Grafting of vinyl monomers onto silk using redox systems. Yellowing of silk

The aim of this study is to investigate the influence of temperature, initiator concentration, and vinyl monomer on silk yellowing during grafting. A series of silk fabrics was treated at four different temperatures (70, 75, 80, and 88°C), with different concentrations of initiator in the range 1–4% owf, with and without methacrylamide (MAA) or 2-hydroxyethyl methacrylate (HEMA). By treating silk with ammonium persulphate (APS), in the absence of a monomer, the degree of silk yellowing increased linearly with increasing both initiator concentration and treatment temperature, indicating that the initiator plays a specific role in enhancing silk yellowing through macroradical formation. The graft copolymerization of MAA (with APS as the initiator) caused only slight changes in the intensity of silk yellowing compared to blank-treated fabrics. On the other hand, the use of HEMA resulted in a deeper yellowing of silk fabrics, especially in the 70–80°C temperature range, due to its higher reactivity and to the tendency to form a homopolymer, leaving unreacted macroradicals on silk fibroin backbone. Compared to APS, other initiators, such as 2,2′-azobis(isobutyronitrile) (AIBN) and 2–2′-azobis-(2-amidino propane) dihydrochloride (ADC), caused a significantly lower degree of silk yellowing when tested in the absebce of a monomer. The yellowness of silk fabrics tended to increase by grafting with HEMA, while decreased by grafting with MAA. The use of variable amounts of monomer (25–150% owf) did not influence the degree of yellowing with ADC as the initiator. The results reported in this study show that the extent of yellowing induced on silk fabrics by grafting MAA and HEMA with APS as the initiator can be limited by a suitable selection of the processing parameters (initiator concentration, temperature). Moreover, the use of both AIBN and ADC appears promising, owing to their negligible effect on silk yellowing. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 239–246, 1998     

Structure and properties of tussah silk fibers graft-copolymerized with methacrylamide and 2-hydroxyethyl methacrylate

Tussah silk fibers were graft-copolymerized with methacrylamide (MAA) and 2-hydroxyethyl methacrylate (HEMA) in aqueous media, using a chemical redox system as an initiator. High weight gain values were obtained with both grafting agents (up to 175%). The extent of homopolymerization was negligible for the MAA grafting system over the entire range of monomer–silk ratios examined, while polymer deposition on the fiber surface occurred when the HEMA–silk ratio exceeded 0.5% (w/w). The moisture content of poly(MAA)-grafted silk fibers was enhanced by grafting. Breaking load, elongation at break, and energy decreased at low weight gain (0–20%) and then remained rather constant. The DSC curves of poly(MAA)-grafted silk showed a new endotherm at about 280°C, due to the melting of poly(MAA) chains. The loss modulus peak of poly(HEMA)-grafted silk fibers broadened and shifted to a lower temperature, showing a tendency to split into two peaks at high weight gain. On the other hand, grafting with poly(MAA) induced a noticeable upward shift of the loss peak. The TMA curves showed that grafting with poly(MAA) resulted in a higher extent of fiber contraction from room temperature to about 250°C. Moreover, the intensity of the final contraction step at about 350°C decreased with increasing weight gain and shifted to a lower temperature. The Raman spectra of grafted fibers were characterized by overlapping of the characteristic lines of both silk fibroin and polymer, the latter showing an intensity proportional to the amount of weight gain. Among the conformationally sensitive vibrational modes of tussah silk fibroin, the amide III range was significantly modified by grafting with both poly(MAA) and poly(HEMA). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1393–1403, 1998     

Grafting of methyl methacrylate onto Antheraea pernyi silk fiber with the assistance of supercritical CO2

Graft copolymerization of methyl methacrylate (MMA) onto Antheraea pernyi silk fibers, initiated by benzoyl peroxide in the supercritical CO₂ was investigated. The grafting degree was determined as a function of impregnating pressure, impregnating time, monomer concentration, initiator concentration, and reaction time. The structural properties of MMA‐grafted fiber were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. Grafted MMA was chemically bonded and/or physically adhered to the surfaces of the fibers. The grafted silk fibers exhibited two steps of weight loss according to the characteristic of each component as demonstrated by the thermogravimetric analysis. The water‐retention values indicated that the hydrophobic nature of the fibers was improved. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1299–1305, 2006     

