Synthesis of block and star copolymers by photoinduced radical coupling process

The general design for the synthesis of AB diblock, and A₂B and AB₂ star copolymers based on the statistical coupling of poly(styrene) (PSt) and poly (methyl methacrylate) (PMMA) macromolecules containing photoreactive benzophenone is presented. For this purpose, mono- and bifunctional initiators for Atom Transfer Radical Polymerization (ATRP) bearing benzophenone group were synthesized and characterized. End- and mid-chain benzophenone functional PSt and PMMA with low molecular weights were obtained by ATRP using these initiators in the presence of CuBr/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) catalytic complex. Poly(styrene-block-methyl methacrylate) (PSt-b-PMMA) copolymers were prepared by photolysis of the solutions containing end functional PSt and PMMA in THF at λ = 350 nm for 60 min in the presence of a hydrogen donor such as N-methyldiethanolamine (NMDEA). The proposed mechanism assumes hydrogen abstraction of photoexcited benzophenone moiety by NMDEA. Ketyl radicals resulting from abstraction reaction undergo radical-radical coupling to form benzpinacol structure at the core. Formation of A₂B and AB₂ type star copolymers upon irradiation of solutions containing appropriate combinations of end- and mid-chain functional polymers was also demonstrated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2938–2947, 2009     

Hyperbranched copolymers made from A2, B2 and type monomers (iv)--Copolymerization of divinyl sulfone with 4, 4′-trimethylenedipiperidine and N-ethylethylenediamine

The new approach for synthesis of hyperbranched polymers from commercially available A2 and type monomers was extended to synthesize hyperbranched copolymers. In this work, hyperbranched copoly(sulfone-amine) was prepared by copolymerization of divinyl sulfone (A2) with 4,4′-trimethylenedipiperidine (B2) and N-ethylethylenediamine ( ). During the reaction, secon-dary-amino groups of B2 and monomers react rapidly with vinyl groups of A2 monomers within 35 s, generating a type of intermediate containing one vinyl group and two reactive hydrogen atoms. Now the intermediates can be regarded as a new type monomer, which further polymerizes to form hyperbranched copoly(sulfone-amine). The polymerization mechanism was investigated with FTIR and LC-MSD. The degree of branching (DB) of hyperbranched copolymers increased with decreasing the ratio of 4, 4′-trimethylenedipiperidine to N-ethylethyl- enediamine, so DB can be controlled. When the initial mole ratio of B2 to was equal to or higher than four, r≥4, resulted copolymers were semi-crystalline, while copolymers with r＜3 were amorphous.     

Photopolymerization of (meth)acrylates in the presence of polyheteroarylenes

The free-radical photopolymerization of (meth)acrylates in the presence of a polyheteroarylene dissolved in a monomer has been studied. The kinetics of the radical polymerization of these monomers mediated by polyheteroarylene and the corresponding model compound has been investigated by differential scanning photocalorimetry and IR spectroscopy. Based on the experimental data, it is inferred that copolymers form due to chain transfer and/or chain termination to polyheteroarylene macromolecules. With the use of ESR spectroscopy, new radicals generated upon the addition of model polyheteroarylene compound to the initial solutions are discovered and characterized. The mechanism of the formation of copolymers is advanced.     

Electron spin resonance study on chemical crosslinking reaction mechanisms of polyethylene using a chemical agent. V. Comparison with polypropylene and ethylene‐propylene copolymer

We studied the chemical reaction process of polypropylene (PP), ethylene‐propylene copolymer (EPM), and ethylene‐propylene‐diene copolymer (EPDM) crosslinking induced by dicumyl peroxide (DCP) using electron spin resonance (ESR). Free radicals appeared at an elevated temperature of around 120 °C and the behavior and kinetics of the reaction process were observed at 180 °C. The radical species detected in PP were alkyl type radicals, formed by the abstraction of hydrogen atoms from the tertiary carbon of polymer chains. For EPDM containing a diene component, the radicals were trapped at double bonds in this diene component to form allyl radicals. The resolutions of these spectra were extremely clear; hence, isotropic spectra of these polymer radicals were obtained. We measured the ESR at high temperatures and confirmed that the process of crosslinking induced by DCP was a free radical reaction. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3383–3389, 2000     

