Effect of photoinitiator on photopolymerization of inorganic–organic hybrid polymers (ORMOCER®)

Inorganic–organic hybrid polymers have been developed and tested for evaluation in optical and electrical applications. Although hybrid inorganic–organic polymers can be synthesized by sol–gel chemistry at first, the physical properties of hybrid inorganic–organic polymers are changed during thin film-making processes, that is, photocuring and thermal curing. To investigate the effect of photoinitiator on the material properties during processing, a model system containing methacrylic groups as organically polymerizable units was selected. The conversion of CC double bond of methacrylic groups depending on some kinds of photoinitiator quantities was characterized by Fourier transform infrared spectroscopy. It was confirmed to correlate the degree of CC double bond conversion with the refractive indices. Thermodynamically, the enthalpy of the photopolymerization of hybrid polymer was investigated by UV–DSC. UV–DSC spectra showed the exothermic nature of photopolymerization of ORMOCER® to be in dependence of photoinitiator quantities. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1979–1986, 2004     

Modification of poly-HEMA with nonreactive POSS derivatives by in situ photopolymerization

Photo-induced polymerization of 2-hydroxyethyl methacrylate (HEMA) in the presence of various amounts of nonreactive polyhedral oligomeric silsesquioxanes (POSS) functionalized with glycidyl, fluoroalkyl or hydroxyl groups was investigated. HEMA/POSS systems were characterized before, during and after the photocuring, with the special emphasis on the photopolymerization kinetics (measured by isothermal differential scanning calorimetry). It was found that the introduction of tested POSS derivatives into HEMA strongly affects the photopolymerization kinetics (enhancement of the gel effect, increase in the polymerization rate and conversion), mainly due to the increase in the viscosity of the initial formulation which leads to a reduction in the termination rate coefficient. However, interactions HEMA–POSS cause also a slight increase in the propagation rate coefficient. The behavior of the polymerization rate coefficients during the reaction suggests that POSS cages may mitigate the inhibitory effect of viscosity on the diffusion of macroradicals by exerting a slip effect. The materials produced are microcomposites due to the partial phase separation occurring during the curing process. Small amounts of added POSS modifiers cause plasticization of the material; at higher loads, POSS domains behave like nanofiller aggregates that increase the glass temperature. The nonreactive POSS have very little effect on thermal decomposition of the poly-HEMA matrix, which can result in a degree from the phase separation; the latter is also the main cause of the deterioration of the mechanical properties of composites compared to a pure polymer matrix.

     

TG/DSC studies of modified 1–vinyl-2-pyrrolidone–divinylbenzene copolymers

In this paper, the synthesis and characterization of porous copolymers of 1-vinyl-2-pyrrolidone with divinylbenzene are presented. They were obtained by suspension polymerization as pure polymers or composite materials with different inorganic fillers. The influence of the type of filler on the textural and thermal properties was investigated in detail. It was found that the value of the porous surface area and the degree of double bonds’ conversion of composites are much lower than in the case of pure copolymers. Thermal properties of the obtained materials were investigated by the means of thermogravimetry and differential scanning calorimetry.     

Methacrylate-based polymer blends containing oligomeric 1,2-polybutadienes

Partly miscible polymer blends with semi-IPNs structure built from polydimethacrylate networks and hydroxyl-terminated liquid polybutadienes with predominant 1,2-structure (LBH) were prepared by photopolymerization method. Photopolymerization kinetics of dimethacrylate–LBH mixtures were monitored by DSC technique under isothermal conditions. Kinetic curves and related parameters, like polymerization rate and degree of double bond conversion were determined as functions of dimethacrylate structure, LBH molecular mass, and its content in the mixture as well as polymerization temperature. The photopolymerization kinetics and activation energy for the polymerization rate were discussed taking into account the phase separation occurring during the curing reaction. The extent of phase separation (based on T _g’s measurements) depended on LBH content and dimethacrylate chemical structure. The effect of LBH content on hardness of polymer blends was also examined.     