Synthesis of well‐defined comb‐like amphiphilic copolymers with protonizable units in the pendent chains: 1. Preparation of narrow polydispersity copolymers of methyl methacrylate and 2‐hydroxyethyl methacrylate by atom‐transfer radical polymerization

Well‐defined methyl methacrylate (MMA) and 2‐(trimethylsiloxy)ethyl methacrylate (Pro‐HEMA) copolymers were prepared by atom‐transfer radical polymerization(ATRP), using CuCl/2,2′‐bipyridine as catalytic system and p‐toluenesulfonyl chloride as initiator. ATRP process of MMA and Pro‐HEMA was monitored by ¹H NMR, and the kinetic curves of the MMA/Pro‐HEMA copolymerization were plotted in terms of the ¹H NMR data. At low content of Pro‐HEMA in the feed composition, the copolymerization can be well controlled with the molecular weight, polydispersity and the monomer distribution in the copolymer chain. With the increase of Pro‐HEMA content in the feed mixture, the composition of the final copolymer deviates from the composition of the feed mixture gradually, and gradient copolymers of MMA/Pro‐HEMA can be obtained. Through the hydrolysis process, well‐defined copolymers of MMA/HEMA were obtained from poly(MMA/Pro‐HEMA). Copyright © 2003 Society of Chemical Industry     

Study on antithrombosis dialytic membrane prepared by preirradiation grafting

A new antithrombosis dialytic membrane with a hydrophilic–hydrophobic microphase structure was prepared by preirradiation grafting of β‐hydroxyethyl methacrylate (HEMA) and styrene (St) onto ethylene–vinyl acetate (EVA). The influence of some effects, such as preirradiation dose, dose rate, grafting reaction temperature, reaction time, and monomer component, on the degree of grafting was determined, and the properties of the grafted films were investigated. Compared with the conventional EVA‐grafted hydrophilic monomer, the EVA films grafted with HEMA and St have superior antithrombogenicity; the antithrombogenicity and permeability of EVA‐g‐(HEMA‐co‐St) were 30 and 20 times higher than those of the ungrafted films, respectively, when the volume ratio (HEMA versus St) was about 7:3. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1321–1327, 2000     

Structure and properties of bombyx mori silk fibers grafted with methacrylamide (MAA) and 2-hydroxyethyl methacrylate (HEMA)

Silk fibers were graft-copolymerized with methacrylamide (MAA) and 2-hydroxyethyl methacrylate (HEMA) in aqueous media, using a chemical redox system as an initiator. High weight gains (300%) were obtained with both monomers, the weight gain being linearly related to the amount of monomer contained in the reaction system. The reaction efficiency attained 95–100%. The extent of homopolymerization was negligible for the MAA grafting system, while large amounts of poly-HEMA covered the surface of silk fibers beyond 70% weight gain. The fiber size increased linearly with the weight gain. The moisture content of MAA-grafted silk fibers was highly enhanced by grafting. The severe grafting conditions caused a partial degradation of the tensile properties of silk fibers, as well as of the degree of fiber whiteness. Following grafting, the breaking load slightly increased, while elongation at break and energy decreased. The decomposition temperature of grafted silk fibers shifted upwards. The Raman spectra of untreated silk fibers showed strong lines at 1667 (amide I), 1451, 1227 (amide III), 1172 and 1083 cm⁻¹. Overlapping of the lines characteristic of both silk fibroin and grafted polymer was observed in the spectra of grafted silk samples. The vibrational mode of the amide III lines of silk fibroin was significantly modified by grafting. © 1996 John Wiley & Sons, Inc.     

