A Synthetic Approach to Star‐Like Polymers of Styrene and Butyl Acrylate by Linking Reactions using Functionalized Methacrylates

Summary: Coupling reactions between terminal functionalized polymer chains were chosen for the synthesis of star‐like polymers consisting of polystyrene and polystyrene‐block‐poly[styrene‐co‐(butyl acrylate)] arms. For the preparation of terminal functionalized polymer chains a side reaction of the 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) mediated free radical polymerization of methacrylates could be used successfully to convert TEMPO terminated polymers into end functionalized polymers. The number of functionalized monomer units attached to the polymer chain is directly related to the TEMPO concentration during this reaction. Different polystyrenes and polystyrene‐block‐poly[styrene‐co‐(butyl acrylate)] block copolymers were functionalized with a variable number of epoxide and alcohol groups at the chain end. For the determination of the optimal reaction parameters for the coupling reactions between these polymer chains, epoxy functionalized polystyrenes were converted with hydroxy functionalized polystyrenes under basic and acidic conditions. By activation with sodium hydride or boron trifluoride star‐like polymers were synthesized under mild conditions. The transfer of the reaction conditions to coupling reactions between end functionalized polystyrene‐block‐poly[styrene‐co‐(butyl acrylate)] copolymers showed that star‐like polymers with more than 12 arms were formed using boron trifluoride as activating agent.

     

First nitroxide-mediated free radical dispersion polymerizations of styrene in supercritical carbon dioxide

Controlled/living character has been demonstrated for the first time in nitroxide-mediated free radical dispersion polymerizations in supercritical carbon dioxide. Styrene was polymerized in the presence of N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide (SG1) at 110 °C. Stabilization was achieved using the inistab concept (initiator+stabilizer), employing a poly(dimethylsiloxane) (PDMS) based azo initiator as well as a polymeric alkoxyamine macroinitiator with the expected structure SG1-polystyrene-PDMS-polystyrene-SG1. In the presence of sufficient amounts of the inistab, the polymerizations proceeded to high conversion to yield the polymeric product as a powder. Control was indicated by the number-average molecular weights increasing linearly with conversion in reasonable agreement with the theoretical values. Although the molecular weight distributions were broad in many cases, chain extensions in bulk and solution using styrene indicated high degrees of ‘living’ character.     

Effects of the oil-water interface on network formation in nanogel synthesis using nitroxide-mediated radical copolymerization of styrene/divinylbenzene in miniemulsion

Nitroxide-mediated radical copolymerization of styrene (99 mol%)/divinylbenzene (1 mol%) employing the nitroxide 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) in aqueous miniemulsion using sodium dodecylbenzenesulfonate as surfactant has been carried out at 125 °C. At a given styrene conversion, the degree of crosslinking increases with decreasing polystyrene-TEMPO macroinitiator concentration in excess of what is predicted based on the increase in primary chain length assuming an ideal controlled/living process. This discrepancy is mainly a result of the oil-water interface effect on the deactivation reaction between propagating radicals and TEMPO. This interface effect causes a marked increase in primary chain length, and therefore an accompanying increase in the number of crosslinks per primary chain. Polymerizations in the presence of free TEMPO minimizes the interface effect, and one then obtains molecular weight distributions and well-defined networks conducive with a controlled/living process.     

Synthesis of poly(styrene-co-isopropenyl acetate) -g-polyisobutylene graft copolymers via combination of radical polymerization with cationic polymerization

