Synthesis of molecular‐weight‐controlled polyfluorene with boronate at one end

We investigated the synthesis of polyfluorene with a pinacol boronate (PinB) moiety at one end and with controlled molecular weight by means of Suzuki–Miyaura coupling polymerization of pinacol (7‐bromo‐9,9‐dioctyl‐9H‐fluoren‐2‐yl)boronate ( 1 ) with a palladium(0) precatalyst in the presence of pinacol 4‐trifluoromethylphenylboronate ( 2 ) as a chain terminator and CsF/18‐crown‐6 as a base. When we used AmPhos Pd G2, which has a propensity for intramolecular catalyst transfer on a π‐electron face, polyfluorene with the PinB moiety at one end and PhCF₃ (derived from 2 ) at the other end was obtained, and the molecular weight increased in proportion to the feed ratio of [ 1 ]₀/[catalyst]₀, though the molecular weight distribution was broad. Since the molecular weight also linearly increased with respect to the conversion of 1 until the middle stage of polymerization, the polymerization appears to involve chain‐growth polymerization through intramolecular catalyst transfer from the Pd catalyst inserted into the C? Br bond of 1 . The broad molecular weight distribution might be mainly due to slow initiation and slow termination with 2 , rather than polymer–polymer coupling. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2498–2504     

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     

Investigation of Mizoroki‐Heck coupling polymerization as a catalyst‐transfer condensation polymerization for synthesis of poly(p‐phenylenevinylene)

Mizoroki‐Heck coupling polymerization of 1,4‐bis[(2‐ethylhexyl)oxy]‐2‐iodo‐5‐vinylbenzene ( 1 ) and its bromo counterpart 2 with a Pd initiator for the synthesis of poly(phenylenevinylene) (PPV) was investigated to see whether the polymerization proceeds in a chain‐growth polymerization manner. The polymerization of 1 with ^tBu₃PPd(Tolyl)Br ( 10 ) proceeded even at room temperature when 5.5 equiv of Cy₂NMe (Cy = cyclohexyl) was used as a base, but the molecular weight distribution of PPV was broad. The polymerization of 2 hardly proceeded at room temperature under the same conditions. In the polymerization of 1 , PPV with H at one end and I at the other was formed until the middle stage, and the polymer end groups were converted into tolyl and H in the final stage. The number‐average molecular weight (M_n) did not increase until about 90% monomer conversion and then sharply increased after that, indicating conventional step‐growth polymerization. The occurrence of step‐growth polymerization, not catalyst‐transfer chain‐growth polymerization, may be interpreted in terms of low coordination ability of H‐Pd(II)‐X(^tBu₃P) (X = Br or I), formed in the catalytic cycle of the Mizoroki‐Heck coupling reaction, to π‐electrons of the PPV backbone; reductive elimination of H‐X from this Pd species with base would take place after diffusion into the reaction mixture. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 543–551     

Poly(aryl ethers) by nucleophilic aromatic substitution. III. Hydrolytic side reactions

The molecular weight of polysulfone, i.e., the aryl polyether that is prepared by the reaction of the disodium salt of bisphenol A with 4,4′-dichlorodiphenyl sulfone in dimethyl sulfoxide (DMSO) solvent is shown to depend, among other things, on the moisture content of the polymerizing system. In the presence of water, hydrolysis of the sulfone monomer occurs concomitant with the polymerization. This leads to a deviation from the desired 1:1 ratio of coreactant groupings and therefore in attendant reduction in possible molecular weight. The hydrolysis is shown to lead to the formation of the sodium salt of 4-chloro-4′-hydroxydiphenyl sulfone and to a lesser extent polymer derived from self-condensation of this salt. At low levels this salt is essentially inert towards the principal polymerization at hand but in somewhat greater amounts functions as an effective chain terminator. Similar hydrolysis of polysulfone chloro endgroups is believed to occur under the aqueous conditions of polymerization but to a lesser extent than for the sulfone monomer. It is shown that polysulfone or similar polyethers are subject to chain cleavage by bases in DMSO solvent. The base attacks the activated position para to the sulfonyl group with the formation of a chain terminating in a bisphenol A type phenolic group and a chain terminating in a phenolic group of the bisphenol S (p-hydroxyphenyl sulfonyl) type. It is shown that cleavage is probably not important under normal conditions of polymer formation. The effect of these hydrolytic side reactions on the attainment of high molecular weight under conditions of imperfect reaction stoichiometry is shown to be consistent with the above conclusions.     

