Synthesis and thermal behavior of phenylethynyl‐terminated linear and hyperbranched polyphenylquinoxalines

A phenylquinoxaline (PQ) AB monomer mixture was treated with monofunctional and difunctional end‐capping agents and with and without a coupling agent to afford phenylethynyl‐terminated linear PQ oligomers. The resulting PQ oligomers were soluble in common organic solvents and had intrinsic viscosities (IVs) of 0.21–0.30 dL/g. The glass‐transition temperature (T_g) of the diphenylethynyl‐end‐capped PQ oligomer on both sides increased the most, from 215 °C (before curing) to 251 °C (after curing). The PQ AB₂ monomer, which acted as both a coupling agent and a monomer for the hyperbranched polymer, was treated with an AB monomer and end‐capping agents to afford phenylethynyl‐terminated hyperbranched polyphenylquinoxalines (PPQs). They were also soluble in common organic solvents, had IVs of 1.00–1.65 dL/g and T_g's of 251–253 °C, and underwent exothermic cure with maxima around 412–442 °C. The T_g's of the cured hyperbranched PPQs ranged from 258 to 261 °C, depending on the number of phenylethynyl groups on the surface. After further curing, they displayed a T_g of 316 °C in one sample and turned into a fully crosslinked network. The dynamic melt viscosities of a linear oligomer (IV = 0.21 dL/g), a hyperbranched sample (IV = 1.00 dL/g), and a linear reference PPQ (IV = 1.29 dL/g) were compared with respect to the processing temperature. The PQ oligomer and hyperbranched PPQ had low melt viscosities. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6318–6330, 2004     

Intramolecular cyclization in the polymerization of ABx monomers: Approaches to the control of molecular weight and polydispersity in hyperbranched poly(siloxysilane)

Different approaches to control the molecular weight of hyperbranched poly(siloxysilane) have been explored. Because the intramolecular hydrosilylation competitively consumes the vinyl groups of the monomer and other oligomeric intermediates, the conventional single-batch bulk process generally affords polymer with a relatively low molecular weight (M_w = 5000) in ca. 60% yield. We have developed a progressive slow addition process that effectively increases the molecular weight of the final polymers and improves preparation yield by reducing the occurrence of cyclization. Using this gradual growth method, polymers with molecular weights in the range of 6–86,000 (M_w) and polydispersities in the range 2–15 were easily obtained in yields of ca. 70–80%. More importantly, both the molecular weight and the polydispersity could be controlled by changing the rate of addition or the amount of monomer fed. The slower the addition, or the larger the amount of monomer added, the higher the molecular weight and polydispersity of the resulting polymer. In seeded polymerizations, a similar trend was observed with a maximum M_w near 84,000 and a yield of 80%, values that are very significantly higher than those obtained by the single batch process described earlier. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3193–3201, 1999     

Synthesis of poly(phosphonosiloxane) and its cyclic monomer via hydrosilylation and phosphonylation of vinylbenzyl chloride

Phosphonylation of polysiloxane and cyclosiloxane oligomers is described. Hydrosilylation of vinylbenzyl chloride (VBC) with a poly(methylhydrosiloxane), or its cyclic monomer, followed by phosphonylation with triethyl phosphite leads to the production of stable phosphonosiloxanes that are characterized by  Si C and  C P bonds. The polymer, which is a liquid with a glass transition temperature of −38.3 °C, is soluble in alcohols and an alcohol and water mixture. The phosphonylated siloxanes dissolve and chelate uranyl nitrate and transition metal salts. The hydrosilylation of VBC yields α and β isomers:  Si CH₂ CH₂ and  Si CH(CH₃); the ratio between these two depends upon the type of solvent and the reaction conversion. A kinetic study of the hydrosilylation reaction of VBC suggests a second order in respect to the reactants. The reaction rate is dependent upon the catalyst concentration and temperature. Hydrosilylation of vinylbenzyl phosphonate could not be accomplished with the platinum (complex) catalyst; this is attributed to the presence of phosphoryl groups that are strong electron donors. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4043–4053, 1999     

