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     

A “click” approach to ROMP block copolymers

Amphiphilic block copolymers can be conveniently prepared via convergent syntheses, allowing each individual polymer block to be prepared via the polymerization technique that gives the best architectural control. The convergent “click‐chemistry” route presented here, gives access to amphiphilic diblock copolymers prepared from a ring opening metathesis polymer and polyethylene glycol. Because of the high functional group tolerance of ruthenium carbene initiators, highly functional ring opening metathesis polymerization (ROMP) polymer blocks can be prepared. The described synthetic route allows the conjugation of these polymer blocks with other end‐functional polymers to give well‐defined and highly functional amphiphilic diblock copolymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2913–2921, 2008     

Dendronized polymers via Diels–Alder “click” reaction

A modular approach toward the synthesis of polymers containing dendron groups as side chains is developed using the Diels–Alder “click” reaction. For this purpose, a styrene‐based polymer appended with anthracene groups as reactive side chains was synthesized. First through third‐generation polyester dendrons containing furan‐protected maleimide groups at their focal point were synthesized. Facile, reagent‐free, thermal Diels–Alder cycloaddition between the anthracene‐containing polymer and latent‐reactive dendrons leads to quantitative functionalization of the polymer chains to afford dendronized polymers. The efficiency of this functionalization step was monitored using ¹H and ¹³C NMR spectroscopy and FTIR and UV–vis spectrometry. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 410–416, 2010     

Combining cationic ring‐opening polymerization and click chemistry for the design of functionalized polyurethanes

A straightforward strategy for the synthesis and functionalization of polyurethanes (PUs) via the use of alkyne‐functionalized polytetrahydrofuran (PTHF) diols is described. The alkyne groups have been introduced into the PTHF chains by the cationic ring‐opening copolymerization of tetrahydrofuran and glycidyl propargyl ether. These PTHF prepolymers were combined with 1,4‐butanediol and hexamethylene diisocyanate for the synthesis of linear PUs with latent functionalization sites. The polyether segments of the PUs have then been coupled with several types of functionalized azides by the copper‐catalyzed azide‐alkyne “click” chemistry, for example with phosphonium containing azides for their antibacterial properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Photo‐initiated thiol–ene “click” hydrogels from RAFT‐synthesized poly(N‐isopropylacrylamide)

Despite the efficiency and robustness of the widely used copper‐catalyzed 1,3‐dipolar cycloaddition reaction, the use of copper as a catalyst is often not attractive, particularly for materials intended for biological systems. The use of photo‐initiated thiol‐ene as an alternative “click” reaction to synthesize “model networks” is investigated here. Poly(N‐isopropylacrylamide) precursors were synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization and were designed to have trithiocarbonate moieties as end groups. This structure design provides opportunity for subsequent end‐group modifications in preparation for thiol‐ene “click.” Two reaction routes have been proposed and studied to yield thiol and ene moieties. The advantages and disadvantages of each reaction path were investigated to propose a simple but efficient route to prepare copper‐free “click” hydrogels. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4626–4636     

Synthesis and characterization of a chlorofunctionalized unsaturated carbosilane oligomer

Acyclic diene metathesis (ADMET) polymerization offers a viable route for the synthesis of chlorofunctionalized unsaturated carbosilane oligomers. The Si Cl bond in unsaturated carbosilane monomers remains inert during metathesis and the use of a highly reactive molybdenum-based, Lewis acid-free alkylidene catalyst affords unsaturated chlorofunctionalized carbosilane oligomers with known vinyl end groups. The first synthesis of an unsaturated carbosilane oligomer functionalized with a Si Cl bond was performed. A chlorofunctionalized silacyclopentene product was also observed, due to a backbiting reaction. This new class of functionalized oligomers has a low glass transition temperature and sites of unsaturation which may be used for further reaction. ADMET chemistry now provides access to a variety of chlorofunctionalized unsaturated carbosilanes which can be used to tailor make hydrolytically stable carbosilane oligomers and polymers via nucleophilic grafting reactions.     

