Syntheses and reactions of functional polymers. XCIII. Syntheses of polymers containing the N-(4-hydroxy-3-nitrophenyl)succinimide structure in the chain and the use of these activated polymer esters of N-blocked amino acids or peptides

Polymers containing the N-(4-hydroxy-3-nitrophenyl)succinimide residue were designed in order to achieve acyl activation of a reacting carboxylic acid in the solid phase. These polymers were prepared through the following three routes: (a) styrene was allowed to copolymerize with N-(4-hydroxy-3-nitrophenyl)- or N-(4-acetoxy-3-nitrophenyl)maleimide, (b) styrene was copolymerized with N-(4-acetoxyphenyl)maleimide in the presence of divinylbenzene (DVB), and the copolymer obtained was hydrolyzed and nitrated, (c) a copolymer of maleic anhydride and styrene was reacted with p-aminophenol, followed by nitration. The polymers prepared by routes b and c were converted to the activated polymer esters of N-blocked amino acids and peptides by using dicyclohexylcarbodiimide (DCC). The acylated polymers thus obtained were treated with amino acid esters and found to give peptides quantitatively without racemization.     

Polymeric formamides as liquid–liquid phase transfer catalysts

Polymeric formamides were prepared by free radical polymerization of N-methyl-N-vinyl-formamide or N-methyl-N-(4-vinylbenzyl)formamide, and copolymerization of these monomers with styrene. These soluble polymers serve as phase transfer catalysts for several reactions under liquid–liquid biphase conditions. The catalytic activity of copolymers containing styrene unit is affected remarkably by composition, and there are maxima at certain composition in both polymers. However, copolymers with an acrylonitrile co-unit scarcely exhibit catalytic activity. Furthermore, it was found that these polymers can extract all alkali metal ions employed here, and that the extraction ability increases with increasing the density of active sites. From these results, it is demonstrated that catalytic activity strongly depends on both cation extraction ability of polymers and lipophilicity around the active sites in the polymer.     

Properties of well‐defined alternating and random copolymers of methacrylates and styrene prepared by controlled/living radical polymerization

The physical properties of well‐defined alternating copolymers poly(methyl methacrylate‐alt‐styrene) and poly(n‐butyl methacrylate‐alt‐styrene), prepared by reversible addition–fragmentation chain transfer polymerization in the presence of Lewis acids, were investigated with differential scanning calorimetry, wide‐angle X‐ray scattering, and dynamic mechanical measurements. The properties were compared with those of random copolymers of the same overall composition and the corresponding homopolymers. Wide‐angle X‐ray scattering data showed that the alternating copolymers possessed a more regular comonomer sequence than the random copolymers. The thermomechanical properties of alternating copolymers and random copolymers were quite similar and typical for amorphous polymers, but in one of the cases studied the glass‐transition temperature for alternating copolymer was remarkably higher than for the random copolymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3440–3446, 2005     

Anionic graft copolymerization of diene polymers with vinyl monomers

A mixture of homopolymer and graft copolymer was obtained by adding the monomer at 0°C to the polylithiodiene solution. Styrene, methyl methacrylate, and acrylonitrile were used as the monomers. Polylithiodienes were prepared by the metalation of diene polymers, i.e., polybutadiene or polyisoprene, with the use of n-butyllithium in the presence of a tertiary amine (N,N,N′,N′-tetramethylethylenediamine) in n-heptane. The graft copolymers were separated by solvent extraction and were confirmed by turbidimetric titration and elementary analysis. Oxidation of the polybutadiene–styrene grafts revealed that the molecular weight of the side chains was the same as the molecular weight of the free polystyrene formed. The grafting efficiency and grafting percentage were studied for polybutadiene–styrene graft copolymers prepared under various conditions.     

