Graft copolymerization of styrene onto poly(vinyl p-nitrobenzoate) by chain transfer reaction

To obtain highly branched graft copolymers, styrene (St) was grafted onto poly(vinyl p-nitrobenzoate) (PVNB) as a trunk polymer through the chain transfer reaction of growing polystyrene (PSt) radicals to the pendent aromatic nitro groups on the trunk polymer. The number of PSt branches increased with St concentration at constant concentrations of PVNB and azobisisobutyronitrile (AIBN) as an initiator, and decreased with AIBN concentration at constant PVNB and St concentrations. The maximum number of branches attained was 43 (P_n of PVNB was 970), which corresponds to 23 monomer units of PVNB per PSt branch. It is confirmed from the results of infrared spectroscopy that the addition of the growing polystyrene radicals occurs not at the benzene rings but at the nitro groups on the benzene rings. Polymerization of St was also carried out in the presence of isopropyl p-nitrobenzoate (IPNB) as a model compound of PVNB. IPNB was found to retard the polymerization of styrene more strongly than PVNB. The chain transfer constant of the polystyrene radicals to IPNB was more than twice as large as that to PVNB.     

Graft frequency of graft copolymers by chain transfer of growing polymer radicals to trunk polymers containing nitro groups

The relationship between the chain transfer constant, extent of monomer conversion, and number of branches was derived for the graft copolymerization through chain transfer of growing polymer radicals to the pendent aromatic nitro groups on the trunk polymer. The equation derived enables us to predict the number of branches for a given monomer trunk polymer. The relationship obtained is compared with the experimental data previously reported for the graft copolymerization of styrene onto poly(vinyl p-nitrobenzoate). The value of α′, the ratio of nitro groups with branches to those which are attacked by polystyrene radicals, is less than unity except for the graft copolymers obtained with high initiator concentrations and at early stages of the reaction. This lowering of α′ is attributed to the steric hindrance of branches already formed on the trunk polymer which prevents the attack of polystyrene radicals on the nitro groups and side reactions, such as reaction of the nitroso groups formed as an intermediate with styrene.     

Graft copolymerization of styrene onto ethylene-vinyl p-nitrobenzoate copolymer by chain transfer reaction

The effect of steric hindrance on the attack of growing polymer radicals to the reaction sites on a trunk polymer was examined in the graft copolymerization of styrene onto a trunk polymer with pendant aromatic nitro groups by chain transfer reaction of growing polymer radicals to the pendant nitro groups. The nitro groups on ethylene-vinyl p-nitro benzoate copolymer (EVNB) are more effectively utilized in the graft copolymerization than those on the vinyl p-nitro benzoate homopolymer (PVNB) previously used as a trunk polymer, because the nitro groups are distributed less frequently on the trunk polymer in the former than in the latter. This was also confirmed by the higher chain transfer constant of growing polystyrene radicals to EVNB compared to that of PVNB.     

Graft copolymerization of styrene onto cellulose acetate p-nitrobenzoate by chain transfer reaction

Styrene was grafted onto cellulose acetate p-nitrobenzoate (CANB) by chain transfer reaction of growing polymer radicals to the pendant nitro groups of CANB. A copolymer with a branch for every 17.2 nitro groups was obtained. This result indicates that the pendant aromatic nitro group is more effective in obtaining a graft copolymer by radical mechanism than pendant double bond on the trunk polymer previously reported, where graft copolymers with a branch for several hundred of double bonds are produced.     

Biodegradable Poly(ε‐Caprolactone)‐Based Graft Copolymers Via Poly(Linoleic Acid): In Vitro Enzymatic Evaluation