Dyeing properties of Bombyx mori silks grafted with methyl methacrylate and methacrylamide

To improve their dyeing and colorfastness properties, degummed Bombyx mori silks were chemically modified by a grafting technique with either methyl methacrylate (MMA) monomer or methacrylamide (MAA) monomer. Both commercial synthetic dyes, that is, acid and basic dyes, and natural dyes extracted from turmeric, without and with potassium aluminum sulfate mordant, were used in this study. Percentage dye uptake increased with the presence of poly(methyl methacrylate) or polymethacrylamide in the silk fibroin structure regardless of the types of the dyestuffs. Furthermore, compared to the degummed silk, the colorfastness to washing of the MMA‐grafted and MAA‐grafted silks dyed with acid, basic, and curcumin dyestuffs were greatly improved. Colorfastness to both acid and basic perspirations with acid and basic dyestuffs was slightly improved, whereas perspiration fastness remained unchanged for curcumin dyeing without and with the presence of the mordant. Also, the low‐light resistances of the degummed and grafted silks dyed by curcumin dyestuff were notably improved by the MMA and MAA grafting technique. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:1169–1175, 2006     

Physical properties of silk fibers grafted with vinyltrimethoxysilane

Silk fibers from Bombyx mori silkworms were grafted using a novel grafting monomer, vinyltrimethoxysilane (VTMSi), with various grafting initiators. The effects of these grafting initiators were evaluated. It was possible to successfully copolymerize VTMSi within the silk fiber matrix without disturbing the fine structure of the fiber matrix, which was shown by FTIR analysis and refractive index measurements. The physical properties of VTMSi grafted silk were analyzed and compared to fibers grafted with conventional monomers such as methyl methacrylate, methacrylamide, and 2‐hydroxyethyl methacrylate. No trend in the tensile strength and elongation at break was observed when grafting silk fibers with VTMSi. Crease recovery in the wet state improved significantly, suggesting that this new grafting technique is important for the production of washable silk fabrics. The thermal stability of VTMSi grafted silk fibers was improved as shown by the shift of the endothermic peak for the thermal decomposition toward higher temperatures. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1764–1770, 2001     

Studies on the graft polymerizations of styrene and methyl methacrylate to hydroxyl terminated polybutadiene

Hydroxyl terminated Polybutadiene (HTPB) was grafted with styrene (St) or methyl methacrylate (MMA) by free radical solution polymerization. The graft copolymerizations were conducted in benzene at 70 °C. The initiators used were benzoyl peroxide (BPO) and azobis-isobutyronitrile (AIBN). The microstructures of theobtained graft copolymers were characterized by¹³C NMR measurement and the DEPT technique, as well as by IR spectrometer. The mechanism of grafting reactions was determined from the microstructures of derived graft copolymers. It showed that graft copolymer resulted when BPO was used as initiator of the vinyl monomer polymerization, but not with AIBN. It appeared that the reaction leading to graft formation was direct attack of oligomeric styrene radicals or double bonds of the HTPB. Whereas the graft copolymerization of MMA to HTPB was the same as that suggested in the literature i.e., by a hydrogen abstract reaction.     

Study of multi‐monomer melt‐grafting onto polypropylene in an extruder

Free‐radical melt‐grafting of the dual‐monomer systems glycidyl methacrylate–styrene (GMA‐St) and hydroxyethyl methacrylate–styrene (HEMA‐St) onto polypropylene (PP) has been studied using a single‐screw extruder. For single monomer grafting systems, degradation of PP was unavoidable and deterioration of the mechanical properties of the grafted PP subsequently occurred because of β‐scission of PP chains during the free‐radical melt‐grafting process. However, for the dual‐monomer systems, it is shown that the addition of styrene as a comonomer can significantly enhance the GMA or HEMA grafting levels on PP and reduce the extent of β‐scission of PP backbone. It has been found that the grafting degree of dual‐monomer melt‐grafted PP, such as PP‐g‐(GMA‐co‐St) or PP‐g‐(HEMA‐co‐St), is about quadruple that of single‐monomer grafted PP for the same monomer and dicumyl peroxide concentrations. Moreover, the melt flow rate of the dual‐monomer grafted PP is smaller than that of the unmodified PP. Hence, PP not only was endowed with higher polarity, but also kept its good mechanical properties. © 2000 Society of Chemical Industry     