Synthesis of arborescent styrene homopolymers and copolymers from epoxidized substrates

The synthesis of arborescent styrenic homopolymers and copolymers was achieved by anionic polymerization and grafting. Styrene and p‐(3‐butenyl)styrene were first copolymerized using sec‐butyllithium in toluene, to generate a linear copolymer with a weight‐average molecular weight M_w = 4000 and M_w/M_n = 1.05. The pendant double bonds of the copolymer were then epoxidized with m‐chloroperbenzoic acid. A comb‐branched (or arborescent generation G0) copolymer was obtained by coupling the epoxidized substrate with living styrene‐p‐(3‐butenyl)styrene copolymer chains with M_w ≈ 5000 in a toluene/tetrahydrofuran mixture. Further cycles of epoxidation and coupling reactions while maintaining M_w ≈ 5000 for the side chains yielded arborescent copolymers of generations G1–G3. A series of arborescent styrene homopolymers was also obtained by grafting M_w ≈ 5000 polystyrene side chains onto the linear and G0–G2 copolymer substrates. Size exclusion chromatography measurements showed that the graft polymers have low polydispersity indices (M_w/M_n = 1.02–1.15) and molecular weights increasing geometrically over successive generations. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Polyampholyte synthesis by cyclopolymerization

The syntheses of N-2-phenylallylacrylamide (I) and N-ethyl-2-phenallylacrylamide (II) are described. Both monomers can be polymerized with radical initiators to form cyclopolymers although complete cyclization does not occur. Lewis acids (ZnCl₂ in the case of I, Et_1.5AlCl_1.5 in the case of II) result in the formation of higher molecular weight polymers in a shorter period of time. Polymers of I and II have been hydrolyzed to polyampholytes. The copolymerization of α-methylstyrene–acrylamide in the presence of azobisisobutyronitrile (AIBN) and ZnCl₂ leads to the formation of a 1:1 copolymer, whereas styrene–acrylamide under the same conditions give a copolymer slightly dependent upon the monomer feed composition. Attempted cyclopolymerization of N-allylacrylamide (monomer I without the phenyl group) with ZnCl₂–AlBN was not successful, only crosslinked polymer being obtained. An explanation is offered for the fact that I does not form a perfect cyclopolymer, although the α-methylstyrene–acrylamide system forms a 1:1 copolymer.     

Aqueous solution properties of pH‐responsive AB diblock acrylamido–styrenic copolymers synthesized via aqueous reversible addition–fragmentation chain transfer

Here we report the synthesis and solution characterization of a novel series of AB diblock copolymers with neutral, water‐soluble A blocks consisting of N,N‐dimethylacrylamide and pH‐responsive B blocks of N,N‐dimethylvinylbenzylamine. To our knowledge, this represents the first example of an acrylamido–styrenic block copolymer prepared directly in a homogeneous aqueous solution. The best blocking order [with poly(N,N‐dimethylacrylamide) as a macro‐chain‐transfer agent] yielded well‐defined block copolymers with minimal homopolymer impurities. The reversible aggregation of these block copolymers in aqueous media was studied with ¹H NMR spectroscopy and dynamic light scattering. Finally, an example of core‐crosslinked micelles was demonstrated by the addition of a difunctional crosslinking agent to a micellar solution of the parent block copolymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1724–1734, 2004     

Synthesis and Evaluation of Thiol Polymers

Thiol polymer, which is known as a reactive and functional polymer, is synthesized and evaluated quantitatively by the modified Ellman method. The synthesis was accomplished by 1) hydrolysis of an isothiouronium salt that is the adduct of 4‐chloromethylstyrene (CMS) homopolymer or CMS‐styrene (St) copolymer with thiourea; 2) hydrolysis of a precursor copolymer made from 4‐vinylbenzyl N‐ethyldithio‐carbamate (VBEC) and St or N‐vinyl‐2‐pyrrolidone (NVP); 3) solvolysis of an iminium salt polymer obtained from the reaction of CMS‐NVP copolymer with N,N‐dimethylthioformamide (TDMF). When a higher thiol content is desired, more severe hydrolysis conditions are required which however, also increase the loss of thiol. Hence, it is clear that the best synthesis of thiol polymers is Method 3. A quantitative yield of functional thiol polymer is obtained by this method, and the product is soluble in DMSO, DMF, and CHCI_3.     