Influence of additives on recycled polymer blends

Polymer systems based on polymer waste offer promising way to increase recycling in the society. Since fillers play a major role in determining the properties and behavior of polymer composites, recycled polymers can also be combined with fillers to enhance the stiffness and thermal stability. In this study, blends of recycled polyethylene and recycled polypropylene with mica and glass fiber were prepared by melt blending technique. The effect of the particle loading, filler type, and filler–matrix interaction on thermal degradation and thermal transition of processed systems were investigated. Thermogravimetric analysis, differential thermogravimetric analysis, and differential scanning calorimetry were used in this investigation. Comparative analysis shows that both fillers produced different effects on thermal properties of the processed systems. These results were confirmed by calculating the activation energy for thermal degradation and thermal transition using Kissinger and Flynn–Wall expressions.     

含液晶基团的聚对亚苯基亚乙炔基类交替共聚物的合成、表征及性能研究

合成了两种含氰基联苯液晶基团的新型聚对亚苯基亚乙炔基(PPE)类交替共聚物,并对其进行了结构表征和性能研究.示差扫描量热仪(DSC)和偏光显微镜(POM)的结果证明了在液晶单元含量较大时聚合物才会出现明显的液晶形态.荧光光谱表明,在降温前后液晶聚合物的发光光谱发生了明显的变化.同时,对聚合物进行能量转移研究发现随着溶液浓度的增加,Frster能量转移更加完全;另外,利用原子力显微镜(AFM)对聚合物降温前后的形态变化进行了观察.结果表明,液晶性质可以导致聚合物形态的变化进而带来发光光谱的改变,为今后制备液晶可控型发光聚合物提供了理论依据.     

Microgel formation in the free radical crosslinking polymerization of ethylene glycol dimethacrylate (EGDMA). I. Experimental

An important feature of free radical crosslinking polymerization of ethylene glycol dimethacrylate (EGDMA) resin is the formation of heterogeneous structure through intramolecular reaction. Such structure formation affects not only the cure behavior and rheological changes of the resin but also the physical properties of the formed polymers. In this study, the reaction kinetics, morphological changes, and characteristics of formed polymers were examined by a differential scanning calorimeter, a Rheometrics Dynamic Analyzer, a dynamic light scattering goniometer, and a Fourier transfer infrared spectrometer. Experimental data showed the formation of bimodal polymers before gelation. These polymers are partially crosslinked and can be considered as microgel particles. © 1995 John Wiley & Sons, Inc.     

Structure and mesophase of a new series of aromatic polyesters

A new series of aromatic polyesters in which the polymethylene flexible spacers are connected with the rigid main chain containing benzene ring were prepared by interfacial polycondensation. The polymers were characterized by hotstage polarized microscopy, differential scanning calorimetry, wide-angle X-ray diffraction and Fourier-transform infrared spectroscopy. The structure and properties of polyesters were investigated. The results showed that the textures of the thermotropic liquid-crystalline polyesters are smectic and/or nematic. The dependence of melting point, clearing point and transition enthalpy of polyesters on length of the alkylene group revealed a regular zig-zag trend. The thermal analysis of polyesters revealed that the clearing transition is an equilibrium process, so the entropy of this transition may be taken as an indication of the degree of the order in mesomorphic state presented in the system. Furthermore, the thermal history of polymer had a significant effect on its thermal behavior. The regular arrangement of methylene segments changed when polymer melted from the crystal state to the liquid-crystalline state. The research also implicated that the conformational change of the methylene flexible spacer was one of the reasons for this thermal effect.     

Polycycloalkylene-siloxane polymers: Synthesis and thermal study

Based on dicyclopentadiene and silacyclopentene, two linear polycycloalkylene-siloxane polymer systems have been synthesized and the thermal stability of the raw polymers evaluated by differential scanning calorimetry and thermal gravimetric analysis. The DSC data in nitrogen indicate that both polymer systems have excellent thermal stability. In air, these polymers begin to oxidize at approximately 150°C, with catastrophic oxidation occurring at about 400°C.     