Random copolymers of poly(styrene-co-isopropenyl acetate) (SIPA) with an average number of 9 initiating sites per chain were synthesized by free radical copolymerization of styrene with a small amount of isopropenyl acetate using 2,2′-azo-bis-(isobutyronitrile) as an initiator at 70 °C. SIPA copolymer could be further used as macroinitiator for the grafting cationic polymerization of isobutylene (IB) from SIPA chain in CH₂Cl₂ at ?40 °C to produce graft copolymers of SIPA-g-PIB. The effect of SIPA concentration ([SIPA]), TiCl₄ concentration ([TiCl₄]) and IB concentration ([IB]) on initiation efficiency of macroinitiator, grafting efficiency of initiating sites, average length of PIB branches of the resulting graft copolymers were investigated. It can be found that almost all of the initiating sites of IPAc units on SIPA chains were active for the cationic polymerization of IB and both initiation efficiency and grafting efficiency were close to 100% at sufficient molar ratio of TiCl₄/IPAc. This synthetic route presents quantitative grafting efficiency and possibility to control length of PIB branches. The graft copolymers of SIPA-g-PIB with average 9-branched PIB chains having terminal functional tert-chlorine groups could be successfully obtained. The average molecular weight of PIB branches in SIPA-g-PIB graft copolymers could be mediated from 3900 to 47,300 g mol^?1 by changing the ratios of macroinitiator to monomer and concentration of TiCl₄.     

Atom transfer radical polymerization of styrene initiated by bromoacetylated syndiotactic polystyrene macroinitiator

Atom transfer radical polymerization of styrene was conducted with bromoacetylated syndiotactic polystyrene as macroinitiator and copper bromide combined with N,N,N′,N′,N′‐pentamethyldiethylenetriamine as catalyst. A two‐stage process has been developed to synthesize the macroinitiator. First, syndiotactic polystyrene (sPS) was functionalized in the side phenyl rings with acetyl groups using the Friedel–Crafts reaction; second, the acetyl groups were converted to bromoacetyl groups by an acid‐catalyzed halogenation reaction. The initiator was found to be active in the polymerization of styrene, leading to the production of graft chains with well‐defined structure. The molecular weight and molecular weight distribution of the graft chains were determined using gel permeation chromatography after cleaving from the sPS backbone using peroxide acid oxidation followed by hydrazine‐catalyzed hydrolysis. The results indicated that the polymerization process was characteristic of a ‘living’ nature. Copyright © 2007 Society of Chemical Industry     

Synthesis and characterization of novel copolymer containing pyridylazo-2-naphthoxyl group via reversible addition–fragmentation chain transfer (RAFT) polymerization

A novel monomer containing pyridylazo-2-naphthoxyl group, 1-(1-(4-vinylbenzyloxy)naphthalen-2-yl)-2-(pyridin-2-yl)diazene (VBNPA), was successfully synthesized and copolymerized with styrene (St) in N,N-dimethyl formamide (DMF) via reversible addition–fragmentation chain transfer (RAFT) polymerization using 2-cyanoprop-2-yl-1-dithionaphthalate (CPDN) as RAFT agent. The polymerization behavior exhibited “living”/controlled characters. The obtained copolymer, poly(St-co-VBNPA), with pre-determinable molecular weight and narrow molecular weight distribution can be used as a carrier in metal ion detection and analysis via pre-concentration technique. The copolymer–metal ion (copper (Cu) and europium (Eu)) complexes were prepared and characterized.     

Synthesis,assembled structure,and chiroptical properties of amino acid-based amphiphilic block copolymers containing carbazole moiety

Novel amphiphilic block copolymers composed of amino acid-based hydrophilic segment and carbazole-containing hydrophobic segment were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. N-Ethyl-3-vinylcarbazole (E3VC) was employed as a carbazole-containing monomer, which can be regarded as a styrene derivative. N-Acryloyl-l-proline methyl ester (A-Pro-OMe) was selected as an amino acid-containing monomer, which is a disubstituted acrylamide with proline moiety in the side chain. Chain extension from poly(A-Pro-OMe) to E3VC could be well controlled under suitable conditions and provided block copolymers with as-designed chain structures and low polydispersities. The block copolymers were also synthesized by RAFT polymerization of A-Pro-OMe using poly(E3VC) as a macro-chain transfer agent (macro-CTA). In both cases, the dithiobenzoate- and dithiocarbamate-terminated CTAs were compared, in terms of the polymerization rate, polydispersity of the product, controlled character, and block efficiency. We investigated the relationship between the ordered structures, optoelectronic and chiroptical properties of the resulting block copolymers, which were evaluated by dynamic light scattering (DLS), UV–vis, fluorescent, and CD measurements.     