Precise synthesis of end‐functionalized thermosensitive poly(vinyl ether)s by living cationic polymerization

A series of poly(2‐methoxyethyl vinyl ether)s with narrow molecular weight distributions and with perfectly defined end groups of varying hydrophobicities was successfully synthesized by base‐assisting living cationic polymerization. The end group was shown to greatly affect the temperature‐induced phase separation behavior of aqueous solutions (lower critical solution temperature‐type phase separation) or organic solutions (upper critical solution temperature‐type phase separation) of the polymers. The cloud points were also influenced largely by the molecular weight and concentration of the polymer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Polymerization of β‐pinene with Schiff‐base nickel complexes catalyst: Synthesis of relatively high molecular weight poly(β‐pinene) at high temperature with high productivity

A series of easily accessible and stable Schiff‐base nickel complexes (complex 1 – 4 ) in conjunction with methylaluminoxane (MAO) were employed for the synthesis of relatively high molecular weight β‐pinene polymers at high temperature with high productivity. The ligand structure of the complex had a substantial effect on the polymerization in terms of the productivity and the molecular weight. With complex 4 in the presence of MAO, high molecular weight polymers of β‐pinene (M_n ～ 10,900) were obtained at 40 °C with an extremely high productivity up to 1.25 × 10⁷ g polyβ‐pinene/mol of Ni. ¹H NMR analyses showed that the obtained β‐pinene polymer was structurally identical to that formed by conventional cationic Lewis acid initiators. The polymerization was presumably initiated by the nickel cation formed by the reaction of the schiff‐base nickel complex and MAO, while the propagation proceeded in a manner typical for a conventional carbocationic polymerization process. Direct evidence for the carbocationic polymerization was offered by the fact that quenching of the polymerization with methanol at a low monomer conversion resulted in incorporation of a methoxyl end group into the polymer chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3739–3746, 2007     

Syndiospecific polymerization of styrene in the presence of cyclic olefins: A new approach for molecular weight,molecular weight distribution,and stereoregularity controls for syndiotactic polystyrene

A new approach for facilitating microstructural controls for syndiotactic polystyrene (sPS), in which, styrene polymerization is conducted in the presence of cyclic olefins and hydrogen, is proposed. Detailed structural analyses revealed that cyclic olefins are not incorporated into the polystyrene main chain; instead, they are capable of interrupting the chain propagation processes by binding onto the active catalyst to form a cyclic‐olefin‐coordinated active site. Thus, in the presence of hydrogen, chain transfer by hydrogen addition occurs selectively, which leads to the generation of drastically lower molecular weight sPS with a narrower range of molecular weight distribution. Chain end structural analyses of the resulting polymers revealed that styrene polymerization under theses conditions involves a selective chain transfer pathway for providing styrene polymers with uniform chain end structures. A unique method for inducing a selective chain transfer reaction by using non‐incorporated cyclic olefins to regulate the chain reaction mechanism is demonstrated. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of high molecular weight atactic polybutene‐1 with a monotitanocene/methylaluminoxane catalyst system

A novel catalyst precursor, the monotitanocene (η⁵‐pentamethylcyclopentadienyl) titanium tricinnamyloxide [Cp*Ti(OCH₂? CH?CHC₆H₅)₃], was synthesized and employed for butene‐1 polymerization in the presence of methylaluminoxane. The effects of the polymerization conditions on the catalytic activity, molecular weight, stereoregularity, and regioregularity of the polymer so obtained were investigated in detail. The results show that the monotitanocene is desirable for the production of atactic polybutene‐1 coupled with good yields under typical polymerization conditions, high molecular weight (weight‐average molecular weight = 5.3–9.6 × 10⁵), and stereoirregularity with the Bernoullian factor B equal to 0.95, which indicates that chain‐end control is predominant. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4068–4073, 2001     

Careful investigation of the hydrosilylation of olefins at poly(ethylene glycol) chain ends and development of a new silyl hydride to avoid side reactions

