Morphology of poly(p‐oxybenzoyl) crystal prepared by direct polycondensation of p‐hydroxybenzoic acid with p‐toluenesulfonyl chloride in pyridine

Poly(p‐oxybenzoyl) (POB) crystals were prepared with the reaction‐induced crystallization of oligomers during the direct polycondensation of p‐hydroxybenzoic acid (HBA) with p‐toluenesulfonyl chloride (TsCl) and N,N‐dimethylformamide in pyridine. Sheaflike lozenge‐shaped POB crystals were obtained, of which the longer diagonal was 7.0–8.0 μm. The influence of the polymerization condition on the morphology was examined to optimize the preparative condition for the crystals exhibiting the clearest habit, and the favorable condition was determined as the molar ratio of TsCl to HBA of 1.3 and polymerization concentration of 3.0%. The crystals possessed extremely high crystallinity and outstanding thermal stability. The formation mechanism of the crystal was proposed as follows. When the number‐average degree of polymerization of the oligomers exceeded a critical value of about 4, they were precipitated to form the hexagonal lamellae. The crystals were grown very quickly to lozenge‐shaped crystal through screw dislocation with the continuous precipitation of oligomers from the solution. Finally, the further polymerization occurred in the precipitated crystal with developing polymer‐chain packing. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3275–3282, 2003     

Dimer effect on fractional polycondensation of poly(p‐oxybenzoyl)

Selective preparation of poly(p‐oxybenzoyl) (POB) crystals was examined from the viewpoint of a dimer effect on fractional polycondensation. Four different copolymerization systems were chosen as the combinations of p‐acetoxybenzoic acid (p‐ABA), m‐acetoxybenzoic acid (m‐ABA), and their dimers. The crystals obtained from the copolymerization of the dimer of p‐ABA (p‐ABAD) and m‐ABA contained only 3.1 mol % of m‐oxybenzoyl moiety even at high content of m‐oxybenzoyl moiety in feed (χ_f) of 40 mol %. p‐Oxybenzoyl homo‐oligomers were more rapidly formed from p‐ABAD in the solution than from p‐ABA, and they were crystallized to form the crystals with segregating co‐oligomers. While co‐oligomers containing more m‐oxybenzoyl moiety were formed in the solution, afterward they were unable to be phase‐separated because of higher miscibility. The further polycondensation proceeded in the precipitated crystal, and finally the POB crystal was selectively formed. Lower polymerization temperature and concentration enhanced the fractionability, and the POB crystals containing less than 1 mol % m‐oxybenzoyl moiety were prepared at χ_f of 30 mol %, 270 °C, and a concentration of 0.5%. The dimer effect on the fractional polycondensation was clearly observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1598–1606, 2008     

Selective preparation of poly(p‐oxybenzoyl) by using fractional polycondensation

Selective preparation of poly(p‐oxybenzoyl) (POB) in the copolymerization system of p‐acetoxybenzoic acid (p‐ABA) and m‐acetoxybenzoic acid (m‐ABA) was examined by using reaction‐induced crystallization of oligomers. Polymer crystals mainly composed of p‐oxybenzoyl moiety were precipitated when the content of m‐ABA in the feed was 30 mol %. The formation of the polymer crystals was attributed to both the reactivity of monomer and the phase‐separation behavior of oligomer. Reactivity of p‐ABA was twice higher than that of m‐ABA, and thereby, the homo‐oligomers of p‐oxybenzoyl moiety were more rapidly formed in solution than do co‐oligomers at the early stage in polymerization. They were selectively precipitated by crystallization to form crystals because of low miscibility. Co‐oligomers containing m‐oxybenzoyl moiety were also formed in solution, but they were unable to be phase‐separated because of higher miscibility. Further polycondensation occurred between oligomers in the precipitated crystals, leading to the formation of POB. This polymerization proceeded with selecting certain monomers by crystallization and afforded a new methodology for fractional polycondensation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2732–2743, 2006     

Novel network morphology of poly(p‐oxybenzoyl)

