Synthesis and characterization of polyphenylenes with polypeptide and poly(ethylene glycol) side chains

We report a novel approach for fabrication of multifunctional conjugated polymers, namely poly(p‐phenylene)s (PPPs) possessing polypeptide (poly‐l ‐lysine, PLL) and hydrophilic poly(ethylene glycol) (PEG) side chains. The approach is comprised of the combination of Suzuki coupling and in situ N‐carboxyanhydride (NCA) ring‐opening polymerization (ROP) processes. First, polypeptide macromonomer was prepared by ROP of the corresponding NCA precursor using (2,5‐dibromophenyl)methanamine as an initiator. Suzuki coupling reaction of the obtained polypeptide and PEG macromonomers both having dibromobenzene end functionality using 1,4‐benzenediboronic acid as the coupling partner in the presence of palladium catalyst gave the desired polymer. A different sequence of the same procedure was also employed to yield polymer with essentially identical structure. In the reverse sequence mode, low molar mass monomer (2,5‐dibromophenyl)methanamine, and PEG macromonomer were coupled with 1,4‐benzenediboronic acid in a similar way followed by ROP of the L‐Lysine NCA precursor through the primary amino groups of the resulting polyphenylene. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1785–1793     

Synthesis of Vinyl Polymer—Poly (α-Amino Acid) Block Copolymers by End-Reactive Oligomers

In order to synthesize block copolymers consisting of segments having dissimilar properties, vinyl polymer - poly (α-amino acid) block copolymers were synthesized by two different methods. In the first method, the terminal amino groups of polysarcosine, poly(γ-benzyl L-glutamate), and poly(γ-benzyloxycarbonyl-L-lysine) were haloacetylated. The mixture of the terminally haloacetylated poly (α-amino acid) and styrene or methyl methacrylate was photoirradiated in the presence of Mo (CO)₆ or heated with Mo(CO)₆, yielding A-B-A-type block copolymers consisting of poly(α-amino cid) (the A component) and vinyl polymer(the B component). The characterization of block copolymers revealed that the thermally initiated polymerization of vinyl compounds by the trichloroacetyl poly(α-amino acid)/Mo(CO)₆ system was most suitable for the synthesis of vinyl polymer - poly-(α-amino acid) block copolymers. In the second method, poly (methyl methacrylate) and polystyrene having a terminal amino group were synthesized by the radical polymerization in the presence of 2-mercaptoethylammonium chloride. Using these polymers having a terminal amino group as an initiator, the block polymerizations of γ-benzyl L-glutamate NCA and e-benzyloxycarbonyl-L-lysine NCA were carried out, yielding A-B-type block copolymer. By eliminating the protecting groups of the side chains of poly(α-amino acid) segment, block copolymers such as poly(methyl methacrylate) with poly(L-glutamic acid) or poly(L-lysine) and polystyrene with poly(L-glutamic acid) and poly(L-lysine) were successfully synthesized.     

Polymerization and conformational studies of poly(trans-3-ethyl-D and L-proline)

Poly(L -trans-3-ethylproline), L -PT3EP, and poly(D -trans-3-ethylproline), D -PT3EP, were prepared by ring opening polymerization of the corresponding N-carboxyanhydrides (NCA) using triethylamine as an initiator. Using circular dichroism spectroscopy, it was shown that the incorporation of an ethyl group at the 3 position of the pyrrolidine ring caused a noticeable change in the conformational behavior of the polymer in solution. The ethyl group limited to some extent rotation of the polymer chain around the C_? ? CO bond and prevented the mutarotation between the two forms found in poly-L -proline polymers.     