Hydrosilylation of olefin groups at poly(ethylene glycol) chain ends catalyzed by Karstedt catalyst often results in undesired side reactions such as olefin isomerization, hydrogenation, and dehydrosilylation. Since unwanted polymers obtained by side reactions deteriorate the quality of end‐functional polymers, maximizing the hydrosilylation efficiency at polymer chain ends becomes crucial. After careful investigation of the factors that govern side reactions under various conditions, it was related that the short lifetime of the unstable Pt catalyst intermediate led to the formation of more side products under the inherently dilute conditions for polymers. Based on these results, two new chelating hydrosilylation reagents, tris(2‐methoxyethoxy)silane (5) and 2,10‐dimethyl‐3,6,9‐trioxa‐2,10‐disilaundecane (6), have been developed. It was demonstrated that the hydrosilylation efficiency at polymer chain ends was significantly increased by employing the internally coordinating hydrosilane 5. In addition, employment of the internally coordinating disilane species 6 in an addition polymerization with 1,5‐hexadiene by hydrosilylation reaction yielded a polymer with high molecular weight (M_n = 9300 g/mol), which was significantly higher than that (M_n = 2600 g/mol) of the corresponding polymer obtained with non‐chelating dihydrosilane, 1,1,3,3‐tetramethyldisiloxane. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 527–536     

Controlled polymerization of epoxides: Metal‐free ring‐opening polymerization of glycidyl phenyl ether initiated by tetra‐n‐butylammonium fluoride in the presence of protic compounds

Metal‐free controlled ring‐opening polymerization of glycidyl phenyl ether (GPE) was achieved using tetra‐n‐butylammonium fluoride (Bu₄NF) as an initiator in the presence of water and ethanol as chain transfer agents (CTAs). Number‐averaged molecular weight of poly(GPE) increased with an increase of [GPE]₀/([Bu₄NF]₀ + [CTA]₀) values, showing relatively narrow molecular weight distributions. NMR spectroscopic analysis exhibited a formation of ethoxy groups as well as FCH₂ at the initiating polymer chain‐end when ethanol was used as the CTA in the polymerization. These results indicate that Bu₄NF acts as a catalyst as well as the initiator for this polymerization system. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

End‐group fidelity of copper(0)‐meditated radical polymerization at high monomer conversion: an ESI‐MS investigation

Copper(0)‐mediated radical polymerization (single electron transfer‐living radical polymerization) is an efficient polymerization technique that allows control over the polymerization of acrylates, vinyl chloride and other monomers, yielding bromide terminated polymer. In this contribution, we investigate the evolution of the end‐group fidelity at very high conversion both in the presence and in the absence of initially added copper (II) bromide (CuBr₂). High resolution electrospray‐ionization mass spectroscopy (ESI‐MS) allows determination of the precise chemical structure of the dead polymers formed during the polymerization to very high monomer conversion, including post polymerization conditions. Two different regimes can be identified via ESI‐MS analysis. During the polymerization, dead polymer results mainly from termination via disproportionation, whereas at very high conversion (or in the absence of monomer, that is, post‐polymerization), dead polymers are predominantly generated by chain transfer reactions (presumably to ligand). The addition of CuBr₂ significantly reduces the extent of termination by both chain transfer and disproportionation, at very high monomer conversion and under post‐polymerization conditions, offering a convenient approach to maintaining high end‐group fidelity in Cu(0)‐mediated radical polymerization. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Transformation of the cationic growing center of poly(tetrahydrofuran) into an anionic one by bis(pentamethylcyclopentadienyl)samarium

Transformation of the cationic growing center of living poly(tetrahydrofuran) [poly(THF)] into an anionic one was achieved in high efficiency (62%) by the end-capping of living poly(THF) with potassium iodide followed by the reduction with bis(pentamethylcyclopentadienyl)samarium (Cp*₂Sm), whereas the direct reduction with Cp*₂Sm without the end-capping resulted in the formation of poly(THF) with pentamethylcyclopentadienyl group at the terminal. The increase in the molecular weight of poly(THF) after the reduction was observed, which indicates the presence of the dimerization of poly(THF) during the reduction. The polymerization of a variety of electrophilic monomers including δ-valerolactone, 2-oxo-1,3-dioxane, and alkyl methacrylates with the macroanion provided good yields of the corresponding block copolymers consisting of both cationically and anionically polymerizable monomers. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2209–2214, 1998     

Effects of end group polarity and molecular weight on the lower critical solution temperature of poly(N‐isopropylacrylamide)