Polymerization of 4‐acetoxybenzoic acid (ABA) with 3,5‐diacetoxybenzoic acid (DABA) was examined to control the morphology of poly(p‐oxybenzoyl) (POB). Polymerizations were carried out at a concentration of 1.0% in an aromatic solvent Therm S‐1000® (mixture of dibenzyltoluene) at 320 °C. Polymerization of ABA yielded the POB fibrillar crystals, but the polymerization with DABA at a concentration in the feed (χ_f) of 0.10–0.15 afforded novel network structures comprised of spheres connected by fibrillar crystals. The diameter of the spheres prepared at χ_f of 0.15, which were 0.7 and 5.0 μm, showed bimodality. The network distance, fibril length, and fibril width were 6.1, 2.6, and 0.1 μm, respectively. They possessed high crystallinity. The network structure was formed as follows. Co‐oligomers were first precipitated in the beginning of the polymerization by liquid–liquid phase separation to form the microdroplets. The fibrillar crystals were formed in the coalesced spheres by the crystallization of oligomers induced by the increase of molecular weight. The fibrillar crystals connecting the spheres gradually appeared owing to the shrinkage of the spheres. The fibrillar crystals grew from the surface of the spheres with the crystallization of homo‐oligomers of 4‐oxybenzoyl units, and finally the network structure was completed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1624–1634, 2005     

Preparation of poly(p‐oxybenzoyl) crystals using direct polymerization of p‐hydroxybenzoic acid in the presence of boronic anhydrides

Poly(p‐oxybenzoyl) (POB) crystals were prepared by reaction‐induced crystallization during direct polymerization of p‐hydroxybenzoic acid in the presence of boronic anhydrides. Polymerizations were carried out at 300 °C in dibenzyltoluene at a concentration of 1% with three kinds of anhydrides of boronic acid such as 3,4,5‐trifluorophenylboronic acid (TFB), 4‐methoxyphenylboronic acid (MPB) and 4‐biphenylboronic acid (BPB). The POB crystals were formed as precipitates in the solution and the morphology was considerably influenced by both the structure of the boronic anhydride and its concentration (c_B). Needle‐like crystals were firmed in the presence of TFB anhydride (TFBA) at c_Bs of 5 and 10 mol % by the spiral growth of lamellae. Spherical aggregates of slab‐like crystals were formed at c_Bs from 50 to 100 mol %. The polymerization with MPB anhydride and BPB anhydride (BPBA) also yielded the needle‐like crystals at c_Bs of 50 and 5 mol %, respectively. The polymerization with TFBA at lower c_B was favorable to prepare the needle‐like crystal. Molecular weight was also influenced by the structure of the boronic anhydride and c_B. M_n increased generally with c_B and BPBA gave the highest M_n of 14.7 × 10³ at c_B of 100 mol %. The loose packing of the molecules in the crystal caused by the bulkiness of the end‐groups made the polymerization in the crystals more efficiently. Morphology and molecular weight of the POB crystals could be controlled by the chemical structure and the content of boronic anhydride. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

One‐pot preparation of aromatic poly(azomethine ester) fibrillar crystals using reaction‐Induced crystallization

Polymerizations of 4‐(4‐acetoxybenzylideneamino)benzoic acid were performed in dibenzyltoluene (DBT) and a mixture of DBT and liquid paraffin at 350 °C for 6 h. Fibrillar crystals of poly[4‐(4‐oxybenzylideneamino)benzoyl] (POAB) having the width of 50–450 nm and the length of over 15 μm were obtained by the crystallization during the polymerization. The fibrillar crystals possessed high crystallinity and the molecular chains aligned perpendicular to the long axis of the fibrillar crystals. Plate‐like crystals were initially formed by the crystallization of oligomers, and then they changed to the fibrillar crystals via the formation of bundle‐like crystals after 1 h. Molecular weight increased by the further polymerization in the crystals. Based on these results, one‐pot preparation of the fibrillar POAB crystals was examined by the polymerization of 4‐acetoxybenzaldehyde and 4‐aminobenzoic acid. The polymerization at 180 °C for 2 h and then at 350 °C for 6 h afforded the fibrillar crystals with a small amount of the ribbon‐like crystals. Although the side‐reaction to generate the p‐benzamide sequences was not completely depressed, the sequence of heating in which 180 °C for the formation of the azomethine linkage and then 350 °C for the formation of the ester linkage was preferable to prepare the fibrillar POAB crystals. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Nonstoichiometric polycondensation of 4‐acetoxybenzoic acid in the presence of monoacetate

