ESI-MS analyses of lake dissolved organic matter in light of supramolecular assembly

A high-performance size-exclusion chromatography (SEC) system was coupled on-line to an electrospray ionization (ESI) interface to detect gas-phase ions by an API 365 LC/MS/MS triple quadrupole analyzer. The SEC fractions of a strongly coloured freshwater solution containing dissolved organic matter-humic substances (DOM-HS) were screened both by UV₂₅₄ and by ESI mass spectrometry (ESI-MS) in the full-scan mode within the m/z range of 100–2,900 amu in negative and positive polarities. The ESI-MS spectra were also collected by direct infusion of the DOM-HS solution in both polarities. ESI-MS spectra did not primarily favour low mass compounds, and negative and positive total ion chromatograms were parallel to the SEC elution profile obtained by UV₂₅₄ detection from DOM-HS solution. The UV₂₅₄ detection overestimated the SEC portion of higher size/mass solutes and underestimated that of solutes of smaller sizes/masses as compared with the total ion chromatogram intensities in negative or positive polarities. The change of mass-weighted and number-weighted average sizes/masses (M _w and M _n) of different SEC fractions was fairly small, in contrast to UV₂₅₄ detection, with increasing elution volume. A reasonable explanation for the great differences between M _w and M _n values, obtained by UV₂₅₄ and ESI-MS detections for eight different SEC fractions, seems to be a supramolecular-type association of relatively small components through weak dispersive forces. M _n values obtained by vapour-pressure osmometry for different SEC fractions were to some extent analogous with those of negative and positive ESI-MS. The shapes obtained by either negative or positive polarities and calculated M _w and M _n values indicated a close structural similarity between each SEC fraction. Positive ion and negative ion spectra of different humic fractions represented quite similar components, and there was no evidence for noteworthy occurrence of multiply charged ions being able to lower mass distributions of negative ion spectra. The effect of nitrogen on the mass spectra seemed to be unimportant, and the weak ions observed at even m/z values correspond most likely to the ¹³C counterparts of the more abundant ¹²C odd ions. No uncontrolled ESI fragmentation was observable and humic solutes seemed to be quite heat-resistant. Direct infusion of the untreated DOM-HS solution and statistical calculation verified that the SEC-separated different fractions really represent distinct entities of the original DOM-HS mixture. ESI-MS results support the opinion that the structural composition of humic solutes in their original combined mixture resembles supramolecular-type associations of smaller molecular size entities possessing similar structural functionalities.     

Synthesis of poly(glycerol)‐block‐poly(methyl acrylate) multi‐arm star polymers

Novel polyfunctional macroinitiators for atom transfer radical polymerization (ATRP) were obtained via esterification of hyperbranched polyglycerol (PG) (M_n = 4 770 g/mol, M_w/M_n = 1.5) with 2‐bromoisobutyryl bromide. Such macroinitiators were used in the presence of CuBr/pentamethyldiethylenetriamine (PMDETA) to initiate methyl acrylate (MA) polymerization, resulting in multi‐arm block copolymers with polyether core and 45–55 PMA arms. PMA arm length was controlled via monomer/initiator ratio and conversion (< 35%). Polymers were characterized by ¹H NMR, ¹³C NMR, SEC, membrane osmometry and DSC.     

Synthesis of arborescent (Dendritic) polystyrenes via controlled inimer‐type reversible addition‐fragmentation chain transfer polymerization

The reversible addition‐fragmentation chain transfer (RAFT) copolymerization of styrene and 4‐vinylbenzyl dithiobenzoate, a RAFT‐based inimer (initiator‐monomer), is described. Controlled polymerization was achieved in bulk conditions using thermal initiation at 110 °C to give arborescent polystyrene (arbPSt). The number‐average molecular weights of the polymers increased linearly with conversion and were much higher than theoretically calculated for a linear polymerization, reaching M_n = 364,000 g/mol with M_w/M_n = 2.65. Branching analysis by NMR showed an average of 3.5 branches per chain. SEC data, which were similar to those measured in arborescent polyisobutylene, supported the architectural analysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7621–7627, 2008     

Control of the molecular weight of hyperbranched polyglycerols

Hyperbranched polyglycerols exceeding M_n > 15,000 g/mol (DP_n > 270) have been prepared, using a modified version of the synthetic protocol reported earlier. In the optimized process polydispersities recorded by SEC remained narrow, with M_w/M_n < 1.7 over a large molecular weight range. The drastic increase of viscositity in the course of the reaction, was found to be responsible for the increased fraction of cycles (MALDI‐TOF MS) at high molecular weights.     