The lower critical solution temperatures (LCSTs) for mass fractionated samples of poly(N‐isopropylacrylamide) (PNIPAM) were studied to determine the effect of polymer molecular weight on the LCST using a high throughput temperature gradient apparatus. PNIPAM fractions prepared by a conventional radical polymerization using azoisobutyronitrile (AIBN) as the initiator had LCSTs that were largely invariant with molecular weight or dispersity. Only slight deviations were noted with lower molecular weight samples. An 18‐kDa sample had a 0.6 °C higher LCST. A 56‐kDa sample had a 0.2 °C higher LCST. PNIPAM derivatives prepared with a triphenylmethyl (trityl) functionalized azo initiator were also prepared and mass fractionated. These samples' LCSTs were identical to those of PNIPAM samples prepared using AIBN initiation when higher molecular weight samples were compared. The trityl‐containing PNIPAM fractions' LCSTs varied when the molecular weight decreased below 100 kDa. Acidolysis of the trityl end groups provided a third set of PNIPAM derivatives whose LCST differed only with samples with M_w values < 60 kDa. These results show there is no effect of molecular weight on LCST until the degree of polymerization is such that end group structure becomes significant. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1492–1501, 2006     

Cationic polymerization of L,L‐lactide

Cationic bulk polymerization of L ,L‐ lactide (LA) initiated by trifluromethanesulfonic acid [triflic acid (TfA)] has been studied. At temperatures 120–160 °C, polymerization proceeded to high conversion (>90% within ～8 h) giving polymers with M_n ～ 2 × 10⁴ and relatively high dispersity. Thermogravimetric analysis of resulting polylactide (PLA) indicated that its thermal stability was considerably higher than the thermal stability of linear PLA of comparable molecular weight obtained with ROH/Sn(Oct)₂ initiating system. Also hydrolytic stability of cationically prepared PLA was significantly higher than hydrolytic stability of linear PLA. Because thermal or hydrolytic degradation of PLA starting from end‐groups is considerably faster than random chain scission, both thermal and hydrolytic stability depend on molecular weight of the polymer. High thermal and hydrolytic stability, in spite of moderate molecular weight of cationically prepared PLA, indicate that the fraction of end‐groups is considerably lower than in linear PLA of comparable molecular weight. According to proposed mechanism of cationic LA polymerization growing macromolecules are fitted with terminal ? OH and ? C(O)OSO₂CF₃ end‐groups. The presence of those groups allows efficient end‐to‐end cyclization. Cyclic nature of resulting PLA explains its higher thermal and hydrolytic stability as compared with linear PLA. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2650–2658, 2010     

Preparation and properties of dimethyl phosphonomethyl methylsiloxane dimethylsiloxane copolymers

Dimethyl phosphonomethylheptamethylcyclotetrasiloxane (II) and 1, 3-bis(dimethyl phosphonomethyl)tetramethyldisiloxane (III) have been prepared by Arbuzov reaction of trimethyl phosphite with bromomethylheptamethylcyclotetrasiloxane (I) and 1, 3-bis(bromomethyl)tetramethyldisiloxane, respectively. Dimethyl phosphonomethylmethylsiloxane dimethylsiloxane copolymers have been prepared by acid-catalyzed ring-opening polymerization of II with hexamethyldisiloxane (MM) as an end-capping reagent and by reaction of II with III as an end-capping reagent. Dimethylsiloxane polymers with dimethyl phosphonomethyldimethylsiloxy end groups have been prepared by acid-catalyzed polymerization of octamethylcyclotetrasiloxane (D₄) and III. Under these conditions hydrolysis of the dimethyl phosphonate ester groups was a problem. On the other hand Arbuzov reaction of trimethyl phosphite with bromomethylmethylsiloxane dimethylsiloxane copolymer gave a dimethyl phosphonomethylmethylsiloxane dimethylsiloxane copolymer with uniform properties. These polymers have been characterized by ¹H-, ¹³C-, ²⁹Si-, and ³¹P-NMR spectroscopy. Their molecular weight distributions have been determined by gel permeation chromatography (GPC) and their thermal stability measured by TGA.     

Synthesis,characterization, and star polymer assembly of boronic acid end‐functionalized polycaprolactone

Boronic acid end‐functionalized polycaprolactone (PCL) polymers were synthesized by ring‐opening polymerization using a pinacol boronate ester‐containing (Bpin) initiator. The polymerization provides access to boron‐terminated polymers (i.e. Bpin‐PCL‐OH) with narrow molecular weight distributions (PDI = 1.09). Postsynthetic manipulation of the polymer's terminal hydroxyl group by copper‐catalyzed azide‐alkyne cycloaddition chemistry provides a series of bis end‐functionalized polymers with significant structural diversity at the termini. Deprotection of the boronate ester end group was accomplished with an acidic solid phase DOWEX resin. The boronate ester deprotection methodology does not result in hydrolysis of the polymeric backbone. The boronic acid‐tipped polymers were converted into star polymer assemblies using thermal dehydration and ligand‐facilitated trimerization. Thermal dehydration of (HO)₂B‐PCL‐OAc to the corresponding boroxine‐based star polymer assembly was inefficient and lead to degradation products. Ligand‐facilitated trimerization using either pyridine or 7‐azaindole as the Lewis base was efficient and mild. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