Isothermal Crystallization Kinetics and Crystalline Morphologies of Poly(butylene adipate-<Emphasis Type="Italic">co</Emphasis>-butylene 1,4-cyclohexanedicarboxylate) Copolymers

In this study,the isothermal crystallization kinetics and crystalline morphology of poly(butylene adipate-co-butylene 1,4-cyclohexanedicarboxylate) (PBAC),which refers to a copolyester containing a non-planar ring structure,were investigated by differential scanning calorimetry and polarized optical microscopy,and compared with those of neat poly(butylene 1,4-cyclohexanedicarboxylate) (PBC).The results indicate that the introduction ofbutylene adipate (BA) unit into PBAC did not change the intrinsical crystallization mechanism.But,the crystallization rate and ability,and equilibrium melting temperature of PBAC copolymers were reduced.All PBC and PBAC copolymers could only form high density of nucleation from melt at given supercooling,while no Maltese cross or ring-banded spherulites could be observed.PBAC copolymers with a high amount of BA unit became amorphous after quenching with liquid nitrogen from melt,while PBC and PBAC copolymers with a low amount of BA unit could still form a large amount of nuclei under the same treatment.     

Photochemical imaging processes for the formation of metallic patterns on polymers

A homogeneous polymer for photometallization containing anthraquinonyl (AQ) and hydroxyalkyl groups was studied, where some of the hydroxyalkyl groups are complexed with copper carboxylate. On irradiation AQ is excited to an n → π^* type of triplet state and subsequently reacts with a hydroxyalkyl group to form the semiquinone radical and the hydroxyalkyl radical. Almost all semiquinone radicals disproportionate to AQ and AQH₂. Copper ions are reduced to catalytic nuclei by AQH₂ as well as by hydroxy-alkyl radicals. Hydroxyalkyl radicals that are not consumed for reduction recombine to form a cross-linked polymer.     

Isothermal Crystallization Kinetics and Crystalline Morphologies of Poly(butylene adipate-co-butylene 1,4-cyclohexanedicarboxylate) Copolymers

In this study, the isothermal crystallization kinetics and crystalline morphology of poly(butylene adipate-co-butylene 1,4-cyclohexanedicarboxylate)(PBAC), which refers to a copolyester containing a non-planar ring structure, were investigated by differential scanning calorimetry and polarized optical microscopy, and compared with those of neat poly(butylene 1,4-cyclohexanedicarboxylate)(PBC). The results indicate that the introduction of butylene adipate(BA) unit into PBAC did not change the intrinsical crystallization mechanism. But, the crystallization rate and ability, and equilibrium melting temperature of PBAC copolymers were reduced. All PBC and PBAC copolymers could only form high density of nucleation from melt at given supercooling, while no Maltese cross or ring-banded spherulites could be observed. PBAC copolymers with a high amount of BA unit became amorphous after quenching with liquid nitrogen from melt, while PBC and PBAC copolymers with a low amount of BA unit could still form a large amount of nuclei under the same treatment.     

Synthesis of achiral PEG‐PANI rod‐coil block copolymers and their helical superstructures

Poly(ethylene glycol) (PEG) was modified with aniline groups at both the end, and then PEG‐PANI rod‐coil block polymers have been synthesized by polymerization of the aniline with the aniline‐modified PEG. FTIR, NMR, and elemental analysis provided the chemical strucutre of the as‐prepared polymers. The achiral rod‐coil copolymer could form different superstructures by means of self‐assembly when adding diethyl ether into its THF solution and the length of PANI segments is a key factor to the superstructures. AFM measurements revealed that they form spring‐like helical superstructures from the short PANI‐containing copolymers while these form fibrous helical superstructures from the longer PANI‐containing copolymer. A possible mechanism of the helical superstructures is suggested in this article and the driving force is believed the π–π stacking of the rigid segment of the copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 12–20, 2008     

Macromolecular N-nitroso-acylamines as initiators for polyreactions. I. Synthesis of block copolymers from polycondensates and olefinic monomers,