Well‐defined graft copolymers based on poly(ε‐caprolactone) (PCL) via poly(linoleic acid) (PLina), are derived from soybean oil. Poly(linoleic acid)‐g‐poly(ε‐caprolactone) (PLina‐g‐PCL) and poly(linoleic acid)‐g‐poly(styrene)‐g‐poly(ε‐caprolactone) (PLina‐g‐PSt‐g‐PCL) were synthesized by ring‐opening polymerization of ε‐caprolactone initiated by PLina and one‐pot synthesis of graft copolymers, and by ring‐opening polymerization and free radical polymerization by using PLina, respectively. PLina‐g‐PCL, PLina‐g‐PSt‐g‐PCL3, and PLina‐g‐PSt‐g‐PCL4 copolymers containing 96.97, 75.04 and 80.34 mol% CL, respectively, have been investigated regarding their enzymatic degradation properties in the presence of Pseudomonas lipase. In terms of weight loss, after 1 month, 51.5 % of PLina‐g‐PCL, 18.8 % of PLina‐g‐PSt‐g‐PCL3, and 38.4 % of PLina‐g‐PSt‐g‐PCL4 were degraded, leaving remaining copolymers with molecular weights of 16,140, 83,220 and 70,600 Da, respectively. Introducing the PLina unit into the copolymers greatly decreased the degradation rate. The molar ratio of [CL]/[Lina] dramatically decreased, from 21.3 to 8.4, after 30 days of incubation. Moreover, reduced PCL content in PLina‐g‐PSt‐g‐PCL copolymers decreased the degradation rate, probably due to the PSt enrichment within the structure, which blocks lipase contact with PCL units. Thus, copolymerization of PCL with PLina and PSt units leads to a controllable degradation profile, which encourages the use of these polymers as promising biomaterials for tissue engineering applications.     

Dehydrochlorinated poly(vinyl chloride-g-styrene). I. Effect of synthesis conditions

Dehydrochlorinated poly(vinyl chloride) (DHPVC) was graft copolymerized with styrene monomer using benzoyl peroxide (Bz₂O₂) as free radical initiator, in vacuum. The effect of synthesis conditions such as time, initiator concentration, the ratio of monomer to polymer, and temperature on various grafting parameters was studied. On the whole, a maximum of 47 wt % polystyrene (PSt) in the graft (DHPVC-g-PSt) was obtained. PSt contents of graft copolymers determined by gravimetry, chlorine analysis, and UV spectroscopy have been compared. A “grafting from” mechanism has been proposed for the graft copolymerization.     

Synthesis and characterization of dendritic-linear-dendritic triblock copolymers based on poly(amidoamine) and polystyrene

Dendritic-linear-dendritic triblock copolymers composed of linear polystyrene (PSt) and poly(amidoamine) dendrons have been successfully synthesized. Two bromines-terminated PSt with M_n = 13,000 was prepared by atom transfer radical polymerization (ATRP) using α,α′-dibromo-p-xylene as initiator. Then the terminal bromines at both ends of PSt chains were replaced by one imine group of piperazine (PZ), and further Michael addition reaction of terminal PZ with excess 1,3,5-triacryloylhexahydro-1,3,5-triazine (TT) produced the first generation (G₁) of the triblock copolymer. Continuous growth of dendrons from G1.5 to G4 at the both ends of PSt chains was carried out by the iterative Michael addition reactions with excess PZ and following TT. The ABA triblock copolymers composed of the G₁-G₄ dendrons and the linear PSt were obtained. Structures of the triblock polymers were characterized by GPC and ¹H NMR spectra. Thermal phase transitions of the polymers were studied by DSC measurements, and all of the copolymers displayed a glass transition temperature.     

Internal plasticization of poly(vinyl chloride) by grafting acrylate copolymers via copper-mediated atom transfer radical polymerization

Internal plasticization of poly(vinyl chloride) (PVC) was achieved in one-step using copper-mediated atom transfer radical polymerization to graft different ratios of random n-butyl acrylate and 2–2-(2-ethoxyethoxy)ethyl acrylate copolymers from defect sites on the PVC chain. Five graft polymers were made with different ratios of poly(butyl acrylate) (PBA) and poly(2–2-(2-ethoxyethoxy)ethyl acrylate) (P2EEA); the glass transition temperatures (T_g) of functionalized PVC polymers range from − 25 to − 50°C. Single T_g values were observed for all polymers, indicating good compatibility between PVC and grafted chains, with no evidence of microphase separation. Plasticization efficiency is higher for polyether P2EEA moieties compared with PBA components. The resultant PVC graft copolymers are thermally more stable compared to unmodified PVC. Increasing the reaction scale from 2 to 14 g produces consistent and reproducible results, suggesting this method could be applicable on an industrial scale.     