Mechanical,thermal and morphological properties of poly(ε‐caprolactone)/zein blends

Blends of poly(ε‐caprolactone) (PCL) with zein (PCL/zein) in different proportions (100/0, 75/25, 50/50, 25/75 and 0/100 wt% containing 5 wt% glycerol) were compared based on their mechanical properties (tensile strength, elongation at break, and Young's modulus), and on their thermal properties, the latter determined by thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA). The morphology of the materials was studied by scanning electron microscopy (SEM). Blends of PCL/zein showed reduced tensile strength and elongation at break, but increased Young's modulus compared to the pure polymers, in agreement with the DMTA and SEM results. These findings indicated that PCL and zein were incompatible. TGA showed that the thermal stability was enhanced by the addition of zein to PCL, whereas SEM showed a poor interfacial interaction between the polymers. Copyright © 2004 John Wiley & Sons, Ltd.     

Alginic acid–silica hydrogel coatings for the protection of osmotic distillation membranes against wet-out by surface-active agents

The formulation of organic–inorganic polymer composites can be used to enhance selected properties, such as susceptibility to microbial attack, thermal stability, mechanical strength and water sorption capability. Accordingly, a series of alginic acid–silica hydrogel films was prepared for testing as protective coating materials for PTFE osmotic distillation membranes. Unprotected hydrophobic membranes are subject to wet-out when contacted by surface-active agents, such as oils and detergents. Films containing 5, 10, 15 and 20 wt.% silica, with and without the addition of glycerol for plasticisation, moisturisation and silica dispersion, were characterised using scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, mechanical strength measurements, and water-swelling measurements. Composites prepared with glycerol addition had better thermal stability, mechanical strength and water sorption capability than those prepared without glycerol addition. Uncoated membranes and membranes coated with composites prepared with glycerol addition were tested for OD performance and resistance to surface-active agents using pure water, orange oil (limonene)–water mixtures, and sodium dodecylbenzene sulfonate detergent solutions. Uncoated membranes showed immediate hydrophobicity loss in the presence of orange oil and detergent. For coated membranes, no wet-out occurred over the 15 h duration of three consecutive 5 h OD trials using orange oil–water mixtures. In the case of detergent solutions, the coating afforded protection to the membrane for 4–5 h. In a separate trial, no wet-out occurred when the coated side of the membrane was placed in contact with 1.2 wt.% orange oil for 72 h.     

Comparison of the properties of the polyimides,polyamides and polyureas derived from 1-[(dialkoxyphosphinyl)-methyl]-2,4- and -2,6-diaminobenzenes and m-phenylenediamine

The physical and thermal properties of various phosphorus-containing polyimides, polyamides and polyureas based on 1-[(dialkoxyphosphinyl)methyl]-2,4- and -2,6-diaminobenzenes as well as of the corresponding common polymers derived from m-phenylenediamine were compared and correlated with their chemical structure. Differential scanning calorimetry (DSC) measurements showed that the introduction of the (dialkoxyphosphinyl) methyl groups in the polymers converted their endothermic pyrolysis under anaerobic conditions to exothermic or reduced the heat adsorbed during their pyrolysis. Thermogravimetric analysis (TGA) showed that the thermal stability of the polymers and the char yield formed during their pyrolysis were in the order polyureas < polyamides < polyimides. All phosphorylated polymers showed a lower degree of polymerization, a lower polymer decomposition temperature and formed higher char residue on pyrolysis than the corresponding common polymers.     

Analytical followup of the gamma initiated synthesis of a molecularly imprinted polymer

A molecularly imprinted polymer (MIP) for the template phenytoin has been prepared by gamma initiated copolymerization of methacrylamide and ethylene glycol dimethacrylate. The progress of polymerization was studied by measuring the monomer conversions and the template binding properties of the resulting polymers, respectively. The consumption rate of the two monomers showed different course. There was no difference observed in the polymerization rates of the MIP and the control polymer (NIP). The template binding properties of the MIP and the NIP changed considerably with the progress of the polymerization process and became similar to those of the thermally initiated polymers after full conversion.     