The synthesis of block copolymers in three-step reactions from linear polycondensates (e.g., nylon 6. nylon 6,6, nylon 6,10 and polyurethane) and olefinic monomers (e.g., styrene, acrylic acid and acrylonitrile, methyl methacrylate, vinyl acetate, vinyl chloride, and isoprene) is reported. Macromolecular radicals are formed by the thermal decomposition of partly nitrosated peptide group containing polycondensates at elevated temperatures (60–200°C). These polyradicals initiate the copolymerization of the olefinic monomers. The conversion and reaction rates were generally high (up to 100% within a few hours). Most of the block copolymers prepared were soluble in organic solvents. Some, however, were insoluble or rubberlike. The reaction mechanism involved are analyzed. Applications are discussed.     

Polymers having stable radicals. I. Synthesis of nitroxyl polymers from 4-methacryloyl derivatives of 2,2,6,6-tetramethylpiperidine

Polymers having stable nitroxyl free radicals, poly-4-methacryloylamino- and poly-4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyls, were synthesized from their precursor polymers by oxidizing them in a methanolic solution of hydrogen peroxide. The precursor polymers were prepared by radical polymerization of 4-methacryloyl-amino/oxy-2,2,6,6-tetramethylpiperidines in various solvents. These polymerizations in acetic acid were found to yield polymers of high molecular weight. The copolymers of the precursor monomers with styrene and methyl methacrylate were also prepared as precursor copolymers. These precursor polymers of a piperidine type were converted to the polymers having stable nitroxyl free radicals by the hydrogen peroxide method. In this report, it was assumed that the post-oxidation reaction introduced a nitroxyl group smoothly and quantitatively at room temperature. Elucidations of the stable radical formation and the electron spin behavior of the stable radical polymers were made in terms of elemental analyses, infrared, ultraviolet, and ESR spectroscopy.     

Cationic photopolymerization with the aid of pyridinium‐type salts

Pyridinium‐type salts containing an N‐ethoxy group belong to the family of onium salts and are photoinitiators appropriate for the polymerization of monomers such as oxiranes and vinyl ethers which are not polymerizable by a free radical mechanism. The initiation is accomplished by direct or indirect (sensitized) photolysis of the onium ion, with the former being restricted to the wavelength range of self absorption, the latter being applicable at wavelengths of visible light. An additionally useful tool, namely free radical‐mediated generation of initiating species enlarges the versatility of pyridinium salts as photoinitiators. In this connection, the oxidation of free radicals by pyridinium‐type ions and the free radical‐induced fragmentation of alkoxy pyridinium ions are addressed in this article. Moreover, an interesting application is noted concerning the synthesis of novel block copolymers with the aid of the onium salt‐based photopolymerization technique.     

Architectures of novel fluorinated block copolymers fuelled by a poor radical polymerizable characteristic of 1,3‐divinyltetramethyldisiloxane

Fluoroalkanoyl peroxide was reacted with 1,3‐divinyltetramethyldisiloxane under very mild conditions to afford the fluoroalkyl end‐capped vinylsilane oligomer containing vinyldimethylsiloxane segments. This fluoroalkyl end‐capped vinylsilane oligomer was applied to the preparation of novel fluorinated block copolymers by the copolymerizations with traditional radical polymerizable monomers. It was demonstrated that these fluorinated block copolymers thus obtained can form the dendritic‐type unimolecular micelles in aqueous solutions, and these fluorinated block copolymers were able to provide suitable host moieties to interact with fullerenes as guest molecules. Copyright © 2006 John Wiley & Sons, Ltd.     

