Testing of the effect of parameters on the cononsolvency of random copolymer gels of N-isopropylacrylamide and N-ethylacrylamide in methanol-water mixed solvents by simple gravimetric method

Random copolymer gels of N-isopropylacrylamide (NIPAM) and N-ethylacrylamide (NEAM) were synthesized in using different monomer compositions in 1:1 methanol-water mixtures and in pure water. The samples were characterized by cononsolvency study in methanol-water mixtures at various temperatures by swelling ratio measurements. It is observed that with the variation of the temperature and monomer compositions in the synthesis reaction mixture, the cononsolvency properties varied significantly. But the variation in the solvents compositions by keeping monomer compositions fixed does not affect the cononsolvency much. All results can be explained on the basis of the differences in thermoresponsive character or difference in the hydrophilicity of PNIPAM and PNEAM in water, preferential adsorption of the solvents by polymer networks, solvent-solvent interactions, heterogeneity of the polymer networks synthesized at different solvent compositions and at different temperatures, difference in their morphological properties, etc.     

Gelation in the Copolymerization of Diallyldimethylammonium Chloride with Acrylamide

Diallyldimethylammonium chloride (DADMAC) was free-radical copolymerized with acrylamide (AA) in water at a total monomer concentration of 4 mol/L and 40°C with different monomer feed compositions. Gelation occurred only for 20/80 DADMAC/AA monomer feed although crosslinking was observed for all monomer feed compositions. The gel point was at 51% conversion, and the swelling ratios of the resulting gels were quite high, from 1400 to 700. Addition of 2‐propanol as a chain‐transfer reagent reduced crosslinking and prevented gelation. These results are mechanistically discussed in connection with the cyclopolymerizability of DADMAC, and significant allylic hydrogen abstraction by the growing polymer radical characteristic of allyl polymerization is proposed.     

Flow birefringence and flexibility of the molecules of copolymers of para- and meta-aromatic polyamides

Flow birefringence (FB) of solutions of poly-p-phenyleneterephthalamide (PpPhTPhA), poly-m-phenyleneisophthalamide (PmPhIPhA) and 13 of their copolymers, with various compositions, has been investigated. The number S of monomer units in a Kuhn segment was determined for all samples from the experimental values of the shear optical coefficient Δn/Δτ. Molecular models for homo- and copolymers were considered. On the basis of these models, an equation expressing the dependence of the chain flexibility parameter 1/S on copolymer composition Z was derived. Good agreement between the experimental dependence of 1/S on Z and the theoretical value confirms the additivity of the structural and deformation mechanisms of flexibility in polymer chains.     

Emulsifier-free polymerization of <Emphasis Type="Italic">n</Emphasis>-butyl acrylate involving trithiocarbonates based on oligomer acrylic acid

The effect of the chain length of oligomer acrylic acid obtained in the presence of a low-molecularmass trithiocarbonate and the position of trithiocarbonate fragment (within the chain or at the chain end) on the process of emulsion polymerization of n-butyl acrylate and characteristics of the resulting dispersions has been studied for the first time. It has been found that, when using an oligomer with trithiocarbonate group located within the chain in the emulsion polymerization of n-butyl acrylate in a wide range of monomer–water phase compositions, triblock copolymers self-organizing in aqueous medium to give stable particles with the core–shell structure are formed. Oligomers with M _n ～ (5–10) × 10³ are optimal for synthesis of stable dispersions. In this case, block copolymers with the controlled length of hydrophobic block and a rather narrow MWD may be obtained. Thin films formed from these copolymers retain the structure of the initial dispersions on solvent removal. If the trithiocarbonate group in the oligomer is located at the chain end, the main polymerization product is a diblock copolymer. In this case, the formation of polymer–monomer particles occurs during a longer period of time, the control of MWD is weakened, and the dispersions of particles lose the aggregative stability after thin film formation.     

Thermooxidative stabilization of acrylonitrile terpolymers obtained under reversible chain-transfer conditions: Effects of synthesis temperature and initiation method

The terpolymerization of acrylonitrile, methyl acrylate, and itaconic acid mediated by a reversible addition-fragmentation chain transfer agent, dibenzyl trithiocarbonate, and initiated by AIBN at 80°C, potassium persulfate at 45–55°C, and radiolysis at 20°C is studied. In all the cases, polymerization proceeds via the pseudoliving mechanism, which is preserved up to ultimately high monomer conversions (80–90%). According to FTIR ATR and NMR spectroscopy, all the synthesized terpolymers are characterized by close monomer compositions and their degree of branching is too low to be detected spectroscopically. However, the thermal behaviors of terpolymers obtained by polymerizations at various temperatures are different, namely, the lower the temperature of terpolymer synthesis, the slower the thermooxidative stabilization processes occurring in it.     

