanning electron microscopy. Optimum percentage grafting was obtained when the concentrations of BPO, acrylonitrile and sodium alginate were 6.19 × 10−3, 7.53 × 10−1 mol L−1 and 1 % w/v, respectively. The optimum reaction temperature and reaction time were 80 °C and 4 h, respectively. The copolymer sample with optimum percentage grafting was evaluated for the removal of lead ions from aqueous solutions in batch mode systems. Langmuir and Freundlich isotherm models were applied to describe the adsorption process. The adsorption data fitted into Langmuir model better than Freundlich model with maximum adsorption capacity of 454 mg g−1 (2.20 mmol g−1) while the kinetic data correlated well to pseudo-second-order kinetic model. The adsorbent could be regenerated using HNO3 as elution solvent, and reused repeatedly without significant loss of its metal adsorption capacity.

Augmentation with PMMA cement

Cements based on polymethyl methacrylate (PMMA) can be used without any problem in a variety of clinical augmentations. Cement-related complications in surgical procedures involving PMMA cements, such as embolism, thermal necrosis, toxicity and hypersensitivity, are often due to other causes. Knowledge about the properties of the cement helps the user to safely employ PMMA cements in augmentations. High radio-opacity is required in vertebral body augmentations and this is provided in particular by zirconium dioxide. In vertebral body augmentations, a low benzoyl peroxide (BPO) content can considerably prolong the liquid dough phase. In augmentations with cement fillings in the region of a tumor, a high BPO content can specifically increase the peak temperature of the PMMA cement. In osteosynthetic augmentations with PMMA, necrosis is rare because heat development in the presence of metallic implants is low due to heat conduction via the implant. Larger cement fillings where there is no heat conduction via metal implants can exhibit substantially higher peak temperatures. The flow properties of PMMA cements are of particular importance for the user to allow optimum handling of PMMA cements. In patients with hypersensitivity to antibiotics, there is no need to avoid the use of PMMA as there are sufficient PMMA-based alternatives. The PMMA cements are local drug delivery systems and antibiotics, antiseptics, antimycotics and also cytostatics can be mixed with the cement. Attention must be paid to antagonistic and synergistic effects.

Prediction of Benzoyl Peroxide in Flour Using Near Infrared Spectroscopy Technique

This research proposed to design a prediction model based on radial basis function neural network and near infrared reflectance spectroscopy in detecting concentration of benzoyl peroxide in flour. Near infrared reflectance spectra acquired from 100 different concentration samples were pre-processed by the standard normal variate method, detection of leverage, and student residual. Near infrared reflectance spectroscopy models were designed to predict benzoyl peroxide in the 36 samples by means of partial least squares, back propagation neural network, and radial basis function, respectively. The results demonstrated that the radial basis function model, with prediction correlation coefficient (R), root mean squared error of prediction, and ratio of performance to standard deviate reaching 0.9937, 15.5095, and 8.8216, respectively, had optimal prediction accuracy and feasibility providing quality evaluation and dynamic monitoring service for quality inspection department and consumers.

Hybrid cationic ring-opening polymerization of epoxy resin/glycidyloxypropyl-polyhedral oligomeric silsesquioxane nanocomposites and dynamic mechanical properties

Glycidyloxypropyl-polyhedral oligomeric silsesquioxanes (G-POSS) were prepared from 3-glycidyloxypropyl-trimethoxysilane (GTMS) by hydrolytic condensation. The hybrid cationic thermal polymerization of G-POSS with bisphenol A epoxy resin (E-51) using diphenyliodonium fluoride borate (DPI·BF4) as a cationic initiator and benzoyl peroxide (BPO) as a co-initiator was investigated by DSC and FTIR. The structure of G-POSS was characterized by liquid chromatography–mass spectrometry (LC/MSD), FTIR and NMR. The effect of BPO content on reaction system, the distribution of G-POSS in the curing system, curing reaction activation energy Ea and dynamic mechanical properties of the E51/G-POSS nanocomposites were characterized. The results showed that octa(3-glycidyloxypropyl)-POSS (G-POSS) had been synthesized and displayed uniform dispersion in E51/G-POSS curing system. The DPI·BF4, which was capable to initiate the thermal ring-opening curing of epoxy resin, showed an initial curing temperature of epoxy resin decreased by 54.7 °C when the added amount of BPO was 2 wt%. The reaction process was well accorded with Kissinger’s kinetics model, and the average curing reaction activation energy Ea was increased as the content of G-POSS increased. The Tg and storage modulus of the E-51/G-POSS nanocomposites reached its optimum when the content of G-POSS was 2 wt%. The Tg of nanocomposite was 8.3 °C higher than that of the pure epoxy resin. The Tg and storage modulus decreased with the further increasing of G-POSS content.