A Convenient Method for Preparation of Amphiphilic Monomethoxypoly (Ethylene Glycol)–Polystyrene Diblock Copolymer by NMRP Technique

Amphiphilic block copolymers are macromolecular compounds of great importance from both fundamental scientific and many technological point of views for a large variety of applications. Amphiphilic diblock copolymer containing segments of monomethoxypoly(ethylene glycol) and polystyrene (MPEG-b-PS) was synthesised by a convenient method for preparation of macroinitiator MPEG-TEMPO for ‘living’ free radical polymerization (NMRP technique). Initially, derivative of MPEG with chlorine function has been prepared in an one-step reaction with thionyl chloride. 1-hydroxy-2,2,6,6-tetramethyl-piperidine (TEMPO-OH) obtained by reduction of 2,2,6,6-tetramethyl-piperidinyl-1-oxy (TEMPO) with sodium ascorbate was coupled with chlorinated MPEG to yield the macroinitiator MPEG terminated with a TEMPO unit (MPEG-TEMPO), which was further used to prepare the diblock copolymer MPEG-b-PS of styrene. The product was purified and identified by ¹H NMR, GPC and, FT-IR.     

Poly(styrene‐co‐N‐butylmaleimide) macroinitiators by controlled autopolymerization and related block copolymers

Autopolymerization of styrene‐N‐butylmaleimide mixtures at 125 or 140°C in the presence of a stable nitroxyl radical [2,2,6,6‐tetramethylpiperidin‐1‐yloxyl (TEMPO)] was found to proceed in a pseudoliving manner. Unimolecular initiators, which were originated by trapping self‐generated radical species with TEMPO, took part in the process. Under the studied experimental conditions, the TEMPO‐controlled autopolymerization with a varying comonomer ratio provided virtually alternating copolymers of narrow molecular weight distributions. The molecular weights of the copolymers increased with conversions. The obtained styrene‐N‐butylmaleimide copolymers containing TEMPO end groups were used to initiate the polymerization of styrene. The polymerization yielded poly(styrene‐co‐N‐butylmaleimide)‐polystyrene block copolymers with various polystyrene chain lengths and narrow molecular weight distributions. The compositions, molecular weights, and molecular weight distributions of the synthesized block copolymers and the initial poly(styrene‐co‐N‐butylmaleimide) precursors were evaluated using nitrogen analysis, gel permeation chromatography, and ¹H‐ and ¹³C‐NMR spectroscopy. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2378–2385, 1999     

Fluorescence and molecular dynamics to study the intramolecular energy transfer in N-vinyl carbazole/styrene copolymers of different molar compositions

Emission spectra, fluorescence polarization, quenching and lifetime measurements were performed on dilute solutions of poly(N-vinyl carbazole) and N-vinyl carbazole/styrene copolymers to study the intramolecular energy transfer between carbazole groups along the polymer chain. Fluorescence anisotropy values for the samples dissolved in a PMMA solid matrix and quenching measurements in toluene by CCl₄ were used to estimate the efficiency of energy transfer as a function of the monomer molar composition. Analysis of the experiments suggests that the copolymer with the highest carbazole content, which corresponds to the highest amount of carbazole excimers, does not show the highest energy transfer efficiency. Intramolecular excimers which strongly increase with the carbazole content and that are mainly due to carbazole-carbazole monomer sequence interactions undoubtedly act as energy transfer traps. Molecular dynamics simulations on isotactic and syndiotactic copolymer fragments were used for obtaining different parameters related to the energy transfer process as a function of the number of styrene monomer units between vinyl carbazole ones.     

TEMPO‐controlled radical suspension polymerization of poly(styrene)‐block‐poly(styrene‐co‐acrylonitrile) and poly(styrene)‐block‐poly(styrene‐co‐butyl methacrylate)

Suspension polymerization expands the study of controlled radical polymerization to high conversions and is known as a method to synthesize polymers with high molecular weights. The radical block copolymerizations of styrene (S) and acrylonitrile (AN) or butyl methacrylate (BUMA) controlled by 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) was performed in an oil/water pressure reactor system at a temperature of 125°C. TEMPO‐terminated styrene homopolymer was employed as macroinitiator. The systems were examined by varying the composition of the monomer mixture at a constant reaction time, as well as by varying the reaction time for a characteristic monomer composition to get all of the possible conversion range. The solubility effects of acrylonitrile in the suspension medium were considered. Furthermore, the yield of the reaction was improved through initiator addition by taking control of the reaction. The polymerizations could proceed under control up to a conversion of 80–90%. By using the copolymerization equations, the solubility of pure acrylonitrile in the suspension medium could be calculated and was found to be 8 wt.‐%.     