Comparing emulsion polymerization of methacrylate-monomers with different hydrophilicity

A comprehensive experimental study concerning the influence of various types of initiator-emulsifier systems on emulsion polymerization of methacrylate monomers (2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA) and butyl methacrylate (BMA)) reveals interesting relations between initiator and surfactant hydrophilicity on the one hand and the hydrophilicity of the monomers on the other hand. For the water-soluble HEMA stable latexes are only obtained if hydrophobic initiators such as 2,2′-azobisisobutyronitrile or dibenzoyl peroxide in combination with alkyl sulfate surfactants with carbon chain lengths greater than 10 or surface active initiators of the 2,2′-azobis(N-2′-methylpropanoyl-2-amino-alkyl-1)-sulfonate type with alkyl chain lengths greater than 8 are employed. Stable nano size range poly(2-hydroxyethyl methacrylate) (PHEMA) particles have been prepared also by batch emulsion polymerization using ionic surface active initiators (inisurfs). The results clearly show that the formation of stable latex particles requires a proper choice of the initiator-emulsifier system regarding its hydrophilic-hydrophobic balance. The PHEMA particles prepared with surface-active initiators keep their identity and spherical shape even in the dried state whereas in the case of the other initiator-emulsifier systems complete coagulation and coalescence occurs during drying.     

Grafting of methyl methacrylate (MMA) onto Antheraea assama silk fiber

Graft copolymerization of methyl methacrylate (MMA) onto nonmulberry silk fiber Antheraea assama was investigated in aqueous medium using the KMnO₄–oxalic acid redox system. Grafting (%) was determined as a function of the reaction time, temperature, and monomer and initiator concentrations. The rate of grafting increased progressively with increase of the reaction time up to 4 h and then decreased. The extent of grafting was maximum at 55°C. The extent was also dependent upon monomer and initiator concentrations up to 75.5 × 10^?2 and 6 × 10^?3 M, respectively. The grafted products were evaluated by infrared spectroscopy and their thermal decompositions were studied by TG and DTG techniques in static air at 20°C min^?1 and 30°C min^?1 in the range 30–800°C. The kinetic parameters for ungrafted and grafted fibers were evaluated using the Coats and Redfern method. The grafted products were found to be thermally more stable than were those of the ungrafted fibers. The surface characteristics of the ungrafted and grafted fibers were evaluated by scanning electron microscopy. The water‐retention values (WRVs) of the grafted fibers were in decreasing order with increase in the grafting (%). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2633–2641, 2001     

Physical,chemical, and dyeing properties of Bombyx mori silks grafted by 2‐hydroxyethyl methacrylate and methyl methacrylate

To obtain silk weight gain and to improve silk properties, Bombyx mori silks were grafted with either 2‐hydroxyethyl methacrylate (HEMA) or methyl methacrylate (MMA). The moisture regain of the HEMA‐grafted and MMA‐grafted silks depended on the hydrophilicity of the used monomers. The acid and alkaline resistances of the HEMA‐grafted and MMA‐grafted silks were clearly improved. Both commercial synthetic dyes, that is, acid and reactive dyes, and a natural dye extracted from turmeric, with potassium aluminum sulfate as a mordant, were used in this study. The results suggested that the dye uptake increased in the presence of poly(2‐hydroxyethyl methacrylate) or poly(methyl methacrylate) in the silk fibroin structures when acid and curcumin dyes were used. The washfastness level of the HEMA‐grafted silk dyed by acid and reactive dyes was similar to that of the degummed silk. However, the colorfastness to washing of the MMA‐grafted silk dyed by an acid dye was improved when the polymer add‐on concentration was 65%. In addition, the washfastness for both grafted silks was improved when they were dyed with natural curcumin dyestuff. The acid and alkaline perspiration fastness properties remained unchanged for the HEMA‐grafted and MMA‐grafted silks when acid, reactive, and curcumin dyes were applied. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Graft copolymerization of methyl methacrylate onto sago starch using ceric ammonium nitrate and potassium persulfate as redox initiator systems

