Christopher W Bielawski

Publications (10)54.56 Total impact

• Chapter: Telechelic Polymers from Olefin Metathesis Methodologies

  Christopher W. Bielawski, Marc A. Hillmyer
  03/2008: pages 255 - 282; , ISBN: 9783527619481
• Article: Synthesis of cyclic polybutadiene via ring-opening metathesis polymerization: the importance of removing trace linear contaminants.

  Christopher W Bielawski, Diego Benitez, Robert H Grubbs
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  ABSTRACT: The synthesis of cyclic polybutadienes using ring-opening metathesis polymerization (ROMP) was accomplished. A cyclic Ru alkylidene catalyst, where a terminal ligand was covalently linked to the Ru alkylidene, was used to polymerize either 1,5-cyclooctadiene (COD) or 1,5,9-trans-cis-trans-cyclododecatriene (CDT). Trace amounts of an acyclic impurity, 4-vinylcyclohexene, found in the COD led to samples which were contaminated with linear polymer. In contrast, CDT, which was free of the impurity, afforded pure cyclic polymer. These results provide a convenient method for discerning samples of pure cyclic polymer from those which contain trace to large amounts of linear polymer. Furthermore, they emphasize the need to use monomers that are free of acyclic impurities when preparing cyclic polymers using ROMP.
  Journal of the American Chemical Society 08/2003; 125(28):8424-5. · 9.91 Impact Factor
• Article: An "endless" route to cyclic polymers.

  Christopher W Bielawski, Diego Benitez, Robert H Grubbs
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  ABSTRACT: A new synthetic route to cyclic polymers has been developed in which the ends of growing polymer chains remain attached to a metal complex throughout the entire polymerization process. The approach eliminates the need for linear polymeric precursors and high dilution, drawbacks of traditional macrocyclization strategies, and it effectively removes the barrier to producing large quantities of pure cyclic material. Ultimately, the strategy offers facile access to a unique macromolecular scaffold that may be used to meet the increasing demand of new applications for commercial polymers. As a demonstration of its potential utility, cyclic polyethylenes were prepared and found to exhibit a variety of physical properties that were distinguishable from their linear analogs.
  Science 10/2002; 297(5589):2041-4. · 31.20 Impact Factor
• Article: Increasing the Initiation Efficiency of Ruthenium-Based Ring-Opening Metathesis Initiators:  Effect of Excess Phosphine

  Christopher W. Bielawski, Robert H. Grubbs
  11/2001;
• Article: Synthesis of End-Functionalized Poly(norbornene)s via Ring-Opening Metathesis Polymerization

  Christopher W. Bielawski, Diego Benitez, Takeharu Morita, Robert H. Grubbs
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  ABSTRACT: The synthesis of a variety of poly(norbornene)s (PNB)s bearing acetoxy, hydroxy, and vinyl end groups was accomplished. PNBs with an acetoxy group at one terminus and a vinyl group at the other were prepared using norbornene, ruthenium-based olefin metathesis catalyst (PCy3)2Cl2RuCHPh, and allyl acetate as a chain transfer agent (CTA). Employing a more active catalyst, (1,3-dimesityl-4,5-dihydroimidazol-2-ylidene)(PCy3)Cl2RuCHPh, and 1,4-diacetoxy-2-butene as the CTA afforded telechelic PNBs bearing acetoxy groups at both ends of the polymer chains. Molecular weights were controlled by varying the initial monomer/CTA ratio and were in agreement with their theoretical values. Using a similar procedure, acetoxy end-terminated PNBs were also obtained by degradation of high molecular weight PNB. Removal of the acetoxy groups afforded the corresponding hydroxy-terminated polymers with number-averaged functionalities close to two. Mechanisms are proposed for the formation of the end-functionalized polymers. Correction factors for characterizing PNBs by gel permeation chromatography (GPC) are also suggested.
  11/2001;
• Article: Tandem Catalysis:  Three Mechanistically Distinct Reactions from a Single Ruthenium Complex

  Christopher W. Bielawski, Janis Louie, Robert H. Grubbs
  12/2000;
• Article: Highly Efficient Ring‐Opening Metathesis Polymerization (ROMP) Using New Ruthenium Catalysts Containing N‐Heterocyclic Carbene Ligands

  Christopher W. Bielawski, Robert H. Grubbs
  Angewandte Chemie International Edition 08/2000; 39(16):2903 - 2906. · 13.45 Impact Factor
• Article: A Ring-Opening Metathesis Polymerization (ROMP) Approach to Carboxyl- and Amino-Terminated Telechelic Poly(butadiene)s

  Takeharu Morita, Bob R. Maughon, Christopher W. Bielawski, Robert H. Grubbs
  08/2000;
• Article: Synthesis of Cross-Linkable Telechelic Poly(butenylene)s Derived from Ring-Opening Metathesis Polymerization

  Bob R. Maughon, Takeharu Morita, Christopher W. Bielawski, Robert H. Grubbs
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  ABSTRACT: The synthesis of ring-opening metathesis polymerization (ROMP) chain transfer agents (CTA)s bearing methacrylate or epoxide end functionality was accomplished. In the presence of these CTAs, the ROMP of cyclooctadiene (COD) initiated with (PCy3)2Cl2RuCHPh afforded the respective telechelic poly(butenylene)s with either methacrylate or epoxide end groups. Control over the polymer molecular weight was demonstrated by varying the COD/CTA ratio. Successful cross-linking by thermal or photochemical initiation of the bis(methacrylate)-functionalized telechelic poly(butenylene)s or through acid catalysis of the bis(epoxide)-functionalized telechelic poly(butenylene)s was accomplished. While cross-linking was found to reduce solubility of the polymers, it greatly enhanced their thermal stability.
  03/2000;
• Article: Synthesis of ABA Triblock Copolymers via a Tandem Ring-Opening Metathesis Polymerization:  Atom Transfer Radical Polymerization Approach

  Christopher W. Bielawski, Takeharu Morita, Robert H. Grubbs
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  ABSTRACT: The synthesis of poly(styrene)-b-poly(butadiene)-b-poly(styrene) (SBS) and poly(methyl methacrylate)-b-poly(butadiene)-b-poly(methyl methacrylate) (MBM) triblock copolymers with poly(butadiene) (PBD) segments containing 100% 1,4-microstructure is described. Bis(allyl chloride) and bis(2-bromopropionate) terminated telechelic PBD's were synthesized by the ring-opening metathesis polymerization (ROMP) of 1,5-cyclooctadiene in the presence of the corresponding difunctional chain transfer agents. These telechelic PBDs were subsequently used as difunctional macroinitiators for the heterogeneous atom transfer radical polymerization (ATRP) of styrene and methyl methacrylate to form SBS and MBM triblock copolymers. Triblock structure was confirmed by selective PBD degradation. In addition, the tandem ROMP−ATRP approach was successfully extended to a “one-pot” synthesis.
  01/2000;