Novel synthesis of branched polypropylene via solid-state shear pulverization

As synthesized by Ziegler–Natta or metallocene catalysis, commercial polypropylene (PP) is linear and has low melt strength. A common approach for improving melt strength is to incorporate long-chain branches (LCBs). We describe the discovery of a novel approach to prepare LCB PP by subjecting linear PP to solid-state shear pulverization (SSSP) with benzoyl peroxide (BPO) as the lone additive. Depending on BPO content, LCB PP can be formed by radical reactions during SSSP or post-SSSP melt extrusion. Using shear rheology, we demonstrated that LCB PP was formed during SSSP of samples with 4 and 6 wt% BPO. Relative to linear PP, the post-SSSP sample (purified of residual BPO) made with 6 wt% BPO exhibited enhanced shear thinning behavior, a decreased dependence of storage modulus (G′) on frequency (ω) at low ω, and a deviation from linear polymer behavior in its van Gurp–Palmen curve. For samples that were prepared with low levels of BPO (0.5–1.5 wt%), LCBs were not formed (within error) during SSSP; instead, LCBs were formed during post-SSSP melt extrusion (with residual BPO). While a sample with 1.5 wt% BPO showed no deviation from linear polymer behavior when tested immediately after SSSP, the same sample after post-SSSP melt extrusion demonstrated enhanced shear thinning behavior, decreased dependence of G′ on ω at low ω, deviation from linear polymer behavior in its van Gurp–Palmen plot, and improved crystallization and tensile properties (as is expected for branched PP). We also showed that the LCB formation is achieved by taking advantage of the near-ambient temperature conditions associated with SSSP and is unattainable via conventional melt processing of PP.

The Effect of Benzoyl Peroxide and Divinyl Benzene on the Properties of Cross-Linked Recycled Polyolefin Blends

The effect of peroxide cross-linking on the properties and morphology of recycled polyethylene (PE)/polypropylene (PP) blends was characterized. The addition of benzoyl peroxide (BPO) decreased the melt flow rate (MFR) and increased the impact strength of the recycled polymer blends. Divinyl benzene (DVB) is often used as a cross-linking agent assistant. Compared with BPO modification, the addition of BPO together with DVB improved the cross-linking efficiency and further increased the impact strength of the recycled polymer blends. The effect of BPO content on the MFR and the mechanical properties was also studied with the DVB content fixed. However, chemical cross-linking slightly reduced the thermal stability of the polymer blends. The morphology of the modified and unmodified polymer blends showed that with the addition of BPO, with or without DVB, the compatibility of the PE/PP blends was improved, resulting in enhanced impact strength.

Effect of interfacial area on heterogeneous free radical grafting of vinyl monomers in supercritical carbon dioxide: Grafting of acrylic acid on poly(vinylidenefluoride) nanoparticles

ABSTRACTThe role of the polymer interfacial area on free radical grafting of acrylic acid (AA) onto poly(vinylidenefluoride) (PVDF) was studied at 65°C using supercritical carbon dioxide (scCO2) as a solvent and swelling agent, benzoylperoxide (BPO) as chemical initiator and PVDF nanoparticles as polymer matrix. Under adopted conditions PVDF particles do not melt neither dissolve in the reaction medium and FTIR analyses performed on carefully washed nanoparticles confirmed the achievement of high grafting levels. The mass fraction of grafted AA increased with the grafting time and the BPO concentration while it decreased when the density of the fluid phase was enhanced. Collected results suggest that the grafting level obtained by free radical grafting of vinyl monomers onto solid polymer in scCO2 can be significantly enhanced by increasing the interfacial area of the matrix. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41541.

A novel antimicrobial orthodontic band cement with in situ-generated silver nanoparticles.

To develop an antimicrobial orthodontic band cement for the prevention of white spot lesions using a novel process that generates silver nanoparticles (AgNP) in situ. Twenty-seven groups of AgNP-loaded Opal Band Cement (OBC) and two control groups were formulated with varying concentrations of additional benzoyl peroxide (0.5, 1.0, 1.5, or 2.0 wt%) and 2,2-(p-Tolylimino) diethanol (0.5 or 1 wt%). Rockwell15T hardness and near-infrared FTIR were used to assess degree of cure, three-point bending was used to determine modulus and ultimate transverse strength (UTS), and Ag(+) ion release was measured for up to 4months in vitro using atomic absorption spectroscopy. Antimicrobial activity against Streptococcus mutans and Lactobacillus acidophilus was tested in vitro by counting colony-forming units for up to 28days. Biocompatibility was evaluated following ISO specifications 7405 (2008), 10993-3 (2003), 10993-5 (2009), and 10993-10 (2010). Most of the experimental groups had hardness, modulus, and UTS values similar to those of the control group. Ag(+) ion release was observed for all AgNP-loaded groups for up to 4months. Increase in Ag loading increased Ag(+) ion release and in vitro antimicrobial effect. The biocompatibility of the optimal AgNP-loaded OBC was comparable to that of negative controls. A novel antimicrobial orthodontic band cement was developed that has comparable mechanical properties to controls, controlled and sustained Ag(+) ion release, significant bacterial inhibition in vitro, and excellent biocompatibility.