Synthesis and characterization of well-defined hydrophilic block copolymer brushes by aqueous ATRP

Homopolymer brushes of poly(N,N-dimethylacrylamide) (PDMA), poly(methoxyethylacrylamide) (PMEA) and poly(N-isopropylacrylamide)(PNIPAM) grown on atom transfer radical polymerization (ATRP) initiator functionalized latex particles were used as macroinitiators for the synthesis of PDMA-b-PNIPAM/PMEA, PMEA-b-PDMA/PNIPAM and PNIPAM-b-PDMA block copolymer brushes by surface initiated aqueous ATRP. The grafted homopolymer and block copolymer brushes were analyzed for molecular weight, molecular weight distribution, chain grafting density, composition and hydrodynamic thickness (HT) using gel permeation chromatography-multi-angle laser light scattering, ¹H NMR, particle size analysis and atomic force microscopy (AFM) techniques. The measured graft molecular weight increased following the second ATRP reaction in all cases, indicating the second block had been added. Chain growth depended on the nature of the monomer used for block copolymerization and its concentration. Unimodal distribution of polymer chains in GPC with non-overlap of molar mass-elution volume curves implied an efficient block copolymerization. This was supported by the increase in HT measured by particle size analysis, equilibrium thickness observed by AFM and the composition of the block copolymer layer by ¹H NMR analysis, both in situ and on cleaved chains in solution. ¹H NMR analysis of the grafted latex and cleaved polymers from the surface demonstrated that accurate determination of the copolymer composition by this method is possible without detaching polymer chains from surface. Block copolymer brushes obey the same power law dependence of HT on molecular weight as homopolymer brushes in good solvent conditions. The NIPAM-containing block copolymer brushes were sensitive to changes in the environment as shown by a decrease in HT with increase in the temperature of the medium.     

Synthesis of polystyrene- block -polycarbonate- block - polystyrene and polycarbonate- graft -polystyrene using tandem condensation polymerization and atom transfer radical polymerization

Summary Polystyrene-block-polycarbonate-block-polystyrene was synthesized by atom transfer radical polymerization of styrene using polycarbonate having two 2-bromoisobutyryloxy end groups as the macroinitiator, which was prepared by condensation polymerization of bisphenol A with triphosgene in the presence of chain-stopper, 2-(4-hydroxyphenyl)-2-(4-(2-bromoisobutyryloxy)phenyl)propane. While polycarbonate-graft-polystyrene was synthesized by atom transfer radical polymerization of styrene using polycarbonate having 2-bromoisobutyryloxy side groups as the macroinitiator, which was prepared by condensation of bisphenol and l,l-bis(4-hydroxyphenyl)- 1 -(4-(2-bromoisobutyryloxy)phenyl)ethane with triphosgene. The molecular weights of polystyrene block or graft chains increased linearly with monomer conversion, and their polydispersities were low throughout the blocking or grafting polymerization process. Received: 25 June 2002/Revised version: 23 October 2002/ Accepted: 25 November 2002 Correspondence to Zhifeng Fu     

Influence of DMF on the polymerization of tert‐butyl acrylate initiated by 4‐oxo‐TEMPO‐capped polystyrene macroinitiator

