Second Step Of Polymerization Research Articles

Natural Polymeric Compound Based on High Thermal Stability Catechin from Green Tea.

Catechin is a plant polyphenol with valuable antioxidant and health-promoting properties. Polymerization is one way to stabilize flavonoids and may cause changes in their specific properties. The aim of this study is to obtain a polymeric complex catechin compound with high thermal stability. As a result of polymerization, a condensed and cross-linked catechin structure was obtained, which guaranteed high thermal resistance and, moreover, the phosphorus groups added in the second step of polymerization ensured that the compound obtained had thermal stability higher than natural condensed tannins. The first step of self-polymerization of (+)-catechin may be an easy way to obtain proanthocyanidins with greater antioxidant activity. The second step of the polymerization obtained a polymeric complex catechin compound that showed better thermal stability than catechin. This compound can potentially be used as a new pro-ecological thermal stabilizer.

A novel polyurethane-based biodegradable elastomer as a promising material for skeletal muscle tissue engineering

A key challenge in skeletal muscle tissue engineering is the choice of a proper scaffolding material as it should demonstrate elastic behavior to withstand and support the dynamic loading of the tissue microenvironment while being biodegradable and biocompatible. In this study, we tested the applicability of a novel biodegradable polyurethane (PU) elastomer chain extended with fibrinogen (Fib) to fulfill these requirements. Biodegradable polyurethane-fibrinogen (PU-Fib) elastomers were synthesized by step-wise condensation polymerization. Firstly, PU prepolymer was synthesized and then Fib was integrated into PU prepolymer during the second step of polymerization. The chemical, thermal, viscoelastic, mechanical and biodegradation properties of PU-Fib were characterized. FTIR-ATR spectrum showed amide bands specific to PU and Fib, DSC thermograms showed the suitable integration between the components. Dynamic mechanical analysis revealed Tg and Tα* transitions at 64.5 °C and 38.4 °C, respectively. PU and Fib had shown chemically compatible interactions and when compared to PCL, PU-Fib possessed viscoelastic properties more suitable to the native tissue. PU-Fib films were produced and seeded with C2C12 mouse myoblasts. Uniaxial cyclic stretch was applied to the cell seeded films for 21 d to mimic the native dynamic tissue microenvironment. Cell proliferation, viability and the expression of muscle-specific markers (immunofluorescent staining for myogenin and myosin heavy chain) were assessed. Myoblasts proliferated well on PU-Fib films; aligned parallel along their long edge, and express myogenic markers under biomimetic dynamic culture. It was possible to culture myoblasts with high viability on PU-Fib elastomeric films mimicking native muscle microenvironment.

Film forming hybrid acrylic/ZnO latexes with excellent UV absorption capacity

Acrylic/ZnO hybrid latexes were synthesized through a two-step emulsion polymerization process. First, a hybrid seed was synthesized by miniemulsion polymerization, which contained all the hydrophobically modified ZnO nanoparticles. Subsequently, this hybrid seed was employed in a seeded semibatch emulsion copolymerization yielding high solids content hybrid latexes (40wt%). Cryo-transmission electron microscopy (cryo-TEM) demonstrated that the dispersion of the ZnO nanoparticles in the initial miniemulsion was not homogeneous, which led to a hybrid seed with two populations, polymer particles containing ZnO and pristine polymer particles. After the second step of polymerization barely the same morphology was obtained. Nevertheless, it was proved by electron tomography (3D-TEM) that the ZnO nanoparticles were encapsulated in the polymer particles. The hybrid films containing ZnO presented a superior UV absorption capacity than their counterpart hybrid acrylic/CeO2 prepared following the same strategy.

