Preparation and properties of epoxy/phenol formaldehyde novolac/hexakis(methoxymethyl)melamine hybrid resins from in situ polymerization

Based on the self‐condensation of hexakis(methoxymethyl)melamine (HMMM), the condensation between HMMM and phenol formaldehyde novolac resin (n‐PF), and the addition reaction of diglycidyl ether of biphenyl A (DGEBA) and n‐PF, a homogeneous, transparent hybrid thermoset was prepared via in situ polymerization of DGEBA, n‐PF, and HMMM. No phase separations were observed even for the DGEBA/n‐PF/HMMM hybrid thermoset containing 40 wt % HMMM. These hybrid thermosets had high glass‐transition temperatures (98–127°C from differential scanning calorimetry and 111–138°C from dynamic mechanical analysis), excellent thermal stability with high 5 wt % decomposition temperatures (>322°C), high char yields (>24 wt %), and improved flame retardancy with high limited oxygen indices (>28.5). The excellent overall properties of these hybrid resins may lead to their applications in high‐performance “green” electronic products. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of interpenetrating polymer networks with hyperbranched polymers through thermal-UV dual curing

The aim of this study was to investigate the possibility of using acrylated hyperbranched polyesters (HBP) as UV curable component in dual curing automotive applications. Dual curing is one of possible ways to obtain fast curing, scratch resistant coatings for use in OEM and car refinish applications. Dual curing systems, upon hardening, can give interpenetrating networks (IPNs).     

Influence of polymerization procedure on polymer topology and other structural properties in highly branched polymers obtained by A2 + B3 approach

Computational studies were carried out to investigate the influence of polymerization procedure on the topology and various macromolecular characteristics of the highly branched polymers formed by the reaction of A₂ and B₃ type monomers through step-growth polymerization reactions. The influence of three different polymerization procedures on the properties of the polymers formed was investigated, namely, (i) slow addition of A₂ over B₃, (ii) slow addition of B₃ over A₂, and (iii) mixed A₂ + B₃. Topology, degree of branching, number and weight average molecular weights, and polydispersity index of the polymers were determined using Monte Carlo simulations, assuming different levels of cyclization ratios during the reactions. Interestingly model polymers obtained by the slow addition of B₃ over A₂ produced much higher degree of branching or truly hyperbranched polymers, when compared with the other two methods, which mainly resulted in linear growth with slight branching.     

Synthesis and properties of polyolefin graft copolymers by a grafting “onto” reactive process

The synthesis of graft copolymers by the grafting “onto” process in the molten state was described. Functional oligomers obtained by telomerization or by ATRP were reacted onto maleic anhydride grafted polypropylene (PP-g-MAH) and poly(ethylene-ter-maleic anhydride-ter-methyl acrylate) (P(E-ter-MAH-ter-MeA)) to obtain PP-g-PMMA and P(E-ter-MAH-ter-MeA)-g-PMMA graft copolymers, respectively. The grafting of different mono-functional oligomers bearing hydroxyl, aliphatic amine or aromatic amine functions was investigated at 180 °C and at 200 °C. The grafting efficiency was very low in the case of hydroxyl-terminated PMMA, while the amine-terminated PMMA led to high yields. In the last part, PP-g-PMMA and P(E-ter-MAH-ter-MeA)-g-PMMA graft copolymers were synthesized by the reaction of aliphatic amine functional PMMA oligomers onto PP-g-MAH and P(E-ter-MAH-ter-MeA), respectively. The influence of the molecular weight of PMMA oligomers was investigated and showed that he grafting efficiency slightly decreases with the increasing molecular weight. However, this process allows the synthesis of PP-g-PMMA graft copolymers containing 6-45 wt% of PMMA side chains. The microstructure of the nanostructured PP-g-PMMA and P(E-ter-MAH-ter-MeA)-g-PMMA graft copolymers was investigated by TEM and SEM. This was established that the addition of PP-g-PMMA in PP/PMMA binary blends allows to control their morphologies and stabilities.     

Synthesis and characterization of star-shaped block copolymer of poly-(?-caprolactone) and poly(ethyl ethylene phosphate) as drug carrier

A series of novel 4-arm biodegradable star block copolymers of poly(?-caprolactone) and poly(ethyl ethylene phosphate) were synthesized via ring-opening polymerization of 2-ethoxy-2-oxo-1,3,2-dioxaphospholane using hydroxyl terminated 4-arm star-shaped poly(?-caprolactone) and stannous octoate co-initiation system. Gel permeation chromatography (GPC), NMR and FT-IR were used to demonstrate the structure and analyze their compositions. The self-assembly behavior of these star-shaped copolymers in aqueous solution was studied by ¹H NMR and fluorescence technique, and the results indicated those copolymers formed nanoparticles in aqueous solution with hydrophobic poly(?-caprolactone) core and hydrophilic poly(ethyl ethylene phosphate) shell. The critical micelle concentration was relative to the length of poly(?-caprolactone) and poly(ethyl ethylene phosphate) block. Paclitaxel was encapsulated in the micelles and the release behavior demonstrated that a longer hydrophobic block resulted in slightly slower release rate from the micelles. These copolymer micelles were biocompatible and potential as drug-delivery vehicles for pharmaceutical application.     