Control of polymer topology through late-transition-metal catalysis

An Erratum has been published for this article in J Polym Sci Part A: Polym Chem (2004) 42 213 In this article, recent examples are reviewed of late-transition-metal catalysis applied to polymer topology control. By the judicious selection or design of late-transition-metal catalysts, polymers with a broad range of topologies, including linear, short-chain-branched, hyperbranched, dendritic, and cyclic topologies, have been successfully synthesized. A distinctive advantage of the catalyst approach is that polymers with complex topologies can be prepared in one pot from simple commercial monomers. A fundamental difference of the catalyst approach with respect to other approaches is that the polymer topology is controlled by the catalysts instead of the monomer structure. In our own laboratory, we have successfully used two strategies to control the polymer topology with late-transition-metal catalysts. In the first strategy, hyperbranched polymers are prepared by the direct free-radical polymerization of divinyl monomers through control of the competition between propagation and chain transfer with a cobalt chain-transfer catalyst. In the second strategy, polyethylene topology is successfully controlled by the regulation of the competition between propagation and chain walking with the Brookhart Pd^II-α-bisimine catalyst. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3680–3692, 2003     

Self‐controlled synthesis of hyperbranched poly(ether‐ketone)s from A2 + B3 approach in poly(phosphoric acid)

Self‐controlled synthesis of hyperbranched poly(ether‐ketone)s (HPEKs) were prepared from “A₂ + B₃” approach by using different monomer solubility in reaction medium. 1,3,5‐Triphenoxybenzene as a hydrophobic B₃ monomer was reacted with commercially available terephthalic acid or 4,4′‐oxybis(benzoic acid) as a hydrophilic A₂ monomer in a hydrophilic reaction medium, polyphosphoric acid (PPA)/phosphorous pentoxide (P₂O₅). The resultant HPEKs were soluble in various common organic solvents and had the weight‐average molecular weight in the range of 3900–13,400 g/mol. The results implied that HPEKs were branched structures instead of crosslinked polymers. The molecular sizes and shapes of HPEKs were further assured by morphological investigation with scanning electron microscopy (SEM) and atomic force microscopy (AFM). Hence, the applied polymerization condition was indeed strong enough to efficiently facilitate polycondensation via “direct” Friedel‐Crafts reaction without gelation. It could be concluded that the polymer forming reaction was kinetically controlled by automatic and slow feeding of the hydrophobic B₃ monomer into the hydrophilic reaction mixture containing hydrophilic comonomer. As a result, hyperbranched structures were formed instead of crosslinked polymers even at full conversion (equifunctional monomer feed ratio). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3326–3336, 2009     

Designing Branched Deoxybenzoin Polyesters as Polymeric Flame Retardants

AB₂ monomers present opportunities to conduct one‐pot syntheses of highly branched or “hyperbranched” polymers, which are known for their distinct physical and chemical properties relative to linear polymers. This paper describes the synthesis of a deoxybenzoin‐containing AB₂ monomer and its use in step‐growth polymerization to prepare branched aromatic polyesters. Highly soluble deoxybenzoin polymers were obtained with degrees of branching reaching 0.36 and estimated molecular weights approaching 20 kDa. The phenolic chain ends of the polymer allowed for post‐polymerization modification by silylation and esterification chemistry. TGA and microscale combustion calorimetry revealed these novel aromatic polyesters to possess the critically important characteristics of flame‐retardant polymers, such as high char yield and low heat release. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1765–1770     

A new approach to control crystallinity of resulting polymers: Self‐condensing ring opening polymerization

The cationic polymerization of 3‐methyl‐3‐oxetanemethanol was initiated using BF₃·OEt₂. The low ratio of catalyst to monomer results in a mainly linear or slightly branched polymer, and the high catalyst to monomer ratio leads to a hyperbranched polymer. The hyperbranched polyether yielded is amorphous, and the essentially linear version obtained is partially crystalline. In other words, the degree of branching and the crystallinity of resulting polymers are dependent on the catalyst to monomer ratio. Therefore a new approach to control the crystallinity of resulting polymers in self‐condensing ring opening polymerization was developed.     

A versatile A2 + B3 approach to hyperbranched polyacenaphthenequinones

A series of hyperbranched polyacenaphthenequinones has been prepared by superelectrophilic aromatic substitution of (substituted) acenaphthenequinone and 1,3,5‐tris‐(4‐phenoxybenzoyl)benzene via a facile A₂ + B₃ approach. Because of the strongly increased reactivity of the second A functionality, gelation was efficiently avoided during the polymerization. The structure of the resulting polymer was characterized by NMR spectroscopy and gel permeation chromatography. Further modification of the hyperbranched polyacenaphthenequinone was explored both on the acenaphthenequinone and aromatic moieties. Moreover, the polymer modified through sulfonation was investigated as a water‐soluble acid catalyst for the degradation of biomass resources. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2596‐2603     