Synthesis of arborescent polystyrene by “click” grafting

A method was developed for the synthesis of arborescent polystyrene by “click” coupling. Acetylene functionalities were introduced on linear polystyrene (M_n = 5300 g/mol, M_w/M_n = 1.05) by acetylation and reaction with potassium hydroxide, 18‐crown‐6 and propargyl bromide in toluene. Polymerization of styrene with 6‐tert‐butyldimethylsiloxyhexyllithium yielded polystyrene (M_n = 5200 g/mol, M_w/M_n = 1.09) with a protected hydroxyl chain end. Deprotection, followed by conversions to tosyl and azide functionalities, provided the side chain material. Coupling with CuBr and N,N,N′,N″,N″‐pentamethyldiethylenetriamine proceeded in up to 94% yield. Repetition of the grafting cycles led to well‐defined (M_w/M_n ≤ 1.1) polymers of generations G1 and G2 in 84% and 60% yield, respectively, with M_n and branching functionalities reaching 2.8 × 10⁶ g/mol and 460, respectively, for the G2 polymer. Coupling longer (M_n = 45,000 g/mol) side chains with acetylene‐functionalized substrates was also examined. For a linear substrate, a G0 polymer with M_n = 4.6 × 10⁵ g/mol and M_w/M_n = 1.10 was obtained in 87% yield; coupling with the G0 (M_n = 52,000 g/mol) substrate produced a G1 polymer (M_n = 1.4×10⁶ g/mol, M_w/M_n = 1.38) in 28% yield. The complementary approach using azide‐functionalized substrates and acetylene‐terminated side chains was also investigated, but proceeded in lower yield. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1730–1740     

Quantification of end groups in polystyrenes by pyrolysis–gas chromatography

The determination of end groups in polystyrenes (PSts) polymerized anionically with n-butyllithium as the initiator was carried out by pyrolysis-gas chromatography (Py-GC). The relative proportions of the end groups decrease with increasing molecular weight (MW). Consequently, the peaks which reflect the structure of the end groups can be distinguished by comparing pyrograms of samples with different MW. By comparing the intensities of these peaks relative to total intensities of all the peaks in the pyrogram, the numberaverage molecular weight (M_n) of the polymer can be estimated. The observed M_n values of PSts estimated by this method are compared with those determined by size exclusion chromatography (SEC). By this method it was possible to make direct determination of M_n values of PSts with MWs between 1000 and ca. 1 million. Furthermore, the calibration curve produced by the relative intensity of one of the most characteristic peaks (2-phenyl-1-heptene; C₄H₉? CH₂C (Ph) = CH₂) for the end group to total intensity of all the peaks in the pyrogram, gave rapid and highly reproducible M_n values. © 1994 John Wiley & Sons, Inc.     

SIZE EXCLUSION CHROMATOGRAPHIC COLUMN PACKED WITH REGENERATED CELLULOSE GELS*

Microporous regenerated cellulose gel particles were prepared by mixing cellulose cuoxam with silk fibroin aspore former, and the mean pore size and pore volume of the pallicles were 525 nm and 7.27 mL g~(-1), respectively. Apreparative size-exclusion chromatography (SEC) column (550 mm×20 mm) packed with the cellulose gel particles wasused for the fractionation of two polysaccharides Dextran 07 (M_w = 7.14×10~4, d= 1.7) and Dextran 50(M_w = 50.5×10~4,d = 3.8) in water phase. The fractionation range of the stationary phase covered M_w from 3×10~3 to 1.1×10~6. The dailythroughput was 2.9 g for Dextran 07 (D07) and 4.3 g for Dextran 50 (D50) with a flow-rate of 1.5 mL min~(-1). The fractionsobtained by using the SEC were analyzed by an analytical SEC combined with laser light scattering (LLS), and thepolydispersity indices of fractions for Dextran 07 and Dextran 50 were determined to be 1.34-1.57 and 1.53-3.36,respectively. The preparative SEC is a simple, rapid, and suitable means not only for the fractionation of polysaccharides inwater but also for other polymers in organic solvents.     