Combining “click” chemistry and step‐growth polymerization for the generation of highly functionalized polyesters

Aliphatic polyesters bearing pendant alkyne groups were successfully prepared by step‐growth polymerization of different building blocks such as adipic acid and succinic acid in combination with an acetylene‐based diol, 2‐methyl‐2‐propargyl‐1,3‐propanediol, besides 1,4‐butanediol and ethylene glycol. It was demonstrated that the alkyne groups survive the high reaction temperatures (200 °C) in the presence of a radical inhibitor. The alkyne loading has been tuned by the ratio of the different monomers used, up to 25 mol % of alkyne groups. Subsequently, the alkyne groups have been reacted with azides by the copper‐catalyzed Huisgen 1,3‐dipolar cycloaddition reaction, a popular type of “click” chemistry. “Click” reactions have been performed quantitatively in the presence of benzyl azide and azide‐terminated poly(ethylene glycol), yielding brush copolymers in the latter case. Kinetic investigations about this click reaction have been performed by means of on‐line Fourier transform mid‐infrared spectroscopy, which was reported for the first time in the field of the click chemistry research. A whole range of functionalized polyesters, based on poly(ethylene succinate) and poly(butylene adipate), is available, the properties of which can be tailored by choosing the appropriate azide compound. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6552–6564, 2008     

Tadpole‐shaped amphiphilic copolymers prepared via RAFT polymerization and click reaction

The tadpole‐shaped amphiphilic copolymers with cyclic polystyrene as the head and a linear poly(N‐isopropylacrylamide) as the tail have been successfully synthesized by combination of reversible addition‐fragmentation chain transfer (RAFT) polymerization and “click” reaction. The synthesis involves two main steps: (1) preparation of a linear acetylene‐terminated PNIPAAM‐b‐PS with a side azido group anchored at the junction between two blocks; (2) intramolecular cyclization reaction to produce the cyclic PS block using “click” chemistry under high dilution. The structures, molecular weights, and molecular weight distributions of the resulted intermediates and the target polymers were characterized by their ¹H NMR, FTIR, and gel permeation chromatography. The difference of surface property between tadpole‐shaped polymer and its linear precursor was observed, and the water contact angles on the former surface are larger than that of the latter surface. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2390–2401, 2008     

Ethylene‐based copolymers with tunable content of polymerizable hindered phenols as nonreleasing macromolecular additives

Four comonomers bearing a highly efficient phenolic antioxidant unit and different methylene spacers between the aromatic ring and the double bond have been prepared and tested in copolymerization with ethylene using metallocene‐based catalysts. The possibility of obtaining a “masterbatch” suitable for melt blending with commercial polyolefins has been evaluated by modifying: (i) the structure of the functionalized comonomer, (ii) the kind of catalyst, and (iii) the polymerization conditions. Characterization of monomers and copolymers was accomplished by using ¹H and ¹³C NMR, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). Using the comonomer with the longest methylene spacer between the aromatic ring and the double bond, and rac‐(EBTHI)ZrCl₂ as catalyst, adjustable amounts of the antioxidant moiety can be incorporated into the polyethylene chains. TGA analysis carried out on some of the copolymers containing the antioxidant group showed no oxygen uptake before decomposition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6393–6406, 2008     

Use of blowing catalysts for integral skin polyurethane applications in a controlled molecular architectural environment: Synthesis and impact on ultimate physical properties

Polyurethane elastomers of a controlled molecular architecture were synthesized using a two‐step polymerization technique. The building blocks of the elastomeric materials included urea–urethane prepolymers end‐capped with diisocyanate groups and had an exact number of urea groups at both ends. Two‐dimensional bifurcated hydrogen‐bonding networks incorporating the urea groups were, with differential scanning calorimetric and dynamic mechanical thermal analyzer techniques, responsible for the increase in the glass‐transition temperature (T_g) of the hard block and sharp interface morphology between the pure “hard” domains and pure “soft” domains. The higher extent of the phase separation between the two phases contributed to higher elastic moduli for the hard blocks and higher tensile strength for the elastomeric samples. Higher elongation values were attributed to the liberation of the elastomeric chain ends that otherwise would have been constrained in the interface region. The higher T_g values of the hard blocks corresponded to an increase in the hardness values and a decrease in the tear‐strength values. The increase in the amount of urea groups within the hard segments, as a result of the increased amount of water and blowing catalyst, resulted in elastomeric foams with higher open‐cell content. This resulted in lower resilience values as measured using the pendulum rebound test and was attributed to the ability of the open cells to absorb and dissipate energy. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2526–2536, 2002     