Synthesis of multiblock hyperbranched‐linear poly(ether sulfone) copolymers

Hyperbranched poly(ether sulfone) was prepared in the presence of an oligomeric linear poly(ether sulfone) to generate multiblock hyperbranched‐linear (LxHB) copolymers. The LxHB copolymers were prepared in a two‐step, one‐pot synthesis by first polymerizing AB monomer to generate a linear block of a desired molecular weight followed by addition of the AB₂ monomer in a large excess (19:1, AB₂:AB) to generate the hyperbranched block. NMR integration analysis indicates that AB₂:AB ratio is independent of the reaction time. Because the molecular weight still increases with reaction time, these results suggest that polymer growth continues after consumption of monomer by condensation into a multiblock architecture. The LxHB poly(ether sulfone)s have better thermal stability (10% mass loss > 343 vs. 317 °C) and lower T_g (200 vs. > 250 °C) than the hyperbranched homopolymer, higher T_g than the linear homopolymer (<154 °C), while little difference in the solubility character was observed between the two polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4785–4793, 2008     

Synthesis of hyperbranched poly(ether nitrile)s by one‐step polycondensation of an AB2 monomer

Hyperbranched poly(ether nitrile)s were prepared from a novel AB₂ type monomer, 2‐chloro‐4‐(3,5‐dihydroxyphenoxy)benzonitrile, via nucleophilic aromatic substitution. Soluble and low‐viscous hyperbranched polymers with molecular weights upto 233,600 (M_w) were isolated. According to the ¹H NMR and GPC data, the unique polymerization behavior was observed, which implies that the weight average molecular weight increased after the number average molecular weight reached plateau region. Model compounds were prepared to characterize the branching structure. Spectroscopic measurements of the model compounds and the resulting polymers, such as ¹H, DEPT ¹³C NMR, and MS, strongly suggest that the ether exchange reaction and cyclization are involved in the propagation reaction. The side reactions would affect the unique polymerization behavior. The resulting polymers showed a good solubility in organic solvents similar to other hyperbranched aromatic polymers. The hydroxy‐terminated polymer was even soluble in basic water. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5835–5844, 2009     

Hyperbranched polymers generated from oxyanionic vinyl polymerization of commercially available methacrylate inimers

Hyperbranched polymethacrylates were prepared by means of oxyanionic vinyl polymerization of commercially available monomers, including hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) methacrylate (PEG‐MA). Hyperbranched polymethacrylates with high molecular weight were obtained with the complex of potassium hydride and 18‐crown‐6 as the initiator. The effect of 18‐crown‐6 is very important, and only oligomer can be obtained in the polymerization without 18‐crown‐6. The molecular structure of the hyperbranched polymers was confirmed with ¹H NMR and ¹³C NMR spectra. The ratio of initiator to monomer significantly affects the architecture of the resultant polymers. When the ratio of initiator to monomer equals 1 in the oxyanionic vinyl polymerization of HEMA, the degree of branching of the resulting polymer was calculated to be around 0.49. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3502–3509, 2005     

UV‐activated hydrosilylation: a facile approach for synthesis of hyperbranched polycarbosilanes

A facile approach for synthesis of hyperbranched polycarbosilane from AB₂ monomer via UV‐activated hydrosilylation is presented in this communication. The polymerization process was monitored using real‐time FTIR spectroscopy and the resulting hyperbranched polycarbosilanes were characterized using ¹H‐NMR, ¹³C‐NMR, ²⁹Si‐NMR and SEC/MALLS. It is found that hyperbranched polycarbosilane can be synthesized from methyldiallylsilane via UV‐activated hydrosilylation with bis(acetylacetonato)platinum(II) as catalyst. The polymerization activated by UV irradiation was much faster than that under thermal conditions. The similar degree of branching, average number of branch units and the exponent of the Mark–Houwink equation demonstrate that the hyperbranched polycarbosilane synthesized via UV‐activated polyhydrosilylation possesses almost the same branching structure as that synthesized via thermal‐activated polyhydrosilylation. Copyright © 2009 John Wiley & Sons, Ltd.     