Polymer‐dispersed liquid‐crystal materials fabricated with frontal polymerization

We report on the morphological and thermal properties of polymer‐dispersed liquid crystals (PDLCs) fabricated with frontal‐polymerization‐induced phase separation (FPIPS). Frontal polymerization is characterized by a rapid‐conversion, high‐temperature, and large‐thermal‐gradient environment. A comparison is made between the morphological and thermal properties of PDLCs fabricated with FPIPS and traditional thermal‐polymerization‐induced phase separation. Characterization includes differential scanning calorimetry to probe the glass and nematic‐to‐isotropic transitions and scanning electron microscopy to evaluate the phase‐separated morphology. In addition, the frontal temperatures and velocities are reported for PDLCs fabricated with frontal polymerization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 204–212, 2003     

Preparation of siloxane‐based urethane dimethacrylates carrying carboxylic groups and the effect of silver nanoparticles on the properties of composite polymer films

This work reports on the synthesis of three acid oligosiloxane‐urethane dimethacrylates and their use to obtain hybrid nanocomposite films, in which the presynthesized silver nanoparticles (NPs) were incorporated before photopolymerization, or produced via in situ photoreduction of the silver nitrate (AgNO₃) precursor into the formulation, without any conventional reducing agent. All samples were characterized by ¹H NMR, FT‐infrared and UV spectroscopies, photodifferential scanning calorimetry (photo‐DSC), transmission electron microscopy (TEM), and energy‐dispersive X‐ray (EDX) analysis. Fourier transformed infrared spectroscopy and photo‐DSC results showed that dimethacrylates having hydrophilic segment of poly(ethylene oxide) type in structure are more reactive than the acid oligosiloxane dimethacrylate. When another urethane dimethacrylate is taken as a comonomer, the photopolymerization rate (0.112–0.132 s^?1) and the degree of conversion (82–93%) significantly increased. Experimental evidence of the existence of nanosilver into the polymer matrix generated upon UV irradiation has been supported by UV spectroscopy, EDX and TEM analysis, the last allowing a visualization of the formation of silver NPs with size between 2 and 15 nm. Mechanical parameters and wettability of the photocrosslinked films are also discussed in the prospect of further potential applications in the biomedical field. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

UV‐Irradiation Cured Organic‐inorganic Hybrid Nanocomposite Initiated by Ethoxysilane‐modified Multifunctional Polymeric Photoinitiator through Sol‐gel Process

The UV‐cured organic‐inorganic hybrid nanocomposite (nano‐Si‐m‐PI) was prepared through the photopolymerization of acrylic resin initiated by ethoxysilane‐modified multifunctional oligomeric photoinitiator (Si‐m‐PI). The esterification reaction of 2‐hydroxy‐4′‐(2‐hydroxyethoxy)‐2‐methylpropiophenone (Irgacure 2959) with thioglycolic acid, and the following addition reactions with dipentaerythritol hexaacrylate and then 3‐aminopropyltriethoxysilane were carried out for preparing the Si‐m‐PI. The Si‐m‐PI exhibits the similar UV absorption and molar extinction coefficient with Irgacure 2959. The photoinitiating activity study by photo‐DSC analysis showed that the Si‐m‐PI possesses high photopolymerization rate at the peak maximum (R_p^max) and final unsaturation conversion (P^f) in the cured hybrid films. From the scanning electron microscope (SEM) observation, the SiO₂ nanoparticles dispersed uniformly in the formed nano‐Si‐m‐PI, whereas the aggregation of nanoparticals occurred in nano‐Irg, which was prepared through the photopolymerization of acrylic resin initiated by Irgacure 2959. Moreover, compared with the UV‐cured pure polymer and nano‐Irg, the nano‐Si‐m‐PI showed remarkably enhanced thermal stability and mechanical properties.     

