Preparation and characterization of polydimethylsiloxanes with narrow molecular weight distribution

The preparation of polydimethylsiloxanes (PDMS) of narrow molecular weight distribution (MWD) by anionic polymerization of hexamethylcyclotrisiloxane (D₃) in an improved polymerization apparatus is described. Using (CH₃)₂Si(OLi)₂ as initiator and (CH₃)₃SiCl (TMCS) as terminating agent, polymers with only methyl groups were obtained with molecular weights ranging from 2 × 10³ to 2 × 10⁶. Kinetic investigations were performed only so far as necessary for controlling the polymerization under the chosen experimental conditions (solvent: n-hexane, solvating agent: hexamethylphosphortriamide (HMPT), polymerization temperature: 25°). The molecular weights of the polymers were determined by light-scattering and, after calibration, by viscometry and GPC. The non-uniformities of the samples with symmetrical MWD were estimated using the 4σ-method. The GPC apparatus had been calibrated with polystyrene and poly-α-methylstyrene samples of extremely small non-uniformity.     

Novel polyisobutylene/poly(dimethylsiloxane) bicomponent networks. I. Synthesis and characterization

The synthesis of novel polyisobutylene (PIB)/poly(dimethylsiloxane) (PDMS) bicomponent networks is described. The synthesis strategy (see Figure 1) was to prepare well-defined and -characterized allyl-tritelechelic polyisobutylenes [ϕ(PIB—C—C=C)₃] and SiH-ditelechelic poly(dimethylsiloxanes) (HSi–PDMS–SiH) and then crosslink these moieties by hydrosilation. The ϕ(PIB—C—C=C)₃ was prepared by living isobutylene polymerization followed by end-quenching with allyltrimethylsilane, whereas the HSi–PDMS–SiH was obtained by equilibrium polymerization of octamethylcyclotetrasiloxane and tetramethyldisiloxane. The detailed structures of the starting polymers were characterized by GPC and ¹H-NMR spectroscopy. A series of PIB/PDMS bicomponent networks of varying compositions and average molecular weights between crosslinks (M _c) of ∼ 20,000 g/mol were assembled. Optimum crosslinking conditions were defined in terms of H₂PtCl₆ catalyst concentration, nature of solvent, time, temperature, and stoichiometry of ∼ CH₂CH=CH₂/∼SiH groups, allowing for the convenient synthesis of well-defined model bicomponent networks. Swelling studies and elemental analysis confirm the correctness of the synthetic strategy. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1891–1899, 1998     

Three‐arm star ring opening metathesis polymers via alkyne‐azide click reaction

The click chemistry strategy is successfully applied for the preparation of three‐arm star (A₃) ring opening metathesis polymers. A well‐defined monoazide end‐functionalized poly(N‐ethyl oxanorbornene) and a poly(N‐butyl oxanorbornene) obtained via ring opening metathesis polymerization using first generation Grubbs' catalyst are simply clicked with the trisalkyne core affording the synthesis of target star polymers. The obtained star polymers are characterized via nuclear magnetic resonance spectroscopy and gel permeation chromatography (GPC). The deconvolution analyses of GPC traces reveal that the click reaction efficiency for the star formation strongly depends on the chemical nature and the molecular weight of ROM polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2344–2351, 2009     

Cyclic Polysiloxanes with Linked Cyclotetrasiloxane Subunits

Cyclic polymers are an important class of macromolecules, but the structural diversity of the backbone is limited. Herein we report the use of the Piers–Rubinsztajn reaction for the one‐step synthesis of cyclic polysiloxanes with novel structural features. Specifically, the B(C₆F₅)₃‐catalyzed coupling of various organic tris(dimethylsiloxy)silane and trialkoxysilane compounds generated a series of cyclic polysiloxanes with cyclotetrasiloxane subunits. The thiolated cyclic polymers were also shown to be effective in directing the circular assembly gold nanoparticles. The presence of constrained rings in the backbone is unprecedented and may offer opportunities for novel applications of these cyclic polymers.     