Functionalization of polymers prepared by ATRP using radical addition reactions

Low molecular weight linear poly(methyl acrylate), star and hyperbranched polymers were synthesized using atom transfer radical polymerization (ATRP) and end‐functionalized using radical addition reactions. By adding allyltri‐n‐butylstannane at the end of the polymerization of poly(methyl acrylate), the polymer was terminated by allyl groups. When at high conversions of the acrylate monomer, allyl alcohol or 1,2‐epoxy‐5‐hexene, monomers which are not polymerizable by ATRP, were added, alcohol and epoxy functionalities respectively were incorporated at the polymer chain end. Functionalization by radical addition reactions was demonstrated to be applicable to multi‐functional polymers such as hyperbranched and star polymers.     

Synthesis of crosslinked poly(α-amino acids) with various functional groups

The esterification of the carboxyl group in copoly(γ-benzyl-L -glutamyl-L -glutamic acid) was carried out using N-hydroxysuccinimide and dicyclohexylcarbodimide to yield the activated site for the coupling reaction with amino compounds. The α-helix stability of the reactive copolymer thus obtained is remarkably affected in the presence of succinimide ring. This copolymer was proved to react nearly completely with amino alcohols such as 2-aminoethanol, 3-aminopropanol, and diethanolamine. The copoly(N⁵-hydroxyalkyl-L -glutamine) thus prepared is insoluble in water, since the benzyl ester remains in this copolymer. The copoly(α-amino acids) having another functional group were also prepared using aminoalkylsilane. Crosslinked poly(α-amino acids) were prepared by the reaction of the reactive copolymer with a low-molecular-weight polymer of PBLG having one amino group on each end of its main chain which was obtained from the corresponding NCA using p-diaminobenzene as an initiator. Another crosslinked polymer was prepared using an alkyl diamine such as 1,6-diaminohexane or 1,12-diaminododecane as a crosslinking reagent. The crosslinked copoly(α-amino acids) bearing the activated site are able to further react with various compounds having amino groups.     

Polymerization of N-carboxy–amino acid anhydrides in the solid state. II. Relation between polymerizability and molecular arrangement in L-leucine NCA and L-alanine NCA crystals

The polymerizability of N-carboxy–amino acid anhydrides (NCAs) of L -leucine and L -alanine was examined in the solid state and in solution. L -leucine NCA shows much higher reactivity in the solid state (when immersed in hexane) than in solution (in acetonitrile), but the opposite is true for L -alanine NCA. However, the two NCAs give similar values of apparent activation energy in each polymerization system. Rather high-molecular-weight polypeptides were obtained in the polymerization of L -leucine NCA in the solid state compared with those obtained in solution, while the molecular weight of polymers obtained from L -alanine NCA was higher in solution than in the solid state. IR spectra showed that α helices form mainly in the polymerization of both L -leucine NCA and L -alanine NCA in the solid state; a small amount of the β structure forms in the latter polymerization. X-ray diffraction and electron microscopy revealed that L -leucine NCA polymerizes predominantly along the c axis in the crystal, while the polymer chains grow in random directions in the crystal of L -alanine NCA. The difference can be explained by the molecular arrangement in the crystal. There are two requirements for high reactivity in the solid state: the five-membered rings of the monomer must form a layer structure and the polymer must occupy nearly the same space as the reacting monomer.     

Polymerization of α-amino acid N-carboxy anhydrides. III. Mechanism of polymerization of L- and DL-alanine NCA in acetonitrile

The polymerization of L - and DL -alanine NCA initiated with n-butylamine was carried out in acetonitrile which is a nonsolvent for polypeptide. The initiation reaction was completed within 60 min.; there was about 10% of conversion of monomer. The number-average degree of polymerization of the polymer obtained increased with the reaction period, and it was found to agree with value of W/I, where W is the weight of the monomer consumed by the polymerization and I is the weight of the initiator used. The initiation reaction of the polymerization was concluded as an attack of n-butylamine on the C₅ carbonyl carbon of NCA. The initiation, was followed by a propagation reaction, in which there was attack by an amino endgroup of the polymer on the C₅ carbonyl carbon of NCA. The rate of polymerization was observed by measuring the CO₂ evolved, and the activation energy was estimated as follows: 6.66 kcal./mole above 30°C. and 1.83 kcal./mole below 30°C. for L -alanine NCA; 15.43 kcal./mole above 30°C., 2.77 kcal./mole below 30°C. for DL -alanine NCA. The activation entropy was about ?43 cal./mole-°K. above 30°C. and ?59 cal./mole-°K. below 30°C. for L -alanine NCA; it was about ?14 cal./mole-°K. above 30°C. and ?56 cal./mole-°K. below 30°C. for DL -alanine NCA. From the polymerization parameters, x-ray diffraction diagrams, infrared spectra, and solubility in water of the polymer, the poly-DL -alanine obtained here at a low temperature was assumed to have a block copolymer structure rather than being a random copolymer of D - and L -alanine.     