Effects of polydepsipeptide side‐chain groups on the temperature sensitivity of triblock copolymers composed of polydepsipeptides and poly(ethylene glycol)

To develop new types of biodegradable polymers possessing predictable responses to changes in temperature, ABA‐type and BAB‐type triblock copolymers composed of various polydepsipeptides (PDP) and poly(ethylene glycol) (PEG) (PDP‐PEG‐PDP and PEG‐PDP‐PEG) were synthesized. The specific focus of this study was on the effect of the different side‐chain groups of various amino acids on the temperature‐responsive behavior of the triblock copolymers. An ABA‐type triblock copolymer containing the less hydrophobic glycine (PGG‐PEG‐PGG) did not exhibit any temperature‐responsive behavior; however, ABA‐type triblock copolymers containing the hydrophobic α‐amino acids, L ‐leucine and L ‐phenylalanine (PGL‐PEG‐PGL or PGF‐PEG‐PGF), did exhibit temperature‐responsive behavior. The cloud point of PGF‐PEG‐PGF was 10 °C lower than that of PGL‐PEG‐PGL. It can be possible to control temperature‐sensitivity by changing not only PDP segment length but also kind of α‐amino acid in PDP segment. Moreover, BAB‐type triblock copolymer containing L ‐leucine (PEG‐PGL‐PEG) showed temperature‐responsive sol‐gel transition. Because polydepsipeptides are biodegradable polymers, the information obtained in this study is useful to design biodegradable injectable polymers having controllable temperature‐sensitivity for biomedical use.© 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3892–3903, 2009     

Radiation chemistry of polybutadiene and butadiene-styrene block copolymers. II. Kinetics and mechanisms of free-radical decay reactions

The decay of free radicals produced in polybutadiene, polystyrene, and block copolymers of butadiene and styrene by γ irradiation at 77 K has been studied at ?110°C in the case of polybutadiene and at ?95°C for the other samples. The free-radical decay rate is best interpreted in terms of an equation based on a second-order decay mechanism of a fraction of the free radicals decaying in the presence of other nondecaying free radicals. Hydrogen gas accelerates the free-radical decay. Increase of radiation dose increases the fraction of the radicals that decay, while increase of the fraction of styrene segments decreases the decaying fraction. In pure polybutadiene the higher the cis content, the greater fraction of decaying free radicals, but the second-order decay constant is less in the high-cis-content polybutadiene and is also less at the higher dose, probably owing to the hindrance of the radiation-produced crosslinks on the free-radical decay. The decrease of the second-order constant with increase of dose is also true for all the block copolymers studied.     

Thermal degradation of copolymers of methyl methacrylate and methyl acrylate. II. Chain scission and the mechanism of the reaction

It has been established that one molecule of carbon dioxide is produced for each chain scission during degradation of methyl methacrylate–methyl acrylate copolymers with molar compositions in the ratios 112/1, 26/1, 7.7/1, and 2/1. Thus the relatively simple measurement of the production of carbon dioxide can be used to determine the extent of chain scission. In this way the relationships between chain scission and volatilization, zip length, copolymer composition, and the production of permanent gases have been established. The rate of chain scission is proportional to a power of the methyl acrylate content of the copolymer less than 0.5, from which it has been concluded that a significant proportion of the initial production of radicals and the subsequent attack of these radicals on the polymer chains is at random and not specifically associated with the methyl acrylate units. A mechanism for the overall thermal degradation process in this copolymer system is presented in the light of these observations.     

Conformational transitions in macromolecules of complex chemical structure during liquid crystalline ordering

Conformational transitions in thermotropic main-chain polymers of complex chemical structure including homopolymers with possibility of conformational transformations in mesogens and random copolymers (CPLs) containing mesogens of the same type and spacers of different lengths were investigated. It was demonstrated that liquid crystalline (LC) state influences conformational transformations in fragments of chain restraining them in comparison with an isotropic melt. It was found that CPLs studied form LC order of smectic type. Peculiarities in spacers behaviour during transition to LC state ensure formation of such type of LC order. Conclusion about dependence of mechanism of smectic LC order formation on chemical structure of rigid components of CPLs is made.     

