Effects of ionizing radiation in ethylene-vinyl alcohol copolymers and in composites containing microfibrillated cellulose

This study reports on the effect of gamma radiation on morphological, thermal, and water barrier properties of pure ethylene vinyl alcohol copolymers (EVOH29 and EVOH44) and its biocomposites with the nanofiller microfibrillated cellulose (2 wt %). Added microfibrillated cellulose (MFC) preserved the transparency of EVOH films but led to a decrease in water barrier properties. Gamma irradiation at low (30 kGy) and high doses (60 kGy) caused some irreversible changes in the phase morphology of EVOH29 and EVOH44 copolymers that could be associated to crosslinking and other chemical alterations. Additionally, the EVOH copolymers and the EVOH composites reduced the number of hygroscopic hydroxyl functionalities during the irradiation processing and novel carbonyl based chemistry was, in turn, detected. As a result of the above alterations, the water barrier properties of both neat materials and composites irradiated at low doses were notably enhanced, counteracting the detrimental effect on water barrier of adding MFC to the EVOH matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Toughening of aromatic diamine-cured trifunctional epoxy resins by modification with N-phenylmaleimide–styrene copolymers containing pendant p-hydroxyphenyl groups

N-Phenylmaleimide (PMI)–N-(p-hydroxy)phenylmaleimide (HPMI)–styrene (St) terpolymers (HPMS), containing pendant p-hydroxyphenyl (HP) groups, were prepared and used to improve the toughness of triglycidyl aminocresol epoxy resin cured with p,p′-diaminodiphenyl sulfone. HPMS was effective as a modifier for the toughening of the epoxy resin. When using 15 wt % of HPMS (1.0 mol % HP unit, M_w 129,000), the fracture toughness (K_IC) for the modified resin increased 190% with a medium loss of flexural strength. The toughening of epoxies could be attained because of the cocontinuous phase structure of the modified resins. The decrease in flexural strength was suppressed to some extent by introducing a functional group into the modifier. The toughening mechanism was discussed in terms of the morphological behavior of the modified epoxy resin system. © 1995 John Wiley & Sons, Inc.     

Novel luminescent polymers containing backbone triphenylamine groups and pendant quinoxaline groups

Novel, conjugated polyfluorene derivatives that comprised an electron-donating triphenylamine group in the backbone and pendant, electron-accepting quinoxaline moieties, were synthesized via the Suzuki coupling reaction and their UV–vis absorption, fluorescence emission and electrochemical properties were investigated. The copolymers were readily soluble in common organic solvents and displayed good film-forming ability and excellent thermal stability. Electroluminescence devices, comprising indium tin oxide/poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonic acid)/emitting polymer/Ba/Al, in which the polymers were employed as emissive layers, exhibited superior performance compared to that of corresponding, poly(9,9-dioctylfluorene) and poly(9,9-dioctylfluorene-co-4,4′-triphenylamine) based devices, indicating that the polymers offer promise as emissive materials in polymeric light-emitting diodes.     

Pareparation of photosensitive polymers containing pendant cinnamic acid,ethyl cinnamate or cinnamaldehyde groups by chemical modification of polystyrene

Summary Soluble polystyrene was chemically modified to introduce pendant cinnamic acid, cinnamate ester, or cinnamaldehyde groups. The sensitivity of these polymers to crosslinking by ultraviolet light was studied by the adhesion method. Both the cinnamic acid and the cinnamaldehyde groups were found to crosslink more effectively than the cinnamate ester, the group which is commonly used in photoresists.     