A new approach to controlled/living radical polymerization by DPE method

Controlled free radical polymerizations of methyl methacrylate and styrene in bulk by 1,1-diphenylethene (DPE) were demonstrated in a two-step process, preheating treatment of initiators followed by a living polymerization of monomers. Over the course of polymerization, continuous growing of polymers with unimodal molecular weight distribution and a relatively small polydispersity index (around 1.5 even in the range of Mn∼105g/mol) on GPC diagrams was observed. In our previous study, the DPE controlled radical polymerization with constant molecular weight throughout the polymerization was caused by the intrinsically low reactivation rate constant (k2) of DPE capped dormant chains. To raise the reaction temperature in order to increase k2, a continuous molecular weight growing but broader or bimodal molecular weight distribution was obtained if the living polymerization was conducted in a one-step process. In this work, a two-step polymerization process was proposed. In the first step, the initiator 2,2′-azobisisobutyronitrile (AIBN), control agent DPE, and small amount of monomer were mixed and heated for a specific time period. Then a living polymerization of monomers was conducted in the second step of polymerization. This two-step new approach had minimized the imperfections of the DPE system; thus the polymerization showed better living characters and revealed its enhanced control abilities.

Synthesis and properties of soap-free poly(methyl methacrylate-ethyl acrylate-methacrylic acid) latex particles prepared by seeded emulsion polymerization

In order to obtain functional polymer latex particles with clean surface and with surface carboxyl groups, P(MMA-EA) seed particles with the diameter of 335 nm were first synthesized via soap-free batch emulsion polymerization of methyl methacrylate (MMA) and ethyl acrylate (EA), and then the seeded emulsion copolymerization of MMA, EA and MAA (methacrylic acid) onto the seed particles were performed in the absence of emulsifier. Influences of ingredients and conditions on polymerization, latex particle size ( D p ) and its distribution were investigated. Results showed that most of the monomers polymerized onto the seed latex particles in the second step of polymerization by using drop-wise addition method, and D p increased from 483 nm to 829 nm with the mass ratio of core/shell monomers [C]/[S] decreased from 1:2 to 1:15. It was found that D p decreased with the increase of MAA and initiator amounts, and the size of the latex particles became uniform with the decrease of MAA amount and with the increase of [C]/[S] value.

Free radical two step synthesis of styrene and acrylate block copolymers with disulphide initiators

AbstractControlled two step block copolymerization of styrene, methyl methacrylate and ethyl acrylate with aliphatic and aromatic disulphides under UV irradiation took place in bulk and in THF solution. In the first step of the polymerization, the most reactive system was ethyl acrylate with aromatic disulphides.The molecular weights and yields of polymerizations increased with reaction time. The macromolecules were terminated by primary. SR radicals and by combination of two macroadicals which was observed by NMR spectroscopy. Aninsignificant portion of uninitiated photopolymerization was detected only for MMA. In the second step of polymerization, the purified macroinitiators from the first step reacted with additional monomers to form block copolymers with a small quantity of unreacted macroinitiator. The molecular weights of copolymers increased, the bonding segments between the blocks being detected by 1H NMR. The overall reaction is an insertion of monomers between two thiyl groups.

Morphological changes in segmented polyurethane elastomers by varying the NCO/OH ratio

AbstractThe morphological changes induced to segmented polyurethane elastomers by varying the NCO/OH ratio during the second step of polymerization, while keeping constant the total hard‐segment content (∼ 30%), were studied by means of fourier transform infared spectroscopy (FTIR), differential scanning calorimetry (DSC), and the thermally stimulated depolarization current method (TSDC). The DSC results gave evidence for the existence of phase separation in thermoplastic polyurethanes, whereas the elastomerc ones appeared to form a more homogeneous network. The FTIR results gave additional evidence regarding phase separation be detecting the sterength of the hydrogen bonds. Moreover, an attempt was made to assess the relative contribution made to the hydrogen bonding in such systems by the two potential acceptors: ester and urethane carbonyls. The TSDC results gave a relaxation mechnism that is due to interfacial (Maxwell–Wagner–Sillars) polarization, providing evidence of the existence of an interfacial phase. The introduced secondary chemical cross‐links was found to affect mainly the irregularly packed hard domains and to form a more homegeneous network at higher values of the NCO/OH ratio. © 1994 John Wiley & Sons, Inc.