BACKGROUND: In a number of studies it has been shown that 2,2,6,6‐tetramethylpiperidinooxy (TEMPO)‐mediated polymerization of acrylates is not facile. Therefore, the object of the study reported here was to prepare poly[styrene‐block‐(tert‐butyl acrylate)] (PS‐b‐PtBA) block copolymers using 4‐oxo‐TEMPO‐capped polystyrene macroinitiator as an initiator, in the presence of small amounts of N,N‐dimethylformamide (DMF). The kinetic analysis and the effect of DMF on the reaction mechanism are also discussed. RESULTS: PS‐b‐PtBA block copolymer was prepared through polymerization of tert‐butyl acrylate (tBA) initiated by 4‐oxo‐TEMPO‐capped polystyrene macroinitiator at 135 °C. The polymerization rate of tBA could be increased by adding a small amount of DMF, and the number average molecular weight of the PtBA block in PS‐b‐PtBA reached 10 000 g mol^?1 with narrow polydispersity. The activation rate constant k_act?tBA of alkoxyamine increased and the recombination rate constant k_rec?tBA decreased with increasing DMF concentration. CONCLUSION: DMF was shown to be a rate‐enhancing additive for the polymerization of tBA using a 4‐oxo‐TEMPO‐capped polystyrene macroinitiator. From the kinetic analysis, it was concluded that the improvement of polymerization with the addition of DMF was due to an increase in k_act?tBA and a decrease in k_rec?tBA. Copyright © 2008 Society of Chemical Industry     

Controllable synthesis of poly(N-vinylpyrrolidone) and its block copolymers by atom transfer radical polymerization

At room temperature atom transfer radical polymerization (ATRP) of N-vinylpyrrolidone (NVP) was carried out using 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclo-tetradecane (Me₆Cyclam) as ligand in 1,4-dioxane/isopropanol mixture. Methyl 2-chloropropionate (MCP) and copper(I) chloride were used as initiator and catalyst, respectively. The polymerization of NVP via ATRP could be mediated by the addition of CuCl₂. The resultant poly(N-vinylpyrrolidone) (PNVP) has high conversion of up to 65% in 3 h, a controlled molecular weight close to the theoretical values and narrow molecular weight distribution between 1.2 and 1.3. The living nature of the ATRP for NVP was confirmed by the experiments of PNVP chain extension. With PNVP-Cl as macroinitiator and N-methacryloyl-N′-(α-naphthyl)thiourea (MANTU) as a hydrophobic monomer, novel fluorescent amphiphilic copolymers poly(N-vinylpyrrolidone)-b-poly(N-methacryloyl-N′-(α-naphthyl)thiourea) (PNVP-b-PMANTU) were synthesized by ATRP. PNVP-b-PMANTU copolymers were characterized by ¹H NMR, GPC-MALLS and fluorescence measurements. The results revealed that PNVP-b-PMANTU presented a blocky architecture.     

Preparation of polystyrene-poly(ethylene glycol) diblock copolymer by ‘living’ free radical polymerisation

Amphiphilic diblock copolymer containing segments of polystyrene and monomethoxypoly(ethylene glycol) (PS-b-PEG) was synthesised by a novel method. Initially, the adduct (BZ-TEMPO) obtained by reacting benzoyl peroxide, styrene, and 2,2,6,6-tetramethyl-piperidinyl-1-oxy (TEMPO) was isolated, characterised and hydrolysed. Conditions for the synthesis and hydrolysis of BZ-TEMPO were investigated and the hydrolysed product (HO-TEMPO) containing a primary hydroxyl group has been isolated in improved yield. The hydroxyl group of HO-TEMPO was coupled with tosylated PEG to yield the macroinitiator PEG terminated with a TEMPO unit (MPEG-TEMPO), which was further used to prepare the diblock copolymer PS-b-PEG by ‘living’ free radical polymerisation of styrene. The product was purified and identified by ¹H n.m.r. and GPC. However, large amounts of homopolystyrene was also formed by simultaneous thermal initiation and polymerisation.     

Synthesis of amphiphilic star block copolymers of polystyrene with PEG core via ATRP—control of chain architecture and the formation of core-shell type globular structure

Amphiphilic star block copolymers made of poly(ethylene glycol) (PEG) core and branched PS arms having controlled chain lengths and numbers were synthesized by atom transfer radical copolymerization (ATRP) of styrene and chloromethylstyrene (CMS) in the presence of tetrafunctional PEG macroinitiator. The chain lengths and number of PS chains were controlled by adjusting the initial feed ratio of CMS to styrene and CMS to hydrophilic tetrafunctional macroinitiator, respectively, for a given polymerization time. The obtained polymers have well defined and controlled architectures. Use of excess amount of CMS and longer reaction time leads to the synthesis of dendrimer like amphiphilic block copolymer having four hyperbranched polymer arms, whose shape is closer to globular core-shell structure compared to general star shape polymers.     