Preparation of 3‐arm star polymers (A3) via Diels–Alder click reaction

Diels–Alder click reaction was successfully applied for the preparation of 3‐arm star polymers (A₃) using furan protected maleimide end‐functionalized polymers and trianthracene functional linking agent (2) at reflux temperature of toluene for 48 h. Well‐defined furan protected maleimide end‐functionalized polymers, poly (ethylene glycol), poly(methyl methacrylate), and poly(tert‐butyl acrylate) were obtained by esterification or atom transfer radical polymerization. Obtained star polymers were characterized via NMR and GPC (refractive index and triple detector detection). Splitting of GPC traces of the resulting polymer mixture notably displayed that Diels–Alder click reaction was a versatile and a reliable route for the preparation of A₃ star polymer. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 302–313, 2008     

Influence of side chains assembly on the structure and transport properties of comb-like polysiloxanes in hydrocarbon separation

We have synthesized a number of comb-like polysiloxanes with linear, branched, cyclic and silicon-containing substituents; most of them are new and previously not studied polymers. The physicochemical properties of comb-like polysiloxanes have been systematically investigated. Differential-scanning calorimetry and wide-angle X-ray scattering data revealed the side-chain microphase assembly for polymers with linear aliphatic substituents, while the polymers with bulky substituents did not form a microphase. It is shown that the ratio of microphase in the polymer is greater, the closer the values of the thickness of the microphase layer and the length of the cross-link. The effect of the side-chain substituent on the hydrocarbon transport properties of comb-like polysiloxanes was studied. All synthesized polymers are promising as membrane materials for a vital process of hydrocarbon separation. This is associated with an increase in the solubility selectivity of n-butane/methane because the solubility coefficient of methane sharply decreases when long side chains are introduced into the polysiloxane. It was shown for the first time that microphase forming polymers have a significantly higher butane/methane selectivity (23.2–27.5) than polysiloxanes not forming a microphase (selectivity 12.3–20.0). The effect is demonstrated on polysiloxanes with various types of side substituents. It was revealed that for the comb-like polysiloxanes, the diffusivity selectivity and permselectivity are proportional to the fraction of the side-chain microphase in the polymer. With the increase in the hydrocarbon microphase share, the diffusion coefficient of the permanent gas methane is decreasing more rapidly than n-butane, which dissolves well in hydrocarbons and plasticizes polymer. Consequently, the polymers forming the microphase have a higher selectivity C₃₊/CH₄ in the separation of a multicomponent hydrocarbons mixture.     

Effects of Chain Ends on Thermal and Mechanical Properties and Recyclability of Poly(γ-butyrolactone)

This work investigates effects of poly(γ-butyrolactone) (PγBL) with different initiation and termination chain ends on five types of materials properties, including thermal stability, thermal transitions, thermal recyclability, hydrolytic degradation, and dynamic mechanical behavior. Four different chain-end-capped polymers with similar molecular weights, BnO-[C(=O)(CH₂)₃O]_n-R, R = C(=O)Me, C(=O)CH=CH₂, C(=O)Ph, and SiMe₂CMe₃, along with a series of uncapped polymers R′O-[C(=O)(CH₂)₃O]_n-H (R′ = Bn, Ph₂CHCH₂) with M_n ranging from low (4.95 kg mol⁻¹) to high (83.2 kg mol⁻¹), have been synthesized. The termination chain end R showed a large effect on polymer decomposition temperature and hydrolytic degradation, relative to H. Overall, for those properties sensitive to the chain ends, chain-end capping renders R-protected linear PγBL behaving much like cyclic PγBL. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2271–2279     

Syntheses and characterization of poly (tetrahydrofuran) polyols with multifunctional oxocarbenium perchlorates as initiator