Polymer grafting onto polyurethane backbone via Diels–Alder reaction

The aliphatic polyurethane with pendant anthracene moieties (PU‐anthracene) was prepared from polycondensation of anthracen‐9‐yl methyl 3‐hydroxy‐2‐(hydroxymethyl)‐2‐methylpropanoate (anthracene diol), 1 with hexamethylenediisocyanate in the presence of dibutyltindilaurate in CH₂Cl₂ at room temperature for 10 days. Thereafter, the PU‐anthracene (M_n,GPC = 12,900 g/mol, M_w/M_n = 1.87, relative to PS standards) was clicked with a linear α‐furan protected‐maleimide terminated‐poly(methyl methacrylate) (PMMA‐MI) (M_n,GPC = 2500 g/mol, M_w/M_n = 1.33), or ‐poly(ethylene glycol) (PEG‐MI) (M_n,GPC = 550 g/mol, M_w/M_n = 1.09), to result in well‐defined PU‐graft copolymers, PU‐g‐PMMA (M_n,GPC = 23800 g/mol, M_w/M_n = 1.65, relative to PS standards) or PU‐g‐PEG (M_n,GPC = 11,600 g/mol, M_w/M_n = 1.45, relative to PS standards) using Diels–Alder reaction in dioxane/toluene at 105 °C. The Diels–Alder grafting efficiencies were found to be over 93–99% using UV spectroscopy. Moreover, the structural analyses and the thermal transitions of all copolymers were determined via ¹H NMR and DSC, respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 521–527     

End-functional poly(methyl methacrylate)s via group transfer polymerization

Hydroxyl-, amine-, and lactone-end-functional poly(methyl methacrylate)s (PMMA) were prepared with controlled molecular weights and M_w/M_n = 1.06–1.19 via group transfer polymerization. This was achieved by the electrophilic termination of silyl ketene acetal ended PMMAs with benzaldehyde, N-trimethylsilyl benzaldimine, and 5,6-dihydro-2H-pyran-2-one, respectively. The number-average degree of functionalization, as determined by NMR/SEC, was in the range of 0.70–0.85. A Lewis acid was used for terminating silyl ketene acetal ended PMMA with N-trimethylsilyl benzaldimine, whereas tetra-n-butyl ammonium bibenzoate was used in the case of benzaldehyde and 5,6-dihydro-2H-pyran-2-one. MALDI-TOF MS analysis of the end-functional polymers indicated the competing formation of cyclic end groups due to a back-biting reaction along with end-functional PMMAs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2514–2531, 2007     

Synthesis of refractive star‐shaped polysulfide by anionic polymerization of phenoxy propylene sulfide using an initiating system consisting of trifunctional thiol derived from five‐membered cyclic dithiocarbonate and amine

Star‐shaped poly(phenoxy propylene sulfide) [poly (PPS)] were synthesized by anionic polymerization using a trifunctional initiator ( I ₁) derived from a trifunctional five‐membered cyclic dithiocarbonate and benzyl amine. Conditions for the anionic polymerization of PPS were optimized to obtain polymers with desired M_ns and narrow M_w/M_ns. The best catalyst and solvent were DBU and DMF, respectively. The star‐shaped structure of the resulting star poly(PPS) was supported by SEC analysis. The refractive indexes (n_D) of the star poly (PPS) were relatively high (>1.64). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 525–531, 2010     

Syntheses of 12‐arm star polymers and star diblock copolymers by nitroxide‐mediated radical polymerization using dendritic dodecafunctional macroinitiators

Dendritic multifunctional macroinitiators having 12 TEMPO‐based alkoxyamines were prepared by the reaction of a benzyl alcohol having 4 TEMPO‐based alkoxyamines with 1,3,5‐tris[(4‐chlorocarbonyl)phenyl]benzene and 1,3,5‐tris(4‐isocyanatophenyl)benzene. Using the dodecafunctional macroinitiators, TEMPO‐mediated radical polymerizations of styrene (St) were carried out at 120 °C, and 12‐arm star polymers ( star‐12 ) with narrow polydispersities of M_w/M_n = 1.06–1.26 were obtained. To evaluate the livingness for the TEMPO‐mediated radical polymerizations of St, hydrolysis of the ester bonds of the 12‐arm star polymers and subsequent SEC measurements were carried out. Furthermore, using star‐12 as the macroinitiator, TEMPO‐mediated radical polymerization of 4‐vinylpyridine (4‐VP) was carried out, and well‐defined poly(St)‐b‐poly(4‐VP) 12‐arm star diblock copolymers with M_w/M_n = 1.18–1.19 were obtained. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3689–3700, 2005     

