Chain Extension and Cyclization of Telechelic Polysarcosines

Summary: Sarcosine N‐carboxyanhydride (Sar‐NCA) was polymerized with 1,12‐diaminododecane (DAD) or 1,13‐diamino‐4,7,10‐trioxatridecane (DATT) as initiators, and telechelic blocks having two secondary amino endgroups were obtained. Their structure was proven by ¹H NMR and MALDI‐TOF mass spectrometry. The SEC measurements indicated narrow molecular weight distribution with polydispersity indices in the range of 1.1–1.2. These difunctional polysarcosines were reacted with three different coupling agents: 4,4′‐diisocyanatodiphenylmethane (MDI), N‐hydroxysuccinimide sebacate, and sebacoyl bisimidazolide. Although the ¹H NMR spectra proved high conversions, only a moderate chain extension was observed. The MALDI‐TOF mass spectra indicated a high extent of cyclization, which limited the chain growth.

MALDI‐TOF mass spectrum of a DATT‐initiated polysarcosine after reaction with sebacoyl bisimidazolide.     

Controlled Synthesis and Characterization of Poly[ethylene‐block‐(L,L‐lactide)]s by Combining Catalytic Ethylene Oligomerization with “Coordination‐Insertion” Ring‐Opening Polymerization

Model poly[ethylene‐block‐(L ,L ‐lactide)] (PE‐block‐PLA) block copolymers were successfully synthesized by combining metallocene catalyzed ethylene oligomerization with ring‐opening polymerization (ROP) of L ,L ‐lactide (LA). Hydroxy‐terminated polyethylene (PE‐OH) macroinitiator was prepared by means of ethylene oligomerization on rac‐dimethyl‐silylen‐bis(2‐methyl‐benz[e]indenyl)‐zirconium(IV)‐dichloride/methylaluminoxane (rac‐MBI/MAO) in presence of diethyl zinc as a chain transfer agent, and subsequent in situ oxidation with synthetic air. Poly[ethylene‐block‐(L ,L ‐lactide)] block copolymers were obtained via ring‐opening polymerization of LA initiated by PE‐OH in toluene at 100 °C mediated by tin octoate. The formation of block copolymers was confirmed by ¹H NMR spectroscopy, fractionation experiments, thermal behavior, and morphological characterization using AFM and light microscopy techniques.

     

One‐Pot Combination of eROP and ROMP for the Synthesis of Block Copolymers

The one‐pot combination of enzymatic ring‐opening polymerization (eROP) and ring‐opening metathesis polymerization (ROMP) is successfully established to construct block copolymers. cis‐1,4‐Diacetoxy‐2‐butene is employed both as a precursor to initiate eROP of ε‐caprolactone or 15‐pentadecanolide and as a chain transfer agent in ROMP. The obtained polymers are systematically characterized by NMR, GPC, DSC, and microTOF‐QII MS. An evaluation of the reaction kinetics indicates the presence of two stages during the one‐pot eROP/ROMP process. Compared with cascade methods, this one‐pot method exhibits many advantages for preparing well‐defined block copolymers, such as mild reaction conditions and the elimination of complex purification steps for intermediates. Thus, this one‐pot combination approach has the potential to be widely used in preparing biocompatible polymeric materials, especially for biological and pharmaceutical applications.

     

Homo and Block Copolymers of Poly(β‐benzyl‐L‐aspartate)s and Poly(γ‐benzyl‐L‐glutamate)s of Different Architectures

Homopolypeptides of linear and star‐like architectures were prepared by polymerizing benzylic‐protected L ‐glutamic acid and L ‐aspartic acid N‐carboxyanhydrides (Glu NCA, Asp NCA) in DMF. The polymerization rate of the Glu NCA is faster than that of Asp NCA. Using a simple monoamino initiator, its hydrochloride, di‐, tri‐, and tetraamino functional initiators, homopolypeptides with well‐defined structures and molar masses were obtained. The molar‐mass averages of the poly(γ‐benzyl‐L ‐glutamate)s lie very close to calculated values, according to the initial [M]:[I] ratios, while those of the linear poly(β‐benzyl‐L ‐aspartate)s were lower than the predicted ones. PBAs had somewhat broader molar‐mass distributions than PBGs.