Studies on thermotropic liquid crystalline elastomers. II. Synthesis and properties of liquid crystalline polyester elastomers

Three series of novel thermotropic liquid crystalline polyester elastomers (TLCPEEs) were prepared by direct polycondensation from terephthalic acid, polyols (M_n = 1000 or 2000), and various diols. The structures and thermal properties of the synthesized TLCPEEs were examined by FTIR spectroscopy, differential scanning calorimetry, thermal optical polarized microscopy, thermogravimetric analysis, and wide-angle x-ray diffraction. The effects of kinds and amount of diols and the molecular weight of polyols on the thermal properties of TLCPEEs were studied. By introducing long flexible spacers (PE-1000 or PE-2000) into the polymer main chain, all polymers showed two-phase morphology under the thermal optical microscopic observation. All of the synthesized polymers, except polymer P1-BPA60 and P2-BPA60, which were prepared from BPA, exhibited thermotropic liquid crystalline properties that were in the smectic phase. © 1995 John Wiley & Sons, Inc.     

Effects of ethylene glycol dimethacrylate as cross-linker in ionic liquid gel polymer electrolyte based on poly(glycidyl methacrylate)

In this study, modified poly(glycidyl methacrylate)-based films for gel electrolyte were prepared by an in situ UV photopolymerization technique. The effects of adding ethylene glycol dimethacrylate (EGDMA) to the polymer host were studied through X-ray diffraction analysis and differential scanning calorimetry. The results from Fourier transform-infrared spectra indicate complete polymerization among the monomers. The addition of EGDMA to the formulation of gel polymer electrolyte increased the loading of 1-butyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide up to 200 wt.% with the highest value of 8.2 × 10^?4 S cm^?1. All the gel polymer electrolyte membranes obeyed the Arrhenius law.     

Polypropylene/carbon nanotube magnetic composites obtained using carbon nanotubes from sawdust

Magnetic polypropylene (PP) nanocomposites with different loadings (from 0.5 to 20 wt %) of carbon nanotubes with iron (CNT‐Fe) were fabricated using the melt‐mixing method. The carbon nanotubes were synthesized by pyrolysis of sawdust from the furniture industry. The morphological characterization shows homogenous dispersion of the filler in the polymer matrix. The addition of only 0.5 wt % CNT‐Fe already results in ferromagnetic behavior in the diamagnetic polymer matrix. The thermal properties were investigated using thermogravimetric analysis and differential scanning calorimetry. The results show an increase in the maximum degradation, crystallization, and melting temperatures of the nanocomposites compared with neat PP. The nanocomposites showed improvement in terms of mechanical and oxygen permeability properties. A very significant result of the work is the high remnant magnetization and coercivity values of the nanocomposites at room temperature whereas most of the works on similar systems show magnetic properties only at very low temperatures.     

Thermo-mechanical behavior and specific volume of highly crosslinked networks based on glycerol dimethacrylate and its derivatives

Three substituent derivatives of glycerol dimethacrylate (GDMA) i.e., acetyloxypropyl dimethacrylate (Acet-GDMA), acryloyloxy-hydroxypropyl methacrylate (GMMA), and acetyloxy-acryloyloxypropyl methacrylate (Acet-GMMA) as well as GDMA were prepared and UV-homopolymerized in the presence of 2,2-dimethoxy-2-phenyloacetophenone. The obtained homopolymers were subjected to dynamic mechanical studies and the deflections versus temperature measurements (HDT) were performed. The content of unreacted double bonds, glass transition temperatures (T _g) as well as degree of inhomogeneity have been examined in all studied systems. Also, expansivity was measured in the function of temperature and the effect of a substituent group on the network properties was investigated. The results show that the hydroxyl-containing networks are characterized by much lower T _g and higher degree of heterogeneity than those devoid of hydroxyls. When homopolymerized, hydroxyl-free dimethacrylates disclosed untypical deflection pattern which suggests that at higher temperatures the decrease in stiffness is compensated or even overrated by the increase in the specific volume. Expansivity measurements revealed twice as large volume increase of the acetylated polymers as opposed to their hydroxyl-containing analogs. Following these findings, a mechanism of thermally induced polymer “swelling” was proposed.