Kinetic modeling of two-step RAFT process for the production of novel fluorosilicone triblock copolymers

Well-defined poly(dimethylsiloxane)-b-poly(2,2,3,3,4,4,4-heptafluorobutylmethacryl-ate-b-poly(styrene) (PDMS-b-PHFBMA-b-PS) triblock copolymers were prepared by two-step reversible addition-fragmentation chain transfer (RAFT) polymerization. A comprehensive mathematical model for the two-step RAFT polymerization in a batch reactor was presented using the method of moments. The model described molecular weight, monomer conversion and polydispersity index as a function of polymerization time. Good agreements in the polymerization kinetics were achieved for fitting the kinetic profiles with the suggested model. In addition, the model was used to predict the effects of initiator concentration, chain transfer agent concentration and monomer concentration on the two-step RAFT polymerization kinetics. The simulated results showed that for the two-step RAFT polymerizations, the effects initiator concentration, chain transfer agent concentration and monomer concentration are identical and the influence degrees are different yet.     

Radiation-induced copolymerization of chlorotrifluoroethylene with ethyl vinyl ether

The radiation-induced copolymerization of chlorotrifluoroethylene with ethyl vinyl ether was investigated in the liquid phase at 20 and ?78°C over a wide range of monomer compositions. A copolymer was obtained in which the monomers alternate with regularity along the polymer chain over the entire range of monomer compositions investigated. Both the rate of copolymerization and the intrinsic viscosity of the resulting copolymer were found to depend strongly on the initial monomer composition, both reaching a maximum value at an equimolar concentration of the monomers. The monomer reactivity ratios were determined and correspond well with calculated values. A decrease in the irradiation temperature was accompanied by a marked decrease in the rate of copolymerization and the intrinsic viscosity of the copolymer.     

Controlled synthesis of multiblock copolymers by pseudoliving radical polymerization via the reversible addition-fragmentation chain-transfer mechanism

With the use of two classes of reversible addition-fragmentation chain-transfer agents??dithiobenzoates and trithiocarbonates??multiblock copolymers based on styrene and n-butyl acrylate, which are the best-studied monomers in these processes, are synthesized. It is shown that the polymers containing dithiobenzoate and trithiocarbonate groups are highly efficient for the synthesis of block copolymers, which is independent of the number of stages at which the polymeric RAFT agents are used in polymerization: In all cases, the polymeric RAFT agent is fully consumed in the polymerization of the ??alien?? monomer. The mechanism governing chain formation during the synthesis of multiblock copolymers, that is, the character of monomer insertion into the polymer chain, via one or both ends, is studied. It is found that the order of monomer loading determines the ratio of chains growing through one or two ends. The thermal stability of amphiphilic multiblock copolymers, their solubility in various solvents, and self-organizing ability are investigated.     

Kinetics of pseudoliving free-radical copolymerization of styrene and methyl methacrylate by the reversible addition fragmentation chain-transfer mechanism

The kinetics of copolymerization of styrene with methyl methacrylate in the presence of tert-butyl dithiobenzoate as a reversible addition fragmentation chain-transfer agent has been studied. Formation of radical intermediates has been investigated. In a wide range of monomer mixture compositions, the kinetic features of pseudoliving radical copolymerization of this monomer pair in the presence of both a low-molecular-mass reversible addition fragmentation chain-transfer (RAFT) agent and a polymer RAFT agent being formed are close to the corresponding features of the homopolymerization of styrene.     

单体组成对甲基丙烯酸甲酯/丙烯酸丁酯RAFT共聚合转移常数的影响

采用Z基团为—CH2C6H5的RAFT试剂为链转移剂,AIBN为引发剂,60℃下进行甲基丙烯酸甲酯/丙烯酸丁酯(MMA/BA)的本体RAFT共聚合,并用GPC法测算不同单体组成下低聚物RAFT的链转移常数(Ctr).实验表明,对BA的均聚合,Ctr高达116,但对MMA的均聚合,Ctr约为0.1.在共聚体系中,Ctr与fMMA之间为非线性关系,随着fMMA的增加呈下降趋势.Ctr随单体组成的变化规律可以很好地解释不同单体组成下RAFT共聚合中分子量及其分布随转化率变化的规律.     