Adhesion properties of benzoyl peroxide crosslinked epoxidized natural rubber (ENR 25)-based pressure-sensitive adhesives

Adhesion properties of crosslinked (epoxidized natural rubber)-based adhesives were studied by using coumarone-indene, benzoyl peroxide, and toluene as tackifying resin, crosslinking agent, and solvent, respectively. The adhesion properties were measured by a Lloyd Adhesion Tester operating at 30 cm min−1. Results show that loop tackiness and peel strength pass through a maximum value at 1 phr (parts by weight per hundred parts of resin) of benzoyl peroxide concentration, an observation that is attributed to the optimum crosslinking of epoxidized natural rubber whereby optimum cohesive and adhesive strength are obtained. However, shear strength increases with increasing benzoyl peroxide concentration wherein the higher rate of increase is observed between 0 and 1 phr of benzoyl peroxide content. This observation is associated with the steady increase in cohesive strength as crosslinking is increased. In all cases, the adhesion properties of adhesives increased with increasing coating thickness. J. VINYL ADDIT. TECHNOL., 22:8–12, 2016. © 2014 Society of Plastics Engineers

Dependence of Adhesion Property of Epoxidized Natural Rubber (ENR 25)/Ethylene-Propylene-Diene Rubber Blend Adhesives Crosslinked by Benzoyl Peroxide

The loop tack, peel strength, and shear strength of crosslinked epoxidized natural rubber (ENR 25)/ethylene-propylene-diene rubber (EPDM) blend adhesives were investigated. Coumarone-indene resin, toluene, and benzoyl peroxide were used as the tackifier, solvent, and crosslinking agent, respectively, throughout the experiment. The adhesive was coated on a polyethylene terephthalate (PET) substrate using a SHEEN hand coater at 60 μm and 120 μm coating thickness. It was cured at 80°C for 30 minutes before testing on a Lloyd adhesion tester operating at testing rates from 10 to 60 cm min−1. Results show that loop tack and peel strength of the ENR 25/EPDM adhesive pass through a maximum value at 2 parts per hundred parts of rubber (phr) of benzoyl peroxide content. This observation is attributed to the increase in crosslinking which enhances the cohesive strength of the adhesive. Further addition of the crosslinking agent decreases the tack and peel strength due to the decrease in wettability of the over-crosslinked adhesive. Shear strength, however, increases steadily with benzoyl peroxide content, an observation which is associated with the steady increase in the cohesive strength. The adhesion properties increase with increasing coating thickness and testing rate.

Dependence of Adhesion Properties of Cross-linked Epoxidized Natural Rubber (ENR 25)-Based Pressure-Sensitive Adhesives on Benzoyl Peroxide Loading in the Presence of Gum Rosin and Petroresin Tackifiers

The effect of benzoyl peroxide loading on the adhesion properties of cross-linked epoxidized natural rubber (ENR 25)-based adhesives was studied using gum rosin and petroresin as tackifiers. Toluene and polyethylene terephthalate (PET) were used as solvent and coating substrate, respectively. The adhesion properties were determined by a Lloyd adhesion tester operating at 30 cm min−1. Results indicate that the loop tack and peel strength of gum rosin and petroresin pass through a maximum value at 2 parts per hundred parts of rubber (phr) and 3 phr benzoyl peroxide concentration, respectively, an observation which is attributed to the optimum cross-linking of ENR 25 where optimum, cohesive and adhesive strength is obtained. The shear strength, however, increases steadily with increasing benzoyl peroxide loading due to the steady increase in the cohesive strength. At the optimum benzoyl peroxide concentration, the petroresin-based adhesive consistently exhibits higher adhesion properties compared to that of gum rosin-based adhesives. The adhesion properties of both adhesive systems increase with increasing coating thickness.

Systematic review on the rapidity of the onset of action of topical treatments in the therapy of mild-to-moderate acne vulgaris

The time until a patient achieves a relevant improvement during the treatment of a skin disease is important for selecting a therapy, but has been largely neglected in reviews and guidelines. The aim of this systematic review was to determine the time until the onset of action (TOA) of topical acne treatments. The primary outcome was the TOA defined as the time until a 25% reduction in the mean number of inflammatory lesions had been achieved. A systematic literature search in Medline and Embase was carried out. Clinical trials that evaluated head-to-head comparisons of treatments in patients suffering from mild-to-moderate papulopustular acne were included. Abstract and full-text screening and data extraction were done independently by two investigators. With respect to inflammatory lesions, different concentrations of benzoyl peroxide (BPO) or adapalene did not seem to influence the TOA. BPO seemed to act more quickly than isotretinoin and tretinoin. Adapalene showed a shorter TOA than isotretinoin. Conflicting results were seen when comparing adapalene with tretinoin, with a tendency for adapalene to be faster. Clindamycin/BPO seemed to act more quickly than adapalene. Inconsistent results were seen for the comparison of clindamycin/BPO and BPO alone with a slight indication of a shorter TOA for clindamycin/BPO. Adapalene/BPO and clindamycin/BPO showed comparable TOA. When interpreting the data, the different study designs and the limited study quality need to be taken into account. Further research is needed to identify treatments that offer an early onset of action and possibly help to optimize patients' adherence. TOA should be considered as an additional outcome in acne trials.