Synthesis of PMMA‐PTHF‐PMMA and PMMA‐PTHF‐PST linear and star block copolymers

Combination of cationic, redox free radical, and thermal free radical polymerizations was performed to obtain linear and star polytetramethylene oxide (poly‐THF)‐polymethyl methacrylate (PMMA)/polystyrene (PSt) multiblock copolymers. Cationic polymerization of THF was initiated by the mixture of AgSbF₆ and bis(4,4′ bromo‐methyl benzoyl) peroxide (BBP) or bis (3,5,3′,5′ dibromomethyl benzoyl) peroxide (BDBP) at 20°C to obtain linear and star poly‐THF initiators with M_w varying from 7,500 to 59,000 Da. Poly‐THF samples with hydroxyl ends were used in the methyl methacrylate (MMA) polymerization in the presence of Ce(IV) salt at 40°C to obtain poly(THF‐b‐MMA) block copolymers containing the peroxide group in the middle. Poly(MMA‐b‐THF) linear and star block copolymers having the peroxide group in the chain were used in the polymerization of methyl methacrylate (MMA) and styrene (St) at 80°C to obtain PMMA‐b‐PTHF‐b‐PMMA and PMMA‐b‐PTHF‐b‐PSt linear and star multiblock copolymers. Polymers obtained were characterizated by GPC, FT‐IR, DSC, TGA, ¹H‐NMR, and ¹³C‐NMR techniques and the fractional precipitation method. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 219–226, 2004     

Synthesis of polystyrene‐b‐poly(ethylene‐co‐butene) block copolymers by anionic living polymerization and subsequent noncatalytic hydrogenation

A series of polystyrene‐b‐polybutadiene (PSt‐b‐PBd) block copolymers with various chain lengths and compositions were synthesized by sequential living anionic polymerization and then converted into the corresponding polystyrene‐b‐poly(ethylene‐co‐butene) (PSt‐b‐PEB) block copolymers through the selective hydrogenation of unsaturated polybutadiene segments. Noncatalytic hydrogenation was carried out with diimide as the hydrogen source. The microstructures of PSt‐b‐PBd and PSt‐b‐PEB were investigated with gel permeation chromatography, ¹H‐NMR, ¹³C‐NMR, Fourier transform infrared, and differential scanning calorimetry. The results showed that the hydrogenation reaction was conducted successfully and that the chain length and molecular weight distribution were not altered by hydrogenation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2632–2638, 2006     

Study on a new kind of polypropylene‐graft‐ polystyrene: Preparation and application

A novel synthetic route for preparing polypropylene‐graft‐polystyrene (PP‐g‐PSt) was set up. With this synthetic route, a series of PP‐g‐PSt copolymers containing different percentages of polystyrene chain were synthesized, based on the different reactivities of two kinds of C? C double bonds on 4‐(3‐butenyl) styrene. Characterization data, including ¹H‐NMR, ¹³C‐NMR, GPC, and DSC, demonstrated that the graft copolymers were all very pure. Furthermore, it was also attempted to use this new kind of propylene–styrene graft copolymer as a compatibilizer. DMA and SEM results illustrated that the PP‐g‐PSt obtained is an efficient compatibilizer for the polypropylene–polystyrene blend. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 314–322, 2004     

Poly(ethylene oxide)‐block‐polystyrene copolymers obtained by radical polymerization involving chain‐transfer processes

Poly(ethylene oxide)‐block‐polystyrene (PEO–PSt) block copolymers were prepared by radical polymerization of styrene in the presence of iodoacetate—terminated PEO (PEO‐I) as a macromolecular chain‐transfer agent. PEO‐I was synthesized by successively converting the OH end‐group of α‐methoxy ω‐hydroxy PEO to chloroacetate and then to the iodoacetate. The chain‐transfer constant of PEO‐I was estimated from the rate of consumption of the transfer agent versus the rate of consumption of the monomer (C_{tr, PEO‐I} = 0.23). Due to the involvement of degenerative transfer, styrene polymerization in the presence of PEO‐I displayed some of the characteristics of a controlled/‘living’ process, namely an increase in the molecular weight and decrease of polydispersity with monomer conversion. However, because of the slow consumption of PEO‐I due to its low chain‐transfer constant, this process was not a fully controlled one, as indicated by the polydispersity being higher than in a controlled polymerization process (1.65 versus < 1.5). The formation of PEO–PSt block copolymers was confirmed by the use of size‐exclusion chromatography and ¹H NMR spectroscopy. Copyright © 2004 Society of Chemical Industry     