Cross‐linking photopolymerization of monoacrylate initiated by benzophenone

The chain‐end structure of the photopolymerized acrylate using benzophenone as an initiator was investigated as well as polymerization behavior. Dodecyl acrylate was used as a monomer in this study. Gelation occurred during ultraviolet (UV) irradiation, whereas a cross‐linker was not employed. Conversion‐time profile below gel point gave a linear first‐order plot suggesting that the steady‐state was held throughout polymerization. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectra of the resultant polymer indicated that most polymers had an acryloyl group at one of the chain‐ends, while some polymers had an acryloyl group at each chain‐end. The cross‐linking reaction leading to gelation would have been caused by the subsequent copolymerization of the residual monomer with the latter polymer having two acryloyl groups. Dissolved oxygen in the monomer solution influenced the polymer structure giving hydroxyl group at chain‐end. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1545–1553     

Tuning the conformation of synthetic co‐polypeptides of serine and glutamic acid through control over polymer composition

Ring opening polymerization (ROP) of N‐carboxy anhydride (NCA) amino acids presents a rapid way to synthesize high molecular weight polypeptides with different amino acid compositions. The compositional and functional versatility of polypeptides make these materials an attractive choice for biomaterials. The functional performance of polypeptide materials is equally linked to their conformation which is determined by the amino acid sequence in the polymer chains. Here, the interplay between composition and conformation of synthetic polypeptides obtained by NCA polymerization was explored. Various copolypeptides from Glu(Bzl) and Ser(Bzl) were prepared to investigate how polypeptide composition affected the conformation of the resulting copolymer. Polymerization kinetics indicated that the copolymerization of Glu(Bzl) and Ser(Bzl) preferentially yielded alternating copolymers. Both the polydispersity and the conformation of the polypeptides were dependent on the Ser(Bzl) content in the polymer, demonstrating that polypeptide functionalities could be tuned directly by altering the relative amounts of amino acids in the chain. This work presents the first step toward an improved understanding and control over polypeptide conformation through modulating the amino acid composition of the material. Understanding this sequence–functionality relationship is essential to advancing the use of ROP as a technique to design smart polypeptide based materials with specific functions. © 2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2331–2336     

AB型两亲聚L-谷氨酸-苄酯-聚乙二醇嵌段共聚物的合成与表征

利用L 谷氨酸和苯甲醇反应制备了L 谷氨酸 苄酯 ,然后将其与三聚光气反应制备了N 羧基 L 谷氨酸 环内酸酐 (NCA) .以聚乙二醇单甲醚 (MPEG)为原料 ,制备了端氨基聚乙二醇单甲醚 (MPEG NH2 ) ,并以此作为引发剂 ,引发NCA开环聚合 ,合成了不同分子量的聚L 谷氨酸 苄酯 聚乙二醇单甲醚 (PBGM )嵌段共聚物 .利用IR、1 H NMR、DSC、GPC等方法对共聚物结构进行了表征 .结果表明 ,MPEG NH2 引发NCA开环聚合得到的是嵌段共聚物 ,通过1 H NMR谱得到共聚物组成及数均分子量 ;随着共聚物中MPEG含量的增高 ,聚L 谷氨酸 苄酯的亲水性有所改善     