Novel polyphosphazenes containing charge-transporting agent and chromophore as pendant groups

Summary Two novel functionalized polyorganophosphazenes containing charge-transporting agent and electro-optical chromophore as side chains for the photorefractive application are synthesized. The structure characterization was carried out by ¹H-NMR, IR and UV-Visble spectra, gel permeation chromatograply and differential scanning calorimetry. Due to the good flexibility of the backbone and the high degree of functionalization, polyphosphazenes are expected to be a good candidate for photorefractive polymeric materials. Received: 13 March 2000/Revised version: 12 July 2000/Accepted: 24 July 2000     

Crosslinking reaction of glycidyl methacrylate copolymers containing oxime-urethane groups using photogenerated pendant amines

Summary Copolymers containing epoxy and oxime-urethane groups were prepared by copolymerization of glycidyl methacrylate (GMA) and benzophenone oxime allylurethane (BAU). The physical properties of these copolymers were characterized by GPC, NMR and DSC analyses. Photo-crosslinking reaction of the copolymers were studied by measuring the insoluble fraction of copolymer films under various reaction conditions. The degree of cross-linking reaction increased with irradiation time, heating temperature and the amount of BAU units in the copolymer. UV and IR absorption spectral studies indicate that thermal cross-linking reaction of the copolymer was catalyzed by the pendant photogenerated amines. Received: 3 March 1998/Revised version: 7 April 1998/Accepted: 15 April 1998     

ABA triblock copolymers containing polyhedral oligomeric silsesquioxane pendant groups: synthesis and unique properties

The synthesis and characterization of POSS containing ABA triblock copolymers is reported. The use of atom transfer radical polymerization (ATRP) enabled the preparation of well-defined model copolymers possessing a rubbery poly(n-butyl acrylate)(pBA) middle segment and glassy poly(3-(3,5,7,9,11,13,15-heptaisobutyl-pentacyclo[9.5.1.1^3,9.1^5,15.1^7,13]-octasiloxane-1-yl)propyl methacrylate(p(MA-POSS)) outer segments. By tuning the relative composition and degree of polymerization (DP) of the two segments, phase separated microstructures were formed in thin films of the copolymer. Specifically, dynamic mechanical analysis and transmission electron microscopy (TEM) observations reveal that for a small molar ratio of p(MA-POSS)/pBA (DP=6/481/6) no evidence of microphase separation is evident while a large ratio (10/201/10) reveals strong microphase separation. Surprisingly, the microphase-separated material exhibits a tensile modulus larger than expected (ca. 2×10⁸ Pa) for a continuous rubber phase for temperatures between a pBA-related T_g and a softening point for the p(MA-POSS)-rich phase. Transmission electron microscopy (TEM) images with selective staining for POSS revealed the formation of a morphology consisting of pBA cylinders in a continuous p(MA-POSS) phase. Thermal studies have revealed the existence of two clear glass transitions in the microphase-separated system with strong physical aging evident for annealing temperatures near the T_g of the higher T_g phase (p(MA-POSS). The observed aging is reflected in wide-angle X-ray scattering as the strengthening of a low-angle POSS-dominated scattering peak, suggesting some level of ordering during physical aging. The T_g of the POSS-rich phase observed in the microphase separated triblock copolymer was nearly 25 °C higher than that of a POSS-homopolymer of the same molecular weight, suggesting a strong confinement-based enhancement of T_g in this system.     

Optical properties of block copolymers containing pendant carbazole groups and in situ synthesized CdS nanoclusters

Ultraviolet–visible absorption spectra and photoluminescence spectra were used to demonstrate efficient charge‐carrier migration in a novel bulk heterogeneous block copolymer system. One moiety of the block copolymer was functionalized with charge‐transporting carbazole groups, whereas the other block formed domains suitable for the in situ synthesis of CdS nanoclusters. The excitation of the cluster‐free copolymers with 350‐nm‐wavelength radiation led to a strong emission peak at 450 nm that was associated with the carbazole groups. When CdS clusters were present in nearby but spatially distinct domains, the carbazole emission was completely quenched and replaced by a very broad emission in the visible range (near 560 nm). The implications of these observations are discussed in the context of the energy‐transfer mechanism and possible device applications. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 177–182, 2003     

Bitumen chemical modification by thiourea dioxide

This work evaluates a novel bitumen modification through the use of a chemical agent, thiourea dioxide, substance which has been traditionally used as a reducing agent. Thermo-gravimetric analysis demonstrated the formation of new chemical compounds, most probably originated through reactions between products from thiourea dioxide thermal decomposition and some highly polar bitumen molecules. As a result of these reactions, which continues even after 60 days, bitumen permanent deformation resistance at high temperature is enhanced, as indicated by a significant increase in its viscosity and elastic features. On the other hand, thiourea dioxide addition produces changes in the bitumen colloidal nature, which improve its flexibility at low in-service temperatures, and consequently its resistance to thermal cracking under loading. In fact, dynamic bending tests indicated a remarkable decrease in the value of binder glass transition temperature, which was further corroborated by differential scanning calorimetry. As a conclusion, thiourea dioxide can be seen as a promising modifying agent, which can extend the in-service temperature range at which bitumen would present a satisfactory performance.     