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     

Thermally curable polyvinylchloride via click chemistry

Novel side‐chain benzoxazine functional polyvinylchloride (PVC‐Benzoxazine) was synthesized by using “Click Chemistry” strategy. First, approximately 10% of chloro groups of PVC were converted to azido groups by using NaN₃ in N,N‐dimethylformamide. Propargyl benzoxazine was prepared independently by a ring closure reaction between p‐propargyloxy aniline, paraformaldehyde, and phenol. Finally, azidofunctionalized PVC was coupled to propargyl benzoxazine with high efficiency by click chemistry. The spectral and thermal analysis confirmed the presence of benzoxazine functionality in the resulting polymer. It is shown that PVC containing benzoxazine undergoes thermally activated curing in the absence of any catalyst forming PVC thermoset with high thermal stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3512–3518, 2008     

Synthesis and solution properties of well‐defined comb‐on‐comb graft polymers

Well‐defined comb‐on‐comb copolymers of styrene, isoprene, and α‐methyl‐styrene are prepared through cascade “grafting‐onto” methods. The polymer main chain is prepared by nitroxide‐mediated radical polymerization while the branches are prepared by anionic polymerization. The “grafting‐onto” approach employs the coupling chemistry of macromolecular anions, such as polystyryllithium, polyisoprenyllithium, or poly(α‐methylstyryl)lithium, toward either benzyl chloride or epoxy ring on precursor backbones. Thus a series of ABA‐, ABB‐, and ABC‐type comb‐on‐comb copolymers are prepared and characterized by gel permeation chromatography equipped with a multi‐angle laser light scattering detector and a viscometer. Unusual “U‐shaped” dependences of radius of gyration, R_g, on molecular weight are observed for comb‐on‐comb products, which are attributable to delayed elution of the densely grafted copolymers from GPC columns. The result also shows that the comb‐on‐comb copolymers exhibit morphologies from hard sphere to cylindrical rod, depending on the length ratio of the main chain to the branches. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5518–5527, 2008     

Facile syntheses of 4‐vinyl‐1,2,3‐triazole monomers by click azide/acetylene coupling

Synthetic strategies for the preparation of a new family of vinyl monomers, 4‐vinyl‐1,2,3‐triazoles, have been developed. These monomers are noteworthy as they combine the stability and aromaticity of styrenics with the polarity of vinylpyridines and the structural versatility of acrylate/methacrylate derivatives. To enable the wide adoption of these unique monomers, new methodologies for their synthesis have been elaborated which rely on Cu‐catalyzed azide/acetylene cycloaddition reactions—“click chemistry”—as the key step, with the vinyl substituent being formed by either elimination or Wittig‐type reactions. In addition, one‐pot “click” reactions have been developed from alkyl halides, which allow for monomer synthesis without isolation of the intermediate organic azides. The high yield and facile nature of these procedures has allowed a library of new monomers including the parent compound, 1‐H‐4‐vinyl‐1,2,3‐triazole, to be prepared on large scales. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2897–2912, 2008     

Carbon nanotubes decorated with terpyridine‐ruthenium complexes

Surface functionalization of CNTs (SWCNTs or MWCNTs) with dendronized alkoxy terpyridine‐Ru(II)‐terpyridine complexes has been accomplished using either the “grafting to” or the “grafting from” approaches. Different sets of easily processable hybrid metallo‐CNTs composites have been efficiently synthesized bearing either monomeric or polymeric side chain tpy‐Ru(II)‐tpy dicomplexes. Their characterization through TGA, UV‐Vis, and Raman techniques revealed various modification degrees depending on the methodology employed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2551–2559, 2009     