The graft copolymerization of methyl methacrylate (MMA) onto sago starch was carried out in aqueous media by different initiators of ceric ammonium nitrate (CAN) and potassium persulfate (PPS) and under a nitrogen gas atmosphere. Using CAN as an initiator, the maximum percentage of grafting (%G) was ascertained to be 246% at the following optimum conditions: a 70°C reaction temperature, a 2‐h reaction period, 2.0 mmol of CAN, 0.4 mmol of nitric acid, and 141 mmol of MMA. The maximum %G achieved with PPS as the initiator was 90%. The optimum conditions were a 50°C reaction temperature, a 1.5‐h reaction period, 47 mmol of monomer, and 1.82 mmol of PPS. The grafting of MMA onto sago starch was confirmed by the IR spectra of pure sago starch, MMA, and MMA grafted sago starch. This material may have application as a biodegradable plastic. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1375–1381, 2001     

Natural rubber‐g‐methyl methacrylate/poly(methyl methacrylate) blends

The grafting of the methyl methacrylate (MMA) monomer onto natural rubber using potassium persulfate as an initiator was carried out by emulsion polymerization. The rubber macroradicals reacted with MMA to form graft copolymers. The morphology of grafted natural rubber (GNR) was determined by transmission electron microscopy and it was confirmed that the graft copolymerization was a surface‐controlled process. The effects of the initiator concentration, reaction temperature, monomer concentration, and reaction time on the monomer conversion and grafting efficiency were investigated. The grafting efficiency of the GNR was determined by a solvent‐extraction technique. The natural rubber‐g‐methyl methacrylate/poly(methyl methacrylate) (NR‐g‐MMA/PMMA) blends were prepared by a melt‐mixing system. The mechanical properties and the fracture behavior of GNR/PMMA blends were evaluated as a function of the graft copolymer composition and the blend ratio. The tensile strength, tear strength, and hardness increased with an increase in PMMA content. The tensile fracture surface examined by scanning electron microscopy disclosed that the graft copolymer acted as an interfacial agent and gave a good adhesion between the two phases of the compatibilized blend. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 428–439, 2001     

Rheology and morphology of polypropylene in situ grafted and blended with methyl methacrylate/n‐buthylacrylate copolymer

The rheology and morphology of polypropylene (PP) modified by grafting and blending with vinyl monomers were studied in this work. The PP powder was impregnated by mixture of methyl methacrylate (MMA)/n‐buthylacrylate (n‐BA) and copolymerized with azobisisobutyronitrile (AIBN) initiator. The simultaneous grafting and blending of PP with MMA‐co‐n‐BA copolymers were performed in a corotating, 40 L/D, twin‐screw extruder in the presence of dicumyl peroxide. The Fourier transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) were used to verify the grafting level and dispersion state of MMA/n‐BA copolymer on PP matrix, respectively, and their rheological properties were studied. It is observed that MMA/n‐BA copolymer is finely dispersed in the PP matrix. In this way, PP can be grafted, blended, and simultaneously compatibilized with polar copolymers, as is seen in SEM images. The results showed that by increasing acrylate monomers grafting on to PP increased. The same trend was observed for AIBN initiator. The gel content of samples with 25% monomers showed an increased from 0.7% to 3.5% by increasing AIBN from 0.2% to 0.4%. The grafting reaction took place with chain scission of PP molecules and also cross‐linking reactions. The optimum grafting of 7.3% with lowest chain scission and cross‐linking were obtained for samples containing 15 wt% monomer and 0.3% AIBN initiator. J. VINYL ADDIT. TECHNOL., 21:290–298, 2015. © 2014 Society of Plastics Engineers     