     

Nanoscale Blends between Immiscible Polymers via Simultaneous Non‐Interfering Polymerisation

Summary: An important topic in polymer science seeks to improve the performances of polymer blends using nanoscale phase segregation. Here, blends between polystyrene and polycaprolactone are realised by a chemical route. The non‐interfering character of the radical polymerisation of styrene and the lanthanide halide initiated ring‐opening polymerisation of caprolactone is assessed. The molecular weights range from 2 000 to 3 500 for polycaprolactone and up to 140 000 for polystyrene, with reasonable polydispersity indexes. From calorimetry measurements, it is shown that polystyrene and low molecular weight polycaprolactone are immiscible. The morphology of the blends between the two immiscible polymers studied by atomic force microscopy is consistent with nanometer‐scale phase segregation.

AFM surface image of a nanoscale blend.     

AB2 Functional Polyesters via Ring Opening Polymerization: Synthesis and Characterization

Aliphatic AB₂ functional polyesters were conveniently prepared by the ring opening polymerization of ε‐caprolactone and L ‐lactide in the presence of the AB₂ functional initiator 2,2‐bis(hydroxymethyl)propionic acid (bis‐MPA) and Sn(Oct)₂ as the catalyst. In L ‐lactide polymerization, both bis‐MPA hydroxyl groups initiated the polymerization reaction, but for ε‐caprolactone polymerization this depended on the monomer to initiator to catalyst ratio. Initiation at two hydroxyl groups occurred at high monomer to initiator ([M]/[I]) ratio and at high Sn(Oct)₂ to monomer ratio. The melting temperatures of the AB₂‐functional PLLA and PCL polymers were comparable to linear polymers with a equal to the per arm in the polymer.

     

Enzymatic Synthesis and Chemical Recycling of Polythiocaprolactone

High‐molecular‐weight polythiocaprolactone (PTCL) was prepared in a green process via lipase‐catalyzed ROP of a cyclic 6‐mercaptohexanoic acid (6MH) oligomer. PTCL was readily depolymerized by lipase to cyclic 6MH in dilute toluene solution, which was then readily repolymerized by the same lipase to produce PTCL with the same $\overline {M} _{{\rm w}} $ as the initial PTCL in a chemical recycling process. The T_m of PTCL was higher than that of the corresponding PCL. A P(TCL‐co‐CL) copolymer with 60 mol‐% TCL (6MH) units showed a higher T_m as the PCL homopolymer. Similar apparent K_m values were obtained for the cyclic 6MH oligomers and caprolactone oligomers, however, the V_max of cyclic 6MH oligomers was significantly lower than that of the corresponding caprolactone oligomers.

     

Controlled Ring‐Opening Polymerization of Lactones and Lactide Initiated by Lanthanum Isopropoxide, 2. Mechanistic Studies

The mechanism of ring‐opening polymerization of some lactones and lactide initiated by lanthanum isopropoxide has been comprehensively investigated. NMR and viscosity analyses demonstrated that three active polymer chains grow per lanthanum atom and that, depending on the coordinating ability of the monomer, propagation proceeds on aggregated or unaggregated active species. It is also demonstrated that inter‐ and intramolecular side reactions are limited and that lanthanum‐based initiator selectivity in ring‐opening polymerization is analogous to that of aluminum ones.

Part of the proposed mechanism for the lanthanum alkoxide initiated polymerization of ε‐caprolactone.     

Synthesis of Novel Linear PEO‐b‐PS‐b‐PCL Triblock Copolymers by the Combination of ATRP,ROP, and a Click Reaction

A new strategy to synthesize a series of well‐defined amphiphilic PEO‐b‐PS‐b‐PCL block copolymers is presented. First, bromine‐terminated diblock copolymers PEO‐b‐PS‐Br are prepared by ATRP of styrene, and converted into azido‐terminated PEO‐b‐PS‐N₃ diblock copolymers. Then propargyl‐terminated PCL is prepared by ROP of ε‐caprolactone. The PEO‐b‐PS‐b‐PCL triblock copolymers with from 1.62 × 10⁴ to 1.96 × 10⁴ and a narrow PDI from 1.09 to 1.19 are finally synthesized from these precursors. The structures of these triblock copolymers and their precursors have been characterized by NMR, IR, and GPC analysis.

