Impact of polymer crosslinking on release mechanisms from long-acting levonorgestrel intrauterine systems
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Polydimethylsiloxane
Prepolymer
Excipient
Castable polyurethane elastomer based on polytetramethylene glycol (PTMEG) and 2,4-toluene diisocyanate (TDI) was prepared with low free TDI monomer content prepolymer (LF-prepolymer), the structure and properties of the prepolymers and corresponding elastomers were characterized. The result showed that, LF-prepolymer exhibit low viscosity, low molecular weight and narrow molecular weight distribution. The polyurethane prepolymer based on LF-prepolymer show higher bashore rebound, lower compression set and better dynamic properties.
Prepolymer
Compression set
Toluene diisocyanate
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Abstract The functionality of a prepolymer, which is defined as the ratio of molecular weight to equivalent weight, is probably the most important single parameter that determines the properties of the cross-linked polymer network. The determination of prepolymer functionality therefore requires accurate knowledge of both number average molecular weight and equivalent weight. Ideally, a suitable prepolymer for propellant binder applications has terminal functionality (OH or COOH). Such a prepolymer theoretically has a functionality of 2.0. Because of uncontrolled chain termination reactions during the prepolymer synthesis, however, not all polymer chains have the desired functional end group. As a result, prepolymers generally have a distribution of functionalities, including onfunctional, monofunctional, and the desired difunctional prepolymer.
Prepolymer
Molar mass distribution
Chain (unit)
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The preparation of polyurethane acrylates prepolymer was composed of two steps.In this paper,every kinds of effect factors were compared and analyzed.The optimal technics of polyurethane acrylates prepolymer preparation was determined.In the first step,the temperature and time of reaction were 60～65℃ and 4h respectively.The ratio(mol)of NCO to OH was 3∶1 and the amount of catalyst was 0 4%.In the second step,the temperature and time of reaction were 70～75℃ and 4h respectively.
Prepolymer
Reaction conditions
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The importance of pharmaceutical excipients in the creation of any dosage form is critical. These excipients are occasionally to blame for product underperformance and dosage form deterioration. Product deterioration and underperformance could be attributed to incompatibilities between drug and excipient or sometimes excipient and excipient either due to the presence of reactive impurities in the excipients or a reaction between the functional groups present on the excipients. Although, the drug and excipient incompatibilities are monitored and reported, excipient-excipient incompatibilities are overlooked due to a paucity of literature. Pharmaceutical companies used to work in a controlled environment (compatibility tests between excipients to determine the best excipients for dosage form creation) and utilize mitigation measures to suppress any incompatibilities between excipients when necessary. In the current paper, we propose a system to predict excipient-excipient incompatibilities that can occur during dosage form development, possible incompatibility reactions, as well as a potential way to counter these incompatibilities by suggesting alternative excipients based on the descriptor knowledge of the excipients. The system was developed and validated using SOM and random forest algorithms. Two systems were developed based on incompatibility and property relationship, this approach provides a wide scope of our system to select compatible excipients in place of incompatible ones. Two systems predicted top 10 key incompatibilities and properties which cover the maximum range of the pharmaceutical research and development. After the validation using random forest, our system was able to find the structural components responsible for these top incompatibilities and properties. The prediction accuracy was found to be >85%. This was confirmed by preparing confusion matrix of the top incompatibilities and properties and assigning values of 0.5 to predict the outcome. The excipients with probability of ≥0.5 were considered active (possessing incompatibility or property) and the excipients with probability
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The importance of pharmaceutical excipients in the creation of any dosage form is critical. These excipients are occasionally to blame for product underperformance and dosage form deterioration. Product deterioration and underperformance could be attributed to incompatibilities between drug and excipient or sometimes excipient and excipient either due to the presence of reactive impurities in the excipients or a reaction between the functional groups present on the excipients. Although the drug and excipient incompatibilities are monitored and reported, excipient-excipient incompatibilities are overlooked due to a paucity of the literature. Pharmaceutical companies used to work in a controlled environment (compatibility tests between excipients to determine the best excipients for dosage form creation) and utilize mitigation measures to suppress any incompatibilities between excipients when necessary. These tactics take time and money to implement, and they increase the cost of developing a dosage form. However, the primary goal of this review is to highlight some of the most prevalent excipient-excipient incompatibilities that can occur during dosage form development, possible incompatibility reactions, as well as a potential method for predicting excipient-excipient incompatibilities based on structural information. The structure incompatibility relationship strategy to forecast incompatibilities between diverse excipients is an idea based on the reactivity of pharmaceutical excipients, and it might be a useful tool in reducing the time, cost, and product failures during the product development due to excipient-excipient incompatibilities.
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Blocked polyisocyanates with low release temperature(110～120 ℃) were synthesized with methyl ethyl ketoxime as blocking agent.The effects of the mole ratio,reacting temperature and time on blocking reaction for prepolymer were studied.The release reaction of blocked prepolymer are discussed and release temperature are determined.The IR spectra for prepolymer,blocked prepolymer and blocked prepolymer release by heating are compared.
Prepolymer
Blocking (statistics)
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The title polyether polyisocyanate prepolymer with excellent performance has been developed based on polyether polyols and TDI. The structure of the prepolymer is characterized. The properties of prepolymer and its acrylic polyurethane coatings are discussed.
Prepolymer
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A procedure is described for making layer-to-layer interconnections in polydimethylsiloxane (PDMS) microfluidic devices. Thin (∼50 μm) perforated PDMS membranes are bonded to thicker (0.1 cm or more) PDMS slabs by means of thermally cured PDMS prepolymer to form a three-dimensional (3D) channel structure, which may contain channel or valve arrays that can pass over and under one another. Devices containing as many as two slabs and three perforated membranes are demonstrated. We also present 3D PDMS microfluidic devices for display and for liquid dispensing.
Polydimethylsiloxane
PDMS stamp
Prepolymer
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ABSTRACT Leftover uncured polydimethylsiloxane (PDMS) polymer is generally discarded. In an effort to minimize this waste, we have developed a method for cryo‐preserving PDMS prepolymer involving a simple storage technique for the preservation and repeated use over 1 month. Aliquots of the uncured PDMS prepolymer were stored at −20 or −80°C, then conveniently and easily thawed at body temperature (37°C). Proposed cryo‐preservation was successfully evaluated using diverse biological and physical tests. This method of cryo‐preserving PDMS reduces both the material waste and labor of soft lithography process and may enable soft lithography to be environmentally friendly relative to previous methods. The method may be popularly accepted for application to a variety of common microdevice fabrication procedures. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131 , 40378.
Polydimethylsiloxane
Prepolymer
PDMS stamp
Soft Lithography
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Polyurethane acrylate prepolymer was synthesized under the optimal conditions as follows:reaction temperature of 75～80 ℃,catalyst dosage of about 0.45%.The effects of prepolymer content and type on cured film performance were studied.The optimum prepolymer content in the formula of adhesive was 50%～60%.The results showed that aromatic prepolymer had significantly higher shear strength than aliphatic prepolymer,but its adhesive layer was harder with lower toughness,aliphatic prepolymer had nice flexility with higher 180 ° peel strength and adhesion than aromatic prepolymer,the higher the nonvolatile matter content,the more completely it cured and the better the comprehensive strength it had,glass transition temperature of aromatic prepolymer was higher than that of aliphatic prepolymer,and aromatic and aliphatic polyurethane respectively contributed shear strength and peel strength for the cured film of adhesive.
Prepolymer
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