Characterization of N-vinyl carbazole/vinyl 4-tert-butyl-benzoate copolymers of several molar compositions: SEC, DSC and intramolecular excimers in dilute solutions

Several N-vinylcarbazole/vinyl p-tert-butyl-benzoate copolymers of different molar monomer compositions and their respective homopolymers have been synthesized by free-radical polymerization. Their solution properties were characterized by size-exclusion chromatography (SEC) coupled with a differential refractive index (RI) and multiangle light scattering (MALS). Differential scanning calorimetry (DSC) was also used to investigate the glass transition temperatures, T_g. In addition, steady-state fluorescence emission spectra in a dilute solution of several fluid and non-fluid solvents were obtained to study the influence of monomer composition on the intramolecular carbazole excimer formation. The amount of excimers strongly depends on the solvent nature and copolymer composition. Molecular Dynamics (MD) simulations on iso- and syndiotactic homopolymer and copolymer fragments were used to obtain the probability of the conformations that satisfy excimer requirements. The analysis of the MD trajectories allows us to evaluate the amount and types of intramolecular excimers for the different systems.     

Quasiliving Carbocationic Polymerization. XV. Forced Ideal Copolymerization of Isobutylene-lsoprene

Forced ideal carbocationic copolymerization of isobutylene and isoprene has been achieved by continuous addition of monomer mixtures of different compositions to cumyl chloride/TiCl₄ charges at -50°C. The overall rate of copolymerization could be kept equal to that of addition rate with up to 10 mol% isoprene in the mixed monomer feed. In this monomer concentration range the composition of the copolymer was identical to that of the feeds. At higher diene concentrations in the feed, chain transfer to monomer and other side reactions (intramolecular cyclization, gel formation) could not be completely avoided. The number-average molecular weight of the copolymers increased almost linearly with the amount of consumed monomers at 10 mol% isoprene concentrations in the feed (i.e., in the quasiliving range). According to ¹H-NMR and ¹³C-NMR spectroscopy, the products are random copolymers.     

Radiolysis of resist polymers. VI. Copolymers of trihalophenylmethacrylate and methyl methacrylate

Copolymers of several compositions of methyl methacrylate (MMA), trichlorophenyl methacrylate (TCPMA), and tribromophenyl methacrylate (TBPMA) have been synthesized and characterized. Gamma radiolysis yields are very sensitive to the presence of the halogenated monomers. With less than 10% of the halogenated monomer in the copolymers. G_s values were found to be much greater than that of PMMA. However, the halogenated monomer introduces a tendency toward crosslinking. The results are consistent with the enhancement of chain scission by dissociative electron capture and the tendency of phenyl radical intermediates to cause crosslinking. These structure-property relationships were found to be valid for all the homopolymers and copolymers investigated in this series.     

The physicochemical properties of polyhydroxyalkanoates with different chemical structures

A set of polyhydroxyalkanoates are synthesized, and a comparative study of their physicochemical properties is performed. The molecular masses and polydispersities of polyhydroxyalkanoates are found to be independent of their chemical structures. It is shown that the temperature characteristics and degrees of crystallinity of polyhydroxyalkanoates are affected by the chemical compositions of the monomers and their quantitative contents in the polymers. The incorporation of 4-hydroxybutyrate, 3-hydroxyvalerate, and 3-hydroxyhexanoate units into the chain of poly(3-hydroxybutyrate) decreases its melting point and thermal degradation temperature relative to these parameters of a homogeneous poly(3-hydroxybutyrate) sample (175 ± 5°C and 275 ± 5°C, respectively). The higher the content of the second monomer units in the poly(3-hydroxybutirate) chain, the greater the changes. The degrees of crystallinity of polyhydroxyalkanoate copolymers are generally lower than that of poly(3-hydroxybutyrate) (75 ± 5%). The effect on the ratio of the amorphous and crystalline phases of the copolymer samples becomes more pronounced in the series 3-hydroxy-valerate-3-hydroxyhexanoate-4-hydroxybutyrate. The prepared samples exhibit different properties ranging from rigid thermoplastic materials to engineering elastomers.     

Rotary friction,dipole moments,conformation and rigidity of polybutylisocyanate molecules in solution

Experimental data on the dependence of the rotatory diffusion coefficients and dipole moments on molecular weight and the theory of hydrodynamic properties and of the size of wormlike chains were used for determining the main conformational characteristics of the polyisocyanate chain S is the number of molecular units in a segment, λ is the length of the projection of the monomer unit on the axis of the molecule, and μ_o is the dipole moment of the monomer unit. The values of S and λ agree with those found previously by hydrodynamic methods. It was shown that the flat cis-structure of the polyisocyanate chain corresponds to values of λ = 2 × 10^?8cm andμ_o = 1·8D. Analysis of experimental data indicates that dimensions of “geometrical” and “electrical” segments in the PBIC chain are identical.     