New oxocarbenium perchlorates, [(C₂H₅)_(4-n)C(CH₂OCH₂CH₂CO⁺ClO)_n, n = 3, 4] were synthesized and used in the preparation of poly (tetrahydrofuran) (PTHF) polyols. The structures of PTHF polyols and corresponding hydrolysis products were determined by ¹H-NMR and FTIR. GPC curves showed that the amount of cyclic oligomers was negligible. The polymerization process was followed by gas chromatography. Kinetic studies showed no termination reaction. The mechanism of the polymerization was discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3391–3399, 1999     

Mixed-matrix membranes comprising graphene-oxide nanosheets for CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> separation: A comparison between glassy and rubbery polymer matrices

The effect of graphene oxide (GO) nanosheets on the CO₂/CH₄ separation performance of a rubbery (poly(dimethylsiloxane), PDMS) as well as a glassy (polyetherimide, PEI) polymer is studied. Interfacial interactions between the nanosheets and both polymers are revealed by FTIR and SEM. The results of gas permeation through the membranes demonstrate that GO nanosheets enhance CO₂/CH₄ diffusivityselectivity of PEI and CO₂/CH₄ solubility-selectivities of the PEI and PDMS polymers, while diminish CO₂/CH₄ diffusivity-selectivity of PDMS. Furthermore, the possibility of overcoming the common tradeoff between CO₂ permeability and CO₂/CH₄ selectivity of rubbery and glassy polymers by incorporating very low amounts of graphene oxide nanosheets is addressed. In other words, at 0.25 wt % GO loading, the PEI membrane shows simultaneous enhancement of CO₂ permeability (16%) and CO₂/CH₄ selectivity (59%). Also, for the PDMS membrane simultaneous enhancement of CO₂ permeability (29%) and CO₂/CH₄ selectivity (112%) is occurred at 0.5 wt % GO loading. Finally, the capability of the well known Nielsen model to predict the gas permeability behavior of the nanocomposites is investigated.     

Synthesis and Characterization of Base‐catalyzed Phenyl Modified PDMS/PHMS Copolymers

A series of phenyl modified polydimethylsiloxane (PDMS) / polyhydrogenmethylsiloxane (PHMS) random copolymers containing both internal Si‐H and terminal SiH₂ and T (MeSiO_3/2) units was synthesized in one step through n‐BuLi‐catalyzed ring‐opening polymerization of cyclic comonomers and characterized by GPC, IR and ¹H and ²⁹Si NMR. Sequential microstructures of these copolymers were determined by ²⁹Si‐NMR spectroscopy. Epoxy‐modified polysiloxanes were prepared and used as comparable standards for the assignment of the NMR spectra. A hydride‐transfer mechanism has been proposed to account for the formation of terminal Si‐H and T group. Detailed sequential analyses and chemical shifts of ²⁹Si‐NMR for various siloxane units are reported for the first time.     

Polymer Structures and Glass Transition: A Molecular Dynamics Simulation Study

Full atomistic molecular dynamics (MD) simulations on five polymers with different chain backbone (C—C, Si—O, and C—O) and different side groups (—H, one —CH₃, and two —CH₃) are performed to study the effects of chain flexibility and side groups on the glass transition of polymers. Molecular dynamics simulations of NPT (constant pressure and constant temperature) dynamics are carried out to obtain specific volume as a function of temperature for polyethylene (PE), poly(propylene) (PP), polyisobutylene (PIB), poly(oxymethylene) (POM), and poly(dimethylsiloxane) (PDMS). The volumetric glass transition temperature has been determined as the temperature marking the discontinuity in slope of the plots of V–T simulation data. Various energy components at different temperatures of the polymers are investigated and their roles played in the glass transition process are analyzed. In order to understand the polymer chain conformations above and below the glass transition temperature, dihedral angle distributions of polymer chains at various temperatures are also studied.     

