Metin H. Acar

Synthesis of block copolymer by combination of living cationic and iniferter polymerization systems

Abstract Functional polytetrahydrofurans containing N , N ′-diethyl dithiocarbamates were synthesized by the living cationic polymerization of tetrahydrofuran using trifluorosulfonic acid anhydride and N , N ′-diethyl dithiocarbamic acid sodium salt as an initiator and terminator, respectively. The molecular weight distribution was narrow and the number average molecular weights of the polymer were very close to the theoretical one, M n,th . N , N ′-diethyl dithiocarbamoyl polytetrahydrofuran was used as a macroiniferter in the photopolymerization of methyl methacrylate and block copolymers were obtained.

Formation of triphenylmethyl cation during the photolysis of phenylazotriphenyl methane : A laser flash photolysis study

The photolysis of phenylazotriphenyl methane (PAT) in dichloromethane and acetonitrile solution at λ inc = 347nm and at 23°C results in the formation of triphenyl methyl (trityl) radicals and trityl ions. The quantum yields in dichloromethane solution are Φ(Ph 3 C)= 0.060 and Φ(Ph 3 C + )= 0.004. Trityl ions are assumed to be formed by electron transfer between radicals formed by the photodecomposition of PAT. The yield of trityl ions is significantly increased upon irradiation of PAT solutions containing also an onium salt (N-ethoxy-2-methyl pyridinium hexafluorophosphate; (EMP + PF - 6 ). This is due to the oxidation of trityl radicals by EMP + ions. Trityl ions generated in this way were found to be capable of initiating the cationic polymerization of cyclohexene oxide.

Synthesis of block copolymers by combination of cationic and initer polymerization system

Trityl terminated poly(butyl vinyl ether) was obtained by the polymerization of butyl vinyl ether with triphenylcarbonium tetrafluoroborate-thiolane initiator system. In this system, thiolane was used to prevent both hydride abstraction of trityl cation and chain transfer of growing chain of butyl vinyl ether cation. Trityl terminated polymers served as thermal initer for the polymerization of methyl methacrylate which proceeded via a quasi-living radical mechanism. This procedure makes it possible to prepare block copolymers.

Morphological similarity of a tri-block copolymer processed at ambient and elevated temperatures

We investigated the effect of temperature on the morphology of a tri-block copolymer (BCP) processed in a capillary rheometer. The material used was a polystyrene-b-poly(2-ethylhexyl acrylate)-b-polystyrene (PS-b-PEHA-b-PS) tri-block copolymer, which was synthesized by ATRP with a molecular weight of 38.5 K consisting of 49 molar % PEHA. According to the rheological data obtained with dynamic viscoelastic oscillatory measurements, order-disorder temperature (ODT) of the BCP was measured at around 110°C. Considering this observation, the samples were studied under different temperatures and pressures (from 110°C to 28°C and from 48 to 75 bar) in capillary rheometer. All processed materials were characterized by using differential scanning calorimetry (DSC) and atomic force microscopy (AFM). It was found that all samples processed by aid of either temperature or pressure showed similar mixed morphologies (a mixture of the ordered and disordered structures i.e., the reduction of microphase separation due to processing).

Synthesis and reactions of polymers with photoactive terminal groups—4. the use of oxocarbenium polymerization for the synthesis of poly(α-methylstyrene) with N-acyl dibenz[b,f]azepine terminal units☆

Abstract N -chlorocarbonyl dibenz[b,f]azepine in conjunction with AgSbF 6 initiated the cationic polymerization of α-methylstyrene in methylene chloride. Polymer samples obtained this way contained terminal dibenzazepine units. Chain extension occurred upon irradiating these polymers with u.v. in benzene solution containing benzophenone or benzil, via cyclobutane formation.

Studies on the Block Copolymerization of Methacrylo-Nitrile and Hexafluorobutylmethacrlate Using Phenylazo-Triphenylmethane as Thermal Iniferter

Abstract The iniferter technique was applied to synthesize a block copolymer of methacrylonitrile (MAN) and 2,3,3,4,4, 4- hexafluorobutylmethacrylate (HFMA). Phenylazotriphenyl methane (PAT) was used as initiator for thermally initiated polymerization which proceeded via quasi-living radical mechanism. This wag informed from the fact that yield and molecular weight (Mn) of the polymers increased with reaction time. The prepolymer obtained from one monomer was used as polymeric iniferter for the polymerization of the other monomer. This way block copolymers were obtained.

Matching medium characterization for microwave brain stroke imaging

A matching medium composed with few ingredients for microwave brain imaging is presented. The medium is characterized by mixing 15% distilled-water (DI), 85% ethylene glycol (EG), and 7.5% by weight carboxymethyl cellulose (CMC). Dielectric property measurements of the material is performed with broadband contact probe technique and a probe with an attached standard RF cable is used to ensure to minimize the connection errors. From 0.5 to 2 GHz measured permittivity and conductivity of the material is ranging from 44 to 25 and 0.2 (S/m) to 2 (S/m), respectively.