Anionic ring-opening polymerization of 2,2-dimethyltrimethylene carbonate

The anionic ring-opening polymerization of 2,2-dimethyltrimethylene carbonate in solution with sec-butyllithium as initiator was found to result under suitable conditions in a bimodal molecular weight distribution, vic. cyclic oligomers and a high-molecular-weight polymer. The concentration of cyclic oligomers approaches that of a ring chain equilibrium. In the kinetically controlled regime high polymer yields were obtained. Optimum reaction conditions for a polymer yield of 85 – 95% are a temperature of ?10°C, an initial monomer concentration of 10 weight-% and toluene as solvent. In THF the ring chain equilibrium is achieved readily. The ceiling temperature was determined to be ≈ 30°C. The homopolymer was characterized by spectroscopic, thermoanalytical and viscosity measurements. A high degree of crystallinity was observed.     

Polylactones 12. Cationic polymerization of 2,2-dimethyltrimethylene carbonate

The polymerization of 2,2-dimethyltrimethylene carbonate ( 1 ) was initiated with borontrifluoride etherate, trifluoromethanesulfonic acid (triflic acid), methyl triflate and ethyl fluorosulfate. The reaction was studied at 20, 50, 80 and 120°C in 1,2-dichloroethane and nitrobenzene. Methyl triflate and triflic acid turned out to be the most reactive initiators. Yet, due to “black biting” degradation, yields > 80% were never obtained. With BF₃ etherate yields up to 98% and molecular weights (M?_n) up to 5200 g/mol were found. From ¹H NMR and IR spectra it can be deduced that methyl triflate alkylates the exocyclic oxygen (carbonyl group) and the resulting carbenium ion reacts with its counterion by ring-opening of the alkyl-oxygen bond. The oligomers and polymers formed in this way initially possess methyl (or ethyl) carbonate groups at one end and triflate groups at the other end of the chain. Elemental analyses and IR spectra prove that no carbon dioxide is lost in the course of the cationic polymerization. DSC measurements showed that crystallinity and melting points of poly( 1 ) largely depend on the polymerization conditions in contrast to the glass transition temperature.     

Thermodynamics of 2,2-dimethyltrimethylene carbonate,of its bulk polymerization process and of poly(2,2-dimethyltrimethylene carbonate) from 0 to 470 K at standard pressure

In the present work the thermodynamic properties of 2,2-dimethyltrimethylene carbonate (DTC) and poly-2,2-dimethyltrimethylene carbonate (PDTC) were studied by precise calorimetry. In adiabatic and dynamic vacuum calorimeters the temperature dependence of the heat capacity of DTC and PDTC was studied between 5 and 470 K. Temperature and enthalpies of physical transitions were determined, and in an isothermal calorimeter energies of combustion of the above compounds were measured. From the results the thermodynamic functions C(T), H°(T)–H°(0), S°(T), G°(T)–H°(0) were calculated for various physical states of the monomer and the polymer from 0 to 470 K. The standard enthalpies of combustion and thermochemical parameters of formation ΔH, ΔS, ΔG of the objects studied were estimated at T =298,15 K and p = 101,325 kPa. The zero entropy S(0) and configurational entropy S of PDTC in the glassy state and the difference in zero enthalpies of the polymer in the glassy and crystalline states H(0)–H(0) were estimated. The results were used to calculate the thermodynamic parameters of the bulk polymerization of DTC (ΔH, ΔS, ΔG) in the range of 0 to 420 K. It was established that for the process DTC → PDTC, ΔG < 0 if the polymer is crystalline and ΔG > 0 in the case of amorphous PDTC (glassy or liquid). The ceiling temperature is T = 500 K.     