     

Effect of Surfactant and Various Salts on Aqueous Solution Properties of Naphthalene‐Labeled Poly(hydrochloride‐quaternized 2‐norbornene‐5‐methylamine) made by Ring‐Opening Metathesis Polymerization (ROMP)

Naphthalene‐labeled cationic poly(hydrochloride‐quaternized 2‐norbornene‐5‐methyleneamine), poly(HCQNBMA)/NA, has been prepared by ring‐opening metathesis polymerization (ROMP), using {RuCl₂(CHC₆H₅)[P(C₆H₁₁)₃]₂} as a catalyst in methylene chloride, followed by hydrogenation, hydrolysis, and quaternization. The effect of salt addition on the aqueous solution properties of poly(HCQNBMA)/NA was examined in terms of reduced viscosity, surface tension and fluorescence studies. The reduced viscosity for poly(HCQNBMA)/NA is dependent on the type and concentration of salts added. The viscosity behavior of cationic poly(HCQNBMA)/NA is in contrast with polybetaines. An increase in KCl concentration causes the reduced viscosity of poly(HCQNBMA)/NA to decrease at constant poly(HCQNBMA)/NA concentration. The general shape of the surface tension versus logarithm of concentration curve for poly(HCQNBMA)/NA shows only a slow decrease with increasing polymer concentration upon addition of various salts. The surface tension increases in the series KF > KCl > KBr > KI in a given polymer concentration. When the naphthalene label was introduced into the poly(HCQNBMA), the behavior of the solution properties of the poly(HCQNBMA)/NA could be clearly defined in terms of fluorescence analysis. The quenching efficiency of NaI or CH₃NO₂ was reduced with increasing KCl concentration arising from compacted conformation of polymer chains. A model of the interaction between poly(HCQNBMA)/NA and surfactant or salt in aqueous solution is proposed.

     

Synthesis of Poly(propylene oxide) with Strict Control of End Functionality, 1. Initiation with (4‐Methoxy)phenoxy Tetraphenylporphynatoaluminum

The polymerization of propylene oxide (PO) initiated by (4‐methoxy)phenoxy tetraphenylporphynatoaluminum (TPPAl‐O‐PMP) was studied with the aim of strictly controlling the end‐group functionality of the resulting poly(propylene oxide) (PPO), together with the molecular weight, in terms of average values and of narrow chain‐length distribution. The influence of the relative amount of reactants used for the preparation of the initiator on the nature and number of end groups was studied by various analytic methods including ¹H NMR and UV spectroscopies and matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF) spectrometry. In spite of apparent living behavior observed from size exclusion chromatograpy (SEC) measurements, large variations in the yield of polymerization, determined after several hours of reaction, indicated a strong dependence of the propagation rate on slight variations around the 1:1 stoichiometry of triethylaluminum to the unmetallated porphyrin and to the phenolic ligand. Associated with the anomalous kinetic behavior, differences in the nature of the end groups were unambiguously evidenced by MALDI‐TOF spectrometry for narrow molecular weight (MW) distributed PPOs obtained with a slight excess of triethylaluminum and a slight deficit in added phenol with regard to porphyrin. A mechanism involving side reactions is proposed to account for the observed kinetic and structural features. Immortal polymerization of PO with strict control of MW distribution and functionality is obtained under appropriate conditions and consistently supported by various methods of MW determination.

Principle of end‐group functionalization in porphyrin catalyzed PO polymerization.     

A Poly(vinyl alcohol)‐graft‐Copolyester: Synthesis of a Novel Graft Copolymer Containing Adamantane Moieties as Guest for Cyclodextrin

A novel graft copolymer is synthesized from commercially available poly(vinyl alcohol) using ring‐opening polymerization. For the polymerization reaction of novel brush‐like poly(vinyl alcohol)‐graft‐poly(?‐caprolactone‐co‐(3‐/7‐(prop‐2‐ynyl)oxepan‐2‐one) 5 Sn(Oct)₂ is used as a catalyst. The formation of the graft copolymer is confirmed by ¹H NMR, ¹³C NMR, and Fourier transform infrared (FTIR) spectroscopy. Furthermore, the modification of the novel synthesized graft copolymer via a “click” reaction to implement adamantane groups is described. The success of the “click” reaction is proven by ¹H NMR spectroscopy and visualized by decomplexation of cyclodextrin with included phenolphthalein.

     

Polymer Synthesis and Modification by Use of Microwaves

Nowadays, microwave‐assisted polymer chemistry is a rapidly growing field of research. In the last few years, various examples of reaction accelerations, selectivities, and higher yields have been reported. In this contribution, the current state of the art is summarized and an overview on microwave‐assisted polymerizations is presented, whereby special attention is given to advantages and promising future trends in this intriguing field of research.