Linear polymers of some vinyl monomers containing a terminal acetylenic group

The synthesis and polymerization of representative acrylic-type esters containing a terminal acetylene group, CH₂?C(R)COO(CHR′)_m? C?CH, where R and R′ are H and CH₃ and m = 1 or 2, by anionic initiation to linear polymers are described. In contrast, crosslinked polymers were formed when radical and cationic initiators were used. Crosslinked polymers were also obtained with organolithium compounds but not with sodium naphthalene and sodium benzalaniline; this observation is discussed and compared to the behavior of the acetylenic acrylic esters which do not contain a terminal acetylenic hydrogen. The unpolymerized acetylenic bonds in the resulting linear polymers were shown to be present by infrared spectroscopic methods and by the following post-reactions of these bonds: (1) the heat- and radical-initiated crosslinking of the polymers through the acetylenic bonds; (2) the post-bromination of the acetylenic bonds; and (3) the reaction of decaborane with the acetylenic bonds. The anionic copolymerization of acrylonitrile and styrene with these acetylenic monomers were performed and compared to the copolymerizations with 1-acryloxy-2-butyne and 1-methacryloxy-2-butyne. Dibromination of the linear polymers affords self-extinguishing polymers, while decaboronation yields soluble polymers which do not soften up to 300°C. The linear polymers may be classified as “self-reactive” polymers which yield thermosetting polymers.     

Dipole moments of some poly(dimethylsiloxane) linear chains and cyclics

Dielectric constant measurements were carried out on poly(dimethylsiloxane) (PDMS) linear chains CH₃-[Si(CH₃)₂O]_x-Si(CH₃)₃ and cyclics

for $\text{x ? 10, 15}\text{and}\text{70}$, in cyclohexane and in benzene at 30°C. Mean-square dipole moments 〈μ²〉 were calculated from these data, using the method of Debye. The values thus obtained for the linear chains are consistent with results previously reported for short, linear PDMS chains in the undiluted state. Discernible differences among the values in the two solvents and undiluted state are manifestations of the “specific solvent effect” known to be important in longer linear chains the networks of PDMS. The cyclics were found to have dipole moments very similar to those of the corresponding linear chains. The cyclics also showed a specific solvent effect, in the same direction as shown by the linear molecules.     

Lipase‐Catalyzed Ring‐Opening Polymerization of β‐Butyrolactone: End‐Group Analysis of Poly(3‐hydroxybutanoate) Using Supercritical Fluid Chromatography

The ring‐opening polymerization of (R,S)‐β‐butyrolactone (BL) in bulk was analyzed with respect to the polymer structure of the resulting poly[(R,S)‐3‐hydroxybutanoate)] [P(3HB)] by isolation of the pure form using preparative supercritical CO₂ fluid chromatography. It was confirmed that the four‐membered BL was polymerized in bulk by lipase to yield the corresponding cyclic, hydroxy‐ and crotonate‐terminated P(3HB)s. The relative ratios of the three types of polymers depended on the lipase concentration as well as on the monomer conversion. It was also confirmed that both cyclic and linear P(3HB) polymer species were subject to hydrolysis, and inter‐ and intramolecular transesterification by lipase to produce two series of polymers having linear and cyclic structures with higher and lower molecular weight. The formation of the cyclic P(3HB) iss regarded as the characteristic feature of the lipase‐catalyzed polymerization of BL.     

Modification of polymethylhydrosiloxane by dehydrocoupling reactions catalyzed by transition metal complexes: Evidence for the preservation of linear siloxane structures

Polysiloxanes with pendant poly(ethylene oxide) side chains (4 were prepared by the dehydrocoupling reaction of poly(methylhydrosiloxane) (PMHS, 3 with 2-(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethoxy)ethanol (1 and poly(ethylene glycol) methyl ether (2 using a metal catalyst. Catalysts investigated were tin(II) 2-ethylhexanoate, Rh(Ph₃P)₃Cl, and Pd₂(dba)₃. The reaction of a cyclic siloxane, D₄^H, with 1 catalyzed by Pd₂(dba)₃ was also carried out to synthesize siloxane 6. The polysiloxanes were characterized by ¹H NMR, ²⁹Si NMR, FT-IR, and GPC. ²⁹Si NMR study of these comb-like polysiloxanes revealed that there is a significant difference in the structure of the siloxane polymers prepared depending upon the catalyst. M, D, and T units were observed when tin(II) was used as a catalyst, but only M and D units were detected when Rh(Ph₃P)₃Cl or Pd₂(dba)₃ was employed. Furthermore, M and T units are negligible for the cyclic siloxane 3 using Pd₂(dba)₃. A mechanism is proposed to account for these observations.     