Nonstoichiometric polycondensation of 4‐acetoxybenzoic acid (ABA) was examined in the presence of three kinds of aromatic monoacetates: 4‐hexyloxyphenyl acetate, 4‐decyloxyphenyl acetate, and 4‐octadecyloxyphenyl acetate. Polymerizations were carried out in liquid paraffin at 320 °C under nonstoichiometric conditions, in which the acetoxy group was in large excess of the carboxyl group. Poly(4‐oxybenzoyl) (POB) was obtained as crystal at the molar ratio of monoacetates in feed (χ) of less than 80 mol %, meaning that the concentration of the acetoxy group was five times that of the carboxylic group. The obtained POB possessed much higher number average degree of polymerization (DP_n), ranging from 353 to 467, than the calculated DP_n on the basis of χ. High molecular weight polymer was synthesized even under nonstoichiometric conditions via crystallization of oligomers and the following solid‐state polymerization in the crystals. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1757–1766, 2005     

Heterograft copolymers via double click reactions using one‐pot technique

The double click reactions (Cu catalyzed Huisgen and Diels–Alder reactions) were used as a new strategy for the preparation of well‐defined heterograft copolymers in one‐pot technique. The synthetic strategy to the various stages of this work is outlined: (i) preparing random copolymers of styrene (St) and p‐chloromethylstyrene (CMS) (which is a functionalizable monomer) via nitroxide mediated radical polymerization (NMP); (ii) attachment of anthracene functionality to the preformed copolymer by the o‐etherification procedure and then conversion of the remaining ? CH₂Cl into azide functionality; (iii) by using double click reactions in one‐pot technique, maleimide end‐functionalized poly(methyl methacrylate) (PMMA‐MI) via atom transfer radical polymerization (ATRP) of MMA and alkyne end‐functionalized poly (ethylene glycol) (PEG‐alkyne) were introduced onto the copolymer bearing pendant anthryl and azide moieties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6969–6977, 2008     

Morphology of poly(p‐oxybenzoyl) prepared in perfluoropolyether

Solvent effect on the morphology of poly(p‐oxybenzoyl) (POB) prepared by the reaction‐induced phase separation of oligomers was examined by the polymerization of p‐acetoxybenzoic acid in perfluoropolyether Aflunox^TM (AFL2507 and AFL606). Polymerization was carried out at 320°C for 6 hr. POB microspheres were formed in AFL2507 by the liquid–liquid phase separation of oligomers due to the low miscibility of oligomers in AFL2507. The molecular weight of the solvent influenced the morphology, and the polymerization in AFL606 of which the molecular weight was lower than AFL2507 yielded whiskers formed by crystallization of oligomers induced by the increase in miscibility compared with that in AFL2507. The solvent structure and its molecular weight influenced the miscibility of oligomers and ultimately controlled the morphology from whisker to microsphere. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis of polymeric core–shell particles using surface‐initiated living free‐radical polymerization

An easy and novel approach to the synthesis of functionalized nanostructured polymeric particles is reported. The surfactant‐free emulsion polymerization of methyl methacrylate in the presence of the crosslinking reagent 2‐ethyl‐2‐(hydroxy methyl)‐1,3‐propanediol trimethacrylate was used to in situ crosslink colloid micelles to produce stable, crosslinked polymeric particles (diameter size ～ 100–300 nm). A functionalized methacrylate monomer, 2‐methacryloxyethyl‐2′‐bromoisobutyrate, containing a dormant atom transfer radical polymerization (ATRP) living free‐radical initiator, which is termed an inimer (initiator/monomer), was added to the solution during the polymerization to functionalize the surface of the particles with ATRP initiator groups. The surface‐initiated ATRP of different monomers was then carried out to produce core–shell‐type polymeric nanostructures. This versatile technique can be easily employed for the design of a wide variety of polymeric shells surrounding a crosslinked core while keeping good control over the sizes of the nanostructures. The particles were characterized with scanning electron microscopy, transmission electron microscopy, optical microscopy, dynamic light scattering, and Raman spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1575–1584, 2007     

Morphosynthesis of poly[4‐(1,4‐phenylene)oxyphthalimide] and copolymers prepared by reaction‐induced crystallization during polymerization