Synthesis,structure, and properties of poly(styrene-co-pentabromobenzyl acrylate) materials

Polymers and copolymers of pentabromobenzyl acrylate (PBBA) with styrene were syn-thesized and characterized. Poly(PBBA) exhibits a rather high glass transition temperature (T_g) and good solvent resistance. The incorporation of PBBA moiety into polystyrene (PSt) enhances T_g, improves the thermal stability, and also does not adversely affect polystyrene's mechanical properties. Copolymers prepared through both emulsion semibatch and batch processes exhibit random chain structures and possess similar properties such as T_g, inherent viscosity, and mechanical properties. Blends of poly(PBBA) and PSt demonstrate immiscible phase behavior, however their thermal stabilities are similar to the copolymers' stability at the same PBBA content. It is thus shown that the thermal stability of the systems investigated in this work is essentially affected by composition, regardless of the distribution and dispersion of the PBBA polymer or copolymers. © 1996 John Wiley & Sons, Inc.     

Synthesis and blend morphology of BA/BC-type binary graft copolymers composed of polyelectrolyte trunks

Poly(α-methylstyrene) (PMS) macromonomer having one vinylbenzyl group per polymer chain was prepared by the couplings of living PMS with p-chloromethylstyrene (CMS). Subsequently, well-defined poly[acrylic acid (AA)-g-α-methylstyrene (MS)] and poly[4-vinylpyridine (4VP)-g-MS] graft copolymers composed of polyelectrolyte trunks were prepared by radical copolymerization of PMS macromonomer with AA and 4VP monomers, respectively. Binary poly(AA-g-MS)/poly(4VP-g-MS) or poly[AA · triethyl amine (Et₃N) salt-g-MS)/poly(4VP-g-MS) graft copolymer blend films were cast from a benzene/methanol mixture. The morphological results of binary graft copolymer blends are discussed with respect to three-phase separated structures.     

Synthesis of poly(cyclohexene oxide)‐block‐polystyrene by combination of radical‐promoted cationic polymerization,atom transfer radical polymerization and click chemistry

The combination of radical‐promoted cationic polymerization, atom transfer radical polymerization (ATRP) and click chemistry was employed for the efficient preparation of poly(cyclohexene oxide)‐block‐polystyrene (PCHO‐b‐PSt). Alkyne end‐functionalized poly(cyclohexene oxide) (PCHO‐alkyne) was prepared by radical‐promoted cationic polymerization of cyclohexene oxide monomer in the presence of 1,2‐diphenyl‐2‐(2‐propynyloxy)‐1‐ethanone (B‐alkyne) and an onium salt, namely 1‐ethoxy‐2‐methylpyridinium hexafluorophosphate, as the initiating system. The B‐alkyne compound was synthesized using benzoin photoinitiator and propargyl bromide. Well‐defined bromine‐terminated polystyrene (PSt‐Br) was prepared by ATRP using 2‐oxo‐1,2‐diphenylethyl‐2‐bromopropanoate as initiator. Subsequently, the bromine chain end of PSt‐Br was converted to an azide group to obtain PSt‐N₃ by a simple nucleophilic substitution reaction. Then the coupling reaction between the azide end group in PSt‐N₃ and PCHO‐alkyne was performed with Cu(I) catalysis in order to obtain the PCHO‐b‐PSt block copolymer. The structures of all polymers were determined. Copyright © 2010 Society of Chemical Industry     

Synthesis of poly[(decanoic acid)‐block‐styrene] diblock copolymers and their self‐assembly behavior in aqueous medium

Diblock copolymers, poly[(10‐hydroxydecanoic acid)‐block‐styrene] (PHDA‐b‐PSt), were synthesized by combining enzymatic condensation polymerization of HDA and atom transfer radical polymerization (ATRP) as of St PHDA was first obtained via enzymatic condensation polymerization catalyzed by Novozyme‐435. Subsequently, one terminus of the PHDA chains was modified by reaction with α‐bromopropionyl bromide and the other terminus was protected by chlorotrimethylsilane. The resulting monofunctional macroinitiator was used subsequently in ATRP of St using CuCl/2,2′‐bipyridine as the catalyst system to afford diblock copolymers including biodegradable PHDA blocks and well‐defined PSt blocks. Polymeric nanospheres were prepared by self‐assembly of the PHDA‐b‐PSt diblock copolymers in aqueous medium. Copyright © 2008 Society of Chemical Industry     