Multiarm star polymers with POSS at the periphery

Azide end‐functionalized polyhedral oligomeric silsesquioxane (POSS‐N₃) was incorporated into the periphery of well‐defined alkyne‐polystyrene₅₀‐poly(divinyl benzene) (alkyne‐PS₅₀‐polyDVB) and alkyne‐poly(tert‐butyl acrylate)₄₃‐poly(divinyl benzene) (alkyne‐PtBA₄₃‐polyDVB) multiarm star polymers via highly efficient azide‐alkyne click reaction, resulting in POSS‐PS₅₀‐polyDVB and POSS‐PtBA₄₃‐polyDVB multiarm star block copolymers respectively, in the solution of tetrahydrofuran/N,N‐dimethyl formamide, CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) at room temperature for 24 h. Linear precursors and star polymers obtained in this study were characterized ¹H NMR, gel permeation chromatography (GPC), and triple detection GPC (TD‐GPC). Absolute molecular weight, hydrodynamic radius, and intrinsic viscosity ([η]) values for all star polymers were determined by TD‐GPC. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Block and star block copolymers by mechanism transformation. IV. Synthesis of S‐(PSt)2(PDOP)2 miktoarm star copolymers by combination of ATRP and CROP

A new tetrafunctional initiator, di(hydroxyethyl)‐2,9‐dibromosebacate (DHEDBS) [HOCH₂CH₂OOCCHBr(CH₂)₆CHBrCOOCH₂CH₂OH], was synthesized and used in preparation of A₂B₂ miktoarm star copolymers, (polystyrene)₂/ [poly(1,3‐dioxepane)]₂ [S‐(PSt)₂(PDOP)₂], by transformation of atom transfer radical polymerization (ATRP) to cationic ring‐opening polymerization (CROP). First, two‐armed PSt with two primary hydroxyl groups sited at the center of macromolecule [(PStBr)₂(OH)₂] was obtained by ATRP of St with the initiation system of DHEDBS/CuBr/bpy, and used as a chain‐transfer agent in the CROP of DOP with triflic acid as the initiator. Therefore, A₂B₂ miktoarm star copolymer S‐(PSt)₂(PDOP)₂ was formed. Its structure was confirmed by the ¹H NMR spectrum. Gel permeation chromatography (GPC) curves show that the polymers obtained have a relatively narrow molecular weight distribution. The hydrolysis product of S‐(PSt)₂(PDOP)₂ was also characterized by ¹H NMR and GPC. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 437–445, 2001     

The effect of the core on the thermotropic behavior of three‐arm star poly[11‐(4′‐cyanophenyl‐4′′‐phenoxy)undecyl acrylate]s synthesized by atom transfer radical polymerization