A new copolymerization process leading to poly(propylene carbonate) with a highly enhanced yield from carbon dioxide and propylene oxide

Using excessively loaded propylene oxide (PO) as a solvent, the copolymerization of carbon dioxide (CO₂) and PO was carried out with zinc glutarate catalyst, consequently producing poly(propylene carbonate) of high molecular weight in a high yield (64–70 g polymer per gram of catalyst) never achieved before. Both the PO used as solvent and the excessively loaded CO₂ were fully recoverable, respectively, and reusable for their copolymerization, indicating that this is a clean, green polymerization process to convert CO₂ to its polycarbonate. The polymer yield was further improved by scaling up the copolymerization process. Among zinc glutarate catalysts prepared through several synthetic routes, one from zinc oxide delivered the highest yield in the copolymerization. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1863–1876, 1999     

Hyperbranched polycarbosiloxane with dendritic boron cores: Synthesis,characterization, and structure regulation

The synthesis, characterization, and structure regulation of hyperbranched polycarbosiloxane with dendritic boron cores were realized in this paper. First, dendritic boron core was synthesized via hydroboration with borane dimethylsulfide and bis(allyloxy)dimethylsilane. Then, the hyperbranched polycarbosiloxanes with dendritic boron cores were synthesized via hydrosilylation with AB₂ type monomer of bis(allyloxy)methylsilane and dendritic boron cores. The molecular structures of the dendritic boron core and resulting hyperbranched polymers were characterized by using Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance, and ¹³C nuclear magnetic resonance spectroscopies. Size exclusion chromatography/multiangle laser light scattering analysis reveals that the structures of hyperbranched polycarbosiloxane can be regulated effectively by incorporation of functional dendritic boron cores. Compared with hyperbranched polycarbosiloxane of the same molecular weight level, the hyperbranched polycarbosiloxane with dendritic boron cores presents narrower molecular weight distribution as well as much smaller hydrodynamic radius and intrinsic viscosity. Thermalgravimetric analyzer analysis indicates that both the decomposition temperature and ceramic yields are increased as the results of the incorporation of dendritic boron cores into hyperbranched polycarbosiloxane. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3930–3941, 2006     

Synthesis of hyperbranched polymer having binaphthol units via oxidative cross‐coupling polymerization

The oxidative coupling polymerization of triphenylamine derivatives having 2‐naphthol moieties with a CuCl‐2,2′‐isopropylidenebis(4‐phenyl‐2‐oxazoline) catalyst under an O₂ atmosphere was carried out. The polymerization of the monomer bearing both the hydroxynaphthoate and naphthol units afforded a hyperbranched polymer with a high cross‐coupling selectivity of > 99%, which showed a number‐average molecular weight of 20.3 × 10³. In addition, the obtained polymer was quite soluble in THF. The photoluminescence and electrochemical properties of the obtained polymers were also examined. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1034–1041, 2008     

A facile synthetic strategy for hyperbranched polymer via combining free radical telomerization and polycondensation

A facile strategy combining free radical telomerization and polycondensation to prepare hyperbranched polymers was developed. By selecting a suitable telogen and a vinyl monomer, the product obtained by telomerization could be regarded as an AB_n type monomer for preparing a hyperbranched polymer via conventional polycondensation. The principles for selecting vinyl monomers and telogens were proposed. The feed ratio of vinyl monomer to telogen was discussed in the theory. For demonstrating the strategy, methyl (meth)acrylate (MA or MMA) and 2‐mercaptoethanol were used as a vinyl monomer and a telogen, respectively. The two‐unit adduct of MA or MMA obtained after purifying was regarded as a model ABB′ monomer. The sequential transesterification demonstrated that the carboxylate group at the terminal unit has higher reactivity than that at penultimate unit because of the different substituents at the respective α‐positions, resulting in lower degree of branching (DB) of obtained polymer. As substitutes, 2‐hydroxyethyl (meth)acrylate and thioglycolic acid were used as a vinyl monomer and a telogen, respectively. The results showed that the hyperbranched polymer obtained by using pseudo one‐pot approach had moderate DB. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7543–7555, 2008     

Preparation of hyperbranched macromolecules with aryl fluoride and phenol terminal functionalities using new monomers and Cs2CO3 or Mg(OH)2 as the condensation agent

New A₂B monomers were synthesized for preparation of hyperbranched aryl ether sulfone macromolecules with aryl fluoride and phenol terminal functionalities. The macromolecules, which possess high thermal stability, were prepared using the divergent approach. A masked phenol with two aryl fluoride groups and a bisphenol with an aryl fluoride group were the monomers used to synthesize these polymers. In both cases, the aryl fluoride group is activated by a sulfone moiety. The synthetic method used for the preparation of the hyperbranched macromolecules gave a fast reaction and a high yield. These methods include, e.g., the use of Cs₂CO₃ and Mg(OH)₂ to generate the phenolate ion in situ. Use of the latter results in the formation of insoluble magnesium fluoride. The best conditions for the reaction utilized the more active nucleophilic polycondensation agent, Cs₂CO₃, and an aryl carbonate as a masked phenol. NMR, SEC, and MALDI-TOF-MS were used to characterize the samples. MALDI-TOF-MS allowed us to identify the different oligomeric species present, and it also indicated that an internal cyclization competes with the polymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2015–2033, 1997     