Chain extension and block copolymer synthesis using silane radical atom abstraction coupled with nitroxide mediated polymerization

Silane radicals were used to abstract bromine termini from monobrominated polystyrene (PStBr) in the presence of excess monomer and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), generating polymer radicals that underwent chain extension. Typically, 70-85% of the PStBr precursors were activated by silane radical atom abstraction (SRAA) and were elongated by nitroxide mediated polymerization (NMP), shifting to higher number-average molecular weight (M_n) values as observed by gel permeation chromatography (GPC). Chain extension did not occur until the temperature was elevated to 130 °C, with no increase in M_n values observed when the reaction was held at 80 °C, which is the temperature of the SRAA phase. The NMP phase of the reaction showed a linear correlation between M_n values and monomer consumption, along with first order kinetics with respect to styrene. SRAA/NMP was then applied to the synthesis of polystyrene-b-poly(n-butyl acrylate) and polystyrene-b-poly(p-methylstyrene), with analysis by GPC indicating the formation of block copolymers with a similar amount of unreacted PStBr remaining. Quantitative activation and elongation of the polymer precursors were prevented due to the ability of both the t-butoxy radicals and tris(trimethylsilyl)silane radicals to add across monomeric double bonds, competing with atom abstraction. Reactions were thus performed in which the monomer was added only after the transition to the higher temperature, which resulted in improved activation of the PStBr.     

Nitroxide mediated living radical polymerization of styrene in miniemulsion—modelling persulfate-initiated systems

Recently we have constructed a mechanistic model describing the nitroxide mediated miniemulsion polymerization (NMMP) of styrene at 135°C, using alkoxyamine initiators to control polymer growth (Nitroxide-Mediated Polymerization of Styrene in Miniemulsion. Modeling Studies of Alkoxyamine-Initiated Systems, 2001b). The model has since been expanded to describe styrene NMMP at 135°C using TEMPO and the free radical initiator, potassium persulfate (KPS). The model includes mechanisms describing reactions in the aqueous and organic phases, particle nucleation, the entry and exit of oligomeric radicals, and the partitioning of nitroxide and styrene between the aqueous and organic phases. Predicted monomer conversions, number average molecular weights and polydispersities were in agreement with experimentally measured values. Model simulations revealed that for systems employing high ratios of TEMPO:KPS, the consumption of TEMPO by polymer radicals derived from KPS decomposition and styrene thermal initiation (using the accepted literature kinetic rates) is not sufficient to lower TEMPO concentrations to levels where polymer growth can occur. By accounting for the consumption of TEMPO by acid-catalyzed disproportionation, TEMPO concentrations are significantly reduced, allowing for accurate model predictions of monomer conversion, number average molecular weight and polydispersity at every experimental condition considered.     

Facile synthesis of multiblock copolymers composed of poly(tetramethylene oxide) and polystyrene using living free-radical polymerization macroinitiator

A facile synthetic strategy for well-defined multiblock copolymers utilizing ‘living’ free-radical polymerization macroinitiator has been presented. Polyurethane composed of alkoxyamine initiating units and poly(tetramethylene oxide) (PTMO) segments was prepared by polyaddition of tolylene 2,4-diisocyanate terminated PTMO with an alkoxyamine-based diol. Polymerization of styrene with the polyurethane macroinitiator was carried out under nitroxide-mediated free-radical polymerization (NMRP) condition. GPC, NMR, and IR data revealed that the polymerization was accurately controlled and well-defined polystyrene chains were inserted in the main chain of macroinitiator to give the poly(tetramethylene oxide)-b-polystyrene multiblock copolymers. The synthesized multiblock copolymers were characterized by tensile test, differential scanning calorimetry, and dynamic mechanical analysis. Mechanical properties of the multiblock copolymers can be tuned by the sufficient molecular weight control of PS chains. Soft segment of PTMO and hard segment of PS were apparently compatible due to the multiblock structure of low molecular weight segments and polar urethane groups.