Photocure properties of high‐heat‐resistant photoreactive polymers with cinnamate groups

New high‐heat‐resistant photoreactive polymers with cinnamate groups were synthesized by the reaction of cinnamic acid (CA) and epoxy resins. Their photocure properties were investigated with Fourier transform infrared spectroscopy, UV–visible spectroscopy, and thermogravimetric analysis (TGA). Their photocure reaction rates and the extent of reaction conversion increased with the intensity of UV irradiation. To investigate their photocure reaction kinetics, their reaction conversion rates were plotted against reaction conversion so that their photocure reactions could be analyzed in terms of an nth‐order kinetics reaction equation. The YX4000H–CA photoreactive polymer with a biphenyl moiety, which was expected to have strong molecular interactions, showed a lower reaction conversion rate and reaction constant, and the highest reaction conversion rate and reaction constant was observed in XP2030–CA with an optimum cure reaction space and a reduction of molecular interactions compared with the other photoreactive polymers. Thermal stability was studied by observation of the changes in the transmittance of the photocured polymer films upon heating and by measurement of the weight loss with temperature with TGA. These photoreactive polymers showed good thermal properties, with almost no transmittance change in the visible range even after they were heated at 250°C for 1 h, and they exhibited little weight loss up to about 250°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of polypyrrole rod doped with p‐toluenesulfonic acid via micelle formation

Rod‐type polypyrrole (PPY) doped with p‐toluenesulfonic acid (TSA) was synthesized by chemical oxidative polymerization via a self‐assembly process. The shape of the PPY particles is mainly determined by the ratio of TSA/pyrrole (PY) and feed rate of the oxidant. Particle of different shapes (rod, grain, and partially rod) exhibit differences in morphology, electrical properties, dispersity, and thermal properties. Wide‐angle X‐ray diffraction patterning analysis was used to investigate the mechanism of rod formation. The effect of the TSA concentration on the PPY structure was investigated using Fourier transform infrared spectroscopy. The PPY rods doped with TSA exhibited better electrical conductivity than granular PPY doped with TSA, and their dispersity and thermal stability were also higher. Self‐orientation of PPY in the micelles of TSA and high crystallinity of the rod particles led to improved thermal stability. Hence, the decomposition temperature of the polymer chain was considerably increased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Influence of low‐temperature plasma conditions on wicking properties of PA/PU knitted fabric

Plasma surface treatment has been extensively applied in the textile industry for the modification of polymer materials. In this study low‐temperature plasma (LTP) is used for surface treatment of polyamide/polyurethane (PA/PU) knitted fabric. The envisaged plasma effect is an increase in the surface energy of the treated textile, leading toward improved hydrophilic properties. The knitted fabric was treated by LTP using three non polymerizing gases: oxygen, air, and carbon dioxide. After plasma treatment, wettability of samples was tested through their wicking properties measuring capillary rise after water bath contact. The PA/PU knitted fabric samples treated with different plasma gases exhibited different hydrophilic performances. The influence of plasma variables (discharge power, time, pressure) was investigated. Although the chemical characteristics of elastan (PU) and nylon (PA) threads are different, the study has demonstrated that plasma treatment can in the same time alter the surface‐wetting behavior of both the components of the knitted fabric. It was also shown how these treatments can be regulated to produce the desired level of hydrophilicity dependently on the request application. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Effect of comonomer type and concentration on the equilibrium swelling and volume phase transition temperature of N‐isopropylacrylamide‐based hydrogels

The effect of incorporating a hydrophilic monomer into poly(N‐isopropylacrylamide) (polyNIPA) hydrogels on the equilibrium swelling and the volume phase transition temperature is reported here. A nonionizable monomer (acrylamide) and three ionizable monomers (itaconic acid, 2‐ethoxyethyl monoitaconate, and 2,2‐(2‐ethoxyethyl) monoitaconate) were studied. Hydrogels with larger swelling capacity than that of the polyNIPA hydrogel were obtained. With the exception of the hydrogel containing 2,2‐(2‐ethoxyethyl) monoitaconate, which did not exhibit the de‐swelling phenomena, the rest showed a volume phase transition. The hydrogels containing 85 wt % acrylamide and 15 wt % comonomer presented the higher shrinking ratio. For some compositions, the T_c of the polyNIPA hydrogel was within the desired temperature range (38–41°C) for controlled‐drug delivery in the human body. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Shape‐memory behaviors of biodegradable poly(L‐lactide‐co‐ϵ‐caprolactone) copolymers

A series of biodegradable poly(L ‐lactide‐co‐?‐caprolactone) (PCLA) copolymers with different chemical compositions are synthesized and characterized. The mechanical properties and shape‐memory behaviors of PCLA copolymers are studied. The mechanical properties are significantly affected by the copolymer compositions. With the ?‐caprolactone (?‐CL) content increasing, the tensile strength of copolymers decreases linearly and the elongation at break increases gradually. By means of adjusting the compositions, the copolymers exhibit excellent shape‐memory effects with shape‐recovery and shape‐retention rate exceeding 95%. The effects of composition, deformation strain, and the stretching conditions on the recovery stress are also investigated systematically. A maximum recovery stress around 6.2 MPa can be obtained at stretching at T_g ? 15°C to 200% deformation strain for the PCLA70 copolymer. The degradation results show that the copolymers with higher ?‐CL content have faster degradation rates and shape‐recovery rates, meanwhile, the recovery stress can maintain a relative high value after 30 days in vitro degradation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008