Melt block copolymerization of ϵ-caprolactone and L-lactide

AB block copolymers of ϵ-caprolactone and (L )-lactide could be prepared by ring-opening polymerization in the melt at 110°C using stannous octoate as a catalyst and ethanol as an initiator provided ϵ-caprolactone was polymerized first. Ethanol initiated the polymerization of ϵ-caprolactone producing a polymer with ϵ-caprolactone derived hydroxyl end groups which after addition of L -lactide in the second step of the polymerization initiated the ring-opening copolymerization of L -lactide. The number-average molecular weights of the poly(ϵ-caprolactone) blocks varied from 1.5 to 5.2 × 10³, while those of the poly(L -lactide) blocks ranged from 17.4 to 49.7 × 10³. The polydispersities of the block copolymers varied from 1.16 to 1.27. The number-average molecular weights of the polymers were controlled by the monomer/hydroxyl group ratio, and were independent on the monomer/stannous octoate ratio within the range of experimental conditions studied. When L -lactide was polymerized first, followed by copolymerization of ϵ-caprolactone, random copolymers were obtained. The formation of random copolymers was attributed to the occurrence of transesterification reactions. These side reactions were caused by the ϵ-caprolactone derived hydroxyl end groups generated during the copolymerization of ϵ-caprolactone with pre-polymers of L -lactide. The polymerization proceeds through an ester alcoholysis reaction mechanism, in which the stannous octoate activated ester groups of the monomers react with hydroxyl groups. © 1997 John Wiley & Sons, Inc.     

Biodegradation of poly(amino acid)s: Evaluation methods and structure-to-function relationships

Two poly(amino acid) systems were studied: (a) poly[N⁵-(2-hydroxyethyl)-L-glutamine] (PHEG) derivatives prepared by NCA polymerization; (b) poly-α,β-[N-(2-hydroxyethyl)-DL-aspartamide] (PHEA) derivatives prepared by thermal polycondensation of aspartic acid to racemic polysuccinimide followed by chemical modification reactions. The degradation of polymers by isolated enzymes and homogenate of kidney tissue was studied in vitro and the effect of polymer structure on the rate of degradation and the size of degradation products was evaluated. A PHEA derivative (modified by tyramine residues in 9.6 % of side chains) was accumulated in the lysosomes of kidney cells of rats and the molecular-weight distribution of the polymer retained inside the lysosomes of living cells and that of the polymer excreted into urine was analysed by a high-sensitivity size-exclusion chromatography using the fluorescence and radioactive labelling. While PHEG derivatives were degraded by isolated mammalian enzymes and a tissue homogenate, no significant degradation of PHEA and derivatives was observed, either in vitro, with isolated enzymes and homogenate or in vivo, under a long-term exposure to the lysosomal enzymes in living cells.     

Sieving polymer synthesis by reversible addition fragmentation chain transfer polymerization

Replaceable sieving polymers are the fundamental component for high‐resolution nucleic acids separation in CE. The choice of polymer and its physical properties play significant roles in influencing separation performance. Recently, reversible addition fragmentation chain transfer (RAFT) polymerization has been shown to be a versatile polymerization technique capable of yielding well‐defined polymers previously unattainable by conventional free‐radical polymerization. In this study, a high molecular weight poly‐(N,N‐dimethylacrylamide) (PDMA) at 765 000 gmol^?1 with a polydispersity index of 1.55 was successfully synthesized with the use of chain transfer agent—2‐propionic acidyl butyl trithiocarbonate in a multistep sequential RAFT polymerization approach. This study represents the first demonstration of RAFT polymerization for synthesizing polymers with the molecular weight range suitable for high‐resolution DNA separation in sieving electrophoresis. Adjustment of pH in the reaction was found to be crucial for the successful RAFT polymerization of high molecular weight polymer as the buffered condition minimizes the effect of hydrolysis and aminolysis commonly associated with trithiocarbonate chain transfer agents. The separation efficiency of 2‐propionic acidyl butyl trithiocarbonate PDMA was found to have marginally superior separation performance compared to a commercial PDMA formulation, POP?‐CAP, of similar molecular weight range.     