Synthesis of well‐defined AB20‐type star polymers with cyclodextrin‐core by combination of NMP and ATRP

The synthesis of an AB₂₀‐type heteroarm star polymer consisting of a polystyrene arm and 20‐arms of poly(methyl methacrylate) or poly(tert‐butyl acrylate) was carried out using the combination of nitroxide‐mediated polymerization (NMP) and atom transfer radical polymerization (ATRP). The NMP of styrene was carried out using mono‐6‐[4‐(1′‐(2″,2″,6″,6″‐tetramethyl‐1″‐piperidinyloxy)‐ethyl)benzamido]‐β‐cyclodextrin peracetate ( 1 ) to afford end‐functionalized polystyrene with an acetylated β‐cyclodextrin (β‐CyD) unit (prepolymer 2 ) with a number‐average molecular weight (M_n) of 11700 and a polydispersity (M_w/M_n) of 1.17. After deacetylation of prepolymer 2 , the resulting polymer was reacted with 2‐bromoisobutyric anhydride to give end‐functionalized polystyrene with 20(2‐bromoisobutyrol)s β‐CyD, macroinitiator 4 . The copper (I)‐mediated ATRP of methyl methacrylate (MMA) and tert‐butyl acrylate (tBA) was carried out using macroinitiator 4 . The resulting polymers were isolated by SEC fractionation to produce AB₂₀‐type star polymers with a β‐CyD‐core, 5 . The well‐defined structure of 5 with weight‐average molecular weight (M_w)s of 13,500–65,300 and M_w/M_n's of 1.26–1.28 was demonstrated by SEC and light scattering measurements. The arm polymers were separated from 5 by destruction with 28 wt % sodium methoxide in order to analyze the details of their characteristic structure. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4271–4279, 2005     

Controlling grafting density and side chain length in poly(n‐butyl acrylate) by ATRP copolymerization of macromonomers

Atom transfer radical polymerization (ATRP) was used for the preparation and subsequent copolymerization of two acryloyl‐terminated poly(n‐butyl acrylate) macromonomers with different degrees of polymerization (DP_nBA = 25 and 42). Homopolymerization of the higher molecular weight macromonomer ( MM1 ; PnBA₄₂‐A, M_n = 5600, DP_MM = 42, M_w/M_n = 1.18) resulted in preparation of a densely grafted polymer with a narrow molecular weight distribution (M_w/M_n = 1.14), but with the limited degree of polymerization DP = 12. The ultimate degree of homopolymerization for the lower molecular weight macromonomer ( MM2 ; PnBA₂₅‐A, M_n = 3400, DP_MM = 25, M_w/M_n = 1.20) was higher, and DP increased from 12 to 22. The limited DP could be because of progressively increasing steric congestion for macromonomers in approaching the growing chain ends of densely grafted polymers. When MMs were copolymerized with nBA, the reactivity of MM was nearly the same as that of nBA monomer irrespective of the differences in the degree of polymerization of the MMs and the initial molar ratio of nBA to MM. Well‐defined graft polymers with different lengths of backbone and side chains, and different graft density were successfully prepared by “grafting through” ATRP. Tadpole‐shaped and dumbbell‐shaped graft polymers were also synthesized by ATRP. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5454–5467, 2006     

Controlled/living polymerization of methacrylamide in aqueous media via the RAFT process

The polymerization of methacrylamide (MAM) was performed in aqueous media via reversible addition fragmentation chain transfer (RAFT) polymerization with the dithiobenzoate chain‐transfer agent (CTA) 4‐cyanopentanoic acid dithiobenzoate (CTP) and 4,4′‐azobis(4‐cyanopentanoic acid) (V‐501) as initiator. The polymerization in unbuffered water at 70 °C with a CTP/V‐501 ratio of 1.5 was controlled for the first 3 h, after which the molecular weight distribution broadened and a substantial deviation of the experimental from the theoretical molecular weight occurred, presumably because of a loss of CTA functionality at longer polymerization times. Conducting the polymerization in an acidic buffer afforded a well‐defined homopolymer (M_n = 23,800 g/mol, M_w/M_n = 1.08). To demonstrate the controlled/living nature of the system, a block copolymer of MAM and acrylamide was successfully prepared (M_n = 33,800 g/mol, M_w/M_n = 1.25) from a polymethacrylamide macro‐CTA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3141–3152, 2005     