Morphosynthesis of poly[4‐(1,4‐phenylene)oxyphthalimide] (POPI) and poly[4‐(1,4‐phenylene)oxyphthalimide‐co‐4‐phthalimide] (POPI‐PPI) was examined by using the crystallization during the polymerization. The POPI fibrillar crystals were obtained as precipitates with the formation of spherical aggregates of plate‐like crystals. Some of the POPI fibrillar crystals were longer than 15 μm. They possessed high crystallinity and the molecules aligned perpendicular to the long direction of the fibers. On the other hand, one‐dimensional structures of POPI‐PPI such as ribbon, cone, rod, and fiber were obtained as precipitates by the copolymerization. The copolymer molecules might align along the long direction of the cone‐like crystals. The morphology of these poly(ether‐imide)s could be controlled by not only the polymerization condition but also with the aid of copolymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

“Click” coupling between alkyne‐decorated multiwalled carbon nanotubes and reactive PDMA‐PNIPAM micelles

Covalent functionalization of alkyne‐decorated multiwalled carbon nanotubes (MWNTs) with a well‐defined, azide‐derivatized, thermoresponsive diblock copolymer, poly(N,N‐dimethylacrylamide)‐poly(N‐isopropylacrylamide) (PDMA‐PNIPAM) was accomplished by the Cu(I)‐catalyzed [3 + 2] Huisgen cycloaddition. It was found that this reaction could simultaneously increase the molecular size and bonding density of grafted polymers when PDMA‐PNIPAM micelles were employed in the coupling system. On the other hand, attachment of molecularly dissolved unimers of high‐molecular weight onto the nanotube resulted in low‐graft density. The block copolymer bearing azide groups at the PDMA end was prepared by reversible addition–fragmentation transfer polymerization, which formed micelles with a diameter of ～40 nm at temperatures above its critical micelle temperature. Scanning electron microscopy was utilized to demonstrate that the coupling reaction was successfully carried out between copolymer micelles and alkyne‐bearing MWNTs. FTIR spectroscopy was utilized to follow the introduction and consumption of alkyne groups on the MWNTs. Thermogravimetric analysis indicated that the functionalized MWNTs consisted of about 45% polymer. Transmission electron microscopy was utilized to image polymer‐functionalized MWNTs, showing relatively uniform polymer coatings present on the surface of nanotubes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7187–7199, 2008     

Synthesis of aromatic oxazolyl‐ and carboxyl‐functionalized polymers: Atom transfer radical polymerization of styrene initiated by 2‐[(4‐bromomethyl)phenyl]‐4,5‐dihydro‐4,4‐dimethyloxazole

The synthesis of a new compound, 2‐[(4‐bromomethyl)phenyl]‐4,5‐dihydro‐4,4‐dimethyloxazole ( 1 ), and its utility in the synthesis of oxazoline‐functionalized polystyrene by atom transfer radical polymerization (ATRP) methods are described. Aromatic oxazolyl‐functionalized polymers were prepared by the ATRP of styrene, initiated by ( 1 ) in the presence of copper(I) bromide/2,2′‐bipyridyl catalyst system, to afford the corresponding α‐oxazolyl‐functionalized polystyrene ( 2 ). The polymerization proceeded via a controlled free radical polymerization process to produce the corresponding α‐oxazolyl‐functionalized polymers with predictable number‐average molecular weights, narrow molecular weight distributions in high‐initiator efficiency reactions. Post‐ATRP chain end modification of α‐oxazolyl‐functionalized polystyrene ( 2 ) to form the corresponding α‐carboxyl‐functionalized polystyrene ( 3 ) was achieved by successive acid‐catalyzed hydrolysis and saponification reactions. The polymerization processes were monitored by gas chromatography analyses. The unimolecular‐functionalized initiator and functionalized polymers were characterized by thin layer chromatography, spectroscopy, size exclusion chromatography, and nonaqueous titration analysis. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Well‐defined polycaprolactone precursors for low surface‐energy polyurethane films

