Chain internal/chain end latent crosslinking in thermoset polymer systems

The combination of both chain‐internal/chain‐end latent crosslinking in a single thermoset polymer system is the subject of this study. A series of linear carbosiloxane/hydrocarbon homopolymers were synthesized by metathesis polycondensation, polymers which serve as the soft phase in the target chain‐internal/chain‐end latent crosslinked materials. These carbosiloxane/hydrocarbon “soft phase” homopolymers exhibited excellent performance parameters, displaying purely amorphous character with glass transition temperatures ranging between ?104 °C and ?90 °C depending on the run length of siloxane or hydrocarbon methylene units within the carbosiloxane/hydrocarbon monomer. These soft phase monomers were then copolymerized with latent chain‐internal crosslinking carbosilane monomers in the presence of latent chain‐end crosslinking molecules thereby generating a new class linear copolymers capable of being moisture cured to produce a new class of silicon‐based thermoset systems. Mechanical properties of these thermosets, show breaking strengths up to 0.5 MPa and elongations up to 100%. Both elastic and plastic behavior can be observed in such systems, depending upon the molar ratio of carbosiloxane/hydrocarbon co‐monomer and the carbosilane co‐monomer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1866–1877, 2010     

Carbosilane/carbosiloxane‐based ADMET homopolymers and copolymers possessing latent reactivity

Reactive methoxy‐functionalized carbosilane and carbosiloxane dienes can be either homopolymerized or copolymerized via acyclic diene metathesis (ADMET) polycondensation chemistry to produce reactive materials with mechanical behavior dependent on the molar ratios of the comonomers. The methoxy‐functional group within the polycarbosilane repeat unit remains inert during the metathesis polymerization and can be triggered subsequently with water to generate crosslinks between polymer chains. In this way, linear, thermoplastic copolymers can be prepared with ADMET chemistry and converted into crosslinked, thermoset copolymers upon exposure to moisture. Crosslinked films containing 5–10% of the crosslinked hard segment are soft and flexible materials. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1544–1550, 2000     

Well‐defined thermosensitive,water‐soluble polyacrylates and polystyrenics with short pendant oligo(ethylene glycol) groups synthesized by nitroxide‐mediated radical polymerization

We report the synthesis and thermosensitive properties of well‐defined water‐soluble polyacrylates and polystyrenics with short pendant oligo(ethylene glycol) groups. Four monomers, methoxydi(ethylene glycol) acrylate (DEGMA), methoxytri(ethylene glycol) acrylate (TEGMA), α‐hydro‐ω‐(4‐vinylbenzyl)tris(oxyethylene) (HTEGSt), and α‐hydro‐ω‐(4‐vinylbenzyl)tetrakis(oxyethylene) (HTrEGSt), were prepared and polymerized by nitroxide‐mediated radical polymerization with 2,2,5‐trimethyl‐3‐(1‐phenylethoxy)‐4‐phenyl‐3‐azahexane as an initiator. Kinetics and gel permeation chromatography analysis showed that the polymerizations were controlled processes yielding polymers with controlled molecular weights and narrow polydispersities. All polymers could be dissolved in water, forming transparent solutions, and undergo phase transitions when the temperature was above a critical point. The thermosensitive properties were studied by turbidimetry and variable‐temperature ¹H NMR spectroscopy. The cloud points of the polymers of DEGMA, TEGMA, HTEGSt, and HTrEGSt were around 38, 58, 13, and 64 °C, respectively. For all four polymers, the cloud point increased with decreasing concentration and increasing molecular weight in the studied molecular weight range of 5000–30,000 g/mol. The removal of the nitroxide group from the polymer chain end resulted in a higher cloud point. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2454–2467, 2006     

Synthesis and characterization of oligo(oxyethylene)/carbosilane copolymers for thermoset elastomers via ADMET