Polymerization of Acrolein by Imidazole

Polymerization of acrolein(AL) in the presence of imidazole(Im) has been investigated in tetrahydrofuran or methanol below room temperature. The polymers obtained, white or pale yellow powders, were found to be composed of vinyl polymer with one Im group attached and having an aldehyde side chain, of which 70–80 mole % of the aldehyde revealed bridge structure. The number-average molecular weight (M _n) of these polymers was determined to be in the range of 317 to 691. The rate of polmerization R_p was expressed by the equation, R + k[Im] [AL]².

The addition of water or dimethyl sulfoxide accelerated the polymerization reaction, while the presence of benzaldehyde or N,N'-dimethylformamide decreased R_p. The structure of addition products in the initial polymerization step was confirmed by IR and NMR spectra, and the observations of polymerization system was carried out by UV and NMR spectra. The polymerization mechanisms were discussed on the basis of these results.     

ABA型聚L-丙氨酸-聚乙二醇嵌段共聚物的合成及其表征

利用L-α-丙氨酸和三聚光气反应制备了N-羧基-α-丙氨酸-环内酸酐(NCA).以聚乙二醇(PEG)为原料.制备了端氨基聚乙二醇(PEG-NH₂),并以此作为引发剂,引发NCA开环聚合.合成了不同组成和分子量的聚L-丙氨酸-聚乙二醇(PLAA-PEG-PLAA)嵌段共聚物.利用IR、¹H NMR、DSC、WAXD、CD等方法对共聚物结构进行了表征.结果表明,PEG-NH₂引发NCA开环聚合得到的是嵌段共聚物,通过¹H NMR谱得到共聚物组成及数均分子量;引入PEG的结果使聚L-丙氨酸的亲水性有所改善;CD测诚结果表明共聚物在水溶液中主链主要以α-螺旋构象存在.     

Highly heterotactic polymerization of methacrylates — Higher order stereoregulation and stereochemical significance

A combination of tert-butyllithium (t-BuLi) and bis(2,6-di-t-butylphenoxy)methylaluminium (MeAI(ODBP)₂) was found to be an efficient initiator for heterotactic living polymerization of certain alkyl methacrylates in toluene at low temperatures. The polymerization of methyl methacrylate (MMA) with t-BuLi/MeAI(ODBP)₂ (AI/Li=5 mol/mol) in toluene at −78°C gave heterotactic-rich poly(methyl methacrylate) (PMMA) with narrow molecular weight distributions (MWDs) (heterotactic triad fraction mr = 68%, ratio of weight- to number-average molecular weights M̄w/M̄n = 1.06-1.17). Other alkyl methacrylates also gave heterotactic polymers under the same conditions; in particular, ethyl and butyl methacrylates gave polymers with heterotactic triad fractions of 87%. The highest triad heterotacticity of 91.6% was obtained for the polymerization of ethyl methacrylate at −95°C. Some characteristic features of this stereospecific polymerization were discussed based on the polymerization results combined with other structural information of the polymer such as chain-end stereostructure and stereosequence distribution in the main chain.     

Preparation of hydrophobic tannins‐inspired polymer materials via low‐ppm ATRP methods