Vinylchloride copolymers obtained by chemical modification of PVC

A homologous series of polyvinylchlorides (PVCs) with the general formula (CH₂−CHCl)_m−(CH₂−CHX)_n, where m can vary gradually from 100 to 50 or less, n from 100 to 50 or more, and X can be small atoms such as H, or benzenethiolate groups, were obtained by substitution reactions of PVC. The microstructural analysis of these polymers carried out by ¹³C nuclear magnetic resonance spectroscopy reveals that chlorines are preferentially substituted in isotactic and heterotactic placements. The molecular weight determined by osmometry confirms that there is no chain scission or crosslinking of the polymer during the reaction. As all polymers of these homologous series have the same chain length, and in all cases the chlorine elimination is preferentialy random in the amorphous part, they may be considered as model compounds of PVC for studies of the relationship between polymer structure and properties ©1997 SCI     

Fluorinated poly(arylenethioethersulfone) copolymers containing pendant sulfonic acid groups for proton exchange membrane materials

Fluorinated sulfo-pendants poly(arylenethioethersulfone) copolymer, which contained 50 mol% sulfonate content per repeat unit (6F-SPTES-50), were synthesized by a nucleophilic polycondensation from 4,4-(hexafluoroisopropylidene)-diphenylthiol, 3,3′-disulfonate-4,4′-difluorodiphenylsulfone and 4,4′-difluorodiphenylsulfone. The 6F-SPTES-50 copolymer possessed high molecular weight, exhibited good film formability and thermal stability, and maintained adequate mechanical strength after immersion in water for 24 h. The proton conductivities of the 6F-SPTES-50 copolymer membrane increased with temperatures, reaching values above 120 mS/cm at 85 °C and 85% relative humidity. Preliminary MEA test shows acceptable performance, which indicated that these materials are promising proton exchange membranes (PEMs) for fuel cells operated at medium temperatures.     

Chemically modified polystyrene containing pendant vinyl groups: a photosensitive polymer exhibiting chemical amplification

Soluble polystyrene, modified to contain pendant vinyl groups, was prepared in high functional yield from PStCH₂Cl or PstCHO via Wittig reactions. The polymer was used to prepare a negative-working photosensitive resist in which absorbed light initiated a free radical crosslinking chain reaction.     

New soluble cyano‐containing poly(arylene ether) copolymers bearing pendant xanthene groups

Homopolymers and copolymers of poly(arylene ether nitrile) (PAEN)‐bearing pendant xanthene groups were prepared by the nucleophilic substitution reaction of 2,6‐difluorobenzonitrile with 9,9‐bis(4‐hydroxyphenyl)xanthene (BHPX) and with various molar proportions of BHPX to hydroquinone (100/0 to 40/60) with N‐methyl‐2‐pyrrolidone (NMP) as a solvent in the presence of anhydrous potassium carbonate. These polymers had inherent viscosities between 0.61 and 1.08 dL/g, and their weight‐average molecular weights and number‐average molecular weights were in the ranges 34,200–40,800 and 17,800–20,200, respectively. All of the PAENs were amorphous and were soluble in dipolar aprotic solvents, including NMP, N,N‐dimethylformamide, and N,N‐dimethylacetamide and even in tetrahydrofuran and chloroform at room temperature. The resulting polymers showed glass‐transition temperatures (T_g's) between 220 and 257°C, and the T_g values of the copolymers were found to increase with increasing BHPX unit content in the polymer. Thermogravimetric studies showed that all of the polymers were stable up to 422°C with 10% weight loss temperatures ranging from 467 to 483°C and char yields of 54–64% at 700°C in nitrogen. All of the new PAENs could be cast into transparent, strong, and flexible films with tensile strengths of 106–123 MPa, elongations at break of 13–17%, and tensile moduli of 3.2–3.7 GPa. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of chemical modification of carboxyl groups in apple residues on metal ion binding