Polymers from 2-allyloxymethyl-2-ethyltrimethylene carbonate and copolymers with 2,2-dimethyltrimethylene carbonate obtained by anionic ring-opening polymerization

2-Allyloxymethyl-2-ethyltrimethylene carbonate ( 1 ) was polymerized in toluene with sec-butyllithium as initiator. The resulting product exhibits a bimodal molecular weight distribution. The low-molecular-weight fraction consists mainly of cyclic oligomers and to a minor portion of acyclic oligomers. With 2,2-dimethyltrimethylene carbonate ( 2 ) as a comonomer, statistical and block copolymers were obtained upon addition of the initiator to a mixture of the monomers or upon consecutive addition of the monomers to the initiator, respectively. The primary structure of these copolymers was unambiguously determined by means of ¹³C NMR spectroscopy of especially the carbonyl region, since the carbonyl carbon atom is a sensitive probe for structural changes in its neighbourhood. All polymers were crosslinked upon using di-tert-butyl peroxide as a source of radicals. The thermal behaviour of the polymers before and after crosslinking was studied.     

Copolymers with soft and hard segments based on 2,2-dimethyltrimethylene carbonate and ε-caprolactone

Thermoplastic elastomers with ABA-block structure, A representing the hard segment and B the soft segment, were prepared by ring-opening polymerization from 2,2-dimethyltrimethylene carbonate (DTC, 1 ) and ε-caprolactone (ECL, 2 ) as monomers. Typical anionic initiators, viz. the dilithium salt of hydroxytelechelic poly(ethylene oxide) 200 ( 4 ) and of polytetrahydrofuran 1000 ( 5 ) and as an insertion initiator the bis(diethylaluminium) salt of triethylene glycol were used. The soft block is formed by a sequence of random (or tapered) structure comprising equimolar amounts of the two monomers and obtained by simultaneous polymerization of DTC and ECL. The hard blocks consist of highly crystalline poly(2,2-dimethyltrimethylene carbonate) sequences. The thermal properties of the polymers depend on the sequence length, the content of heterodiads in the soft block and the thermal history of the samples. Copolymer films with short end blocks and high content of heterodiads show rubber-elastic properties at normal conditions.     

Synthesis, characterization, and in vitro 5-Fu release behavior of poly(2,2-dimethyltrimethylene carbonate)-poly(ethylene glycol)-poly(2,2-dimethyltrimethylene carbonate) nanoparticles

Novel ABA-type amphiphilic triblock copolymers composed of poly (ethylene glycol) (PEG) as hydrophilic segment and poly (2,2-dimethyltrimethylene carbonate) (PDTC) as hydrophobic segment were synthesized by ring-opening polymerization of 2,2-dimethyltrimethylene carbonate (DTC) initiated by dihydroxyl PEG. The influence of introducing PEG block on crystalline behavior of PDTC segment was investigated by DSC. Polymeric micelles in aqueous medium were characterized by fluorescence spectroscopy and dynamic light scattering. The critical micelle concentration of these copolymers was in the range of 5.1-50.5 mg/L. Particle size was 80-280 nm. Core-shell-type nanoparticles were prepared by the dialysis technique. Zeta potential was measured by laser Doppler anemometry, and all nanoparticles had negative zeta potential. Transmission electron microscopy images demonstrated that these nanoparticles were spherical in shape. Anticancer drug 5-fluorouracil (5-Fu) as a model drug was loaded in the polymeric nanoparticles. X-ray powder diffraction demonstrated that 5-Fu was encapsulated into polymeric nanoparticles as molecular dispersion. In vitro cytotoxicity of nanoparticles was evaluated by MTT assay. In vitro release behavior of 5-Fu was investigated, and sustained drug release was achieved.     

Synthesis and ring-opening polymerization of 2-acetoxymethyl-2-alkyltrimethylene carbonates and of 2-methoxycarbonyl-2-methyltrimethylene carbonate; a comparison with the polymerization of 2,2-dimethyltrimethylene carbonate