The novel hydrophobic coating material was received for the first time by a two‐step synthetic route. Firstly, the 15‐functional brominated macroinitiator was prepared by the esterification methodology. Next step covers synthesis of star‐like polymers by poly(n‐butyl acrylate) (PBA) arms polymerization via three low‐ppm atom transfer radical polymerization (ATRP) approaches including application of copper and silver wire in SARA and ARGET ATRP, respectively, as driving forces in redox cycle of catalyst, and an external stimulus in the form of electric current (seATRP) as the third approach in copper(II) regeneration system. As expected, the electrochemically mediated technique allows synthesis of tannic acid‐inspired coating polymers in precisely controlled manner during the entire polymerization process, proved by linear first‐order kinetics plot in contrast to above‐mentioned methods, low dispersity (Ð = 1.18) of star‐shaped polymers, and high efficiency of initiation (? _i = 81%) determined after detaching of polymers side arms. Macromolecules received by all low‐ppm ATRP solutions were characterized by preserved chain‐end functionality (theoretical dead chain fraction; DCF_theo <1%). Adhesive and hydrophobic properties of received polymer materials were investigated by contact angles (θ) and free surface energy (FSE) calculations. Prepared polymer films besides excellent hydrophobic properties have great potential as a self‐healing solution.     

Polymerization of N-carboxy anhydrides by organotin catalysts

Organotin compounds were found to lead to polymerization of N-carboxy anhydrides. The polymerization was studied in detail using γ-benzyl N-carboxyl-t-glutamate anhydride (BGA). Compounds such as tributyltin methoxide, bis(tributyltin)oxide, and N-tributyltin imidazole polymerized BGA while others like dibutyltin dichloride, which are Lewis acids, failed. Polymerization of BGA in dioxane at various monomer to dibutyltin dimethoxide ratios showed a first order reaction to monomer. The plot of In M₀/M₁ vs time showed two stage kinetics, the second one being faster. The pseudo first order rate constants were smaller than those for primary amine initiated polymerizations and much smaller than that for polymerization initiated by sodium methoxide. The molecular weights were independent of the monomer to initiator ratio both in dioxane and in DMF. In the reaction of an equimolar amount of tributyltin methoxide with NCA, the methyl ester of the amino acid was formed.The mechanism suggested is that of addition of the organotin compound to the NCA forming an organotin carbamate which decarboxylates, leaving an active -N-Sn-group which adds to another NCA molecule. This process is repeated in every step of the propagation.     

Star polymers by cross‐linking of linear poly(benzyl‐L‐glutamate) macromonomers via free‐radical and RAFT polymerization. A simple route toward peptide‐stabilized nanoparticles

Poly(benzyl‐L ‐glutamate) (PBLG) macromonomers were synthesized by N‐carboxyanhydride (NCA) polymerization initiated with 4‐vinyl benzylamine. MALDI‐ToF analysis confirmed the presence of styrenic end‐groups in the PBLG. Free‐radical and RAFT polymerization of the macromonomer in the presence of divinyl benzene produced star polymers of various molecular weights, polydispersity, and yield depending on the reaction conditions applied. The highest molecular weight (M_w) of 10,170,000 g/mol was obtained in a free‐radical multibatch approach. It was shown that the PBLG star polymers can be deprotected to obtain poly(glutamic acid) star polymers, which form water soluble pH responsive nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Living radical polymerization of methylstyrenes by a stable nitroxyl radical,and stability of the aminoxy chain end

Radical polymerization of 2-, 3-, and 4-methylstyrenes (MeSts) was investigated with benzoyl peroxide (BPO) as an initiator, in the presence of 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MTEMPO). The polymerization was performed in bulk for 3.5 h at 95°C, and then continued for a defined time at 125°C, to give the corresponding poly(MeSt)s with narrow polydispersity in high yield. It was found that the polymerization proceeded in accordance with a living mechanism, because the molecular weight of the resulting polymers was proportional to the conversion, and to the reciprocal of the initial concentration of MTEMPO. It was found that steric hindrance between the methyl group of 2-MeSt, and the tetramethyl ones of MTEMPO, significantly contributed to the rate of polymerization, and to the stability of the growing polymer chain end. The stability decreased in the order of 2- > 3- > 4-MeSt, by occurrence of decomposition, which was caused by disproportionation of the growing chain end. However, the steric hindrance had no effect on the tacticity of the resulting polymer. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 , 269–276, 1998