Synthesis of poly(p‐phenylene) macromonomers and multiblock copolymers

Rigid‐rod poly(4′‐methyl‐2,5‐benzophenone) macromonomers were synthesized by Ni(0) catalytic coupling of 2,5‐dichloro‐4′‐methylbenzophenone and end‐capping agent 4‐chloro‐4′‐fluorobenzophenone. The macromonomers produced were labile to nucleophilic aromatic substitution. The molecular weight of poly(4′‐methyl‐2,5‐benzophenone) was controlled by varying the amount of the end‐capping agent in the reaction mixture. Glass‐transition temperatures of the macromonomers increased with increasing molecular weight and ranged from 117 to 213 °C. Substitution of the macromonomer end groups was determined to be nearly quantitative by ¹H NMR and gel permeation chromatography. The polymerization of a poly(4′‐methyl‐2,5‐benzophenone) macromonomer [number‐average molecular weight (M_n) = 1.90 × 10³ g/mol; polydispersity (M_w)/M_n = 2.04] with hydroxy end‐capped bisphenol A polyaryletherketone (M_n = 4.50 × 10³ g/mol; M_w/M_n = 1.92) afforded an alternating multiblock copolymer (M_n = 1.95 × 10⁴ g/mol; M_w/M_n = 6.02) that formed flexible, transparent films that could be creased without cracking. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3505–3512, 2001     

Synthesis and self‐assembly morphologies of amphiphilic multiblock copolymers [poly(ethylene oxide)‐b‐polystyrene]n via trithiocarbonate‐embedded PEO macro‐RAFT agent

An amphiphilic multiblock copolymer [poly(ethylene oxide)‐b‐polystyrene]_n [(PEO‐b‐PS)_n] is synthesized by using trithiocarbonate‐embedded PEO as macro‐RAFT agent. PEO with four inserted trithiocarbonate (M_n = 9200 and M_w/M_n = 1.62) groups is prepared first by condensation of α, ω‐dihydroxyl poly(ethylene oxide) with S, S′‐Bis(α, α′‐dimethyl‐α″‐acetic acid)‐trithiocarbonate (BDATC) in the presence of pyridine, then a series of goal copolymers with different St units (varied from 25 to 218 per segment) are obtained by reversible addition‐fragmentation chain transfer (RAFT) polymerization. The synthesis process is monitored by size exclusion chromatography (SEC), ¹H NMR and FT‐IR. The self‐assembled morphologies of the copolymers are strongly dependent of the length of PS block chains when the chain length of PEO is fixed, some new morphologies as large leaf‐like aggregates (LLAs), large octopus‐like aggregates (LOAs), and coarse‐grain like micelles (CGMs) are observed besides some familiar aggregates as large compound vesicles (LCVs), lamellae and rods, and the effect of water content on the morphologies is also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6071–6082, 2006     

Glycoconjugated polymer: Synthesis and characterization of poly(vinyl saccharide)‐block‐polystyrene‐block‐poly(vinyl saccharide) as an amphiphilic ABA triblock copolymer

Styrene (St) was polymerized with α,α′‐bis(2′,2′,6′,6′‐tetramethyl‐1′‐piperidinyloxy)‐1,4‐diethylbenzene ( 1 ) as an initiator (bulk, [St]/] 1 ] = 570) at 120 °C for 5.0 h to obtain polystyrene having 2,2,6,6‐tetramethylpiperidiloxy moieties on both sides of the chain ends ( 2 ) with a number‐average molecular weight (M_n) of 14,300 and a polydispersity index [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] of 1.14. 4‐Vinylbenzyl glucoside peracetate ( 3a ) was polymerized with 2 as a macromolecular initiator and dicumyl peroxide (DCP) as an accelerator in chlorobenzene at 120 °C. The polymerization with the [ 3a ]/[ 2 ]/[DCP] ratio of 30/1/1.2 for 5 h afforded a product in a yield of 73%; it was followed by purification with preparative size exclusion chromatography to provide the ABA triblock copolymer containing the pendant acetyl glucose on both sides of the chain ends ( 4a ; M_n = 21,000, M_w/M_n = 1.16). Similarly, the polymerization of 4‐vinylbenzyl maltohexaoside peracetate produced the ABA triblock copolymer containing the pendant acetyl maltohexaose on both side of the chain end ( 4b ; M_n = 31,800, M_w/M_n = 1.11). Polymers 4a and 4b were modified by deacetylation into amphiphilic ABA triblock copolymers containing the pendant glucose and maltohexaose as hydrophilic segment, 5a and 5b , respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3978–3985, 2006     