AR (apple residue) was used as an alternative and cheap material for binding metal ions due to the presence of carboxyl and phenolic functional groups. The binding capacity of copper, lead, and cadmium by AR was pH dependent. Carboxyl groups of AR were esterified by acidic methanol to determine the contribution of carboxyl groups to metal ions binding. The extent of esterification was determined by analyzing the amount of methanol released in the sample hydrolysates by gas chromatography. The effect of esterification on binding metal ions was investigated in batch experiments by unmodified and modified AR. All esterified AR showed significant decreases in binding copper, lead and cadmium. The loss in the capacity of metal ion binding was proportional to the extent of esterification. The capacity of metal binding decreased with increase in the concentration of methanol in the respective hydrolysates or the modified AR. The data indicate that carboxyl groups on AR play an important role in the metal ion binding.     

Amphiphilic block copolymers with pendant thiol groups in side chains by RAFT polymerization

A new synthetic approach to thiol functional, well-defined amphiphilic block copolymers, which can be used to prepare multifunctional polymers and polymeric nanoparticles, is presented. Starting with a hydrophilic macroRAFT transfer agent and hydrophobic (meth)acrylate monomers that possess protected thiol groups, amphiphilic block copolymers are prepared in high yield. It is proven that the protected thiol groups in the monomer do not interfere with the RAFT polymerization process. Polymers with defined molecular weight, narrow polydispersities (PDI < 1.30) and varying length of the hydrophobic block are presented. Polymers with thiol groups in side chains and chain ends are obtained by aminolysis. With pyrene fluorescence spectroscopy and NMR measurements, it is shown that all synthesized polymers self-assemble into micelles. Furthermore, the possible application of these new polymers is exemplified by the preparation of polymer nanoparticles.     

酯化改性聚乙烯醇的研究

以氯乙酰氯作为酯化剂和聚乙烯醇反应,得到了酯化改性聚乙烯醇,其结构经IR表征。考察了反应时间、反应温度对聚乙烯醇酯化改性产物酯化程度的影响,通过正交实验确定了聚乙烯醇酯化改性的最佳工艺条件,聚乙烯醇与氯乙酰氯的物质的量之比为1：2,反应温度为60％,反应时间为6h。对酯化改性产物的耐水性进行了测试,酯化改性产物的耐水性达到了94．7％。     

Facile synthesis of functional copolymers with pendant vinyl groups by using asymmetrical divinyl monomers

Polymers bearing pendant vinyl groups have attracted significant attraction because they can be further modified for required applications, but their syntheses are still a big challenge. Herein, allyl methacrylate was catalyzed using a phosphazene base to homopolymerize or copolymerize with 2‐(N, N‐dimethylamino) ethyl methacrylate, affording vinyl functional polymers, which were further successfully tailored by the thiol–ene coupling reaction. The result showed that both the homopolymerizations and copolymerizations could proceed at room temperature with very high monomer conversions. The contents of pendant double bonds in the copolymers were approximately equal to the monomer feeds, but the LCST of the statistical copolymers linearly decreased with increasing AMA content. This strategy offered a new scalable and facile strategy for vinyl functional polymers, would have a wide practical application in many fields. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42758.     

Metal catalyzed photocrosslinking of polymers containing pendant propargyl groups

Polymers containing the pendant propargyl groups can be effectively crosslinked upon UV irradiation in the presence of a small amount of W(CO)₆. The alkyne-tungsten carbonyl complex was formed initially as evident by IR spectroscopy, which was involved in the subsequent crosslinking reaction. Analyses by UV, IR, and ¹³C NMR CP/MAS spectroscopic methods confirmed the polymer crosslinking as a result of the conversion of the acetylenic units to the polyene and diacetylene moieties in the crosslinked system.