The polymerization of 2-acetoxymethyl-2-alkyltrimethylene carbonates (alkyl = methyl: AMTC, alkyl = ethyl: AETC) and of 2-methoxycarbonyl-2-methyltrimethylene carbonate (MMTC) in toluene with sec-butyllithium as initiator results in the respective polymer with yields between 78% and 88%. The analysis of the polymer microstructure by means of NMR spectroscopy reveals linear chains without branching due to an attack of the active chain end at the ester moiety of the repeating units. Poly(MMTC) and poly(-AETC) afford crystalline materials upon precipitation from solution while poly-(AMTC) is amorphous; after quenching from the melt all materials are amorphous. Copolymerization of AMTC, AETC and MMTC with 2,2-dimethyltrimethylene carbonate (DTC) results in random copolymers. The kinetics of the polymerization of AETC and MMTC revealed that the ester side chain enhances the rate of propagation compared to the polymerization of DTC. The apparent rate constants of propagation in toluene with lithium alcoholate as active sites at 23°C were determined to be k_app^DTC = 4 ċ 10⁻³ s⁻¹, k_app^AETC = 4,28 ċ 10⁻² s⁻¹, and k_app^MMTC = 2,57 ċ 10⁻² s⁻¹. Studies of ring-chain equilibria in solution of tetrahydrofuran revealed that on the basis of the theory of Jacobson-Stockmayer the characteristic ratios of the polymers are C_∞^PDTC = 7,1, C_∞^PMMTC = 8,6, C_∞^PAETC = 9,9, and C_∞^PAMTC = 13,4.     

Heterogeneous catalytic ring opening polymerization of 2,2-dimethyltrimethylene carbonate with metal alkoxides as initiators in protic conditions

The polymerization of 2,2-dimethyltrimethylene carbonate (DTC) by using new heterogeneous systems as initiators has been investigated. These systems are obtained by grafting various Lewis acid metal alkoxides belonging to group IIb (Zn), IIIa (Al), IIIb (Y and Nd) as well as IVb (Ti and Zr) on porous solids (silica, alumina and zinc oxide). Adding alcohol in excess to the reaction mixture induces a transfer reaction which allows to synthesise functionalized polycarbonates. In most cases, the degree of polymerization is controlled by the [monomer]/[alcohol] ratio. It was found that the activity depends both on the metal and on the solid support. Y alkoxides offer the best activities while those belonging to group IVb are less efficient. The porous solid acts as a chemical ligand rather than only as a mechanical support of the active centres.     

Copolymers obtained by means of anionic ring-opening polymerization. Poly(2,2-dimethyltrimethylene carbonate)-block-polypivalolactone

The anionic ring-opening polymerization of mixtures of 2,2-dimethyltrimethylene carbonate (5,5-dimethyl-1,3-dioxan-2-one) ( 1 ) and pivalolactone (2,2-dimethyl-3-propanolide) ( 3 ) in toluene as a solvent and with potassium dihydronaphthylide as initiator, results in formation of block copolymers with yields of ca. 90%. In tetrahydrofuran as a solvent the polymer yields are ca. 65% only. In toluene, 1 polymerizes first and subsequently 3 resulting in a blocky structure of the copolymer. According to a mechanistic study, the active species is first a 1 -alcoholate, later a 3 -alcoholate and finally a 3 -carboxylate. The copolymers are soluble in deuterochloroform up to a mole fraction of pivalolactone of ca. 0,40. By means of ¹³C NMR spectroscopy the blocky structure of the copolymers prepared in toluene was confirmed. In tetrahydrofuran as a solvent 1-3 and 3-1 -diads are formed to a significant extent. The copolymers were characterized by thermoanalytical and thermomechanical measurements.     

The glass transition of blends of poly(2,6-dimethylphenylene oxide) and polystyrene-block-poly(2,2-dimethyltrimethylene carbonate)

The miscibility of poly(2,6-dimethylphenylene oxide) (PPO) with polystyrene-block-poly(2,2-dimethyltrimethylene carbonate) (PS-block-PDTC) was studied and compared with the corresponding PPO/PS blends. PPO/PS-block-PDTC blends show two thermal transitions in the temperature range investigated; that is the melting of the DTC block and the glass transition of the mixed PPO/PS block phase. The T_g values obtained are discussed by means of the Fox and Gordon-Taylor equation. The influence of the PDTC block leads to higher T_g values of the PPO/PS block mixture than of the corresponding homopolymer blend.     