For the purpose of developing model coating systems, it is important to use well‐defined coating precursors. In this work, polyester oligomers were synthesized by controlled ring‐opening polymerization of ε‐caprolactone and 4‐tert‐butyl‐ε‐caprolactone via an activated monomer mechanism. These well‐defined oligomers, including 3‐armed hydroxyl‐functionalized polyesters and perfluoroalkyl‐end‐capped linear polyesters, have been obtained with controlled functionality and low‐molecular weight polydispersity and without the formation of cyclic structures, as demonstrated by MALDI‐ToF MS analyses. The polymer architecture and functionality can be tuned by using different initiating alcohols. These oligomers have been used as precursors to prepare model low surface‐energy polyurethane coatings. Upon the addition of about 1 wt % of fluorine in the polyurethane films, the advancing contact angles for water and hexadecane have been increased to 105° and 78°, respectively; the surface enrichment of fluorinated species has been confirmed by X‐ray photoelectron spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 218–227, 2008     

Novel thermotropic esters‐based polymers with broad nematic processing windows

In this study, a new series of semiflexible liquid crystalline (LC) polyesters and poly(ester‐amide)s were synthesized and characterized. Polymers based on 4‐hydroxybenzoic acid (4‐HBA), 6‐hydroxy‐2‐naphthoic acid (HNA), suberic acid (SUA), and sebacic acid (SEA) were modified with hydroquinone (HQ) and different concentrations of 4‐acetamidophenol (AP) to obtain a polyester and two poly(ester‐amide)s, respectively. All polymers were successfully prepared using conventional melt‐condensation techniques. The polymers were characterized by inherent viscosity measurements, SEC, hot‐stage polarizing microscopy, DSC, and TGA. The mechanical behavior was investigated using DMTA and tensile testing. All linear polymers have T_gs in the range of 50–80 °C and melt between 120 and 150 °C. Our polymers display good thermooxidative stabilities (5% wt loss at ～ 400 °C) and exhibit homogeneous nematic melt behavior over a wide temperature range (ΔN ～ 250 °C). The liquid crystal phase was lost when high concentrations of nonlinear monomers such as 3‐HBA (>27 mol %) and resorcinol (RC) (>23 mol %) were incorporated. The LC polyester based on 4‐HBA/HNA/HQ/SUA/SEA could easily be processed into good quality films and fibers. The films display good mechanical properties (E′ ～ 4 GPa) and high toughness, that is, ～ 15% elongation at break, at room temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6565–6574, 2008     

RAFT synthesis of amphiphilic (A‐ran‐B)‐b‐C diblock copolymers with tunable pH‐sensitivity

RAFT homopolymerization of 2‐(diisopropylamino)ethyl methacrylate (DPA) and 2‐(diethylamino)ethyl methacrylate (DEA) and their random copolymerization were investigated. The random copolymers of DPA‐ran‐DEA were synthesized and used as macro‐CTA to prepare poly(DPA‐ran‐DEA)‐b‐poly(N‐(2‐hydroxypropyl) methacrylamide) amphiphilic block copolymers. The ¹H NMR and GPC measurements confirmed the successful synthesis of these copolymers. The potentiometric titration results showed that the pK_b values of these copolymers were in the range of 6.7 ～ 7.7 and linearly varied with the DPA/DEA composition, regardless of the block length of HPMA. The pH‐induced micellization in PBS solution was verified by fluorescence spectroscopy. The dynamic light scattering evaluation showed that the hydrodynamic diameters of these micelles are between 37 ～ 43 nm © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3740–3748, 2008     

The effect of branching on the physical properties of 73/27 4‐hydroxybenzoic acid/2‐hydroxy‐6‐naphthoic acid

The 73/27 4‐hydroxybenzoic acid (HBA)/2‐hydroxy‐6‐naphthoic acid (HNA) copolyester was prepared by the inclusion of two crosslinkable oligomers. These systems were synthesized by melt polymerization and characterized using differential scanning calorimetry, thermogravimetric analysis, polarized optical microscope and wide‐angle X‐ray diffraction. The transition from thermoplastic to thermosetting character occurred when 10 wt% or above of oligomer was added to the 73/27 HBA/HNA random mixture. The melt rheology of the HBA/HNA copolyesters containing two oligomers was investigated. The copolyesters displayed an increase in complex viscosity and transition from liquid‐like to solid‐like behavior as the oligomer content increased, and finally there was no melting transition when the oligomer content reached 10 wt%. Shear storage modulus measured by a dielectric mechanical analysis decreased slightly with increasing oligomer content. An adhesive test using an aluminum sheet revealed an increase in the lap shear strength up to 5 wt% of oligomer content without a significant reduction in shear storage modulus. On the other hand, the 73/27 HBA/HNA containing 10 wt% oligomer displayed a dramatic decrease in lap shear strength. Copyright © 1999 John Wiley & Sons, Ltd.     