Acyclic diene metathesis (ADMET) polymerization has been used to synthesize latent reactive processable elastomers constructed of carbosilane and polyether segments. Two types of latent modes have been introduced: “chain‐internal” and “chain‐end” sites through the use of labile silicon methoxy functionalities. These latent reactive groups are inert when exposed to metathesis conditions allowing formation of the linear copolymer; subsequently exposure to moisture triggers hydrolysis of the methoxy groups and formation of a chemically crosslinked thermoset. The thermoset's mechanical response can be potentially varied from plastic to elastic behavior, depending on the ratio of carbosilane and oligooxyethylene monomers employed. Different lengths of glycols and numbers of methylene groups between them in the polymer backbone have been investigated to explore structure/property relationship. Polymers composed of oligooxyethylenes with eight methylene groups in between them exhibited fully amorphous character, while the ones with up to 20 methylene groups between glycol units showed their semicrystalline nature. The concentration of “chain‐internal” and “chain‐end” crosslink sites enhances strength; modification to the run length and structure of the soft phase enhances elasticity. Resultant materials have been subjected to mechanical tests using Instron; generated stress/strain curves have shown plastic and elastic behavior. Depending on the composition obtained samples have shown moduli from 0.3 to 115 MPa, tensile strengths from 0.6 to 10 MPa and elongations from 20 to 700%. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3992–4011, 2008     

Synthesis and polymerization of amphiphilic methacrylates containing permanent dipole azobenzene chromophores

New amphiphilic photochromic methacrylates with the structures of 4‐[ω‐methacryloyloxyoligo(ethyleneglycol)]‐4′‐cyanoazobenzene (MEn) and 4‐methacryloyloxy‐4′‐{2‐cyano‐3‐oxy‐3‐[ω‐methoxyoligo(ethyleneglycol)]prop‐1‐en‐1‐yl}azobenzene (MEnMe) and oligo(oxyethylene) segments of different lengths were synthesized. These methacrylates were characterized by the presence of permanent dipole azobenzene chromophores and hydrophilic oligo (oxyethylene) segments. The methacrylates were obtained with six‐step and five‐step synthetic sequences, respectively, in 12–47% overall yields. The radical polymerization of the MEn monomers afforded a 50% yield of the corresponding polymers as orange solids with a number‐average molecular weight of about 40 kD. No solid polymer was obtained from the radical polymerization of the MEnME compounds. Two‐dimensional NMR spectra allowed the unequivocal assignment of the NMR signals and demonstrated a significant contribution of internal charge transfer to the electronic distribution of the azobenzene chromophore. Relaxation time measurements confirmed that the flexible polyether segment effectively decoupled photochromic groups from the polymer backbone. Optical microscopy, differential scanning calorimetry analysis, and X‐ray diffraction data demonstrated the presence of interdigitated smectic mesophases. The stability of mesophases showed a significant dependence on the chemical structure of the analyzed compounds. The glass‐transition temperatures of the polymers were rather low because of the plasticizing effect of the spacers. The monomers and polymers were used for the deposition of Langmuir films and Langmuir–Blodgett–Kuhn multilayers. A strong influence of the macromolecular structure on the film properties was observed. The photoresponsive properties of monomers and polymers were investigated with irradiation at different wavelengths. Isomerization kinetics were independent of both molecular weight and spacer length. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2957–2977, 2001     

Narrow disperse polymers using amine functionalized dithiobenzoate RAFT agent and easy removal of thiocarbonyl end group from the resultant polymers

A novel amine functionalized RAFT agent, 2‐cyanoprop‐2‐yl(4‐N,N‐dimethylaminophenyl) dithiobenzoate has been synthesized and used to control the polymerization of vinyl monomers. This dithiobenzoate RAFT agent, although air sensitive, controlled the polymerization of MMA and St very well in an inert atmosphere and the polymerization results obtained were marginally better than using the most popular 2‐cyanoprop‐2‐yl dithiobenzoate RAFT agent. The living nature of these polymerizations was confirmed by kinetics study and chain extension reactions to yield narrow disperse di‐block copolymers. Most importantly, use of this novel RAFT agent simplified the removal procedure of the color causing end thiocarbonyl group from the RAFT derived polymers and thereby leading to polymers with improved appearance. The removal of end group from the polymer was confirmed by ¹H NMR and UV‐vis spectroscopic techniques. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Spacer‐length‐dependent association in polymers with multiple‐hydrogen‐bonded end groups

Herein, we investigate the influence of spacer length on the homoassociation and heteroassociation of end‐functionalized hydrogen‐bonding polymers based on poly(n‐butyl acrylate). Two monofunctional ureido‐pyrimidinone (UPy) end‐functionalized polymers were prepared by atom transfer radical polymerization using self‐complementary UPy‐functional initiators that differ in the spacer length between the multiple‐hydrogen‐bonding group and the chain initiation site. The self‐complementary binding strength (K_dim) of these end‐functionalized polymers was shown to depend critically on the spacer length as evident from ¹H NMR and diffusion‐ordered spectroscopy. In addition, the heteroassociation strength of the end‐functionalized UPy polymers with end‐functionalized polymers containing the complementary 2,7‐diamido‐1,8‐naphthyridine (NaPy) hydrogen‐bond motif is also affected when the aliphatic spacer length is too short. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Triptycene‐containing polyetherolefins via acyclic diene metathesis polymerization