R‐RAFT approach for the polymerization of N‐isopropylacrylamide with a star poly(ε‐caprolactone) core

Reversible addition‐fragmentation chain transfer (RAFT) polymerization is a more robust and versatile approach than other living free radical polymerization methods, providing a reactive thiocarbonylthio end group. A series of well‐defined star diblock [poly(ε‐caprolactone)‐b‐poly(N‐isopropylacrylamide)]₄ (SPCLNIP) copolymers were synthesized by R‐RAFT polymerization of N‐isopropylacrylamide (NIPAAm) using [PCL‐DDAT]₄ (SPCL‐DDAT) as a star macro‐RAFT agent (DDAT: S‐1‐dodecyl‐S′‐(α, α′‐dimethyl‐α″‐acetic acid) trithiocarbonate). The R‐RAFT polymerization showed a controlled/“living” character, proceeding with pseudo‐first‐order kinetics. All these star polymers with different molecular weights exhibited narrow molecular weight distributions of less than 1.2. The effect of polymerization temperature and molecular weight of the star macro‐RAFT agent on the polymerization kinetics of NIPAAm monomers was also addressed. Hardly any radical–radical coupling by‐products were detected, while linear side products were kept to a minimum by careful control over polymerization conditions. The trithiocarbonate groups were transferred to polymer chain ends by R‐RAFT polymerization, providing potential possibility of further modification by thiocarbonylthio chemistry. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Unexpected end‐groups of poly(acrylic acid) prepared by RAFT polymerization

Low‐molecular‐weight poly(acrylic acid) (PAA) was synthesized by reversible addition fragmentation chain transfer polymerization with a trithiocarbonate as chain‐transfer agent (CTA). With a combination of NMR spectroscopy and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, the PAA end‐groups of the polymer were analyzed before and after neutralization by sodium hydroxide. The polymer prior to neutralization is made up of the expected trithiocarbonate chain‐ends and of the H‐terminated chains issued from a reaction of transfer to solvent. After neutralization, the trithiocarbonates are transformed into thiols, disulfides, thiolactones, and additional H‐terminated chains. By quantifying the different end‐groups, it was possible to demonstrate that fragmentation is the rate limiting step in the transfer reaction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5439–5462, 2004     

Polymer having a trithiocarbonate moiety in the main chain: Application to reversible addition–fragmentation chain transfer controlled thermal and photoinduced monomer insertion polymerizations

A polymer having a trithiocarbonate moiety in its main chain was synthesized with a cyclic, five‐membered dithiocarbonate as a building block. The trithiocarbonate in the polymer acted as a reversible addition–fragmentation chain transfer reagent to mediate a controlled insertion polymerization of styrene into the polymer main chain, giving the corresponding sequence‐ordered polymer having a well‐defined polystyrene segment in the main chain. During the polymerization, the polystyrene segment in the main chain gained its molecular weight, which maintained a linear relationship with the conversion of styrene. The insertion polymerization of styrene was induced not only thermally but also by ultraviolet irradiation. This photoinduced polymerization was well controlled by the trithiocarbonate moiety to give the corresponding polymer, whose structure was virtually the same as that obtained by the thermal polymerization. © 2006 Wiley Periodicals, Inc. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6324–6331, 2006     

End‐functionalization of syndiotactic polystyrene by vinylsilane inducing selective chain transfer reactions

Structurally well‐defined end‐functionalized syndiotactic polystyrene (sPS) can be prepared by conducting a simultaneous selective chain transfer reaction during the syndiospecific polymerization of styrene in the presence of vinylsilanes. The production of vinylsilane end‐capped sPS involves a unique selective chain transfer pathway via the incorporation of a terminal vinylsilane unit at the polymer chain end by 2,1‐insertion. This unusual insertion pattern situates the bulky silyl functional group at a closer β‐position from the active catalyst center, thus deactivating the propagating chain by a steric jam between the vinylsilane end group and the active catalyst. Subsequently, chain releasing by hydrogen addition (in the presence of H₂) or by β‐elimination (in the absence of H₂) can take place, which leads to the production of end‐functionalized sPS with precise controls of stereoregularity and of the location of functionality. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1690–1698, 2010