Preparation,copolymerization kinetics,and viscoelastic behavior of copolymers of 1,3-butadiene and 1,4-diphenyl-1,3-butadiene

1,4-Diphenyl-1,3-butadiene reacts readily with sec-butyllithium in toluene to form adducts. Although this 1,4-substituted conjugated diene did not homopolymerize or copolymerize with styrene, with butadiene it formed copolymers having compositions varying from one end of the chain to the other. The monomer reactivity ratios found were r₁ = 8.2, r₂ = 0 in toluene and r₁ = 2.1, r₂ = 0 in toluene–tetrahydrofuran (0.2%) solution. The intramolecular composition distribution of these polymers varied from an initial butadiene-rich composition, dependent on the ratio of monomers charged, to the equimolar composition of the alternating copolymer. In spite of this compositional heterogeneity, the crosslinked polymers exhibited a single glass transition characteristic of the mean composition. A secondary, high-temperature dispersion observed in the dynamic viscoelastic properties of some of the products is shown to be attributable to network topological effects.     

Simultaneous determination of the styrene unit content and assessment of molecular weight of triblock copolymers in adhesives by a size exclusion chromatography method

The content of styrene units in nonhydrogenated and hydrogenated styrene‐butadiene‐styrene and styrene‐isoprene‐styrene triblock copolymers significantly influences product performance. A size exclusion chromatography method was developed to determine the average styrene content of triblock copolymers blended with tackifier in adhesives. A complete separation of the triblock copolymer from the other additives was realized with size exclusion chromatography. The peak area ratio of the UV and refraction index signals of the copolymers at the same effective elution volume was correlated to the average styrene unit content using nuclear magnetic resonance spectroscopy with commercial copolymers as standards. The obtained calibration curves showed good linearity for both the hydrogenated and nonhydrogenated styrene‐butadiene‐styrene and styrene‐isoprene‐styrene triblock copolymers (r  = 0.974 for styrene contents of 19.3–46.3% for nonhydrogenated ones and r  = 0.970 for the styrene contents of 23–58.2% for hydrogenated ones). For copolymer blends, the developed method provided more accurate average styrene unit contents than nuclear magnetic resonance spectroscopy provided. These results were validated using two known copolymer blends consisting of either styrene‐isoprene‐styrene or hydrogenated styrene‐butadiene‐styrene and a hydrocarbon tackifying resin as well as an unknown adhesive with styrene‐butadiene‐styrene and an aromatic tackifying resin. The methodology can be readily applied to styrene‐containing polymers in blends such as poly(acrylonitrile‐butadiene styrene).     

Chain scission efficiency and reactive-ion etch resistance of alternating copolymers of styrene and olefins trisubstituted or tetrasubstituted with electron-withdrawing groups

Alternating copolymers of styrene (St) with electron-deficient olefins trisubstituted or tetrasubstituted with cyano and carboalkoxy groups have been subjected to ⁶⁰Co γ-radiolysis together with a series of copolymers of methyl methacrylate (MMA) and St. The chain scission susceptibility G_s—G_x determined by membrane osmometry drastically decreases as St is incorporated in poly(methyl methacrylate) (PMMA). Whereas the alternating St-MMA copolymer is slightly crosslinked upon irradiation, an alternating copolymer of St with diethyl 2-cyano-1,1-ethylenedicarboxylate maintains a fairly high degradation sensitivity (G_s—G_x = 1.2). The reactive-ion etch rates were determined for the series of polymers in CF₄/O₂ (92/8). The etch resistance is significantly increased by introduction of St units in PMMA, and the highly substituted alternating copolymer etches as slowly as the MMA(50)—St(50) copolymers. Thus the alternating copolymer of NCCH=C(CO₂Et)₂ with St behaves like PMMA when exposed to high-energy radiation but is comparable to PSt in plasma environments.     