Several new triptycene‐containing polyetherolefins were synthesized via acyclic diene metathesis (ADMET) polymerization. The well‐established mechanism, high selectivity and specificity, mild reaction conditions, and well‐defined end‐groups make the ADMET polymerization a good choice for studying systematic variations in polymer structure. Two types of triptycene‐based monomer with varying connectivities were used in the synthesis of homopolymers, block copolymers, and random copolymers. In this way, the influence of the triptycene architecture and concentration in the polymer backbone on the thermal behavior of the polymers was studied. Inclusion of increasing amounts of triptycene were found to increase the glass transition temperature, from ?44 °C in polyoctenamer to 59 °C in one of the hydrogenated triptycene homopolymers ( H‐PT2 ). Varying the amounts and orientations of triptycene was found to increase the stiffness ( H‐PT1 ), toughness ( PT1₁‐b‐PO₁ ) and ductility ( PT1₁‐ran‐PO₃ ) of the polymer at room temperature. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Precision ADMET polyolefins containing dithiane: Synthesis,thermal properties,and macromolecular transformation

1,3‐Dithiane and its derivatives are widely used as powerful acyl anion equivalent to a range of useful transformations that are needed in the synthesis of natural products. In this work, a series of polyolefins containing pendant dithiane groups have been designed and synthesized via acyclic diene metathesis polymerization (ADMET) polymerization and subsequent hydrogenation. The structures of these polymers were characterized by ¹H NMR, ¹³C NMR, and FT‐IR, and successful incorporation of the dithiane groups was proved. With different contents of the dithiane moieties, these ADMET polymers exhibited distinct thermal properties different from each other as evidenced by differential scanning calorimetry and thermal gravimetric analysis. The dithiane units in the ADMET polymer with 20 methylene carbons between the adjacent dithiane groups were transformed into thiol groups via reaction with Bu₃SnH. This work provided a convenient route to synthesize polyethylene with pendant thiol groups that are evenly distributed in the chain. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2468–2475     

End group effect on the thermo‐sensitive properties of well‐defined water‐soluble polystyrenics with short pendant oligo(ethylene glycol) groups synthesized by nitroxide‐mediated radical polymerization

The effects of hydrophobic chain end groups on the cloud points of thermo‐sensitive water‐soluble polystyrenics were investigated. Well‐defined poly (4‐vinylbenzyl methoxytris(oxyethylene) ether) (PTEGSt) and poly(α‐hydro‐ω‐(4‐vinylbenzyl)tetrakis(oxyethylene)) (PHTrEGSt) were prepared by nitroxide‐mediated radical polymerization using α‐hydrido alkoxyamine initiators including two monomer‐based initiators. The polymers were reduced with (n‐Bu)₃SnH to replace the alkoxyamine end group with hydrogen. In the studied molecular weight range (M_n,GPC = 3000 to 28,000 g/mol), we found that the hydrophobic end groups decreased the cloud point by 1–20 °C depending on the molecular weight and the largest depression was observed at the lowest molar mass. The cloud points of PTEGSt and PHTrEGSt with two hydrophobic end groups, phenylethyl and alkoxyamine, exhibited a monotonic increase with the increase of molecular weight. For polymers with only one hydrophobic end group, either phenylethyl or alkoxyamine, the cloud point initially increased with the increase of molecular weight but leveled off/decreased slightly with further increasing molar mass. For polymers with essentially no end groups, the cloud point decreased with the increase of chain length, which represents the “true” molecular weight dependence of the cloud point. The observed molecular weight dependences of the cloud points of polystyrenics with hydrophobic end group(s) are believed to result from the combined end group effect and “true” molecular weight effect. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3707–3721, 2007     

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.     