A novel chromatographic method for determining the polydispersity index for polymers with a specified number of functional groups

A novel chromatographic method is proposed to determine the polydispersity index, without reference to standards, for polymers that contain a specified number of functional groups. Refractive index and ultraviolet-visible (or infrared) detectors are employed for detecting the weight and number fractions, respectively, of the sample eluted in size exclusion chromatography (SEC). Pyrene-labeled polystyrenes were used to demonstrate the validity of this method. The polydispersity index, M_w/M_n, measured by the new method underestimates the true value by 3%, whereas the application of the calibration curve overestimates the polydispersity index of the same sample by 6%. An illustrative SEC model including the effect of diffusion was used to explain the production of errors in different directions by the two methods.     

Melt crystallization and morphology of poly(ε‐caprolactone)‐poly(ethylene glycol) diblock copolymers with different compositions and molecular weights

Ring opening polymerization of ε‐caprolactone was realized in the presence of monomethoxy poly(ethylene glycol) with M_n = 1000 and 2000, using Zn(La)₂ as catalyst. The resulting PCL‐PEG diblock copolymers with CL/EO repeat unit molar ratios from 0.2 to 3.0 were characterized by using DSC, WAXD, SEC, and ¹H NMR. The crystal phase of PCL blocks exist in all polymers, and the crystallization ability of PCL blocks increases with CL/EO ratio. PEG blocks are able to crystallize for copolymers with CL/EO below 1.0 only. Melt crystallization results were analyzed with Avrami equation. The Averami exponent n is around 3.0 in most cases, in agreement with heterogeneous nucleation with three dimensional growth. The morphology of the crystals was observed by using POM. Rod‐like crystals were found to grow in 1, 3 or 2, 4 quadrants for samples with low molecular weights. In the case of a copolymer with M_n,PEG = 2000 and M_n,PCL = 800, PEG blocks could crystallize and grow on PCL crystals after PCL finished to form rod‐like crystals, leading to formation of poorly or well structured spherulites. The spherulite growth rate (G) was determined at different crystallization temperatures (T_c) ranging from 9 to 49 °C. All the copolymers present a steady G decrease with increasing crystallization temperature due to lower undercooling. On the other hand, increase of CL/EO ratio leads to increase of G in the same T_c range. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 286–293, 2010     

Synthesis of well‐defined cyclodextrin‐core star polymers

The synthesis of 21‐arm methyl methacrylate (MMA) and styrene star polymers is reported. The copper (I)‐mediated living radical polymerization of MMA was carried out with a cyclodextrin‐core‐based initiator with 21 independent discrete initiation sites: heptakis[2,3,6‐tri‐O‐(2‐bromo‐2‐methylpropionyl]‐β‐cyclodextrin. Living polymerization occurred, providing well‐defined 21‐arm star polymers with predicted molecular weights calculated from the initiator concentration and the consumed monomer as well as low polydispersities [e.g., poly(methyl methacrylate) (PMMA), number‐average molecular weight (M_n) = 55,700, polydispersity index (PDI) = 1.07; M_n = 118,000, PDI = 1.06; polystyrene, M_n = 37,100, PDI = 1.15]. Functional methacrylate monomers containing poly(ethylene glycol), a glucose residue, and a tert‐amine group in the side chain were also polymerized in a similar fashion, leading to hydrophilic star polymers, again with good control over the molecular weight and polydispersity (M_n = 15,000, PDI = 1.03; M_n = 36,500, PDI = 1.14; and M_n = 139,000, PDI = 1.09, respectively). When styrene was used as the monomer, it was difficult to obtain well‐defined polystyrene stars at high molecular weights. This was due to the increased occurrence of side reactions such as star–star coupling and thermal (spontaneous) polymerization; however, low‐polydispersity polymers were achieved at relatively low conversions. Furthermore, a star block copolymer consisting of PMMA and poly(butyl methacrylate) was successfully synthesized with a star PMMA as a macroinitiator (M_n = 104,000, PDI = 1.05). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2206–2214, 2001