Newly designed hydrogel with both sensitive thermoresponse and biodegradability

The synthesis and characterization of thermoresponsive hydrogels on the basis of N‐isopropylacrylamide (IPAAm) copolymers crosslinked with biodegradable poly(amino acids) are described. This hydrogel was prepared with two kinds of reactive IPAAm‐based copolymers containing poly(amino acids) as the side‐chain groups and activated ester groups. We introduced the graft chains by decarboxylation polymerization of amino acid N‐carboxyanhydrides initiated from lateral amino groups in the PIPAAm copolymer. The hydrogels easily crosslinked with degradable poly(amino acid) chains by only mixing the copolymer aqueous solutions. The gelling method in this study would provide some of the following innovative features: (1) no necessary removal of unreacted monomers and so forth, (2) simpler loading of drugs into the hydrogels (only mixing when gelling), and (3) easier insertion into the body. On the basis of the swelling ratio measurement of the hydrogel, large volume changes dependent on temperature changes were observed. Moreover, the enzymatic temperature‐dependent degradation was confirmed. The results suggested that these hydrogels could be used for an injectable or implantable matrix of temperature‐modulated drug release. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 779–787, 2003     

Self-crosslinkable polymers. I. Copolymerization of glycidyl methacrylate with 2-vinylpyridine and 2-vinyl-5-ethylpyridine

A soluble and self-crosslinkable linear copolymer with pendant epoxy and pyridyl groups was obtained from glycidyl methacrylate (M₁) and 2-vinylpyridine (M₂) or 2-vinyl-5-ethylpyridine (M₂) by the action of azobisisobutyronitrile. The monomer reactivity ratios were determined in tetrahydrofuran at 60°C: r₁ = 0.510, r₂ = 0.620 with 2-vinylpyridine and r₁ = 0.57, r₂ = 0.62 with 2-vinyl-5-ethylpyridine. These were consistent with the calculated values with the reported Q and e values for these monomers. The intrinsic viscosities of the copolymers with 2-vinylpyridine and with 2-vinyl-5-ethylpyridine were found to be 0.17–0.19 and 0.26–0.38, respectively, in tetrahydrofuran at 30°C; they were independent of the copolymer composition. The copolymers were amorphous, had no clear melting points, and became insoluble crosslinked polymers under heating without further addition of any curing agents.     

Flexibilized styrene‐N‐substituted maleimide copolymers. I. Multiblock copolymers prepared from styrene‐maleimide telechelics and polytetrahydrofuran

Telechelic copolymers of styrene and different N‐substituted‐maleimides (SMIs) with a molecular weight of 2000–8000 g/mol were synthesized using the starved‐feed‐reactor technique and were nearly bifunctional when the monomer feed had a high styrene concentration. The COOH‐terminated rigid SMI blocks were polycondensated with OH‐terminated poly(tetrahydrofuran) (PTHF) blocks, with a molecular weight of 250–1000 g/mol, which are the flexible parts in the generated homogeneous multiblock copolymer. The entanglement density, which is closely related to the toughness of materials, increased in these flexible SMI copolymers (ν_e = 5.2 · 10²⁵ m⁻³) compared to the unflexibilized ones (ν_e = 2.4 · 10²⁵ m⁻³). The glass transition temperature of these flexibilized, single‐phase multiblock copolymers was still high enough to qualify them as engineering plastics. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3550–3557, 2000     

Preparation and characteristics of photocrosslinkable hydrophilic polymer having cinnamate moiety

The reaction of copolymer of N,N-dimethylacrylamide (DMAA) and bromoethyl methacrylate with potassium cinnamate produced water-soluble photosensitive polymers. Photosensitive polyDMAA films were irradiated with a 400 W high-pressure mercury lamp (λ > 280 nm) to produce crosslinked polymers, which were swollen in water. The degree of swelling was controlled by the irradiation time and content of cinnamate moieties in copolymers. Higher cinnamoylation and longer irradiation time resulted in higher yield of crosslinked polymers and less swellability. Partial degelation upon irradiation at λ ～ 254 nm was observed. The advantage of gelation via photodimerization over conventional chemical crosslinking methods is discussed in conjunction with biomedical applications. © 1992 John Wiley & Sons, Inc.     