Graft copolymers by acyclic diene metathesis and atom transfer radical polymerization techniques

Precise graft copolymer architectures were achieved by combining the macromonomer technique with the acyclic diene metathesis (ADMET) reaction. These well‐defined copolymer structures were the result of proper monomer design before metathesis polymerization. Features such as length of the graft, nature, and concentration of the graft site along the backbone were manipulated via the combination of living atom transfer radical polymerization methods with ADMET chemistry. Furthermore, the physical behavior of these materials was altered such that they presented dissimilar thermal properties of either the homopolymers or random copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2816–2827, 2003     

Side‐chain ferrocene‐containing (meth)acrylate polymers: Synthesis and properties

A comprehensive investigation on the synthesis and properties of a series of ferrocene‐containing (meth)acrylate monomers and their polymers that differ in the linkers between the ferrocene unit and the backbone was carried out. The side‐chain ferrocene‐containing polymers were prepared via atom transfer radical polymerization. The kinetic studies indicated that polymerization of most monomers followed a “controlled”/living manner. The polymerization rates were affected by the vinyl monomer structures and decreased with an increase of the linker length. Methacrylate polymerization was much faster than acrylate polymerization. The optical absorption of monomers and polymers was affected by the linkers. Thermal properties of these polymers can be tuned by controlling the length of the linker between the ferrocene unit and the backbone. By increasing the length of the linker, the glass transition temperature ranged from over 100 to ?20 °C. Electrochemical properties of both monomers and polymers were characterized. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Polyurethanes from polyols obtained by ADMET polymerization of a castor oil‐based diene: Characterization and shape memory properties

The acyclic diene metathesis polymerization (ADMET) of 1,3‐di‐10‐undecenoxy‐2‐propanol, a castor oil based diene, is reported. 10‐Undecenol was used as renewable comonomer to end‐cap polymer chains and limit the molecular weight. The poly ols obtained in this way were reacted with 4,4′‐methylenebis(phenylisocyanate) (MDI) to yield a series of amorphous and semicrystalline polyurethane networks. The thermal stability and the thermomechanical and mechanical properties of these thermosets have been studied and showed good shape memory properties for the semicrystalline polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Fatty acid derived phosphorus‐containing polyesters via acyclic diene metathesis polymerization

The acyclic diene metathesis (ADMET) polymerization of a phosphorus‐containing α,ω‐diene prepared from a plant oil derived building block is reported. Different ruthenium based metathesis catalysts and conditions were tested to optimize the ADMET polymerization of this monomer. Undecylenyl undecenoate was used as fully renewable comonomer to obtain polyesters with different phosphorus contents and to increase the renewable content of the final polymers. Copolymerization caused marked variations in the molecular weights leading to polyesters from 6 to 38 KDa. The effect of the ADMET polymerization temperature in the thermal properties of the copolymers was studied and their thermal degradation and flame retardant properties were evaluated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5760–5771, 2009     

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     

Synthesis and postfunctionalization of well‐defined star polymers via “double” click chemistry

In this article, the synthesis and the functionalization of well‐defined, narrow polydispersity (polydispersity index < 1.2) star polymers via reversible addition‐fragmentation chain transfer polymerization is detailed. In this arm first approach, the initial synthesis of a poly(pentafluorophenyl acrylate) polymer, and subsequent, cross‐linking using bis‐acrylamide to prepare star polymers, has been achieved by reversible addition fragmentation chain transfer polymerization. These star polymers were functionalized using a variety of amino functional groups via nucleophilic substitution of pentafluorophenyl activated ester to yield star polymers with predesigned chemical functionality. This approach has allowed the synthesis of star glycopolymer using a very simple approach. Finally, the core of the stars was modified via thiol‐ene click chemistry reaction using fluorescein‐o‐acrylate and DyLigh 633 Maleimide. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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     

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     

Phosphorus‐containing renewable polyester‐polyols via ADMET polymerization: Synthesis,functionalization, and radical crosslinking

An α,ω‐diene containing hydroxyl groups was prepared from plant oil‐derived platform chemicals. The acyclic diene metathesis copolymerization (ADMET) of this monomer with a phosphorus‐containing α,ω‐diene (DOPO II), also plant oil derived, afforded a series of phosphorus containing linear polyesters, which have been fully characterized. The backbone hydroxyls of these polyesters have been acrylated and radically polymerized to produce crosslinked polymers. The thermomechanical and mechanical properties, the thermal stability, and the flame retardancy of these phosphorus‐based thermosets have been studied. Moreover, methyl 10‐undecenoate has been used as chain stopper in selected ADMET polymerizations to study the effect of the prepolymers' molecular weights on the different properties of the final materials. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1649–1660, 2010