Copolymerization of carbon dioxide and propylene oxide using an aluminum porphyrin system and its components

The catalytic activities of tetraphenylporphinatoaluminum chloride (TPPAlCl) and its propylene oxide adduct (TPPAl(PO)₂Cl) were investigated in detail together with a quarternary salt Et₄NBr for the copolymerization of carbon dioxide and propylene oxide. In addition, for the components and starting raw materials of the catalyst systems, catalytic activities were examined for the copolymerization. The TPPAlCl catalyst delivered oligomers containing ether linkages to a large extent, regardless of its PO adduction. And cyclic propylene carbonate, as byproduct, was formed in a very small portion. Using the TPPAlCl coupled with Et₄NBr as a catalyst system, the formation of ether linkages was reduced significantly in the copolymerization; however, the obtained oligomer still contained ether linkages of 25.0 mol % in the backbone. On the other hand, the formation of cyclic carbonate was increased to 22.4 mol % relative to the oligomer product. The results indicate that the salt, which was coupled with the TPPAlCl catalyst, plays a key role in reducing the formation of ether linkage in the oligomer and, however, in enhancing the formation of cyclic carbonate. Similar results were obtained for the copolymerization catalyzed by the TPPAl(PO)₂Cl/Et₄NBr system. That is, the formation of ether linkages was not restricted further by the PO adduction of the TPPAlCl component in the catalyst system. Only oligomers with a relatively high molecular weight were produced. This indicates that the PO adduction of the TPPAlCl component contributes highly to the initiation and propagation step in the oligomerization, consequently leading to a relatively high molecular weight oligomer. In contrast, the Et₄NBr, as well as the Et₂AlCl, produced only cyclic carbonate in a very low yield. Furthermore, tetraphenylporphine exhibited no catalytic activity, regardless of using together with Et₄NBr. On the other hand, the Et₂AlCl coupled with Et₄NBr provided a low molecular weight oligomer having ether linkages of 92.3 mol % in addition to the cyclic carbonate. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3329–3336, 1999     

Hyperbranched Aromatic Polyesters

Summary: Having developed a theoretical model of hyperbranched polymerization involving AB₂ and B₂ monomers we present preliminary results of a test of its validity for the system consisting of 4,4-bis(4-hydroxyphenyl)pentanoic acid (AB₂ monomer) and bisphenol A (B₂ monomer). The monomers reacted at room temperature to yield the title hyperbranched polyesters. Diisopropylcarbodiimide (condensation water remover) along with an effective catalyst were used for that purpose. The total of AB₂ monomer was introduced at once to a reactor containing B₂ core monomer or it was divided into 3 or 5 equal portions and each of them introduced after the monomers previously present have reacted to a predetermined conversion. GPC measurements of the resulting molecular mass distribution gave inconclusive results because of poor reproducibility of polymer isolation/purification procedure and/or insufficient accuracy of GPC technique.     

Polysiloxane‐containing benzoxazine moieties in the main chain

Polysiloxanes containing thermally curable benzoxazine units in the main chain have been synthesized. For this purpose, first the diallyl functional benzoxazine monomer is synthesized through the Mannich and respective ring closing reactions of 4,4′‐isopropylidenediphenol (bisphenol A), formaldehyde, and allyamine. Subsequent hydrosilylation reaction of the resulting allylic monomer (B‐ala) with 1,1,3,3‐tetramethyldisiloxane (TMDS) in the presence of Pt catalyst yields the corresponding oligo(B‐ala‐tetramethyldisiloxane)s (OBTMDS). Using the anionic polymerization route, OBTMDS was then converted to poly(bisbenzoxazinedimethylsiloxane)s (PBDMSs) by reacting with readily available cyclic oligomer octamethylcyclotetrasiloxane (D4) or decamethylcyclopentasiloxane (D5) in the presence of tetrabutylammonium hydroxide as catalyst. The structures of the precursor diallyl monomer, the intermediate oligomer, and the resulting polymers are confirmed by Fourier transform infrared and ¹H NMR analysis. Curing behavior of the products at various stages has also been studied by differential scanning calorimetry. Flexible transparent films of the PBDMSs are obtained by solvent casting. Thermal properties of the cured polymers are also investigated by thermogravimetric analysis. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010