A calculation of thermal degradation initiated by random scission,unsteady radical concentration

Changes in molecular weight distribution and in sample volume were calculated for thermal degradation of a polymer. The thermal degradation scheme consists of random scission initiation, depropagation and disproportionation termination reactions. An unsteady radical concentration was considered. There are two parameters, normalized zip length z/x₀ and radical number per initial chain length z′x₀, describing the thermal degradation scheme with an unsteady radical concentration. The effects of the initial number-average molecular weight and order of the disproportionation termination reaction on changes in molecular weight, the sample volume and polydispersity are not significant as long as these two parameters have the same value for each polymer sample. Molecular weights of a degrading sample calculated from the steady state radical concentration tend to be over-estimated and sample volumes tend to be underestimated compared to those calculated with an unsteady radical concentration. The validity of approximations used in the calculation assuming a steady state radical concentration is examined by comparing with results calculated with an unsteady radical concentration for various values of the two parameters. An unrealistically large build-up of monomer radicals is found for both calculations based on the steady state and the unsteady radical concentrations. Two special treatments of monomer radicals can dissipate the build-up of monomer radicals: (1) their immediate vaporization, or (2) an enhanced rate of the termination reaction for the monomer radicals. As a guide, the model based on an unsteady radical concentration is preferred, if the value of z′x₀ exceeds 0.1.     

Design and synthesis of trivalent Tn glycoconjugate polymers by nitroxide-mediated polymerization

A new synthetic method for preparing Tn glycoconjugate polymers, containing tumor-associated carbohydrate antigens, by controlled living radical polymerization is reported. To mimic the authentic structures of Tn glycopeptide antigens and to explore the controlled living radical polymerization, three tumor-associated carbohydrate antigens (GalNAc, GalNAcα1-O-Ser, and GalNAcα1-O-Thr) were attached to a styrene-type monomer through a diethylene glycol spacer. Under nitroxide-mediated polymerization, controlled living radical polymerization proceeded to afford defined glycopeptide polymers with different Tn densities and compositions. The polydispersity index (PDI) and molecular weights were increased and conversions were decreased upon increasing the concentration of Tn glycoconjugate monomers. The resulting Tn glycoconjugate polymers were characterized by NMR and IR. The spectral data indicate that the Tn glycoconjugate moiety did attach to the polymer chain and Tn glycoconjugate density could be adjusted through the nitroxide-mediated polymerization conditions. The number of Tn units containing in the polymer chains could be estimated by NMR integration. This synthetic approach provides a new and efficient tool for constructing novel Tn glycoconjugate polymers.     

X-ray photoelectron spectroscopy: A new method for determination of copolymer composition,and monomer reactivity ratios and monomer sequence distribution therefrom

Copolymer compositions and reactivity ratios for the radical copolymerization of styrene with acrylonitrile have been determined by x-ray photoelectron spectroscopy (XPS). The results obtained by this technique were confirmed by elemental as well as ¹H-NMR (nuclear magnetic resonance) analysis. The monomer sequence distributions have also been calculated utilizing the monomer reactivity ratio values obtained by three different techniques viz., XPS, ¹H-NMR, and elemental analysis. The agreement between the monomer sequence distributions in the copolymer chain by these methods is very satisfactory. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2049–2056, 1997     

Preparation of rechargeable biocidal polypropylene by reactive extrusion with diallylamino triazine

Biocidal polypropylene (PP) was prepared by using a reactive extrusion process, in which PP was grafted with an N-halamine precursor, 2, 4-diamino-6-diallylamino-1, 3, 5-triazine (NDAM). After chlorination the grated PP was converted to biocidal halamine structures. Effects of monomer and initiator concentration on grafting yield, thermal properties, and biocidal efficacy were studied. The Fourier transformed spectroscopy (FTIR) results and nitrogen analysis confirmed the graft polymerization on PP backbone during the reactive extrusion. The results also indicated that at low monomer concentration, increase in initiator concentration led to increase in PP chain scission and decrease in mixing torque, or polymer chain length. As the monomer concentration increases, grafted monomer content in the products showed a steady increase, indicating more grafting copolymerization in the system. The halogenated products exhibited potent antimicrobial properties against Escherichia coli, and the antimicrobial properties were durable and regenerable.