Copolymerization of 2,2-dimethyltrimethylene carbonate with 2-allyloxymethyl-2-ethyltrimethylene carbonate and with ε-caprolactone using initiators on the basis of Li,Al, Zn and Sn

The homopolymerization of 2,2-dimethyltrimethylene carbonate ( 1 ), 2-allyloxymethyl-2-ethyl-trimethylene carbonate ( 2 ) and ε-caprolactone ( 3 ) with sec-butyllithium (sec-BuLi), tri-sec-butoxyaluminium (Al(O-secBu)₃), diethylzinc (ZnEt₂) and dibutyldimethoxytin ((Bu)₂Sn(OMe)₂) in toluene at 80°C results in a reaction product consisting of a high-mole-cular-weight polymer and a homologous series of oligomers. The weight ratio polymer/oligomers, under standardized conditions, depends on the type of initiator. The sequence of monomeric units in the copolymers is statistical, for all initiators used. For sec-BuLi and Bu₂Sn(OMe)₂ the distribution arises both from random addition of the monomers to the active chain end and from transesterification, while with Al(O-secBu)₃ and ZnEt₂ the addition of the monomers is non-selective. For poly[(2,2-dimethyltrimethylene carbonate)-stat-(2-allyloxymethyl-2-ethyltrimethylene carbonate)] the carbonyl region of the ¹³C NMR spectrum is suitable for diad analysis, for poly[(2,2-dimethyltrimethylene carbonate)-stat-(ε-caprolactone)] the methyleneoxy region is most indicative. The assigment of the diads was made on the basis of model compounds.     

Oxidation of poly(2,2-dimethyltrimethylene sulfide) in solution

Oxidation of poly(2,2-dimethyltrimethylene sulfide) was carried out in chloroform solution at 25°C using trifluoroacetic acid and hydrogen peroxide. Six samples were obtained with weight fractions of sulfoxide comonomer ranging between 0,11 and 0,58, without any content of sulfone groups. When it is attempted to obtain samples with more than 60% of sulfoxide units, sulfone groups are formed. ¹H NMR data show the reaction to take place in a random way. Copolymers exhibit only one glass transition temperature which increases with the number of sulfoxide units, The extrapolated glass transition temperature for the theoretical polysulfoxide corresponds to a value in the range of 261 to 264 K.     

Poly(methyl methacrylate)-block-poly(2,2-dimethyltrimethylene carbonate); site transformation from a group transfer polymerization to an anionic ring-opening polymerization

Poly(methyl methacrylate)-block-poly(2,2-dimethyltrimethylene carbonate) was prepared by a group transfer polymerization (GTP) of methyl methacrylate (MMA), followed by an anionic metal-free polymerization of 2,2-dimethyltrimethylene carbonate (DTC). It was shown that the anionic metal-free polymerization of DTC can be initiated either by the system silyl ether/tris(dimethylamino)sulfonium trimethylsilyldifluoride (TASF) or by the system 1-methoxy-1-trimethylsilyloxy-2-methyl-1-propene (MTS) in combination with TASF. The latter can be considered as a model compound for the living PMMA end in a GTP polymerization. The transformation of the trimethylsilyl ketene acetal end into an anionic species was achieved by desilylation with TASF. In the presence of DTC the resulting enolate reacts as carbanion with the carbonyl group of the carbonate moiety. Thus, at the linkage of the two blocks a disubstituted malonic acid derivative is formed. GPC analysis of the copolymers reveals a unimodal and rather narrow distribution of molecular weights. The block structure expected from the way of preparation is confirmed by ¹³C NMR analysis. The ¹H NMR analysis gives the composition of the block copolymers and reveals that the larger the PMMA block, the less efficient is the initiating ability, leading to a larger PDTC block as expected from the monomer to initiator ratio; correspondingly more homo-PMMA is formed. Thermal analysis of the block copolymers shows a melting transition of the PDTC block which is by about 20°C lower than that of the homopolymer: the glass transition temperature of the PMMA block is hidden under the melting transition of the PDTC block.     

Sequential reordering in condensation polymers, 5. Preparation and characterization of copolymers via transesterification of a polycaprolactonepoly(2,2-dimethyltrimethylene carbonate) blend

A blend of polycaprolactone (PCL) and poly(2,2-dimethyltrimethylene carbonate) (PDTC) containing catalytic amounts of dibutyltin dimethoxide was prepared from solution. The blend was then subjected to melt-mixing at 200°C and samples were taken after different times. According to thermal analysis data, with the increase of reaction time a gradual loss of the crystallizability of the blend components is observed, and after 70 min at 200°C the system becomes completely amorphous. ¹³C NMR data suggest that the loss of crystallizability of the blend is accompanied by an abrupt decrease in PCL and PDTC sequence lengths reaching after 70 min at 200°C an average length of about two repeating units each. These effects are explained by transesterification reactions between the lactone and carbonate units.     