     

Synthesis and Characterization of Comb‐Like Copolymers Based on Poly(ε‐caprolactone) and Poly(α‐olefin)

Comb‐like copolymers based on a polyolefin backbone of poly(10‐undecene‐1‐ol) (PUol) with poly(ε‐caprolactone) (PCL) side chains are synthesized in two steps. After synthesis of PUol by metallocene‐catalyzed polymerization, the side‐chain hydroxyl functionalities of this polar polyolefin are used as an initiator for the ring‐opening polymerization (ROP) of ε‐caprolactone (CL). In this context, copolymers with different lengths of PCL grafts are prepared. The chemical structure and the composition of the synthesized copolymers are characterized by ¹H and ¹³C NMR spectroscopy. It is shown that the hydroxyl end groups of PUol act effectively as initiating sites for the CL ROP. Size‐exclusion chromatography (SEC) measurements confirm the absence of non‐attached PCL and the expected increase in molar mass after grafting. The thermal and decomposition behaviors are investigated by DSC and thermogravimetric analysis (TGA). The effect of the length of the PCL grafts on the crystallization behavior of the comb‐like copolymers is investigated by DSC and wide‐angle X‐ray scattering (WAXS).

     

Synthesis of Poly(L‐lactide)‐Functionalized Multiwalled Carbon Nanotubes by Ring‐Opening Polymerization

MWNTs are modified to possess hydroxy groups and are used as coinitiators to polymerize L ‐lactide by the surface‐initiated ring‐opening polymerization. FT‐IR and TEM observations reveal that the PLLA is covalently attached to the MWNTs (MWNT‐g‐PLLA), and the weight gain as a result of the functionalization is determined by TGA analysis. Two kinds of solvents, namely DMF and toluene, are used to carry out the two series of polymerizations at 140 and 70 °C, respectively, for 2–20 h. The amount of grafted PLLA increases with the reaction time either in DMF or in toluene, but it increases more significantly in DMF at 140 than in toluene at 70 °C, with the reaction time being the same. The grafted PLLA layer on the MWNT is more uniform when the reaction is performed in DMF than in toluene, and some bare surfaces are observed in the TEM image of the MWNT‐g‐PLLA prepared in toluene. The MWNT‐g‐PLLAs are well dispersed in the organic solvents as well as in the PLLA matrix. Incorporation of MWNT‐g‐PLLA greatly improves the tensile modulus and strength without a significant loss of the elongation at break. The specific interaction between the MWNT‐g‐PLLA and the polymer matrix is quantified by way of the Flory‐Huggins interaction parameter, B, which is determined by combining the melting point depression and the binary interaction model.

     

Counterion Effect of Amine Salts on Ring‐Opening Polymerization of 1,3‐Benzoxazines

The effect of nucleophilicity of counterions of amine HX salts as catalysts on the ring‐opening polymerization (ROP) of 1,3‐benzoxazines is investigated. The significant reduction observed for the ROP temperature is related to the nucleophilicity of counterions and found to show a general trend as I^? > Br^? > Cl^?, as studied by differential scanning calorimetry and Fourier transform infrared spectroscopy. Moreover, the latent character of the amine salts is also demonstrated by tracking the benzoxazine–amine salt mixtures using ¹H NMR spectroscopy. The spectral analysis gives evidences for the dormant nature of the amine HX salts toward benzoxazine at room temperature in solvent. Besides, thermal stabilities of the cured benzoxazine monomers with and without catalysts are investigated by thermogravimetric analysis.     

Synthesis and Ring‐Opening Metathesis Polymerization of New Oxanorbornene Dicarboximides with Fluorine Pendant Groups

The synthesis of exo‐N‐3,5‐bis(trifluoromethyl)phenyl‐7‐oxanorbornene‐5,6‐dicarboximide (TFMPhONDI, 2a ), exo‐N‐4‐fluorophenyl‐7‐oxanorbornene‐5,6‐dicarboximide (FPhONDI, 2b ), and exo‐N‐pentafluorophenyl‐7‐oxanorbornene‐5,6‐dicarboximide (PFPhONDI, 2c ) monomers is described. Poly(norbornene dicarboximide)s were obtained via ROMP using bis(tricyclohexylphosphine)benzylidine ruthenium(IV) dichloride ( I ) and tricyclohexylphosphine [1,3‐bis(2,4,6‐trimethylphenyl)‐4,5‐dihydroimidazolilydene][benzylidene] ruthenium dichloride ( II ). Poly‐TFMPhONDI ( 3a ) bearing a trifluoromethylaryl moiety showed a higher T_g and improved mechanical properties as compared to poly‐FPhONDI ( 3b ) and poly‐PFPhONDI ( 3c ).