“Three‐arm star” poly[11‐(4′‐cyanophenyl‐4′′‐phenoxy)undecyl acrylate]s were synthesized by atom transfer radical polymerization (ATRP) of 11‐(4′‐cyanophenyl‐4′′‐phenoxy)undecyl acrylate using two new trifunctional initiators: 1,3,5‐tri‐ (methyl 2‐bromopropionate)benzene and 2,4,6‐tri[4′‐methyl(2′′‐bromopropionate)phenoxymethyl]mesitylene. The polymers synthesized with 1,3,5‐tri(methyl 2‐bromopropionate)benzene (series II) contained 14–127 repeat units according to gel permeation chromatography relative to linear polystyrene (GPC_PSt) and 13–271 repeat units according to GPC with a light scattering detector (GPC_LS). Those synthesized with 2,4,6‐tri[4′‐methyl(2′′‐bromopropionate)phenoxymethyl]mesitylene (series III) contained 14–87 repeat units according to GPC_PSt and 10–120 repeat units according to GPC_LS. The absolute molecular weight, size, and shape of both series of polymers were characterized by light scattering in CH₂Cl₂, and their thermotropic behavior was analyzed using differential scanning calorimetry; both types of properties were compared to those of the other architectures, especially the corresponding three‐arm star poly[11‐(4′‐cyanophenyl‐4′′‐phenoxy)undecyl acrylate]s synthesized previously using 1,3,5‐trisbromomethylmesitylene as the initiator. The size and shape of the three‐arm star polymers in CH₂Cl₂ are similar, although the isotropization temperature in the solid state decreases and the breadth of the isotropization transition increases with increasing size and flexibility of the trifunctional core. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4363–4382, 2008     

Modified horner–emmons reaction of polymeric phosphonates: Versatile synthesis of pendant stilbene-containing polymers

Poly[styrene-co-(diethyl vinylbenzylphosphonate)] and poly[methylmethacrylate-co-(diethyl vinylbenzylphosphonate)] were prepared and used in modified Horner-Emmons reactions to synthesize polymers with covalently attached stilbene groups. This versatile new method allowed for the preparation of polymers with either electron-donor (OCH₃, CH₃) or electron acceptor (Br, NO₂) substituents on the stilbene aromatic ring. The resulting polymers were characterized by ¹H NMR, FT-IR, UV-visible, DSC, and size exclusion chromatography. Efficient transformation of polymeric phosphonates to the polymeric stilbene derivatives was realized. Size exclusion chromatographic analyses demonstrated that the reaction conditions have no deleterious effect on the molecular weight distribution of the various polymers that were prepared. Photochromic behavior was demonstrated for one of the derivatives. © 1995 John Wiley & Sons, Inc.     

Vinyl ethers with a functional group: Living cationic polymerization and synthesis of monodisperse polymers

The living cationic polymerization of vinyl ethers (VEs) having a (polar) functional pendant has been achieved by the hydrogen iodide/iodine (HI/I₂) initiating system to give polymers with a very narrow molecular weight distribution (MWD) (M_w/M_n ≤ 1.2). The functional pendants include benzyl, saturated or unsaturated ester, (poly) oxyethylene, and substituted phenoxyl groups. Although these polar groups often disturb cationic vinyl polymerization by inducing chain transfer and termination, the HI/I₂ initiator cleanly polymerized the “functionalized” VEs without side reactions, mostly in nonpolar media at low temperatures below −15 °C. The HI/I₂-initiated living polymerization also provided facile methods to synthesize new functional polymers, including water-soluble polymers, macromolecular amphiphiles, and macromers, all having a narrow MWD. The simplest example is the living polymerization of VEs carrying an oxyethylene chain [-(CH₂CH₂O)_n-R] as pendant, which directly yields water-soluble polymers. The debenzylation of poly(benzyl VE) prepared with HI/I₂ led to poly(vinyl alcohol). Polymers of the saturated ester-containing monomers (2-acetoxyethyl and 2-benzoyloxyethyl VEs) were readily hydrolyzed into poly (2-hydroxyethyl VE), soluble in water and swellable in methanol. This lead was extended to the synthesis of a new amphiphile, poly(cetyl VE-b-2-hydroxyethyl VE), from a block copolymer of cetyl and 2-acetoxyethyl VEs prepared by their sequential living polymerization initiated with HI/I₂. An adduct between HI and 2-vinyloxyethyl methacrylate [CH₃-CH(I)-OCH₂CH₂OCOC(CH₃) =CH₂] was found to initiate living polymerizations of VEs in the presence of iodine; the products were methacrylate-type macromers carrying a poly(VE) side chain with a narrow chain-length distribution.