Differential microemulsion polymerization as a new root for entrapment of drugs

Nanosized particles derived from poly(methyl methacrylate) as well as copolymer of methyl methacrylate (MMA) and 2‐hydroxyethyl methacrylate (HEMA) were synthesized by differential microemulsion technique in the presence of ammonium persulfate as water‐soluble initiator. The polymerization was stabilized by adding biologically safe emulsifiers namely the sodium dodecyl sulfate (SDS) or polyvinyl pyrrolidone (PVP) either alone or in conjunction with polyethylene glycol. The turbidity measurements, surface tension, ζ potential, and morphological characterizations of the obtained nanosized poly MMA and its copolymer with HEMA in different monomer feed compositions were investigated. It is found that increasing HEMA content leads to increase in the particle size, turbidity measurements but the negatively charged ζ potential decreased. However, when SDS is used, the surface tension of the prepared lattices increased, whereas it is decreased by using PVP. Kinetic studies of (MMA/HEMA) in ratio of 95/5 wt % in the presence of SDS or PVP revealed that the emulsifier concentration has a considerable effect on the rate of polymerization and the power of the emulsifier. The entrapment of drug was investigated using two active molecules different in water solubility (sodium warfarin and ibuprofen). It is noted that entrapment efficiency is independent of HEMA content in the monomer feed composition but dependent on type of drug and the amount of drug introduced. Hence, higher entrapment efficiency was attained for sodium warfarin (more hydrophilic) than that of ibuprofen (more hydrophobic) and they were 95.5 and 85%, respectively. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Homogeneous graft copolymerization of acrylonitrile onto high α‐cellulose in a dimethyl acetamide and lithium chloride solvent system

Homogeneous graft copolymerization of acrylonitrile (AN) monomer onto high α‐cellulose was investigated in a lithium chloride/N,N‐dimethyl acetamide (DMAc/LiCl) solvent system. Benzoyl peroxide (BPO) and azobisisobutyronitrile (AIBN) were used as radical initiators. By varying temperature, time, and monomer concentrations in grafting reactions, the optimum conditions for both initiator systems were fixed. The graft yield for the AN–BPO system was higher than that for the AN–AIBN system. The optimum conditions of reactions were at temperatures of 70 and 60°C with initiator concentrations of 0.4% (0.36 mmol) and 2% (1.24 mmol) for the AN–AIBN and AN–BPO systems, respectively, at a monomer concentration of 5% (14.1 mmol) solution. The number of grafts per cellulose chain was in the range from 2.2 to 1.1 for AN–BPO and 0.5 to 2.1 for the AN–AIBN system. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 630–637, 2003     

Synthesis and polymerization of a new iodine‐containing monomer

A new iodine‐containing methacrylate monomer, 3,4,5‐triiodobenzoyloxyethyl methacrylate (TIBEM), was synthesized by coupling 2‐hydroxyethyl methacrylate (HEMA) with 3,4,5‐triiodobenzoic acid. The monomer was characterized by ¹H nuclear magnetic resonance, infrared (IR), and ultraviolet spectra. Homopolymerization and copolymerization of the monomer with methyl methacrylate (MMA) were carried out using 2,2′‐azobis isobutyronitrile as the initiator. A terpolymer of TIBEM, MMA, and HEMA was also synthesized. The copolymers were characterized by IR, gel permeation chromatography, differential thermal analysis, and thermogravimetric analysis (TGA). High molecular weight polymers were produced with MMA at different feed compositions of TIBEM. The polymers were found to be freely soluble in common solvents for acrylic polymers. TGA showed little decomposition of the copolymer below 280°C. Copolymers showed good radiopacity at 25 wt % of TIBEM in the feed. These copolymers could find applications in medical and dental areas where radiopacity is a desirable feature of the implants. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2580–2584, 2003     

天然橡胶接枝甲基丙烯酸羟乙酯的合成与表征

以甲基丙烯酸羟乙酯(HEMA)为接枝单体,过氧化二苯甲酰(BPO)为引发剂,合成了天然橡胶(NR)接枝聚甲基丙烯酸羟乙酯(NR-g-HEMA)。研究了BPO和HEMA用量、反应温度、反应时间以及NR塑炼时间对单体转化率、接枝率和接枝效率的影响,并采用红外光谱对接枝产物进行了表征。结果表明:当BPO用量为3%,HEMA用量为30%,反应温度为80℃,反应时间和NR塑炼时间分别为4h和30min时,NR-g-HEMA的接枝率达16%。