     

Synthesis of Aliphatic‐Aromatic Copolyesters by a High Temperature Bulk Reaction Between Poly(ethylene terephthalate) and Cyclodi(ethylene succinate)

Summary: Cyclodi(ethylene succinate) (C2) easily reacts with poly(ethylene terephthalate) (PET) in the melt leading to the formation of high molar mass PET‐Poly(ethylene succinate) copolymers (PET‐PES). Copolyesters with a PET/C2 starting mass ratio of 90/10, 80/20, 70/30 and 50/50 were synthesized and characterized by ¹H NMR and MALDI‐TOF MS. The 50/50 copolyester was almost random, while copolyesters with higher ethylene terephthalate contents exhibited some block copolymer character. MALDI‐TOF MS/SEC off‐line coupling was used to determine copolyester absolute average molar masses. The results indicate that the conventional SEC polystyrene calibration strongly overestimates copolyester molar masses. The melting temperatures and crystallinity of the 90/10, 80/20 and 70/30 copolyesters were significantly higher than those of comparable PET‐aliphatic polyester copolymers.

     

Transition Metal‐Catalyzed Ring‐Opening Polymerization of Silicon‐Bridged [1]Ferrocenophanes in the Presence of Functional Silanes: Molecular Weight Control and Synthesis of Telechelic Poly(ferrocenylsilanes)

The transition metal‐catalyzed ring‐opening polymerization of dimethyl[1]silaferrocenophane (fcSiMe₂) ( 1 ), fc = Fe(η‐C₅H₄)₂), in the presence of MePhSiH₂, or the chlorosilanes ClMe₂SiH, ClMePhSiH, or ClPh₂SiH has been shown to allow access to poly(ferrocenylsilane)s R¹R²R³Si? [fcSiMe₂]_n? H ( 4 , 6 – 8 ), and R¹? [Me₂Sifc]_m? SiR²R³? [fcSiMe₂]_n? H ( 5 ) with controlled molecular weights and which are capped by the corresponding R¹R²R³Si and Si? H groups ( 4 , 5 : R¹ = H, R² = Me, R³ = Ph, 6 : R¹ = Cl, R² = R³ = Me, 7 : R¹ = Cl, R² = Me, R³ = Ph, 8 : R¹ = Cl, R² = R³ = Ph). Materials with molecular weights in the range M _n of 3.5 × 10³ to 2.5 × 10⁴ and polydispersities of 1.3–2.2 were prepared. All of the silanes examined in this study were found to be more reactive as capping agents than the previously studied Et₃SiH; the order of reactivity for molecular weight control was determined to be MePhSiH₂ ≈ ClMe₂SiH ≈ ClMePhSiH ≈ ClPh₂SiH > Et₃SiH. In addition, the reactivity of the resulting Si? Cl end‐functionalities of poly(ferrocenylsilane)s 6 and 7 was explored, and reactions with commercial poly(ethylene glycol) methyl ether yielded poly(ethylene oxide)–block–poly(ferrocenylsilane) diblock copolymers, 10 and 11 . The Si? H end group, however, was much less reactive and attempts to utilize this functionality for hydrosilylation of divinyl‐terminated poly(dimethylsiloxane) to form block copolymers was ineffective.

     

A New Insight Into the Mechanism of the Ring‐Opening Polymerization of Trimethylene Carbonate Catalyzed by Methanesulfonic Acid

The ring‐opening polymerization (ROP) of trimethylene carbonate (TMC) initiated by a monoalcohol and catalyzed by CH₃SO₃H is investigated, in an effort to reveal extra features of the known activated monomer/active chain‐end (AM/ACE) combined mechanism. Size‐exclusion chromatography (SEC) profiles obtained with high‐molar‐mass samples show a poly(trimethylene carbonate) (PTMC) fraction generated by AM/ACE with a molar mass that is exactly twice that of the PTMC fraction coming from pure AM. Conversely, PTMC prepared with a diol is perfectly unimodal and keeps its molar mass dispersity below 1.1. This suggests that the side AM/ACE mechanism may be a bidirectional AM mechanism, and that PTMC with a narrow unimodal molar‐mass distribution can be obtained easily from a diol regardless of this side propagation.