Photocrosslinking of copolymers of vinyloxyethyl methacrylate-styrene initiated by sulfonium salts. II. Photocrosslinking behaviors

Vinylether was used as a cationically polymerizable moiety and incorporated into sidechain of polymers as copolymers of vinyloxyethyl methacrylate (VEM) and styrene (St). Photoirradiation of the copolymers containing a small amount of benzyl(4-hydroxyphenyl) methylsulfonium salt (BSS) resulted in a high crosslinking density as evidenced by a low degree of swelling, which is ascribed to the high reactivity of the vinyloxy moieties. The sensitivity of this photoreaction is significantly high because of a large kinetic chain length of the cationic polymerization of vinylethers, while copolymers of glycidyl methacrylate and St showed crosslinking to much less extent when irradiated under the same condition. The ability of other sulfonium salts, (4-hydroxyphenyl) methyl(4-nitrobenzyl) sulfonium salt and (4-hydroxyphenyl) methyl(1-naphthylmethyl)sulfonium salt, to induce photocrosslinking was also examined. © 1992 John Wiley & Sons, Inc.     

Hyperbranched copolymers made from A2, B2 and BB′2type monomers (iv)

The new approach for synthesis of hyperbranched polymers from commercially available A₂ and type monomers was extended to synthesize hyperbranched copolymers. In this work, hyperbranched copoly(sulfone-amine) was prepared by copolymerization of divinyl sulfone (A₂) with 4,4′-trimethylenedipiperidine (B₂) and N-ethylethylenediamine (BB’₂). During the reaction, secondary-amino groups of B₂ and BB’₂ monomers react rapidly with vinyl groups of A₂ monomers within 35 s, generating a type of intermediate containing one vinyl group and two reactive hydrogen atoms. Now the intermediates can be regarded as a new type monomer, which further polymerizes to form hyperbranched copoly(sulfone-amine). The polymerization mechanism was investigated with FTIR and LC-MSD. The degree of branching (DB) of hyperbranched copolymers increased with decreasing the ratio of 4, 4′-trimethylenedipiperidine to N-ethylethylenediamine, so DB can be controlled. When the initial mole ratio of B₂ to BB′₂was equal to or higher than four,r≥4, resulted copolymers were semi-crystalline, while copolymers withr3 were amorphous.     

1:1 alternating copolymers of 1-bicyclobutanecarbonitrile with styrene

High molecular weight, 1:1 alternating copolymers of 1-bicyclobutanecarbonitrile with styrene were prepared in tetramethylenesulfone solution by complexing the electron-poor bicyclobutane monomer with zinc chloride. Methyl 1-bicyclobutanecarboxylate under these conditions gave copolymers containing a slight excess of styrene units (ratio 1:1.3 to 1:1.8). High molecular weight homopolymers of 1-bicyclobutanecarbonitrile and of methyl 1-bicyclobutanecarboxylate were prepared similarly. The tendency of the bicyclobutane nitrile to form 1:1 alternating copolymers is as great as that of its vinyl analog, acrylonitrile, and the synthesis of other alternating copolymers from this monomer should be possible.     

Poly(ethylene terephthalate) copolymers containing 5‐nitroisophthalic units. II. Crystallization studies

The microstructure and crystallization behavior of a set of poly(ethylene terephthalate‐co‐5‐nitroisophthalate) copolymers (PETNI) containing 5‐nitroisophthalic units in the 10–50 mol % range were examined and compared to those of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate‐co‐isophthalate) (PETI) copolymers. A ¹³C NMR analysis of PETNI copolymers in a trifluoroacetic acid solution indicates that they are random copolymers with average sequence lengths in accordance with ideal polycondensation statistics. Differential scanning calorimetry (DSC) studies show that PETNI containing 5‐nitroisophthalic units up to 20 mol % are able to crystallize and that crystallization takes place in these copolymers at much slower rates than in PET. Wide‐angle X‐ray diffraction from powder and fibers reveals that crystallizable PETNI adopts the same triclinic crystal structure as PET, with the nitroisophthalate units being excluded from crystallites. Fourier transform infrared in combination with cross‐polarization/magic‐angle spinning ¹³C NMR spectroscopy demonstrates the occurrence of a gauche–trans conversion encompassing the crystallization process. A correlation between DSC and spectroscopic data leads us to conclude that the content of trans conformer in the noncrystallized phase of PETNI is higher than in both PET and PETI copolymers and suggests that secondary crystallization in the homopolymer must proceed by a mechanism different than that in copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1553–1564, 2001