Synthesis and characterization of block comb‐like copolymers P(A‐MPEO)‐block‐PSt

Amphiphilic block comb‐shaped copolymers, poly[poly(ethylene oxide) methyl ether acrylate]‐block‐polystyrene [P(A‐MPEO)‐block‐PSt] with PSt as a handle, were successfully synthesized via a macromonomer technique. The reaction of MPEO with acryloyl chloride yielded a macromonomer, A‐MPEO. The macroinitiator PSt capped with the dithiobenzoate group (PSt‐SC(S)Ph) was prepared by reversible addition–fragmentation transfer (RAFT) polymerization of styrene in the presence of benzyl dithiobenzoate, and used as macroinitiator in the controlled radical block copolymerization of A‐MPEO at room temperature under ⁶⁰Co irradiation. After the unreacted macromonomer A‐MPEO had been removed by washing with hot saturated saline water, block comb‐shaped copolymers were obtained. Their structure was characterized by ¹H NMR spectroscopy and gel permeation chromatography. The phase transition and self‐assembling behaviour were investigated by atomic force microscope and differential scanning calorimetry. Copyright © 2004 Society of Chemical Industry     

Thermal analyses of graft copolymers of poly (methyl methacrylate) main chain with poly (propylene oxide-b-ethylene oxide) graft chain

Poly(methyl methacrylate-g-(propylene oxide-b-ethylene oxide)) and poly (methyl methacrylate-g-(ethylene oxide-b-propylene oxide)), comprising chemically dissimilar sequences, exhibit intramolecular phase separation. These compositions have applications in coatings and as surface-tension modifiers. This paper presents the thermal behavior of these graft copolymers: separate samples of the homopolymer and of the grafts were also analyzed to provide comparisons. The phase behavior has been analyzed by differential scanning calorimetry and by dynamic-mechanical thermal measurements. Two glass transitions (T_g) are observed, caused by the partial incompatibility within the copolymers. The activation energy of the T_g relaxation process of the main chain is decreased by the graft chain. The influence of poly(propylene oxide-b-ethylene oxide) grafts on the thermal degradation of the poly(methyl methacrylate) (PMMA) main chain was studied by using thermogravimetric analysis. Prolysis of the graft copolymers occurs in three stages and begins on the graft chain and at a lower temperature than the pyrolysis of pure PMMA. Both the phase behavior and the thermal stability are found to depend sensitively on the composition of the copolymer. © 1993 John Wiley & Sons, Inc.     

Drag reduction characteristics of graft copolymers prepared by the gamma irradiation of poly(oxyethylene) in the presence of acrylic acid

Graft copolymers were prepared by irradiation of poly(oxyethylene), PEO, aqueous solutions in presence of acrylic acid. Chain transfer to PEO controls the graft length, the measured chain transfer constant of the acrylic acid radicals to PEO being 4.11 × 10^?4 at 25°C. The drag reduction characteristics of the graft copolymers were measured in the Reynolds number range 10⁴–10⁵ in a smooth-walled tube, 0.635 cm inside diameter. The drag reduction falls to near zero as the solution pH is lowered to 3, evidence of the formation of a PEO-poly(acrylic acid) coacervate.     

Dehydrochlorinated poly(vinyl chloride)-g-polystyrene. II. Characterization and physical properties

Dehydrochlorinated poly(vinyl chloride)-g-polystyrene (DHPVC-g-PSt) prepared by free radical grafting was characterized, and some of its physical properties were evaluated. The presence of graft was established by the appearance of new absorption peaks in the IR spectra of the graft copolymer. GPC analysis showed increase in the average molecular weights of the graft copolymer upon increase in the PSt content. Besides, GPC revealed the uniform PSt distribution of DHPVC-g-PSt. A marked improvement in the thermal stability of DHPVC-g-PSt over that of DHPVC and DHPVC/PSt blends was observed. Graft copolymers with high percent grafting were thermally more stable than even the original PVC. Stress–strain data indicated decrease in yield stress, breaking stress and elongation, along with an increase in the initial modulus, upon increase in PSt content of the graft copolymer.