UV‐induced crosslinking of ring opening metathesis block copolymer micelles

Statistical and amphiphilic block copolymers bearing cinnamoyl groups were prepared by ring opening metathesis polymerization (ROMP). The UV‐induced [2 + 2] cycloaddition reaction of polymer bound cinnamic acid groups was studied in polymer thin films as well as in block copolymer micelles. In both cases, exposure to UV‐light for 10 min led to a crosslinking conversion of about 60%, as determined by FT‐IR spectroscopy and UV–vis absorption measurements. Time based IR‐spectroscopy revealed a maximum conversion of 78% reached after an irradiation time of about 16 min. For micelles obtained from polymers bearing 5 mol % or more cinnamoyl groups, the crosslinking reaction proceeded smoothly, yielding in crosslinked particles which were stable in a non‐selective solvent (CHCl₃). Diameters determined by dynamic light scattering in the selective solvent (MeOH) were similar for both, non‐crosslinked and crosslinked micelles, whereas diameters of crosslinked micelles in the non‐selective solvent (CHCl₃) were significantly larger compared to MeOH samples. This strategy of direct self assembly of block‐copolymers in a selective solvent followed by “clean” crosslinking, without the need for additional crosslinking reagents or crosslinking initiators, provides a straight forward approach toward ROMP‐based polymeric nano‐particles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2402–2413, 2008     

Structural recovery (physical ageing) of the friction coefficient of polymers

Most of the mechanical properties of the polymers are subject to structural recovery (physical ageing). The aim of this work was, therefore, to evaluate the sensitivity of the friction coefficient to physical ageing. The apparent friction coefficient is the ratio of the tangential force to the normal load applied to a moving tip in contact with the surface of a material. This coefficient includes a “true friction” at the interface and a “geometrical friction,” which is the lowing and bulk dissipative effect. In the case of solid polymers, the material underneath the moving tip may display various types of behavior: elastic, viscoelastic, elastoplastic (elastic and plastic strains are present in the contact area), or fully plastic. Scratching and sliding experiments were performed on PMMA to determine the true friction coefficient over a wide range of contact deformations. An analysis of the true friction coefficient as a function of the physical ageing (structural recovery) showed that the friction decreases with increasing structural recovery of the polymer in the case of sliding. Whatever the level of physical ageing, at a high contact strain (fully plastic contact), the true friction coefficient tended to a unique and high value independent of the thermal history of the polymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1337–1347, 2008     

Cationic Bis‐N‐Heterocyclic Carbene (NHC) Ruthenium Complex: Structure and Application as Latent Catalyst in Olefin Metathesis

An unexpected cationic bis‐N‐heterocyclic carbene (NHC) benzylidene ether based ruthenium complex ( 2 a ) was prepared through the double incorporation of an unsymmetrical unsaturated N‐heterocyclic carbene (U₂‐NHC) ligand that bore an N‐substituted cyclododecyl side chain. The isolation and full characterization (including X‐ray diffraction studies) of key synthetic intermediates along with theoretical calculations allowed us to understand the mechanism of the overall cationization process. Finally, the newly developed complex 2 a displayed interesting latent behavior during ring‐closing metathesis, which could be “switched on” under acidic conditions.     

Synthesis and crosslinking behavior of a novel linear polymer bearing 1,2,3‐triazol and benzoxazine groups in the main chain by a step‐growth click‐coupling reaction

The click‐coupling reaction was applied to polycondensation, to synthesize a high‐molecular weight prepolymer having benzoxazine moieties in the main chain. For the polycondensation, a bifunctional N‐propargyl benzoxazine was synthesized from bisphenol A, propargylamine, and formaldehyde. The propargyl group was efficiently used for the copper(I)‐catalyzed alkyne‐azide “click” reaction with p‐xylene‐α,α′‐diazide, to give the corresponding linear polycondensate having 1,2,3‐triazole junctions. The polycondensation proceeded in N,N‐dimethylformamide (DMF) at room temperature. By this highly efficient “click‐” polycondensation reaction, the benzoxazine ring in the monomer was successfully introduced into the polymer main chain without any side reaction. The obtained polymer (=prepolymer) underwent thermal crosslinking to afford the corresponding product, which was insoluble in a wide range of organic solvents and exhibited higher thermal stability than the polymer before crosslinking. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2316–2325, 2008