Solid‐state amidization and imidization reactions in vapor‐deposited poly(amic acid)

The condensation polymerization of 4,4′‐oxydianiline with pyromellitic dianhydride for the formation of poly(amic acid) and the subsequent imidization for the formation of polyimides were investigated for films prepared with vapor‐deposition polymerization techniques. Fourier transform infrared spectroscopy, thermal analysis, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry of films at different temperatures indicated that additional solid‐state polymerization occurred before imidization. The experiments revealed that, upon vapor deposition, poly(amic acid) oligomers formed that had a number‐average molecular weight of about 1500 Da. Between 100–130 °C, these chains underwent an additional condensation reaction and formed slightly higher molecular weight oligomers. Calorimetry measurements showed that this reaction was exothermic [enthalpy of reaction (ΔH) ～ ?30 J/g] and had an activation energy of about 120 kJ/mol. The experimental ΔH values were compared with results from ab initio molecular modeling calculations to estimate the number of amide groups formed. At higher temperatures (150–300 °C), the imidization of amide linkages occurred as an endothermic reaction (ΔH ～ +120 J/g) with an activation energy of about 130 kJ/mol. The solid‐state kinetics depended on the reaction conversion as well as the processing conditions used to deposit the films. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5999–6010, 2004     

Chemistry of olefin polymerization reactions with chromium‐based catalysts

Detailed GC analysis of oligomers formed in ethylene homopolymerization reactions, ethylene/1‐hexene copolymerization reactions, and homo‐oligomerization reactions of 1‐hexene and 1‐octene in the presence of a chromium oxide and an organochromium catalyst is carried out. A combination of these data with the analysis of ¹³C NMR and IR spectra of the respective high molecular weight polymerization products indicates that the standard olefin polymerization mechanism, according to which the starting chain end of each polymer molecule is saturated and the terminal chain end is a C?C bond (in the absence of hydrogen in the polymerization reactions), is also applicable to olefin polymerization reactions with both types of chromium‐based catalysts. The mechanism of active center formation and polymerization is proposed for the reactions. Two additional features of the polymerization reactions, co‐trimerization of olefins over chromium oxide catalysts and formation of methyl branches in polyethylene chains in the presence of organochromium catalysts, also find confirmation in the GC analysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5330–5347, 2008     

Synthesis of methacrylate derivatives oligomers by dithiobenzoate‐RAFT‐mediated polymerization

Reversible addition fragmentation chain transfer (RAFT) was used to synthesize methacrylic acid oligomers and oligo(methacrylic acid)‐b‐poly(methyl methacrylate) (PMAA‐b‐PMMA) with targeted degree of polymerization ≈ 10. Characterization is by size‐exclusion chromatography (SEC) and electrospray mass‐spectrometry. SEC data are presented as hydrodynamic volume distributions (HVDs), the only proper means to present comparative and meaningful SEC data when there is no unique relationship between size and molecular weight. The RAFT agent, (4‐cyanopentanoic acid)‐4‐dithiobenzoate (CPADB), produced dithiobenzoic acid as a side product during the polymerization of methacrylate derivatives. Precipitation in diethyl ether proved to be an easy way to remove this impurity from the PMAA‐RAFT oligomers. Both unpurified and purified macro‐RAFT agent were used to prepare amphiphilic PMAA‐b‐PMMA copolymers. Diblock copolymer prepared from the purified PMAA homopolymer had a narrower HVD in comparison to those obtained from the equivalent unpurified macro‐RAFT agent. This work shows that while cyanoisopropyl‐dithiobenzoate or CPADB are good RAFT agents for methacrylate derivatives, they exhibit some instability under typical polymerization conditions, and thus when oligomers are targeted, optimal control requires checking for the degradation product and appropriate purification steps when necessary (the same effect is present for larger polymers but is unimportant). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2277–2289, 2008