Linear polymers of acrylic monomers containing an acetylenic moiety

1-Acryloxy-2-butyne and 1-methacryloxy-2-butyne were synthesized and polymerized by means of anionic initiators to soluble linear polymers containing acetylenic bonds in the pendant side chains. In contrast, insoluble, crosslinked polymers were formed when cationic and radical initiators were used. The unpolymerized acetylenic bonds in the resulting linear polymers were shown to be present by infrared spectroscopic methods and by the following post-reactions of these bonds: (1) the thermal- and radical-initiated crosslinking of the linear polymers through the acetylenic bonds; (2) the post-bromination of the acetylenic bonds; and (3) the reaction of decaborane with the acetylenic bonds. The anionic copolymerization of both monomers with a number of selected monomers was performed and the copolymer reactivity ratios for several of the comonomer pairs were determined. Dibromination of the linear polymers affords self-extinguishing polymers with apparently good hydrolytic stability. Decarbonation of the linear polymers yields soluble polymers which do not soften up to 300°C. The linear polymers and copolymers, as well as their partially brominated and partially decaboronated products, may be classified as “self-reactive” polymers which yield thermosetting polymers.     

Copolymerization of ethylene with styrene catalyzed by a linked bis(phenolato) titanium catalyst

Copolymerization of ethylene with styrene, catalyzed by 1,4‐dithiabutanediyl‐linked bis(phenolato) titanium complex and methylaluminoxane, produced exclusively ethylene–styrene copolymers with high activity. Copolymerization parameters were calculated to be r_E = 1.2 for ethylene and r_S = 0.031 for styrene, with r_E r_S = 0.037 indicating preference for alternating copolymerization. The copolymer microstructure can be varied by changing the ratio between the monomers in the copolymerization feed, affording copolymers with styrene content up to 68%. The copolymer microstructure was fully elucidated by ¹³C NMR spectroscopy revealing, in the copolymers with styrene content higher than 50%, the presence of long styrene–styrene homosequences, occasionally interrupted by isolated ethylene units. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1908–1913, 2006     

Synthesis,characterization, and applications in photovoltaic cells of oxetane‐functionalized P3HT derivatives

Several crosslinkable oxetane‐functionalized copolymers, containing regio‐regular segments of 3‐hexylthiophene, are synthesized using the Grignard metathesis polymerization. The optical and electrochemical properties of the new polymers, both in the soluble and crosslinked forms, are reported. These polymers are used in the preparation of organic photovoltaics upon blending with PCBM as electron‐acceptor. The effect of the crosslinking of these copolymers, once the blend films are formed, on the devices performance is also studied. In particular, the insertion of the oxetane‐functionalized thiophene comonomers leads to a decrease of the devices performance, which is further decreased upon crosslinking of the copolymer. However, the stability of the devices overall improves upon crosslinking of the copolymer. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 652–663     

Novel pH‐sensitive polymers containing sulfonamide groups

Novel pH‐sensitive polymers were synthesized by copolymerizing a monomer derivatized from 4‐amino‐N‐[4,6‐dimethyl‐2‐pyrimidinyl]benzene sulfonamide with N,N‐dimethylacrylamide. The linear copolymers showed pH‐sensitive solubility, while chemically crosslinked hydrogels exhibit a relatively sharp transition in swelling around physiological pH. These changes were found to be reversible. By varying the type of sulfonamide and the copolymer composition, a new class of pH‐sensitive polymers with a broad range of transition pH can be synthesized.     

Linear polymers of allyl acrylate and allyl methacrylate

Allyl acrylate and allyl methacrylate were polymerized by anionic initiators to soluble linear polymers containing allyl groups in the pendant side chains. The pendant unpolymerized allyl groups of the resulting linear poly(allyl acrylates) were shown to be present by: (1) the disappearance of the acrylyl and methacrylyl double bond absorptions in the infrared spectra in the conversions of monomers to polymers; (2) postbromination of the allyl bonds in the linear polymer; (3) the disappearance of the allyl groups absorptions in the infrared spectra of the brominated linear polymers; and (4) the thermal- and radical-initiated crosslinking of the linear polymers through the allyl groups. Allyl acrylate and allyl methacrylate show great reluctance to copolymerize with styrene under anionic initiation, but copolymerize readily with methyl methacrylate and acrylonitrile. Block copolymers were prepared by reacting allyl methacrylate with preformed polystyrene and poly(methyl methacrylate) anions. The linear polymers and copolymers of allyl acrylate may be classified as “self-reactive” polymers which yield thermosetting polymers. Bromination of the linear polymers offers a convenient method of producing self-extinguishing polymers.