Copolymers obtained by means of anionic ring-opening polymerization. Poly(2,2-dimethyltrimethylene carbonate-tapered-ϵ-caprolactone)

The anionic ring-opening polymerization of mixtures of 2,2-dimethyltrimethylene carbonate and ?-caprolactone in toluene as solvent, with sec-butyllithium or potassium dihydronaphthylide as initiator, results in the formation of polymers of the (A-X-B)_n type, where A represents a poly(2,2-dimethyltrimethylene carbonate) block, B represents a poly(?-caprolactone) block and X stands for a block of the two monomers with a composition gradient; n represents the number of portions by which the monomer mixture is added to the initiator or the living system. From the time-conversion curves it follows that the reactivity of the carbonate monomer is higher than that of the lactone. This difference in reactivity of the monomers is the reason for the special polymer architecture represented by (A-X-B)_n. The properties of these polymers depend upon the ratio of the monomers and the number n of additions. The polymers are characterized by spectroscopic, thermoanalytical, and thermomechanical measurements.     

Polymerization of acrylonitrile by a ternary catalyst: FeCl3/2,2′-dipyridyl/epoxypropane

The ternary system FeCl₃/2,2′-dipyridyl ( 1 ) (Dip)/epoxypropane ( 2 ) was found to be active as catalyst for the polymerization of acrylonitrile ( 4 ). The lack of one of the catalyst components makes the system inactive for polymerization. The active species is concluded to be partially alkoxylated ferric chloride complexed with 1 , and the polymerization might be initiated by the alkoxy group of the complex. Copolymerization of 4 and styrene indicates that the polymerization is anionic at 30°C. At 50 and 80°C, however, both anionic and radical polymerizations seem to take place.     

Block polymers obtained by means of anionic polymerization. Polystyrene-block-poly(ε-caprolactone) and polystyrene-block-poly(2,3-dimethyltrimethylene carbonate)

The anionic ring-opening polymerization of ε-caprolactone and 2,2-dimethyltrimethylene carbonate in toluene as solvent with polystyryllithium or lithium polystyrylethoxide resp. lithium polystyrylmethoxide as initiators, results in the formation of the corresponding block polymers as major products, beside small amounts of homopolymer. The block copolymers were isolated chromatographically from the mixture and analyzed spectroscopically.     

Synthesis of Poly(trimethylene carbonate) Oligomers by Ring‐Opening Polymerization in Bulk

Telechelic poly(trimethylene carbonate) (PTMC) oligomers are synthesized and carefully characterized with molar masses between 300 and 5000 g mol^?1 in bulk by ring‐opening polymerization (ROP) with 1,3‐dioxan‐2‐one (trimethylene carbonate or TMC) as monomer and 1,4‐butanediol (BDO) as co‐initiator. 1,5,7‐Triazabicyclo[4.4.0]dec‐5‐ene (TBD) organic catalyst and tin(II) bis(2‐ethylhexanoate) (Sn(Oct)₂) organometallic initiator are chosen comparatively. Due to the bi‐functionality of BDO and relatively low TMC/BDO feed ratios, it is proved that PTMC chains are elaborated from one or both the BDO alcohol functions, producing two coexisting kinds of PTMC chains with BDO unit at the chain end or in the backbone. Additionally, PTMC chains bear permanent and fast exchange reactions at 100 °C, leading to both a dynamic redistribution of chains and their extension with BDO unit numbers mainly from 0‐4 but up to 6. Longer reaction times and lower TMC/BDO molar ratios bring about more predominant exchange reactions and MALDI‐TOF allows to detail the structures evolutions deeply. Better average molar masses control and narrower distributions are obtained with TBD as compared to Sn(Oct)₂. PTMC molar masses can be predicted simply by the TMC/BDO feed ratio with TBD. Kinetically, TBD is the most efficient. The glass transition temperature T_g is found to respect Flory–Fox model.